Federal Registers - Table of Contents Federal Registers - Table of Contents
• Publication Date: 11/07/1991
• Publication Type: Proposed Rules
• Fed Register #: 56:57036
• Standard Number: 1910.1052; 1910.19; 1915.1102 ; 1926.61
• Title: Occupational Exposure to Methylene Chloride

DEPARTMENT OF LABOR

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION

29 CFR PARTS 1910, 1915 and 1926

[DOCKET NO. H-71]

RIN: 1218-AA98

OCCUPATIONAL EXPOSURE TO METHYLENE CHLORIDE

AGENCY: Occupational Safety and Health Administration (OSHA), Department of Labor

ACTION: Proposed rule

SUMMARY: The Occupational Safety and Health Administration (OSHA) proposes to amend its existing regulation for employee exposure to methylene chloride (MC, also known as methylene dichloride, dichloromethane or DCM). The Assistant Secretary has determined, based on animal and human data, that the current permissible exposure limits (PELs) do not adequately protect employee health. OSHA proposes to reduce the existing 8-hour time-weighted average (TWA) exposure from 500 parts MC per million parts of air (500 ppm) to 25 parts per million. The Assistant Secretary also proposes to delete the existing ceiling limit concentration of 1,000 ppm and proposes to reduce the existing short-term (5 minutes in any 2 hours as a maximum peak concentration) exposure limit (STEL) from 2,000 ppm to 125 ppm, measured as a 15-minute TWA. In addition, the Agency proposes to set an "action level" of 12.5 ppm, measured as an 8-hour TWA, in order to minimize the compliance burden for employers whose employees have consistently very low exposure to MC. The proposal also contains provisions for exposure control, personal protective equipment, employee exposure monitoring, training, medical surveillance, hazard communication, regulated areas, emergency procedures and recordkeeping.

Two of the considerations which may affect OSHA's final PELs for MC are the impact of pharmacokinetic data on OSHA's current risk estimates and the impact of Title III of the Clean Air Act Amendments of 1990 on the MC industry profile. OSHA is soliciting information on pharmacokinetics (Issue 6) and on the potential impacts of the Clean Air Act Amendments (Issue 9). Based on its review of the data in the record, including the information received in response to the above cited issues, OSHA may promulgate PELs which differ from those proposed. The final PELs may vary from those proposed by as much as a factor of five. Examples of federal agencies which have used pharmacokinetic data to reduce risk estimates from those originally calculated are the EPA, which decreased that Agency's risk estimates by a factor of 8.8, and the Consumer Product Safety Commission, which found that the pharmacokinetic data would support lowering the risk estimates by a factor of 2.2 compared to their original risk estimates.

This proposed standard applies to all employment in general industry, shipyards, longshoring and construction.

DATES: Comments concerning the proposed standard must be postmarked on or before April 6, 1992.

ADDRESSES: Comments are to be submitted in quadruplicate to: The Docket Office, Docket No. H-71, Room N-2634, United States Department of Labor, 200 Constitution Avenue, N.W., Washington, D.C. 20210, telephone No. (202) 523-7894.

Comments limited to 10 pages or less in length also may be transmitted by facsimile to (202) 523-5046 or 8-523-5046 (for FTS), provided that the original and 3 copies of the comment are sent to the Docket Officer thereafter.

FOR FURTHER INFORMATION CONTACT: Mr. James F. Foster, OSHA Office of Public Affairs, United States Department of Labor, Room N-3641, 200 Constitution Avenue, N. W., Washington, D.C. 20210. Telephone (202) 523-8151.

SUPPLEMENTARY INFORMATION:

INFORMATION COLLECTION REQUIREMENTS:

5 CFR Part 1320 sets forth procedures for agencies to follow in obtaining OMB clearance for information collection requirements under the Paperwork Reduction Act of 1980, 44 U.S.C. 3501 et seq. This proposed MC standard requires the employer to allow OSHA access to records. In accordance with the provisions of the Paperwork Reduction Act and the regulations issued pursuant thereto, OSHA certifies that it has submitted the information collection requirements for this proposal to OMB for review under section 3504(h) of that Act.

Public reporting burden for this collection of information is estimated to average five minutes per response. Send any comments regarding this burden estimate, or any other aspect of this collection of information, including suggestions for reducing this burden, to the Office of Information Management, Department of Labor, Room N-1301, 200 Constitution Avenue, N.W., Washington, D. C. 20210; and to the Office of Information and Regulatory Affairs, Office of Management and Budget, Washington, D.C. 20503.

I. General:

The preamble to the proposed standard on occupational exposure to Methylene Chloride (MC) discusses events leading to the proposal, physical and chemical properties of MC, manufacture and use of MC, health effects of exposure, degree and significance of the risk presented, an analysis of the technological and economic feasibility, regulatory impact and regulatory flexibility analysis, and the rationale behind the specific provisions set forth in the proposed standard. The discussion follows this outline:

I. General

II. Pertinent Legal Authority

III. Events Leading to the Proposed Standard

IV. Request for Information

V. Chemical Identification, Production Technologies and Industrial Uses

A. Chemical Identification

B. Production Technologies and Industrial Uses

1. MC Production

2. Polyurethane Foam Blowing

3. Aerosols

4. Polycarbonate Resin

5. Pharmaceuticals

6. Manufacturing of Paint and Paint Removers/Strippers

7. Paint Stripping

8. Degreasing and Metal Cleaning

9. Cellulose Triacetate Fiber and Cellulose Triacetate Photographic Film Production

10. Electronics

11. Miscellaneous Usages (Food extraction, Ink use, Pesticide Manufacturing, Solvent Recovery and Other uses)

VI. Technological Feasibility Assessment of Engineering Controls to Reduce Employees' Exposures

A. MC Production

B. Polyurethane Foam Blowing

C. Aerosols

D. Polycarbonate Resin

E. Pharmaceuticals

F. Manufacturing of Paint and Paint Removers/Strippers

G. Paint Stripping

H. Degreasing and Metal Cleaning

I. Cellulose Triacetate Fiber and Film Base Production

J. Electronics

K. Miscellaneous Usages (Food extraction, Pesticide formulation, Solvent recovery, and Ink manufacture)

VII. Health Effects

A. Introduction

B. Disposition and metabolism of MC

1. Absorption and distribution of MC

2. Metabolism of MC

C. Carcinogenicity

1. Animal studies

a. Mouse studies

b. Rat studies

c. Hamster study

d. Summary of animal studies

2. Epidemiologic studies

a. Studies of fiber production workers

b. Studies of film production workers

c. Summary of epidemiological studies

3. Mutagenicity studies

a. Bacterial studies.

b. Yeast and Drosophila studies

c. Studies in mammalian cells

d. Summary of mutagenicity studies

D. Other toxic responses

1. CNS toxicity

a. Animal studies

b. Human studies

c. Summary of CNS toxicity studies

2. Cardiac toxicity

a. Animal studies

b. Human studies

c. Summary of cardiac toxicity

3. Hepatic toxicity

a. Animal studies

b. Human studies

c. Summary of human hepatotoxicity

4. Reproductive toxicity

a. Animal studies

b. Human studies

c. Summary of reproductive effects

E. Conclusion

VIII. Preliminary Quantitative Risk Assessment

A. Introduction

B. Choice of data base

C. Selection of the most appropriate studies

D. Selection of data sets

E. Statistical methods and predictions

1. Choice of model

2. Species to species extrapolation

3. Prediction of risk

F. Other models

G. Other risk assessments

H. Pharmacokinetics

I. Conclusions

IX. Significance of Risk

X. Summary of Preliminary Regulatory Impact and Regulatory Flexibility Analysis

A. Methodology

B. Industry Profile

C. Technological Feasibility

D. Substitution

E. Total Costs of Regulation

F. Benefits Analysis

G. Economic Impacts

H. Regulatory Flexibility Analysis

I. Environmental Impacts

XI. Environmental Impact

XII. Summary and Explanation of the Proposed Standard

A. Scope and Application

B. Definitions

C. Permissible Exposure Limits

D. Exposure Monitoring

E. Regulated Areas

F. Methods of Compliance

G. Respiratory Protection, and Other Protective Clothing and Equipment

H. Emergency Situations

I. Medical Surveillance

J. Communication of MC Hazards to Employees

K. Recordkeeping

L. Observation of Monitoring

M. Dates

N. Appendices

XIII. Public Participation

XIV. State Plan Requirements

XV. Authority and Signature

XVI. Proposed Standard and Appendices

Appendix A: Substance Safety Data Sheet and Technical Guidelines for Methylene Chloride

Appendix B: Medical Surveillance for Methylene Chloride

Appendix C: Qualitative and Quantitative Fit Testing Procedures for Respirators

II. PERTINENT LEGAL AUTHORITY:

This proposed standard and issuance of a final standard is authorized by sections 6(b), 8(c), and 8(g)(2) of the Occupational Safety and Health Act of 1970 (the Act), 29 U.S.C. 655(b), 657(c) and 657(g)(2). Section 6(b)(5) governs the issuance of occupational safety and health standards dealing with toxic materials or harmful physical agents. It states:

The Secretary, in promulgating standards dealing with toxic materials or harmful physical agents under this subsection, shall set the standard which most adequately assures, to the extent feasible, on the basis of the best available evidence, that no employee will suffer material impairment of health or functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the period of his working life. Development of standards under this subsection shall be based upon research, demonstrations, experiments, and other information as may be appropriate. In addition to the attainment of the highest degree of health and safety protection for the employee, other considerations shall be the latest available scientific data in the field, the feasibility of the standards, and experience gained under this and other health and safety laws. Whenever practicable, the standard promulgated shall be expressed in terms of objective criteria and of the performance desired.

Section 3(8) defines an occupational safety and health standard as "a standard which requires conditions, or the adoption or use of one or more practices, means, methods, operations, or processes, reasonably necessary or appropriate to provide safe or healthful employment and places of employment." The Supreme Court has held under the Act that the Secretary, before issuing any new standard, must determine that it is reasonably necessary and appropriate to remedy a significant risk of material health impairment, Industrial Union Department v. American Petroleum Institute, 488 U.S. 607 (1980). The Court stated that "....before he can promulgate any permanent health or safety standard, the Secretary is required to make a threshold finding that a place of employment is unsafe---in the sense that significant risks are present and can be eliminated or lessened by a change in practices" (488 U.S. at 642). The Court also stated "that the Act does limit the Secretary's power to require the elimination of significant risks" (488 U.S. at 644, n. 49).

The Court indicated however, that the significant risk determination is "not a mathematical straightjacket." The Court stated that "OSHA is not required to support its finding that a significant risk exists with anything approaching scientific certainty." The Court ruled that "a reviewing court [is] to give OSHA some leeway where its findings must be made on the frontiers of scientific knowledge," [and that] "the Agency is free to use conservative assumptions in interpreting the data with respect to carcinogens, risking error on the side of overprotection rather than underprotection" (488 U.S. at 655, 656). The Court also stated that "while the Agency must support its finding that a certain level of risk exists with substantial evidence, we recognize that its determination that a particular level of risk is 'significant' will be based largely on policy considerations". (488 U.S. at 655, 656 n. 62).

After OSHA has determined that a significant risk exists and that such a risk can be reduced or eliminated by the proposed standard, it must set a standard "which most adequately assures, to the extent feasible on the basis of the best available evidence, that no employees will suffer material impairment of health..." Section 6(b)(5) of the Act. The Supreme Court has interpreted this section to mean that OSHA must enact the most protective standard possible to eliminate a significant risk of material health impairment, subject to the constraints of technological and economic feasibility, American Textile Manufacturers Institute, Inc. v. Donovan, 452 U.S. 490 (1981). The Court held that "cost-benefit analysis is not required by the statute because feasibility analysis is" (452 U.S. at 509). The Court stated that the Agency could use cost-effectiveness analysis and choose the least costly of two equally effective standards (452 U.S., 531, n. 32).

Section 8(c)(3) gives the Secretary authority to require employers to "maintain accurate records of employee exposures to potentially toxic materials or harmful physical agents which are required to be monitored or measured under section 6." Section 8(g)(2) gives the Secretary authority to "prescribe such rules and regulations as he may deem necessary to carry out their responsibilities under this Act."

In addition, the Secretary's responsibilities under the Act are amplified by its enumerated purposes which include:

Encouraging employers and employees in their efforts to reduce the number of occupational safety and health hazards at their places of employment and stimulating employers and employees to institute new programs and to perfect existing programs for providing safe and healthful working conditions [29 U.S.C. 651(b)(1)];

Authorizing the Secretary of Labor to set mandatory occupational safety and health standards applicable to business affecting interstate commerce, and by creating an Occupational Safety and Health Review Commission for carrying out adjudicatory functions under the Act: [29 U.S.C. 651(b)(3)];

Building upon advances already made through employer and employee initiative for providing safe and healthful working conditions [29 U.S.C. 651(b)(4)];

Providing for the development and promulgation of occupational safety and health standards [29 U.S.C. 651(b)(9)] and providing for appropriate reporting procedures which will help achieve the objectives of this Act and accurately describe the nature of the occupational safety and health problem [29 U.S.C. 651(b)(12)].

Exploring ways to discover latent diseases, establishing causal connections between diseases and work in environmental conditions [29 U.S.C. 651(b)(6)];

Encouraging joint labor-management efforts to reduce injuries and diseases arising out of employment [29 U.S.C. 651(b)(13)]; and

Developing innovative methods, techniques, and approaches for dealing with occupational safety and health problems [19 U.S.C. 651(b)(5)].

Because the MC standard is reasonably related to these statutory goals, and the Agency's judgment is that the evidence satisfies the statutory requirements, and because the proposed standard is feasible and substantially reduces a significant risk of cancer and other adverse health effects, the Secretary preliminarily finds that the proposed standard is necessary and appropriate to carry out her responsibilities under the Act.

III. EVENTS LEADING TO THE PROPOSED STANDARD

The present OSHA standard for MC requires employers to assure that employee exposure does not exceed 500 ppm as an 8-hour TWA,1000 ppm as a ceiling concentration, and 2000 ppm as a maximum peak for a period not to exceed 5 minutes in any 2 hours (29 CFR 1910.1000, Table Z-2). This standard was adopted by OSHA in 1971 pursuant to section 6(a) of the OSH Act, 29 U.S.C. 655, from an existing Walsh-Healey Federal Standard. The source of this Walsh-Healey Standard (Ex. 7-1) was the American National Standards Institute (ANSI) standard for acceptable concentrations of MC (ANSI - Z37.23-1969), which were intended to protect workers from injury to the neurological system including loss of awareness and functional deficits linked to anesthetic and irritating properties of MC which had been observed from excessive, acute or large chronic exposures to MC in humans and experimental animals.

In 1946, the American Conference of Governmental Industrial Hygienists (ACGIH) recommended a Threshold Limit Value (TLV) of 500 ppm for MC (Ex. 2). In 1975, the ACGIH lowered the recommended TLV to 100 ppm (Ex. 7-11).

In March 1976, the National Institute for Occupational Safety and Health (NIOSH) published "Criteria for a recommended standard for Methylene Chloride" (Ex. 2), which recommended a reduction of the occupational exposures to MC to 75 ppm as an 8-hour TWA, and a lower peak exposure not to exceed 500 ppm. Further exposure reduction based on the ambient level of carbon monoxide was also recommended.

In 1984, the International Labor Office-Geneva (Ex. 7-50) listed MC standards for Romania, Poland and the USSR as 145, 14.5, and 14.5 ppm (500, 50 and 50 mg/m3), respectively.

In February 1985, the National Toxicology Program (NTP) reported the final results of animal studies indicating that MC is a potential cancer causing agent (Ex.7-008). Subsequently, the Environmental Protection Agency (EPA), upon receipt of the NTP studies, initiated a risk assessment evaluation to determine whether or not MC presents an unreasonable risk to human health or environment and to determine if regulatory actions are needed to eliminate or reduce exposures.

On May 14, 1985, EPA announced its determination that MC was a probable human carcinogen. EPA classified MC as Group B2, in accordance with its interim guidelines for cancer risk (49 FR 46294), and hence announced the initiation of a 180-day priority review (50 FR 20126) under section 4(f) of the Toxic Substances Control Act (TSCA). In meeting its mandate under section 4(f) of TSCA to initiate a regulatory action, on October 17, 1985, EPA published an Advance Notice of Proposed Rulemaking (ANPR) (50 FR 42037) for the purpose of collecting the necessary information required for initiating a rulemaking. In this notice, EPA established December 16, 1985, as its deadline for receiving comments.

On April 11, 1985, the U.S. Consumer Product Safety Commission (CPSC) released its risk assessment findings for MC and began to consider a regulatory action to ban MC containing products and to develop a voluntary hazard communication program for consumers.

On December 18, 1985, the U.S. Food and Drug Administration (FDA) published a proposal to ban the use of MC as an ingredient in aerosol cosmetic products (50 FR 51551). This proposal was based on a risk assessment that used the NTP animal data.

On July 19, 1985, Owen Bieber, President of International Union, United Automobile, Aerospace and Agricultural Implement Workers of America (UAW), petitioned OSHA to act expeditiously on reducing workers' exposure to MC. Specifically, Mr. Bieber requested that: (1) OSHA publish a hazard alert; (2) OSHA issue an emergency temporary standard (ETS); and (3) OSHA begin work on a new permanent standard for controlling MC exposure. Subsequently, the following unions joined UAW in petitioning OSHA to act on revising the current standard:

A. International Union, Allied Industrial Workers of America;

B. Glass, Pottery, Plastics and Allied Workers International Union;

C. United Furniture Workers of America;

D. The Newspaper Guild;

E. Communication Workers of America; and

F. United Steelworkers of America.

In March 1986, in preliminary response to the UAW petition, OSHA issued a "Guideline for Controlling Exposure to Methylene Chloride." This document was intended to provide information to employers and workers on risks and methods of controlling exposure (Ex. 8-11).

In April 1986, NIOSH published a Current Intelligence Bulletin #46 on MC reflecting the findings of the NTP study (Ex. 8-26).

In it, NIOSH concluded that MC should be regarded as a potential occupational carcinogen and that exposure should be controlled to the lowest feasible level.

In May 29, 1986, the BNA Occupational Safety and Health Reporter published the announced intention of ACGIH to lower the TLV for Methylene Chloride (MC) from 100 ppm to 50 ppm and to classify MC as an A2 carcinogen (an industrial substance suspect of carcinogenic potential for man) (Ex. 8-27).

On August 20, 1986, the CPSC issued a proposed rule [51 FR 29778] "that would declare household products containing other than contaminant levels of MC to be hazardous substances." The CPSC noted the proposal was prompted by evidence that inhalation of MC vapor increased the incidence of various malignant and benign tumors in rats and mice. Accordingly, the commission proposed to require that household products which can expose consumers to MC vapor be treated as hazardous substances and be labeled as provided by section 2 (p)(1) of the Federal Hazardous Substances Act (FHSA) (15 U.S.C. 1261 (p)(1)). The FHSA requires the use of labels which 1) indicate that exposure to a product may present a cancer risk; 2) explain the factors (such as level and duration of exposure) that control the degree of risk; and 3) explain the precautions to be taken.

On November 17, 1986, OSHA notified the UAW that OSHA denied the request for an Emergency Temporary Standard, but agreed that work on a permanent standard should commence (Ex. 3A).

On November 24, 1986, OSHA announced, in an Advance Notice of Proposed Rulemaking (ANPR) [51 FR 42257], that it was considering revising the present occupational health standard for MC. The Agency based this action on animal studies which indicated the present standard may not provide adequate protection against potential cancer risks and other adverse health effects. The ANPR summarized OSHA's information regarding the production and use of MC, occupational exposure to MC, and the potential adverse health effects associated with MC exposure. In addition, the notice invited interested parties to submit comments, recommendations, data, and information on a variety of issues related to the regulation of MC. OSHA received 43 comments in response to the ANPR. Those comments are discussed in the appropriate sections of the proposal, below.

On December 5, 1986, the FDA reopened the comment period for 30 days on the above-cited proposal to ban the use of MC in cosmetic products [51 FR 43935]. The reopening enabled interested parties to submit comments on studies received after the close of the initial comment period regarding MC comparative pharmacokinetics, metabolism, and genotoxicity.

On September 14, 1987, the CPSC issued a statement of interpretation and enforcement policy, in lieu of continuing with rulemaking, which expressed the Commission's determination that consumer products containing MC and capable of exposing consumers to significant amounts of MC may pose cancer risk to humans and, therefore, are subject to the above-described hazardous substance labeling requirements. The CPSC explicitly retained the option of resuming the rulemaking if voluntary compliance with and enforcement of the Commission's interpretation did not adequately induce firms to label their products appropriately.

While pursuing this course of action, OSHA has also been participating in an interagency committee to define regulatory needs for chlorinated solvents in general. This effort is being led by EPA, and it includes representatives from OSHA, FDA, and CPSC. Its focus is on manufacturing, use, and disposal of the highest volume chlorinated solvents, which may be used as substitutes for MC including, perchloroethylene, trichloroethylene, carbon tetrachloride, methyl chloroform, and CFC-113. All of these chemicals are considered to be toxic to humans or hazardous to the environment. Three of them have positive evidence of carcinogenicity. The interagency committee was created: (l) to avoid duplication and inconsistency among the several government agencies regulating chlorinated solvents; (2) to account for potential interchangeability among these solvents; and (3) to avoid transfer of risks from one medium -- air, water, waste -- or one population -- workers, consumers, general public -- to another as a result of piecemeal and uncoordinated regulation. All information derived from the interagency committee will be shared and incorporated into OSHA's docket on MC.

In 1988, ACGIH officially lowered the TLV for MC to 50 ppm as an 8-hour TWA.

On June 29, 1989, the FDA issued a final rule that banned the use of MC in cosmetic products [54 FR 27328]. The Agency based its final rule on scientific studies that showed inhalation of MC caused cancer in laboratory animals. The FDA concluded, accordingly, "that continued use of MC in cosmetic products may pose a significant risk to human health . . . " The Agency considered comments and information regarding the application of a physiologically-based pharmacokinetic model to the prediction of human cancer risk. The FDA determined that the risk assessment developed using animal studies should not be changed to reflect the "pharmacokinetic and metabolic data and hypothesized GST metabolic mechanism of carcinogenicity."

On August 8, 1990, the Consumer Product Safety Commission (CPSC) issued a General Order (55 FR 32282) that required manufacturers, importers, packagers and private labelers of consumer products containing 1% or more of MC to report to the CPSC information on the labeling and marketing of those products. The CPSC indicated that the information obtained would aid the Commission in evaluating the CPSC's policy concerning the labeling of MC- containing products as hazardous substances, pursuant to the Federal Hazardous Substances Act.

IV. REQUEST FOR INFORMATION AND COMMENTS

OSHA requests public comment on the information and proposed regulatory text presented in this NPRM and on other relevant issues. That input will assist the Agency in evaluating the proposed rule and in ensuring that the final rule sets appropriate requirements for protection of employees exposed to MC. OSHA requests that parties who suggest changes in proposed regulatory provisions include supporting information with their comments. OSHA also requests that interested parties who have MC-related health data not discussed in this notice submit that information to the Agency.

Comment is requested on the following issues:

1. Do the proposed provisions provide adequate protection for workers against all known hazards associated with exposure to MC?

2. Please provide information regarding the inclusion of provisions for medical examinations, respirators, personal protective clothing and equipment, work practices, emergencies, regulated areas, maintenance of records, employee information and training, and labels and signs. What form should such provisions take in the final standard? To what extent are these provisions currently being employed by industry and what are their costs?

3. Does OSHA's proposed 25 ppm standard for MC substantially eliminate significant risk and is it feasible and appropriate? Should a different exposure limit be set, and if so, what is the supporting evidence?

4. In order to further protect against adverse effects from worker exposure to MC, OSHA has proposed a 15-minute short term exposure limit (STEL) of 125 ppm. Please provide information and supporting data regarding the adequacy of the proposed STEL. Should OSHA promulgate a different STEL? If so, what evidence is available to support a different STEL?

5. Should OSHA set an action level for occupational exposure to MC? Is the proposed 12.5 ppm level appropriate? Should a different action level be set? If so, what evidence supports the suggested change? What provisions should be triggered by the action level?

6. In its current quantitative risk assessment, OSHA relied primarily on the NTP mouse bioassay to estimate the cancer risk to humans exposed to MC. OSHA determined that the NTP study provided the best available data for MC risk assessment, demonstrating a statistically significant carcinogenic dose- response relationship. Continuing research on the metabolism of MC has elucidated some of the pharmacokinetic differences between rodents and humans. These data suggested that risks extrapolated from test animals to humans based on applied dose methods, such as those used by OSHA in this proposal, may have overestimated the human cancer risks.

The use of pharmacokinetic data in risk assessments requires that assumptions be made concerning the mechanism of carcinogenic action of MC. Furthermore, the incorporation of estimated values for a number of parameters in pharmacokinetic models may increase the uncertainties of the risk assessment results. These uncertainties and assumptions will be evaluated in light of new data collected during the rulemaking process.

The information acquired through the rulemaking will aid OSHA in resolving the uncertainties, and in determining if species differences should be incorporated into a pharmacokinetic model for estimating cancer risk to humans exposed to MC.

OSHA has serious concerns about the best utilization of the pharmacokinetic models in cancer risk assessments for MC. OSHA solicits comments and information on the following aspects of this issue:

a) How can pharmacokinetics be best applied to the risk assessment of MC and what are the current limitations of this approach in the quantitation of health risks? What weight should OSHA give to pharmacokinetic data in its risk assessments and why?

b) Given that five separate risk assessments have utilized the pharmacokinetic models for MC in five different ways (resulting A in from 0 to 170 fold reduction in the final risk when compared with assessments not utilizing pharmacokinetic data), how can OSHA best utilize the existing pharmacokinetic data and still be certain of protecting worker health?

c) Which parameters in the pharmacokinetic models are most sensitive to errors in measurement or estimation? Can an increased database reduce the uncertainties in these parameters?

d) How much confidence can be placed in the human in vitro MC metabolism data, especially that for lung tissue? How will human variability in these parameters affect the extrapolation of risk from rodent species?

e) Are there any studies in progress which attempt to verify the predictive ability of the model in vivo, (i.e., by giving doses in a lifetime bioassay which will produce cancer in a species other than the B6C3F1 mouse and the F344 and Sprague-Dawley rats)?

f) OSHA recognizes the large areas of uncertainty which exist in applied dose risk assessment procedures. If pharmacokinetic modeling reduces these uncertainties, can the reduction in uncertainty be quantified? Are additional uncertainties introduced into the risk assessment process by the use of pharmacokinetic models?

g) By using the pharmacokinetic models in the risk assessment process, one is making an assumption about the carcinogenic mechanism of action of methylene chloride. Are there any new studies on the carcinogenic mechanism of action of MC which would support or refute this assumption?

h) If the carcinogenic process is, in fact, not the result of the metabolite(s) from the GST pathway alone, but is due to a combination of metabolites or a combination of the parent compound plus the metabolites, how would the pharmacokinetic model and the subsequent risk assessments be affected? Can these effects be quantified?

i) One of the assumptions made in the pharmacokinetic model is that the target tissues for MC are liver and lung. Can this model predict cancer incidences at other sites? If not, is there a way to factor in consideration of possible MC-induced human cancers at other sites than liver and lung?

j) OSHA solicits information supporting or refuting interspecies allometric scaling based on body weight or body surface area.

7. OSHA has noted in the Health Effects Section, below, that carbon monoxide is formed as a metabolite of MC in humans and that exposure to both MC and carbon monoxide may be more harmful than exposure to either substance alone. How should the standard deal with the effects of simultaneous occupational exposures to carbon monoxide and MC? Should the permissible exposure limit for MC be lower when exogenous carbon monoxide is present, as NIOSH has suggested? How should an air monitoring strategy deal with such exposures when combined?

8. Please submit any additional or updated epidemiological studies or updated information on exposures for the employee populations in the studies OSHA has included in this proposal. Such information would be useful to the Agency in assessing the risk of occupational exposure to MC.

9. Title III of the Clean Air Act Amendments of 1990 (P.L. 101-549, 104 Stat. 2399) established a list of hazardous air pollutants (including MC) and required EPA to set emissions standards which "require the maximum degree of reduction in emissions of the hazardous air pollutants subject to this section (including a prohibition on such emissions, where achievable) that the Administrator, taking into consideration the cost of achieving such emission reduction, and any non-air quality health and environmental impacts and energy requirements, determines is achievable for new or existing sources..." EPA has not yet determined how it will regulate MC emissions. Further, EPA has not developed any information on the extent and magnitude of MC use, including projection of any change in the current industry profile. Therefore, at this time, it is expected that EPA may take action which could impact the magnitude and the extent of MC use, including possible change in the industry profile (both number of firms and number of workers).

OSHA believes that, if engineering devices for the control of ambient emissions become more readily affordable and efficient, there will be a possibility of increasing MC usage because of its established performance qualities and desirable safety characteristics (low flammability). On the other hand, if compliance with the requirements of the Clean Air Act makes it less desirable for industry to continue the use of MC, some industries may abandon, either totally or partially, the use of MC. OSHA is interested in obtaining information or comments on the predicted impact of the Clean Air Act Amendments on the production, use and industry profile for MC. OSHA will use this information to determine how the Clean Air Act Amendments may change the overall population risk for MC exposure. OSHA will take into consideration any comments received regarding these impacts of the Clean Air Act Amendments in its preparation of the final RIA for MC.

10. What, if any, changes made to improve productivity or product quality in the way MC is produced or used, have also resulted in changes (reductions or increases) in worker exposures to MC?

11. In the printing industry, MC has been identified as a constituent of ink and the solvent used to clean the printing plates (blanket wash). Current information indicates that MC use in ink formulation is being phased out through substitution. Because of the availability of a substitute for MC in ink formulation, OSHA has determined that it would be reasonable to project a similar decline or even elimination of MC use in blanket wash. OSHA is requesting public comments to verify the extent and magnitude of the current and future use of MC in blanket wash, if any.

12. Information gathered in response to the EPA call-in announcement indicates that MC usage in pesticides and in pesticide manufacture has already been, or is being, phased out. OSHA is soliciting information on the extent and magnitude of MC usage in pesticide manufacturing, if any.

13. What are the appropriate compliance strategies utilizing engineering controls, work practices, and respirators for reducing exposures to MC in particular workplace situations? Please state the extent to which the following control methods are protective and feasible for particular industries and employee activities:

a. Engineering controls such as ventilation, collection, isolation, containment, substitution of product or process, and modification of process or equipment; and

b. Work practices, housekeeping and administrative controls.

What is the lowest feasible exposure level that can be achieved for particular application groups by engineering controls and work practices alone? Are there any unique conditions in certain work settings where MC is produced or used where feasible engineering controls are not available?

14. Please provide information on engineering and work practice controls that would lower workers exposure to or below the proposed 25 ppm 8-hour TWA. Please include the cost and time necessary for their implementation.

15. OSHA's proposed rule for Methods of Compliance (54 FR 23991) does not require employers to institute all feasible engineering controls when only a negligible reduction in exposure is thereby achieved. Instead of using "negligible reduction" as the cut-off-point, should OSHA quantify the boundaries of exposure reduction and subsequent attainment level? If quantifiable boundaries of exposure reduction are included, how should they weigh consideration of health concerns (e.g., carcinogenesis) and safety hazards (e.g., phosgene production)?

16. Based on the description of production and process technology (Section V, below), OSHA believes that the engineering feasibility determinations for the industrial facilities surveyed by OSHA are representative of the pertinent industries. Further, the rulemaking record indicates that it is technologically feasible to comply with the proposed PELs using engineering controls. OSHA is requesting public comment on these determinations. Are there particular circumstances where respirator use would be necessary to comply with the proposed PELs? Please explain any such circumstances and the frequency with which they would be expected to arise.

17. OSHA requests information regarding the number of workers exposed to MC, their current exposure levels, the methods of monitoring used to measure these exposures, the duration and frequency of exposure, the duties being performed, and the Standard Industrial Classification (SIC) Codes for industries and processes that utilize MC.

18. Are there specific activities which are generally known to cause exposure in excess of the proposed PELs? Should the standard include specific provisions prohibiting some or all such activities? Should the standard include provisions specifying controls that are known or proven to be effective in reducing workers' exposure?

19. As noted in Issue 11, there are some industries which have substituted away from use of MC. OSHA is seeking additional information on the feasibility of chemical substitutes for MC in industrial processes. What are the feasible chemical substitutes for MC and what are their limitations, if any? What are the differences in cost if these substitutes are used (including any necessary changes in equipment design, changes in product quality, or other costs incurred by substitution)? What are the impacts of substitution for MC with regard to safety (i.e., flammability, explosivity) and health (i.e., carcinogenicity, CNS effects) effects?

20. Has OSHA accurately estimated all costs associated with achieving compliance with the proposed new rule? Is compliance economically feasible for the affected industries? How would the time allowed to implement engineering controls and work practices affect these costs?

21. Is it appropriate to adjust the cost of compliance through giving credit for the sale of old equipment, savings on maintenance costs and time for repairs and decreased loss of product or shutdown time, when engineering controls are implemented?

22. In order to perform an economic feasibility analysis of the MC proposal, the Agency has developed a financial and economic profile of each industry producing and using MC products. OSHA solicits information covering the last five (5) years to aid in the preparation of the economic feasibility analysis.

23. How does the proposed standard affect industry's economic position, particularly with regard to foreign import competition in the domestic U.S. Market, and the price of U.S. goods for export?

24. The MC record includes copies of the Preliminary Regulatory Impact Analysis and a report from OSHA's contractor, CONSAD, entitled "Economic Analysis of OSHA's Proposed Standards for Methylene Chloride", October 24, 1990 (Ex. 15a). Comments are requested on these analyses of the feasibility and the cost-effectiveness of the proposed standard and alternatives.

25. The Agency has prepared a draft Preliminary Regulatory Flexibility Analysis analyzing the impacts of the proposed standard on the small businesses which OSHA believes may be affected and has adapted the proposed standard to take into account the circumstances of small business where appropriate. Additional information is requested regarding:

a. What kinds of small businesses produce or use MC and how many of them would be affected by regulating exposures to MC?

b. Do any Federal rules duplicate, overlap or conflict with OSHA regulations concerning exposure to MC?

c. Will difficulties be encountered by small entities when attempting to comply with requirements of the proposed standard? Can any of the requirements be altered or simplified for the benefit of small entities while still achieving comparable protection for the health of employees of small entities?

d. What timetable would allow small entities sufficient time to comply?

26. OSHA has determined that employees in the shipyard industry are exposed to MC at levels which potentially exceed the proposed PELs.

a. Do the proposed requirements appropriately cover MC-related hazards to which shipyard employees are exposed?

b. Are there any MC exposure situations which are unique to shipyard employees? c. What efforts have been made to control or prevent shipyard employee exposure to MC?

d. To what extent have employers controlled or protected employees from MC exposure such as through the use of engineering and work practice controls or respirators, respectively?

e. What has the implementation of any such measures cost? What has been the experience with those measures, in terms of effectiveness and reliability?

f. To what extent can shipyards reduce or eliminate the use of MC, through the use of mechanical methods of paint stripping or through substitution (see Issues 11 and 19)?

g. At its August 12, 1991 meeting, the SESAC discussed whether or not OSHA should allow employers whose employees use MC on fewer than 30 days a year to comply with the draft proposed PELs by any mix of engineering, work practices and respiratory protection. Some SESAC members noted that this threshold would allow small shipyards reasonable flexibility in determining how to comply with the PELs. OSHA solicits comments, supported by cost and benefit data, on the appropriateness of setting such a threshold for the shipyard industry or for other industries.

If OSHA were to set a threshold, at what point should it be set? Can a threshold be set that provides useful regulatory relief without unacceptably compromising employee protection? Are there sectors of the shipyard industry, or of other industries, for which the threshold approach would be particularly suitable?

27. OSHA has determined that many employees performing construction work have exposure to MC at levels which potentially exceed the exposure limits set by the proposed rule.

a. Do the proposed requirements appropriately cover MC-related hazards to which construction workers are exposed? Are there situations unique to the construction industry which indicate that any of the proposed provisions would be inappropriate for the construction industry? Are there additional provisions that should be included in the rule in order to provide adequate protection for construction employees?

b. Are there any MC exposure situations which are unique to the construction industry? What exposure levels have been experienced by construction workers?

c. What efforts have been made to control or prevent construction worker exposure to MC?

d. To what extent have employers controlled or protected employees from MC exposure, such as through the use of engineering and work practice controls or respirators, respectively?

e. What has the implementation of any such measures cost? What has been the experience with those measures, in terms of effectiveness and reliability?

f. To what extent can construction firms reduce or eliminate the use of MC in paint stripping through use of mechanical methods or substitution (see Issues 11 and 19)?

28. OSHA has determined that employees in agriculture may be exposed to MC at levels which potentially exceed the proposed PELs.

a. What processes or products in agriculture result in employee exposure to MC? What levels of exposures have been measured? What are the frequency and duration of such exposures?

b. Do the proposed requirements appropriately cover MC-related hazards to which agricultural employees are exposed?

c. Are there any MC exposure situations which are unique to agricultural employees?

d. What efforts have been made to control or prevent agricultural employee exposure to MC?

e. To what extent have employers controlled or protected employees from MC exposure such as through the use of engineering and work practice controls or respirators, respectively?

f. What has the implementation of any such measures cost? What has been the experience with those measures, in terms of effectiveness and reliability?

29. OSHA has provided for changes in the frequency of monitoring based on changes in the workplace or a demonstrated reduction in the exposure levels from above the PEL or STEL to below the PEL and STEL. The Agency is also considering adding a provision to the final rule which would explicitly increase the required frequency of monitoring from 6 months to 3 months, whenever a periodic monitoring sample was above the PEL or STEL. The frequency could again be reduced to 6 months upon collection of two samples at least 7 days apart which were below the PEL and STEL. Would this type of provision be necessary to give adequate guidance to employers as to when it is appropriate to increase monitoring frequency?

30. In the proposed regulatory text, the respirator selection table (Table 1) indicates the respirators that OSHA is proposing to allow in various ambient concentrations of MC. Filter-type respirators would not be allowed except in emergency escape situations. Does the respirator selection table in the proposed rule appropriately regulate the choice of respirators? What, if any, types of respirators should be prohibited from use by employees exposed to MC? What would be the basis for any such suggested ban?

As noted in the Summary and Explanation, NIOSH intends to further study the breakthrough characteristics of MC in organic vapor cartridges and canisters in order to better assess the effectiveness of filter respirators for protecting employees from MC exposure. Is additional information available on the breakthrough times of organic vapor cartridges under various conditions? Have other sorbents been tested for their potential usefulness in MC filter respirators? Are there any circumstances under which filter respirators would provide adequate protection for employees exposed to MC? If so, please provide supporting data.

31. Should OSHA adopt the respiratory protection provisions contained in the proposed Methods of Compliance standard (54 FR 23991) instead of the provisions in the MC proposal? If so, are there any modifications that would need to be made in the provisions of that proposed standard in order to provide appropriate protection against exposures to MC?

32. Are there conditions, in addition to those proposed, under which respirator use should be permitted? OSHA has proposed to require fit testing for each employee who would wear a negative pressure respirator. Can employees who wear negative pressure respirators be adequately protected without quantitative fit testing? Do other fit testing protocols exist which would adequately assess respirator fit, in addition to the fit tests described in appendix C?

33. OSHA has proposed to require that each employee who must wear a respirator, but does not meet the 10-day minimum exposure requirement for inclusion in medical surveillance, be offered at least a cardiopulmonary examination to assess the employee's ability to wear a respirator. Is this appropriate? Should eligibility for the cardiopulmonary system evaluation be based on a certain minimum exposure period? If so, what should that exposure period be?

34. Are the medical tests specified in this proposed rule appropriate for facilitating early detection of the adverse health effects resulting from MC exposure? If not, please identify those tests regarded to be inappropriate and give the specific reasons. Are there other tests which should be required because they would be useful for diagnosing MC-related toxicity? For example, should OSHA require chest X-rays, urine analysis or liver function tests, notwithstanding indications that those tests are performed as "general" medical surveillance measures, rather than as means to detect MC effects?. Please include medical evidence to support your position.

35. Does the coverage of employees under medical surveillance include all employees whose exposures warrant coverage? If not, how should the coverage be expanded? If the present requirements for inclusion are retained, how much of the total MC-exposed workforce will be eligible to participate?

36. What additional provisions for medical surveillance should be included in the standard? What kind of clinical tests should be offered to employees exposed in emergency situations?

37. OSHA did not include a provision for Medical Removal Protection (MRP) in the proposed MC standard. Would MRP be beneficial for employees exposed to MC, due to the risk of material impairment to health? Do the health risks justify the inclusion of MRP provisions in the final rule? If OSHA decides to set MRP requirements for MC-exposed workers, what should these provisions be? Please provide information and data supporting your views.

38. OSHA is aware that many employees may be splashed with MC in the course of their occupational exposure. Therefore, the Agency is considering whether the proposed rule for MC should include requirements for quick-drench showers and eye-wash facilities to protect employees from the potentially serious health effects of MC splashes. Quick drench showers that could drench an employee with piped-in water applied with force, and eye-wash facilities that could flush the eyes repeatedly with a great amount of water, are already required in the OSHA health standard for formaldehyde (29 CFR 1910.1048(j)). In addition, the health standards for 1,2-dibromo-3-chloropropane (29 CFR 1910.1044(l)), acrylonitrile (29 CFR 1910.1045(m)) and ethylene oxide (29 CFR 1910.1047 (Appendix A)) provide for wash and shower facilities to protect employees' eyes and skin from hazards.

OSHA seeks to determine if the eye and skin hazards of MC exposure necessitate promulgation of requirements for hygiene facilities to supplement those imposed through existing §1910.141. In addition, the Agency seeks to determine if compliance with the hygiene facility requirements set out in one or another of the standards cited above would adequately protect employees. Accordingly, OSHA solicits comments regarding the following questions:

a) What concentration of MC causes serious eye or skin effects? What are those effects? To what extent do they impair employee health and safety?

b) Are there circumstances in which employees would contact liquid MC at concentrations that would cause serious eye or skin effects? What are those circumstances? Are there any additives commonly used in MC formulations which would add or detract from the skin and eye health effects? What are the effects of these additives?

c) To what extent would compliance with existing or proposed requirements for personal protective equipment obviate a requirement for hygiene facilities?

d) To what extent are MC-exposed employees already provided with hygiene facilities, such as quick-drench showers and eye-wash stations which would protect them from serious eye and skin effects? Do those systems provide adequate protection? How could that protection be improved? Which industries are most likely to have hygiene facilities in place? Which are least likely?

e) What quick-drench shower or eye-wash systems are available for installation? What do they cost? To what extent do their features differ? How long from the time an order is placed does it take to get systems installed? How many employees are expected to share a single shower or eye-wash facility? How close are those facilities to employee work stations? How close should they be?

f) Are there industries where it would not be feasible to install quick-drench showers or eye-wash stations? Should OSHA limit the application of such a requirement to those employers who have a set minimum number of employees (such as 10)? Also, how necessary or feasible would such a requirement be for employees exposed to MC in the construction industry?

OSHA also requests information on any experience with eye or skin exposure, including the number of incidents, the severity of incidents, the number of lost work days resulting from those incidents, any measures taken to reduce eye and skin hazards and any measures taken to treat employees after eye or skin contact with MC.

39. As discussed in the Health Effects Section, OSHA is concerned that MC can be absorbed through the skin. What additional dermal absorption studies for MC are available? What is the extent of potential adverse health effects resulting either from dermal exposure alone or from a combined exposure by inhalation and dermal routes?

40. What types of personal protective equipment, such as protective clothing or barrier creams have been effective for protecting employees from exposure to MC in terms of decreased permeation rates. What are the costs and availability of such products?

41. In order to underscore the importance of keeping hands and mouth free of contamination with MC, OSHA is considering adding a provision in the final rule to prohibit the following activities in regulated areas, eating, drinking, smoking, gum or tobacco chewing and applying cosmetics. Are these prohibitions reasonable and appropriate? Should any additional activities be prohibited in regulated areas?

42. What measurement and analytical methods are available for use in determining compliance with the MC proposed PEL of 25 ppm or the 12.5 ppm action level? Can these methods determine compliance with the proposed STEL of 125 ppm? How accurate are these methods? Are there any specific conditions for sample collection and preservation that should be included in the final standard so that reliable results can be obtained? In the proposed rule, requirements are set for the accuracy of analytical methods used in exposure monitoring. Are these requirements reasonable? Should OSHA consider more or less stringent requirements for these methods?

43. OSHA has evidence indicating inconsistency between data collected using sampling badges and those collected by adsorption on charcoal collection devices. OSHA solicits information on the conditions under which these sampling devices should or should not be used for measuring workplace exposures.

44. Should work places relying on objective data to document the fact that employees are not exposed at or above the action level be required to install alarm devices sensitive to concentrations at or below the action level? Are passive diffusion devices reliable enough to detect short-term low level exposure of employees to MC? Can they detect levels as low as 12.5 ppm?

45. Please provide any information available on potentially significant (negative or positive) environmental effects that may occur as a result of the proposal if implemented.

46. Substitution of other chemicals or processes for methylene chloride in certain industrial segments may impact the composition of waste streams generated by these facilities (impacting water quality and hazardous waste operations). OSHA is interested in obtaining information on how the chemical composition and volumes of these waste streams would change as the result of substitution for MC and whether the volume of waste requiring special treatment or disposal as hazardous waste would change as the result of substitution?

47. The National Environmental Policy Act (NEPA) of 1969 (42 U.S.C. 4321 et seq.) requires that each Federal agency consider the environmental impact of major actions significantly affecting the quality of the human environment. Any person having information, data or comments pertaining to possible environmental impacts is invited to submit them with accompanying documentation to OSHA's docket. Such impacts might include:

a. Any positive or negative environmental effects that could result should a revised standard be adopted;

b. Beneficial or adverse outcomes between the human environment and productivity;

c. Any irreversible commitments of natural resources which could be involved should a standard be implemented; and

d. Estimates of the degree of reduction of MC and any other chlorinated hydrocarbons in the environment by the proposed OSHA standard and alternatives.

In particular, consideration should be given to the potential direct or indirect impacts of any action, MC substitute, or alternative actions on water, soil and air pollution, energy usage, solid waste disposal, or land use. Since there are reports of soil, air and water contamination by MC, what confounding effects does the continuous release of MC (e.g., at rates of 9 million pounds per year or more) have on the in-plant and New York State control populations in the Rochester, N.Y. plant epidemiological studies submitted to the record?

48. What other issues raised in the "Request for Information and Comments" for MC regulation (see Federal Register 51 (No. 228), pp. 42264 to 42266) should be further discussed prior to promulgation of a revised MC standard?

V. CHEMICAL IDENTIFICATION, PRODUCTION TECHNOLOGIES, AND INDUSTRIAL USES

A. Chemical Identification

Methylene chloride (MC) also called dichloromethane (DCM) [chemical abstracts Service Registry Number 75-09-2] is a halogenated aliphatic hydrocarbon with a chemical formula of CH(2)Cl(2), a molecular weight of 84.9, a boiling point of 39.8 deg C (104 deg F) at 760 mm Hg, a specific gravity of 1.3, a vapor density of 2.9 and a vapor pressure of 350 mm Hg at 20 deg C (68 deg F). Concentration of MC in saturated air at 25 deg C reaches 550,000 ppm. MC has low water solubility (1.3 gm per 100 gm of water at 20 deg C), an extensive oil and fat solubility, and a low flammability potential. It is used as a flame suppressant in solvent mixtures (lower explosive limit of 12% and upper explosive limit of 19%). It is a colorless volatile liquid with a chloroform-like odor and its odor threshold varies between 100 to 300 ppm. Contact with strong oxidizers, caustics and active metal powder may cause explosions and fires. Decomposition products during combustion or fire include phosgene, hydrogen chloride and carbon monoxide.

B. Production Technologies and Industrial Uses

1. MC Production

MC is manufactured domestically in six plants owned by four companies. These companies are: Occidental Chemical in Belle, WV; Dow Chemical U.S.A. in Freeport TX, and in Plaquemine, LA; LCP Plastics, Inc. in Moundsville, WV; and Vulcan Materials Company in Geismar, LA and Wichita, KS. The approximate annual capacity of these six plants is 105, 150, 190, 80, 80, and 130 millions of pounds, respectively. The total annual capacity of the plants averages 735 million pounds a year (Ex. 15b). The actual production of MC, however, was estimated to be approximately 520 million pounds (234,000 metric tons) in 1987, down from an estimated 607 million pounds (275,000 metric tons) in 1984 (Ex. 7-220). The breakdown of the volumes of MC handled in 1988 for each industrial application group is shown in Table 1 (Ex. 15).

MC is produced commercially in the United States by two processes, (1) thermal chlorination of methane; and (2) hydrochlorination of methanol to produce methyl chloride followed by chlorination of the methyl chloride. In the first process, thermal chlorination of methane, methane and chlorine are fed to a reactor at moderate pressure and high temperature (340-370oC).

TABLE 1. - ESTIMATED MC HANDLED
__________________________________________________________
  | Estimated MC
Application Group | Handled
  | (millions of pounds)
______________________________ | __________________________
  |  
Production | (467)
Polyurethane | 54
Distribution/Formulation | 250
Aerosols | 106
Polycarbonate | 7
Pharmaceuticals | 28
Manufacture of Paints | 28
Manufacture of Paint Removers | 155
Paint Stripping | 52
Degreasing | 41
Cellulose Triacetate and |  
Film Base Production | 11
Electronics | 40
Miscellaneous Usage (Food |  
Extraction, Pesticide |  
formulation, and Ink) | 38
Solvent Recovery. | 37
  | _________
  | *497
______________________________ | _________________________
Note*: Netting out rehandling, estimated total consumption equals 467 million pounds manufactured, minus 7 million pounds exported, plus 37 million pounds recovered from used solvent.
__________________________________________________________

All four chlorinated methanes (methyl chloride, methylene chloride, chloroform and carbon tetrachloride) are produced by a chain reaction, with hydrogen chloride as a byproduct. The products of the reaction (including unreacted methane, HCl and Cl2) are separated by fractionation, scrubbing and drying operations. The relative yields of the different chlorinated methanes can be varied by recycling and control of the methane/chlorine feed ratio to optimize the yield of the desired products. MC may undergo secondary chlorination at ambient temperature during which chloroform and carbon tetrachloride are produced. Only one plant (Dow at Freeport, TX) is believed to produce MC by chlorination of methane. In the thermal chlorination process, for every mole of Cl2 introduced, a mole of HCl as a by-product is produced. Therefore, unless HCl is consumed locally in the production facility, its disposal may have environmental and economic impacts.

In the second and more widely used process, hydrogen chloride and methanol are reacted catalytically to produce methyl chloride. Methyl chloride is then reacted with chlorine in a process similar to that described above to produce MC. MC is separated from the other products of the reaction and purified by fractionation, scrubbing and drying operations. Stabilizers are usually added to prevent breakdown and inhibitors may be added to prevent corrosion.

MC production, by either method, is accomplished in an enclosed system and bypasses are considered to be an integral part of the continuous production process. As discussed in the control section, this continuous production process contributes significantly to the elimination or substantial reduction of worker exposure to MC vapors. After production, MC is stored in outdoor tanks and is shipped in bulk quantity by rail car, tank truck, barge or in 55-gallon drums.

MC is the predominant solvent used for paint removal, metal degreasing, and in pharmaceutical and aerosol products. It is also used as a blowing agent in the production of polyurethane foams, in the cleaning of printed circuit boards, in the extrusion of triacetate fibers, and in a wide variety of other important industrial processes. The following are descriptions of these uses of MC.

2. Polyurethane Foam Blowing

There are currently an estimated 180 foam blowing establishments consuming 54 million pounds of MC with an estimated 1169 exposed workers. MC is used as a blowing agent and as a solvent for cleaning equipment in the production of polyurethane foam (PU). OSHA has no information on the quantity of MC used in foam blowing which is subsequently released into the air. However, the Agency has assumed that all of the MC consumed by these facilities is released into the air (Ex. 15).

In general, commercial PU products are complex plastics formed by the reaction of liquid isocyanate components with liquid polyol resin components. These components may also contain cell blowing agents, combustion retarding agents and catalysts. The finished products are polyurethanes or isocyanate plastics. PU products can be classified as rigid polyurethane foams, flexible polyurethane foams, and polyurethane elastoplastics.

The bulk of rigid polyurethane foam is made from polyether polyols, combustion-retarding agents, polymeric isocyanates, and low boiling halocarbon blowing agents. MC is not incorporated into the production mix, but is used only for filling and cleaning the mixing head.

Flexible foams are prepared from polyether polyols and TDI (toluene diisocyanate) and polymeric isocyanates. Carbon dioxide gas is the usual blowing agent. For very soft, low-density flexible foams, a small quantity of chlorofluorocarbon or chlorocarbon blowing agent may be added.

PU elastoplastics are made from either polyester or polyether polyols and diisocyanates. PU elastoplastics are available as pourable or injectable (Reaction Injection Molding) liquid systems, preformed pelletized solids, and sheetstock. These elastoplastics may contain combustion-retarding agents (Ex. 7-135).

a. Use of Rigid Foam. PU rigid foam is used in the refrigeration industry, in construction and in plumbing as insulation material, for roofing and piping, and in refrigerated and air-conditioned containers and transportation tanks. Because of low thermal conductivity and good mechanical properties, rigid PU foam has several advantages over other insulation materials. These advantages include simplified production, reduced material usage, low weight, good weatherability and low water absorption. Another advantage is its ability to be sprayed to produce foam layers of any thickness on vertical or horizontal surfaces.

Rigid PU foam used as core material has important functions in the conventional assembly of various structures (e.g. bathrooms). The automotive industry uses foam for headliners and cavity foaming for interior liners of vehicles. Since 1970, rigid PU foam has been used in shipbuilding to make older barges unsinkable. The leaking barges are filled with rigid foam between the outer and inner walls at dry dock and thus made water tight. Certain types of PU foam have been introduced in specialized horticulture and in seeding nurseries. They are suited for vegetative reproduction (cuttings) in landscaping arrangements and as floral foam. Rigid PU is also used in surfboards and sailboats, weather protected VHF antennas and self-supporting cupolas of rigid PU foam ("radomes"). PU foam has good permeability to electromagnetic waves, good weather resistance and high strength to weight in high winds.

b. Use of Flexible Foam. PU flexible foam is useful for mattress and upholstery construction because of its properties of low weight, high air permeability, good heat and humidity transfer, durability, comfort and physiological compatibility. PU flexible foam has good "cushioning properties". That is, the ability to decrease shock-acceleration in relation to the surface load, make it particularly suitable for packaging sensitive goods. PU flexible foams are also used to optimize room acoustics over a wide frequency range because of their good sound absorption properties. Flexible foams are permeable to x-rays, and so are used for the support of body parts during x-ray examinations. Elastic bandages and bindings are further examples of uses of flexible PU foam for medical applications. PU flexible foam also has applications in sports and leisure activities, for example, as cushioning in gym, judo and wrestling mats, and as impact protection for high jumping and pole vaulting. Popular toys such as balls and frisbees are also made from flexible PU foam.

c. Use of PU Elastomers

The third major category of PU products is PU elastoplastics. The largest single application of high quality cast PU elastoplastics is the production of conveyor and roller systems. Because of high resistance to wear and tear, PU elastoplastics have a long life expectancy in rough conditions (i.e. in metal processing factories). Milling rolls made from PU elastomers are used in both the steel and paper industries where a high pressure load bearing capacity and/or high wear resistance are required. Naphthalene diisocyanate (NPI)/polyester-based cellular PU elastomers have peculiar and desirable dampening properties. Another large volume application for PU elastomers is in the construction of sports fields. PU elastomer systems are resistant to hydrolysis and rotting in all types of climates. PU elastomers are also used for pipe seals in underground construction, including formwork mats for relief concrete and wire and cable coatings in the electrical industry. Also, PU split leather has replaced leather in the shoe industry, because PU split leather has better abrasion resistance and less moisture uptake. In addition, torsion resistant ski boots and sports shoe soles are produced from polyelastomers.

d. Production technology. The following describes the production technology of polyurethane foam with the "one shot" process. This process is carried out without the use of solvent and is generally very fast, specifically in the presence of catalysts. Foam materials are prepared by simultaneously mixing the co-reactants directly with additives (blowing agents (e.g., MC), catalysts, foam stabilizers and flame retardants). The variability and the sequence of production processes and the type of equipment needed for each process affect worker exposure to MC.

Polyurethane foam ingredients, polyol and isocyanate, are delivered in drums containing approximately 250 liters. Two tanks per ingredient are installed. One tank contains materials which have to be conditioned before they are ready for processing. The other tank feeds the processing machine. The chemicals can be pumped from one tank to the other. The processor may alter the formulation by adding auxiliary agents such as blowing agents, catalysts, and pigment pastes to the main components. If direct metering is used, the additives are blended in line on the suction side of the pump with the use of premix chambers. The formulation of the materials is accomplished apart from the metering equipment if machines with recirculation are used. At the blending stations, additives and auxiliary materials are metered with pumps and blended together by means of stirrers or static mixers. The mixture is then transferred to the machine tanks. Blending stations recharge the machine tank by pumping the materials against the tank pressure on demand from level switches, thereby achieving continuous production.

One of the most important processing parameters is temperature. Controlling the temperature is referred to as "conditioning" the materials in the tanks. Any change in temperature causes a change in viscosity, which in turn, influences the metering pumps. Adjusting viscosity and its associated temperament can be accomplished by changing the pressure in the machine tanks.

Metering pumps are necessary for processing flowable ingredients into reaction mixtures. Feed pumps are used to ensure proper and constant feeding of the metering pumps. Different metering devices are needed, depending on whether high or low pressure machines are used, or whether the process is batch or continuous.

Since mixing is very important for polyurethane processing, the mixhead is commonly referred to as the heart of the machine. Within the mixhead is the mixing chamber, in which the components are brought together to form the reaction mix. The conditions for mixing must be constant during the process.

The reaction mix can be poured into open or closed molds. Pouring into open molds or onto a substrate can be done at one spot or along a pattern. Pouring into a closed mold is done through fill holes or gates. The diverter cone is one of the oldest devices for smoothing. The stream of the reaction mix coming from the mixing chamber is diverted to the wall of the outlet tube.

Although MC does not enter into the chemical reaction of PU production, MC is used as a blowing agent in the production of flexible PU and is used as a flushing media of the mixing head in the production of rigid foam. The cleaning of the mixing chamber and all the elements of the mixers with agitators is usually done by purging solvents. The small volumes of the impingement mixers allow purging with air. For example, in the process of mixing some of the reaction mixture is left behind in the mixing chamber after each pour. MC is used to flush the residual foam mix if the duration between shots is longer than the cream time of the material.

The preferred agents for rigid polyurethane integral skin foams are low boiling halogen alkanes. Integral skin foams are formed from PU foam molding in such a way that parts consisting of a cellular core and a solid skin result. The skin is formed as an integral part and from the same material as the core foam. Although the standard blowing agent monofluoro-trichloromethane (R11), provides a satisfactory skin, 40% of this blowing agent can be replaced by MC to further improve the skin formation (Ex. 7-136).

e. Substitutes for MC in foam blowing. The substances that can be substituted for MC in foam blowing operations pose serious environmental problems. Chlorofluorocarbon (Freon CFC 113), is currently used as an auxiliary blowing agent in some foam manufacturing facilities. The emissions of this chemical are considered to be a leading cause of the depletion of the earth's ozone layer. Freon is also more expensive than MC and requires storage in potentially dangerous pressurized vessels.

To date no chemicals or chemical formulations have been developed that clean foam equipment as effectively and safely as MC. Although other chlorinated solvents may be effective, they are more acutely toxic and more flammable than MC. Dimethyl formamide has been found effective for use as a dip tank solution in which the foam trough is soaked overnight. However, it is not practical for use where there is potential employee exposure due to its high toxicity (OSHA TWA is 10 ppm) (Ex. 10-4).

Trichlorofluoromethane (F11), dichlorodifluoromethane (F12) and 1,1,2-trichloro- 1,2,2-trifluoroethane can also be substituted as blowing agents for MC. 1,1,2-Trichloro- 1,2,2-trifluoroethane can be used instead of MC to produce rigid foam skin. Furthermore, 1,1,1-tri- chloroethane may function satisfactorily as a substitute when flushing the residual foam from the mixing chamber after the pour. However, none of these have been documented to effectively replace MC (Ex. 7-136) in large production facilities.

A new foam pouring technology has resulted in the development of foam formulations that do not require an auxiliary blowing agent, yet achieve the desired physical properties of the foam. This newly-patented technology has not yet reached commercial production, and therefore, manufacturers currently rely on the pouring methods described above (Ex. 10-4).

3. Aerosols

There are an estimated 217 aerosol packing establishments consuming 106 million pounds of MC with an estimated 2,182 exposed workers. MC is used as a solvent, co-solvent, and vapor pressure suppressant in aerosol manufacture. MC aerosol use areas and subcategories are listed in Table 2. All of the MC used in the categories listed is released into the air during consumer use. Emissions during aerosol packing can result from: evaporation during product-solvent mixing operations; during aerosol can charging and MC transfer operations; volatilization of suspended droplets; and spills. The exact amount of MC released into the air from aerosol packing is not known (Ex. 15).

An aerosol is composed of the hardware (can, dip tube, valve spring, and button) and the contents (propellent, an active ingredient, and a solvent). A propellent is defined by the Department of Transportation as "a material which can expel the contents of an aerosol container at room temperature". The typical propellent is a liquified gas with a vapor pressure greater than atmospheric pressure (14.7 psia) that forces the contents of the can out when the valve is activated at room temperature (Ex. 7-133). MC cannot function alone as a propellent because of its low vapor pressure relative to other propellants (e.g. at room temperature, 25oC: MC, 350 mm Hg; dichlorotetrafluoroethane, 1444 mm Hg) (Ex. 7-133).

TABLE 2. - AEROSOL USE AREAS AND SUBCATEGORIES
___________________________________________________________
Use Areas | Subcategories
___________________ | _______________________________________
  |  
Pesticides | Foggers; Direct Sprays; Residual
  |       Insecticides.
Paints and | Spray Paints; Wood Stains; Varnishes;
          Finishes |       Finishes; Primers; Paint
  |       Removers/Strippers; Rust removers.
Automotive and | Brake Cleaners; Carburetor and
          Industrial |       Choke Cleaners; Engine Cleaners.
          Products. |  
Household | Silicones; Spray Undercoatings;
          Products. |       Mold Release Agents; other
  |       automotive and industrial products.
Other Products | Artificial Snow; Glass Frosting;
  |       Electronic Cleaners; Water
  |       Repellents, Paper, Carpet, Rubber
  |       Adhesives.
___________________ | _______________________________________

An active ingredient is a material essential for the specific application for which the aerosol was formulated (e.g., cleaning agent, insecticide, etc.). The active ingredients, solvents, and propellants are combined so that an effective, attractive, and acceptable product is obtained (Ex. 7-133).

A solvent such as MC brings the active ingredient into solution with the propellants. Most propellants have poor solvent characteristics; in many cases, active ingredients are not soluble in propellants. In order to obtain a homogeneous mixture, it is necessary to add a liquid with the necessary solvent properties. It is sometimes desirable to have another liquid present which is not miscible with the propellent (e.g. water and propylene glycol). In these cases, a co-solvent such as MC or ethyl alcohol is added to obtain a homogeneous mixture. Another function of a solvent such as MC is to help produce a spray with a particle size that is most effective for a particular application. Solvents prevent the propellants from evaporating completely in air shortly after discharge from the can. Therefore, a solvent also assists in atomization and allows for a higher delivery rate (Ex. 7-133). MC is used as a solvent because of its high vapor pressure (350 mm Hg) when compared with other economically viable solvents, its high boiling point (39.8 deg C), its compatibility with many types of formulations, and because it depresses the vapor pressure of high pressure propellants. As a result, the flammability of the mixture is reduced and the dispersion of the aerosol spray is enhanced (Ex. 15 B).

Depending on the volume of aerosol production, MC is shipped in tank cars, or in fifty-five (55) gallon drums. MC is either transferred directly from the shipping containers to the packaging line (to avoid loss of solvent due to volatilization), or it is transferred to storage tanks for mixing with other products (i.e. active ingredients and solvents). The aerosol can is charged with the active ingredients and solvent (either individually or premixed), and then filled with the propellant in an explosion proof room (Ex. 4-112). The valve and valve stem are added and the can is crimped shut. Cans are then placed in a hot water bath to test the integrity of the can at a specific temperature (temperature based on the percentage of MC and other components in the can). The cans are weighed to meet minimum requirements, checked for leaks, labeled, capped and packaged for shipment. Many companies contract out aerosol packing due to high plant costs. Some companies fill other companies' products as well as their own, while others only fill aerosols for other companies. Most production lines can be modified to accommodate different products. These modifications, however, can reduce the efficiency of a plant (Ex. 15). Due to the various interrelated functions served by chlorinated solvents in aerosols or other packaging (e.g. paint formulation), there are no direct one-for-one substitutes. Modification of a formulation may require changes in the design of the container. There are many potential substitutes for MC in aerosols. Substitutes with diversified uses include 1,1,1-trichloroethane, tetrachloroethane, mineral spirits and water soluble formulas. Substitutes with limited uses include 1,1,2-trichloro- 1,2,2- trifluoroethane.

OSHA notes that some packagers have discontinued the use of MC because of health concerns or the development of solvents or co-solvents with equivalent or better properties than MC (Ex. 15).

4.Polycarbonate Resin

OSHA has identified four polycarbonate resin manufacturers with an estimated 67 workers, producing a total of 710 million pounds of polycarbonate annually. MC is used as a solvent in the polycarbonate resin production. OSHA estimates that a total of 7 million pounds of MC are released to the air by polycarbonate resin manufacturers. These plants include the General Electric plant at Mt. Vernon, Indiana, the Bayer U.S.A. (Mobay Corporation) at Baytown, Texas, the Dow Chemical plant at Freeport, Texas and the Mobay plant at New Martinsville, West Virginia (Ex. 7-9, 7-141, 10-27).

Polycarbonate resin is an important engineering resin because of its unique properties (e.g. optical clarity and shatter proof properties). Polycarbonates are a special class of polyesters derived from the reaction of carbonic acid derivatives with aromatic, aliphatic, or mixed diols. They may be produced by the Schotten-Baumann reaction of phosgene with a diol in the presence of an appropriate hydrogen chloride acceptor (e.g. bisphenol-A with phosgene in the presence of an excess of pyridine), or by a melt transesterification reaction between the diol and a carbonate ester. That is, the phosgene first reacts with phenol to produce diphenyl carbonate, which in turn reacts with bisphenol-A to yield phenol in a molten solvent-free polymer. Transesterification is reported to be the least expensive route. That process was phased out, however, because there were many polycarbonate products which could not be produced using transesterification (Ex. 7-138).

Many medical devices are produced from polycarbonate (e.g., blood oxygenators used to purify blood and intravenous harnesses). No good substitute is available for these applications. Polycarbonate can be sterilized both by autoclave and by gamma radiation.

Some other key applications for polycarbonate resin are in computers and business equipment, aircraft, small and large appliances, telephones, safety and sports helmets and optical discs. Polycarbonate sheets are used extensively in signs, windows and window protection, walkways, and roofing structures. Polycarbonate sheet is also used in greenhouses, solar and construction glazing, and skylights. Polycarbonates have also been used for energy recovery, both in the commercial and residential building industry (e.g., in active and passive solar energy collection applications). In the automobile industry, polycarbonates are used for weight reduction which impacts vehicle fuel economy. Safety equipment manufacturers have used polycarbonates for hardhats and safety glasses. Other items made from polycarbonates include the canopy for jet fighters, some missile parts and "bullet resistant glass" (Ex. 10-27).

Generally, the interfacial process is used in the production of polycarbonate resins. That is, during polymerization, a jacketed vessel equipped with an agitator is charged with the reactants and MC solvent. Phosgene gas is bubbled through the reactor contents. The reaction requires approximately 1-3 hours and is carried out at temperatures below 40 deg C (104 deg F). Pyridine and MC are recycled during the process (Ex. 8-11).

The polymerized-liquified reactor contents are then pumped to wash tanks for removal of residual pyridine using hydrochloric acid and water. MC is removed by steam stripping. The polycarbonate polymer is precipitated from the polymer-MC stream with an organic compound, such as an aliphatic hydrocarbon, and is separated by filtration, The filtered polymer is transferred to a dryer, while the solvent is recovered in a distillation column (Ex. 8-11).

Both General Electric and Bayer now use the interfacial process described above. In this process the bisphenol-A is dissolved as a disodium salt in aqueous caustic and reacted with phosgene bubbled into a methylene chloride layer. Reaction occurs at the solution's interface with the polymer "growing" into the methylene chloride layer. The polymer chain length is controlled by addition into the reaction mixture of a monohydroxyphenolic compound. The methylene chloride layer is then separated, and the polymer is isolated by removal of solvent. At this stage, the various producers use a number of different processes, including devolatilization extrusion, granulation, and spray drying.

In devolatilization extrusion, a higher boiling solvent may be substituted for MC, concentrated, and run through a vacuum vented extruder to form pellets.

The granulation process introduces the methylene chloride solution into hot water. The solvent boils off and the friable polycarbonate resin is deposited. After drying, amorphous polycarbonate pellets are formed by extrusion of the granules.

Spray drying vaporizes the MC solvent with the concurrent precipitation of powdered polycarbonate resin. The powder is then extruded into pellets or other articles (Ex. 7-142). Most of the commercial polymer is produced and characterized in solution. Some is converted to film, whereas solutions are used to apply coatings to polycarbonate parts.

GE-PBG is the largest U.S. manufacturer of polycarbonate resin. At the GE bisphenol-A manufacturing plant, MC is a recrystallization solvent for bisphenol-A. Recrystallized bisphenol-A is dried and fed to the polycarbonate resin production process. MC is captured and recycled back for reuse, employing state-of-the-art engineering controls. Primary recovery means include low temperature condensation and carbon adsorption with regeneration. The overall MC recovery rate in this operation is 99.5%. GE is currently planning to change the bisphenol-A (BPA) production process to make the process a solventless one, by using a melting process to produce BPA instead of the MC recrystallization process (Ex. 7-216, 7-230).

At the GE Polycarbonate Resin Plant, MC is also used as a process solvent to carry polycarbonate polymer through the reaction and purification process. The polycarbonate resin is then isolated and the MC is recovered through a distillation process and recycled. Numerous process vents are combined and routed to vent absorbers. The overall MC recovery rate in this operation is 99.8%.

At the GE Polycarbonate-Polysiloxane Resin Plant (LR Resin), which is small compared to the Polycarbonate Resin Plant, MC is also used as a process solvent in the operation. At this operation, the overall MC recovery rate is approximately 93%.

As indicated above, the use of MC is a critical element in maintaining the product quality and safety specifications. Also, other solvents may crystallize, craze, crack, or mar the surface of objects made from polycarbonates.

Pyridine, cresylic acid solvents, and p-dioxane are the nonhalogenated solvents which can be used as substitutes for MC. Hydrocarbons and aliphatic alcohols, esters, and ketones do not dissolve polycarbonates, and thus cannot be used as substitutes for MC in this application. Chlorobenzene, which may be used in the processing of polycarbonates, is an adequate high temperature solvent, but the polymer may crystallize and set to a hard gel state on cooling. Acetone promotes rapid crystallization of the normally amorphous polymer, and causes catastrophic failure of stressed polycarbonate parts. Aliphatic and aromatic hydrocarbons promote crazing of stressed molded samples (Ex. 7-138, 7-139, 7-140).

5. Pharmaceuticals

An estimated 28 million pounds of MC are used in 76 pharmaceutical production facilities, exposing an estimated 1,007 workers. Most of the MC is used in pill coatings. MC is also used in the manufacturing of antibiotics, vitamins, contraceptives, and drugs used in the control of hypertension and diabetes (Ex. 10-8). It is estimated that 43% of the MC is released into the air during the production process and that 57% is recovered and processed for reuse (Ex. 7-9).

The pharmaceutical industry utilizes MC as an extraction solvent in the purification of pharmaceutical products and in pill coatings.Pharmaceuticals that are purified using MC as an extraction solvent include reserpine, cephalothin, cephaloride, cephaprin, tolbutamide, and estrone. Those purification operations separate pharmaceutical products from by-products by solvent extraction either in a reactor or in a vertical column. MC is used because of its superior solvency and high volatility.

In the pharmaceutical industry MC is used in four successive stages of pharmaceutical production: chemical reaction, product separation, purification, and drying.

In the chemical reaction stage, raw material solids and solvents other than MC, are mixed in a reactor vessel in which the chemical reaction is carried out, sometimes under elevated temperature and pressure. The stainless steel or glass-lined carbon steel reactor vessel is either an open tank or an enclosed vessel and is equipped with an agitator. Peripheral equipment such as condensers, a refrigeration unit, or a vacuum system can be added to allow the reaction to take place at very high or low temperatures and/or pressures. Some reactors are equipped with a condenser for recirculation of the solvent.

After completion of the chemical reaction, the pharmaceutical products are separated during the product separation stage, the effluent is pumped from the reactor to a holding tank where the reaction products are washed to remove unreacted raw materials and by-products. The washed reaction products are then piped to various separation process tanks. Product separation often utilizes an extraction process in which a solvent preferentially dissolves one of the reaction products.

Distillation, crystallization and filtration are among the purification techniques used after product separation or extraction. Following product separation the crude extracted product is purified by crystallization of the desired compound from a supersaturated solution. A filter press is usually used to separate the concentrate from the solvent. The purified product and remaining solvent are then separated in a centrifuge. The cake may be further washed by water or another solvent to remove impurities before drying.

After the completion of purification processes, products are moved to dryers, such as tray, rotary or fluidized bed dryers which use hot air circulation or are operated under a vacuum to remove the remaining solvents or water from the centrifuged or finished product.

MC is released during storage, reaction, separation, purification, and drying processes. Storage emissions result from displacement of air containing the solvent during tank charging. Reactor emissions result from displacement of air containing MC during reactor charging, solvent evaporation during the reaction cycle, venting of uncondensed MC from the overhead condenser during refluxing, purging of vaporized MC following a solvent wash, and opening of reactors during the reaction cycle to take quality control samples. Distillation condensers can emit MC as uncondensed solvent. During crystallization, emissions can result from the venting of vaporized solvent if the crystallization is being done by solvent evaporation. If crystallization is accomplished by cooling of the solution, there is little emission. Dryers are potential large emission sources, emission rates vary during drying cycles, and with the type of dryer being used. Emissions from air dryers are normally greater than those from vacuum dryers mainly because air dryers emissions are more dilute and difficult to control.

Among the possible substitutes considered (or tested) by some manufacturers were methanol and ethanol. However, these substances were rejected as substitutes, due to flammability and health concerns. Petroleum distillates are being used instead of MC by some facilities.

6. Manufacturing of Paint and Paint Removers/Strippers

a. Paint and Coatings Formulation. There are an estimated 390 paint formulation establishments with an estimated 1,808 exposed workers consuming 28 million pounds of MC. MC is used as a co-solvent in the formulation of paints and surface coatings, and as a co-solvent in aerosol spray paints. All MC in paints and surface coatings is released into the air (Ex. 15).

Paints and surface coatings can be classified into one of three categories based on their intended use. These categories are architectural coatings, product finishes for original equipment manufacturing, and special purpose coatings. Paint and surface coatings are formulated using binders, (a film-forming synthetic polymer or resin), a dispersion medium ( i.e., a volatile solvent) and, in most cases, pigments and additives. Binders comprise the non-volatile portion of a coating's liquid component. They bind or cement a paint or coating to a surface. Synthetic resins, natural resins, and drying oils are the three types of binders used in paints and coatings. Synthetic resins represent over 90 percent of binder usage. Solvents, such as MC, are used to dissolve the binders so the paint or coating has a consistency suitable for application. Pigments are finely powdered insoluble solids dispersed in a liquid medium. These solids can significantly affect the properties of a coating system. Pigments may also be used for corrosion inhibition, reinforcement, and filler, as well as for color and opacity. Additives are used in paint formulation in relatively small quantities to facilitate manufacturing, and to improve package stability, application ease, and final appearance or performance. These additives rarely exceed 1 or 2 percent of the total formulation. They can be classified by function as paint driers, anti-skinning agents, mildew inhibitors, rheological modifiers, and latex paint additives. When paints or coatings are applied to a substrate, the dispersion medium evaporates under ambient or forced dry conditions and the remaining film-forming components coalesce to produce an adherent film. A wide variety of solvents are used by paint formulators to achieve cost-performance objectives including:

Aliphatic hydrocarbons (e.g.,hexane, heptane);

Aromatic hydrocarbons (e.g.,acetone, methyl ethyl ketone);

Alcohols (e.g.,methanol, isopropanol);

Ketones (e.g.,acetone, methyl ethyl ketone);

Esters (e.g.,ethyl acetate, n-butyl acetate);

Ethers (e.g.,dioxane);

Chlorinated hydrocarbons (e.g.,MC, 1,1,1 trichloroethane);

and water.

Of the chlorinated hydrocarbons, MC and 1,1,1-trichloroethane are the preferred chlorinated solvents because of their low flammability, fast evaporation rates, and high range of solvency (Ex. 15).

b. Paint Remover Formulation. There are an estimated 293 paint remover formulation establishments with an estimated 760 exposed workers, consuming 155 millions of pounds of MC. Organic paint stripping formulations are generally designed for optimum cost performance by careful consideration of the characteristic property of the organic paint film to be stripped, the sensitivity of the substrate that comes into contact with the stripping formulation, and the workplace and disposal environment in which the stripping is performed. There are four major end use applications areas for paint strippers. These are architectural, original equipment manufacturing and after market goods, government and military goods, and consumers. OSHA notes that the critical considerations in the selection of paint strippers are different for each of these application areas. A typical paint stripping formulation employs (Ex. 15)

A primary solvent: For fast penetration and swelling of paint film (e.g., methylene chloride);

A co-solvent: To increase penetration and solvency effectiveness (e.g., methanol, ethanol);

An activator: To attack film-substrate bond strengths (e.g., alkyl-arene-sulfonates, sodium lauryl sulfate);

A thickener: To provide thixotropy (i.e., the property of a liquid or gel that is characterized by the loss of viscosity under stress, and regaining of viscous state when stress is removed) if needed; (e.g., hydroxypropylmethylcellulose);

An evaporation retardant: To prevent evaporation before penetration (e.g., paraffin wax (mp 46-57 deg C) at 1-3 wt percent);

A corrosion inhibitor: To protect the metal substrate from chemical attack (e.g., sodium benzoate).

Other additives may also be included, depending on the chemical nature of the film, the substrate, and stripping process cost performance requirements (Ex. 15).

MC is currently the primary solvent in the formulation of organic paint stripping agents. MC has the ability to penetrate, blister, and lift paint coatings. Organic paint stripping agents typically act by penetrating the cured paint film matrix, expanding interstitial structures to produce swelling of the film, dissolving uncured synthetic polymers and non-volatile formulation additives, creating physical stress on physical and chemical bonds at the film-substrate interface, lifting cured film from substrate, and entering between the lifted film and substrates to prevent re-bonding to the substrate (Ex. 15).

MC is shipped in tank trucks to paint stripper formulation sites across the nation. Formulated MC paint strippers are stored in drums or packaged in various size containers. Those drums and other containers are then shipped to industrial end points or to retail markets for consumer use (Ex. 15).

7. Paint Stripping

MC has the unique ability to penetrate, blister, and lift paint coatings, therefore, it is the preferred paint remover (stripper). MC paint strippers are used in aircraft maintenance firms (large&small), furniture refinishing firms, and industrial firms.

An estimated 75 large aircraft stripping firms with an estimated 1,671 exposed workers consume 10 million pounds of MC. There are also 225 small aircraft stripping firms with approximately 799 exposed workers, which consume 3 million pounds of MC. The furniture stripping industry is estimated to have 4,000 establishments, with approximately 5,720 exposed workers consuming 14 million pounds of MC. In addition, there are an estimated 1,930 industrial firms with approximately 6,942 exposed workers, which consume 25 million pounds of MC (Ex. 15).

Most paint stripping operations purchase their stripper ready to use. However, some furniture refinishing operations make their own formulas. They purchase crude MC and mix it with other ingredients such as toluene, methyl ethyl ketone, and methanol. Although these formulations vary, the most effective ones contain between 70-90 percent MC (Ex. 7-132).

In aircraft maintenance (large and small), MC-based paint removers are often used to strip old paint from airplanes prior to repainting. The stripper is usually sprayed onto the painted surface as a fine mist and allowed to blister the paint. The paint is then manually scraped off using nonmetallic scrapers and shoveled into drums. The application of stripper to hard to reach areas is generally accomplished manually using a brush or scraping tool which has been dipped into an open container of stripper. Finally, the airplane is washed with water or solvent rinse and brushed down to remove the remaining stripper and old paint (Ex. 15).

In commercial furniture refinishing operations, paint is stripped by either dipping the piece in an open tank containing the stripper (dip tank), spraying or brushing recycled stripper on the surface of the furniture in a large open tank (flow over system), combining use of a dip tank and a flow over system, or by manually applying MC with a brush. Stripping methods have not been standardized in this industry due to the diversity in size, construction, finish of items to be stripped, and the types of work areas and stripping solutions used. Typically, when a dip tank is used, a piece of furniture is manually placed in the dip tank and left until paint blisters. If a piece is not completely submerged it may be manually rotated to allow complete coverage. The piece is then removed to another area to be manually scraped. This process is repeated until the surface is clean of paint. Hard to reach areas are hand brushed with MC stripper. The furniture is then washed down with water and allowed to air dry. When the flow over system is used, the furniture is placed in a large open tank which connects to a small reservoir of stripping solution. The solution is then pumped through a brush onto the surface of the furniture and allowed to blister the paint. The portion of the solution that does not adhere to the furniture is recycled through the system and back into the reservoir. Then, the blistered paint is scraped off. The furniture is then washed down and allowed to dry. Paint chips and paint sludge are manually collected in drums or trash cans and disposed of as normal refuse. The spent stripping solution is either recycled, disposed of as hazardous waste, stored on site or left to evaporate. Because of economic considerations, MC is not usually recovered from spent solution (Ex. 7-132).

Industrial use includes removal of paint from paint conveyor hooks and trolleys, reworking of defective paint and coatings, and cleaning of paint booths. This is done by dipping and spraying of parts, removal of blistered paint, and washing down to remove excess solvents (Ex. 15).

Some alternatives to MC used in the furniture refinishing industries include petroleum distillates, acetone, mineral spirits, alkali, and water soluble formulas (Ex.15).

An alternative to MC paint stripping that is being tested in the stripping of aircraft is plastic media blasting. This process blasts small plastic beads, usually 30 to 40 mesh in size, with rough edges onto the painted surface. This process is less labor intensive, (generally ten times faster than the MC stripping process), and generates less waste for disposal, so it has some cost advantages over MC paint stripping. While bead blasting may save time, special efforts are necessary to protect certain components of an aircraft such as plastic windows, surfaces that are protected with soft cadmium coatings, and radomes that are painted with rain-erosion coatings. The biggest disadvantage is that beads abrade the aircraft metal surface, potentially causing damage and reducing the life of the plane. Chemical strippers can, however, corrode aircraft surfaces, and deteriorate concrete floors as well. Plastic media blasting can also raise enormous metallic and paint dust clouds if proper blasting and control equipment are not used and correct procedures are not followed. Some other potential problems with abrasive blasting which limits their use are (1) personnel resistance to change; (2) trapped media in aircraft; (3) physical handling of blast nozzle, workstand, etc.; (4) seam seal on dynamic components (Ex. 8-22).

8. Degreasing and Metal Cleaning

OSHA estimates that there are 90,293 exposed workers in 22,652 establishments using 23,664 cold degreasers consuming 31 million pounds of MC; approximately 271 exposed workers in 124 establishments using 129 open top degreasers consuming 7 million pounds of MC; and approximately 177 exposed workers in 107 establishments using 111 conveyorized vapor degreasers consuming 3 million pounds of MC. Out of the 41 million pounds of MC used in degreasing, it is estimated that 37 million pounds are reclaimed (recovered) in 40 reclamation plants throughout the U.S. (Ex. 15).

MC is used as a degreasing solvent to remove drawing compounds, cutting fluids, coolants, and lubricants from metal parts. It can be used in cold cleaning, open top vapor degreasing, or conveyorized vapor degreasing. It is difficult to characterize the establishments that use MC for metal cleaning or degreasing because of widespread and nonspecific use patterns. MC is generally chosen when other organic solvents fail to provide the desired characteristics such as non-flammability, non-reactivity with metals, the ability to dissolve a broad range of greases and industrial chemicals, high solvency for most industrial contaminants, and a rapid rate of evaporation (Ex. 4-41). The three methods of metal degreasing are described, as follows,

(i) Cold Degreasing. - Most cold degreasers are open top stainless steel tanks. The cleaning operations used in cold degreasing include spraying, flushing, brushing and immersion in the solvent. Typically, dirty parts are sprayed with MC and then soaked in the degreasing tank. When cleaning is completed, the parts are usually suspended over the tank to drain or are placed on a rack outside the tank with the solvent drippings directed back into the tank or otherwise collected for subsequent reclamation. Some degreasers are equipped with agitators that operate while the parts are immersed in the solvent. This enhances the cleaning efficiency of the solvent (Ex.15).

MC is also applied with a rag to provide a soft abrasive cleaning action. This activity is categorized as "cold cleaning" (Ex. 15).

(ii) Vapor Degreasing. - Open top vapor degreasers operate by condensing hot solvent vapor on colder metal parts. The typical open top vapor degreaser consists of two sections: a lower section with a reservoir containing liquid solvent and a heat source which boils the solvent to create a vapor, and an upper section containing only the vapor and emission control systems. Metal parts soiled with grease, oil, metal particles, etc., are lowered, usually in a basket, into the solvent vapor zone of the tank with the aid of a manually-operated or automatic crane. The hot vapor condenses on the cooler metal parts and the condensate dissolves the soil, carrying it along as it drains back into the boiling liquid reservoir below. When the metal parts reach the vapor temperature, the condensation stops. The vapor degreasing process takes advantage of the fact that the solvent boils at a much lower temperature than the oil and grease. If the temperature of the liquid reservoir is maintained at the boiling point of the solvent, only pure solvent vapor is found in the vapor zone of the degreaser. As water can interfere with the degreasing activity, degreasers are also equipped with a water drain off valve. The cleaning efficiency of this process can be increased by spraying immersed parts with solvent or by dipping them into the hot MC liquid.

(iii) Conveyorized Degreasing. - These are operated with either cold or vaporized solvents. Parts are placed on a conveyor which carries them into the liquid solvent or through the vapor zone and out the other end for drying and or subsequent handling. Conveyorized degreasers are generally continuously loaded and are almost always hooded or enclosed.

Use of the vapor degreasing process has increased in recent years due to improved equipment design. However, MC cannot be used in vapor degreasing of parts soiled with grease or oil that has a high paraffinic content because a high rate of solvent flushing is required in such circumstances. Furthermore, MC can not be used on thin parts because they heat too quickly and good condensation cannot be achieved (Ex. 4-041).

Degreasing equipment must be cleaned periodically to maintain its efficiency. High exposure to MC is possible when tanks are being cleaned because the worker often simply empties the tank of solvent, rinses it with water from a high pressure hose and then climbs inside the tank to scrub it with brushes (Ex. 7-132).

Many solvents are being used besides MC for degreasing. Examples are 1,1,1-trichloroethane, mineral spirits, and perchloroethylene. In addition, a wide variety of petroleum distillate products such as gasoline, kerosene, and turpentine are used (Ex. 15). The feasibility of using these substitutes depends on the characteristics of the parts to be cleaned and the level of cleaning desired. Since the same tanks or equipment are used for multiple tasks, emptying the tanks containing the substitute whenever a higher level of cleaning is required, may render the use of substitutes impractical in some facilities.

9. Cellulose Triacetate Fiber and Cellulose Triacetate Photographic Film Production

a. Cellulose Triacetate. MC is used by one company, Celanese Corp., at Cumberland, Md., as a solvent for spinning cellulose triacetate fibers. It is estimated that all of the approximately 4.5 million pounds of MC used at this facility are released to the air (Ex. 7-9).

The first cellulose fiber manufactured was cellulose triacetate (CTA). However, CTA was not soluble in solvents that were then available and safe to use. Because of this, CTA was never produced on a large scale in the early days of rayon and the process did not reach the commercial production scale for many years.

In later years, this situation changed. The manufacture of cellulose triacetate now proceeds on a large scale: Tricel (British Celanese Ltd.) is made in Great Britain. Arnel is made by the Celanese Corporation of America. Trilan is produced by Canadian Celanese Ltd. The two main reasons for the development of these fibers are:

(i) The availability of solvents such as formic acid, glacial acetic acid, dioxan and cresol that are easy to use, safer than chloroform to handle, inexpensive and available in large quantities. MC, which is also an excellent and inexpensive solvent for the production of secondary acetate, has been used for triacetate production since 1930.

(ii) The development of the synthetic fibers such as Nylon, Orlon and Terylene has demonstrated that there are many applications for hydrophobic fibers for which the hydrophilic viscose and (secondary) cellulose acetate rayons and natural fibers are not satisfactory substitutes.

The raw material for the manufacture of cellulose triacetate, is either purified cotton linters or specially pure grades of wood pulp. In either case, the cellulose is pretreated with acetic acid (acetylation). There are two methods of acetylation used in the treatment of cellulose triacetate. In the first method, the activated cellulose is esterified with acetic anhydride and acetic acid, using sulfuric acid, as a catalyst. When acetylation is complete, all of the cellulose fiber will have passed into solution. The cellulose triacetate is then precipitated into water, washed and dried in percentage of spinning. The dry-spun cellulose triacetate fiber is passed over a wick containing an anti-static agent and is collected on cap-spinning bobbins if it is in the continuous filament form. If required for staple, a number of ends are collected into a tow as they leave the spinneret, no twist is inserted, and the tow is crimped and cut to the desired length.

MC is a good solvent for dry spinning the fiber. Ordinary secondary fiber can be processed using acetone as a solvent, since acetone (80% acetone/20% water) dissolves ordinary secondary fiber whereas MC only swells this fiber. Conversely, MC (80% MC/20% water) dissolves cellulose triacetate but only swells secondary acetate. This property also makes MC useful for distinguishing secondary acetate from triacetate fibers.

Some of the advantages of CTA fibers are described here. Cellulose triacetate is resistant to boiling water. In addition, it can be heat-set like synthetic fabrics so that it will hold pleats that have been deliberately inserted even if subsequently washed (without shrinking like Nylon and Terylene) and so that it will resist subsequent creasing. Also, the chemical resistance of triacetate is generally superior to that of secondary acetate, and it has biological resistance (defenses against bacterial, fungal and insect attack). It is a bright fiber and can be subdued by the incorporation of titanium dioxide. In addition, it has very high electrical resistance, which is only exceeded among textile materials by Terylene, Polyolefins, Teflon and glass.

Nearly all of the cellulose triacetate is used for ladies' apparel. Much of it is used to make 100 percent continuous- filament open fabric. High bulk Tricel is used in knitwear.

The solvents which can substitute for MC in the manufacture of cellulose triacetate are: chloroform, formic acid, glacial acetic acid, dioxan (slowly) and cresol (slowly). Triacetate is swollen by acetone (also partly dissolved), ethylene dichloride and trichloroethylene.

In the second method of acetylation that involves the use of a non-solvent process, the activated cellulose is esterified with acetic anhydride in the presence of a non-solvent such as benzene, which preferably has a slight swelling action on the esterified cellulose. An acid catalyst such as sulfuric acid, toluene sulfonic acid, or perchloric acid is used. The acid catalyst is then removed from the fiber using a heated non-solvent medium with acetic acid. The purified solid cellulose triacetate is then dried.

Also, the wet spinning process can be used instead of the dry spinning process to produce cellulose triacetate. In this process, which does not involve the use of MC, cellulose triacetate is dissolved in glacial acetic acid and extruded into either water or dilute acetic acid. Arnel 60 was wet-spun, and it was considerably stronger than ordinary dry-spun Arnel. But it has been discontinued, and probably all of today's triacetate fiber is dry-spun (Ex. 7-137).

b. Flexible photographic film base manufacturing. MC is used in the film industry for casting of cellulose triacetate film base and light sensitive emulsions as well as for film splicing. Typical cellulose casting products using MC are films for still cameras, motion pictures, micrographic, and graphic arts.

The principal application of MC in this industry is as a process solvent in the casting of cellulose triacetate, which is used as the base for photographic film (Ex. 15). The manufacture of cellulose triacetate film starts with the pouring of a film substance on a metal drum or a continuous metal belt. After evaporation, a film having a thickness of .02 to .03 mm forms. The film is then passed through a water sealer by means of a heated cylinder onto a chromium roller where it is dried. For safety reasons, the drum and metal belt are in a hermetically sealed channel separated from the water sealed environment and closed off by a moderately high nitrogen pressure. The cellulose triacetate is in solution in an organic solvent, of which 65% is MC. Other components of the solvent are methanol, dibutylpthalate, and triphenylphosphate (Ex. 7-26).

Exposures can occur during the evaporation of the MC into the air during manufacturing, set up of materials, disruption in apparatus, and when pouring the film onto the metal drums (Ex. 7-26).

In film splicing, MC is used as a solvent in the glue used to splice pieces of film together. The MC dissolves the plastic interfaces of the pieces and then evaporates, leaving the pieces "welded" together. This process is either done manually or by machine (Ex 15).

10. Electronics

There are an estimated 1,059 electronics establishments consuming 40 million pounds of MC with an estimated 4,720 exposed workers. MC is used in the electronics industry primarily as a photoresist stripper. Resist strippers are used in the production of integrated circuits and printed circuit boards. MC is also used in this sector as a vapor degreaser to remove the flux from the printed circuit boards after soldering (Ex. 8-28). Based on available documentation, OSHA believes that all of the MC used by the electronic production facilities is released into the air, rather than recovered.

MC is also used in the manufacture of semi-conductors to degrease semiconductor wafers, before, during and after fabrication of the integrated circuits on them. In addition, MC is used in the diffusion process to introduce dopant impurities which modify the electrical properties of a semiconductor (Ex. 15).

Printed circuit boards are plastic sheets on which conductive paths are formed in a specific pattern for the purpose of interconnecting electronic components such as semiconductor devices, resistors, and capacitors. Printed circuit boards can be one-sided, double-sided, or multi-layer. In general, laminated printed circuit boards are processed into electronic circuits by the following steps:

(i) Application of a polymer-based photosensitive resist over the entire board surface;

(ii) Masking of the resist with the appropriate circuit design;

(iii) Photoexposure of the resist;

(iv) Development and removal of either exposed or unexposed soluble photoresist depending on whether the resist is positive or negative, respectively;

(v) Etching to remove the exposed copper; and

(vi) Stripping (removal) of the remaining resist (Ex. 4-41).

Potential solvent substitutes for MC for this application include: 1,1,1-trichloroethane, chlorofluorocarbons (CFCs), acetone, alkali (caustic) and Yzio Dip. However, some firms reject these substitutes because of a lack of effectiveness and reactivity of metal with the solvents. The chemicals OSHA found most often mentioned as having been considered (or tested) and rejected as substitutes were 1,1,1-trichloroethane, acetone and alkali (caustic), except for its use in flux removal (Ex. 15).

OSHA notes that aqueous cleaning is an alternative to the use of MC (vapor degreasing) for the removal of flux from printed circuit boards. This method involves the use of water under pressure to clean boards, provided that the flux used (before the soldering of boards) is water soluble. Sometimes a detergent is added to the water when the wet soldering process is used. Aqueous cleaning has proven to be an effective method for the removal of flux from printed circuit boards (Ex. 7-134).

The best alternatives for many electronics uses are blends that substitute CFCs for methylene chloride. Because of the issue of ozone protection in the stratosphere, international treaties have been signed to limit the production of CFCs. OSHA has assumed, therefore, that no CFC substitution will take place due to this proposed regulation.

11. Miscellaneous Uses

a. Food Extraction. MC is used to extract desirable constituents and mixtures of constituents from solid food raw materials, intermediate products and by-products (Ex. 4-32). The three major applications of MC that have been identified in food processing are the decaffeination of coffee, the extraction of hops, and the manufacturing of oleoresin. OSHA estimates that these operations consume over 10 million pounds of MC each year.

The two companies previously known to use MC for decaffeination were General Foods and Tetley. General Foods has indicated that they have phased out the use of MC. Tetley, in turn indicates that MC decaffeination accounts for only a small portion of the estimated consumption. For all practical purposes, MC is no longer used in decaffeination by either of the companies (Ex. 15).

Only one manufacturer, Hopstract Inc., uses MC to extract hops. It is estimated that less than 40,000 pounds are used for this purpose. Also, it is estimated that approximately 30,000 pounds of MC are being used in the manufacture of oleoresin spices (Ex. 15).

MC is also used to extract gossypol from cottonseed products, nitrite from various crops, lecithin, phosphatide, cephalin and digalactosyl diglycerides from potatoes, the aroma-containing fractions from cocoa and antioxidants from glucose-ammonia browning reaction products (Ex. 4-32).

Heterogeneous solid-liquid extraction was used in some decaffeination processes. In most cases, an occluded aqueous solution is produced by steaming green coffee beans. This solution contains both dissolved non-caffeine coffee solids and caffeine, and becomes progressively leaner in caffeine as extraction proceeds. MC or supercritical CO2 are used as solvents in the external solution, the extract. The extract becomes progressively richer in caffeine as the extraction proceeds, but, if things are arranged properly, it should contain scarcely any non-caffeine solutes.

The solids involved in most food extraction processes consist of a matrix of insoluble solids, the "marc" and occluded solution. It may also contain undissolved solute and a nonextractible secondary phase (e.g. coffee oil in water-soaked coffee grounds). This secondary phase can be treated as part of the marc. In decaffeination, the coffee oil which is naturally present in green coffee beans significantly affects the amount of the solvent absorbed by the beans.

The overall extraction process can be controlled and the absorption of solvent by green coffee beans can be minimized by using a combination of solid-liquid and liquid-liquid extraction. A green-coffee solution which contains almost no caffeine, is used to extract caffeine from green coffee beans in a diffusion battery. The caffeine is then extracted from the green-coffee solution by using a solvent such as MC. Steam is then used to thoroughly strip MC from the green coffee solution. The solution of caffeine in MC is treated so as to recover caffeine and caffeine free MC, which is reused in the extraction process. The green coffee beans are then washed to remove extract which clings, steamed to remove any MC which has been indirectly absorbed, dried and roasted. The produced roasted coffee contains no more than 3% and usually less than 1.5% caffeine. Steaming, drying and roasting are also necessary when heterogeneous solid-liquid extraction is used, but steaming must be carried out for a much longer period (Ex. 4-32).

Benzene was used in the early 1900's to extract caffeine from coffee and still is used in certain hop extraction sequences. Supercritical, dense CO2 gas is now used commercially to extract caffeine from coffee and to extract bitter flavoring agents (humulones and isohumulones) from hops. Solutions of CO2 in acetone have also been used in coffee extraction and solutions of CO2 in acetone and butane have been used for extracting hops (Ex. 4-32).

b. Ink Use. MC is used in the formulation of ink and ink solvents. It is estimated that there are 37 ink solvent manufacturers, with approximately 143 exposed employees, which consume 9 million pounds of MC, and 10,482 ink solvent users, printing and newspaper firms, with approximately 34,868 exposed employees which use 9 million pounds of MC. Printing and newspaper firms use an ink solvent formulation called "blanket wash" to clean printing plates and equipment.

Many different ink and solvent formulas are necessary for printing, because the paper and other materials used in printing have different textures. Printing inks are compounded from pigments or solid ingredients which supply the body and color; the fluid ingredient or vehicle which carries, distributes, and binds the pigments to the surface; and various waxes and other compounds.

Finished inks are packed in metal cans, in metal or plastic pails or in metal or fiber drums, and occasionally, in tote bins. High volumes of fluid ink (e.g. news, flexo or gravure) are usually delivered in tank cars.

The main processes, cited by ink and ink solvent formulators, where exposures occur, were the actual formulation of the products and the filling of cans and drums.

Petroleum distillates, Agatane, mineral spirits, and the use of water soluble formulas have been considered as potential substitutes for MC (Ex. 4-32).

c. Pesticide Manufacturing. In the formulation of pesticide products, MC is sometimes used as a solvent in order to produce liquid products from granular active ingredients. There are an estimated 60 manufacturers with 120 exposed employees who use 10 million pounds of MC.

Products which have been substituted for MC include petroleum distillates (most often used), aqueous formulas, perchloroethylene, carbon tetrachloride, mineral spirits, and Agatane. Substitution is unlikely in most of the industry because the processes are engineered for a particular chemical and replacing the current solvent would require significant modifications to equipment designs and operational functions.

d. Solvent Recovery. Reclamation is the process of restoring a waste solvent to a condition that permits its reuse. There are an estimated 40 recovery facilities employing approximately 161 workers, which collect an estimated 37 million pounds from degreasing and pharmaceutical firms. The MC that is used in paint removers is not usually recoverable (Ex. 10-8). OSHA notes that MC may be recovered in other industries as in electronics. OSHA believes, however, that such additional recovery operations handle little MC.

Solvents are stored both before and after reclamation in containers ranging in sizes from 55 gallon drums to 2000 gallon tanks. Once waste solvent is received it can either be piped or loaded manually into recovery process equipment.

There are three major steps in solvent recovery: Initial treatment, distillation, and purification. The initial treatment consists of vapor recovery and/or mechanical recovery. The former includes condensation, adsorption, and absorption while the latter includes decanting, filtering, draining, settling, and centrifuging. The solvent recovered from the initial treatment is passed through the distillation process to remove dissolved impurities. The final purification process removes water by decanting (mechanically separating water and solvent layers), or by salting (passing the solvent through a calcium chloride bed where the water is removed by adsorption). Special additives are added to the solvent during the purification process in order to renew the solvent. Any waste materials left after the solvent has been reclaimed are disposed of by either incineration, land filling, or by deep well injection. Points of possible emissions include storage areas, tank vents, containers, and incinerator stacks (Ex. 15). The MC recovery industry is expected to continue as long as waste that contains recoverable MC is available.

e. Other Uses. OSHA is aware that MC is used in the construction and shipyard industries. OSHA's contractor, CONSAD Research Corporation, has collected preliminary use and exposure information concerning these industries. Discussion of this data can be found in the "Summary of Preliminary Regulatory Impact and Regulatory Flexibility Analysis", below. MC is also used in cleaning petroleum or asphalt barges and in the textile industry as a dye carrier solvent. Another use of MC is as a solvent, primarily for cleaning up tools and resin spills, in the manufacturing of fiberglass products such as boats, tub enclosures, and automotive parts (Ex. 15).

VI. Technological Feasibility Assessment of Engineering Controls to Reduce Employees' Exposures

The technological feasibility of engineering controls for the reduction of workers' exposure depends mainly on the physical and chemical characteristics of the toxic substance to be controlled, and its associated production or process technologies.

In the assessment of the technological feasibility of engineering controls, OSHA used available published information as well as information gained from OSHA's site visits. Methylene Chloride, CH(2)Cl(2), MC, the substance to be controlled, is a colorless liquid with a chloroform-like odor. The MC odor threshold varies from 25 to 300 ppm. MC has a boiling point of 39.8 deg C (104 deg F) and a high vapor pressure at work room temperatures. At 20 deg C (68 deg F) and 25 deg C (77 deg F) the vapor pressures are 350 and 440 mmHg, respectively. MC is corrosive to some surfaces. The physical contact of MC with strong oxidizers, caustics and active metal powder may cause explosions and fires. Decomposition products during combustion or fire include toxic by-products such as phosgene, hydrogen chloride and carbon monoxide (partial oxidation).

This document includes a separate section for each industrial sector involved in the production or the use of MC. Each section addresses the technological feasibility of achieving the proposed PELs.

As indicated before, in determining the technological feasibility of engineering controls, the combined physical and chemical characteristics of MC are considered. Based on the record developed to date, OSHA has tentatively concluded that the engineering and work practice controls needed to achieve a 25 ppm PEL and a 125 ppm STEL are technologically feasible.

The assessment of the feasibility of engineering controls relied primarily on CONSAD's (OSHA's contractor) evaluation and analysis, where it was demonstrated that the use of local exhaust ventilation (LEV) and other similar controls are capable of achieving the PELs in most establishments. In addition, OSHA's independent evaluation of the data collected during several site visits to the various MC facilities, has proven to be consistent with CONSAD's conclusion, and has supported its technological feasibility determination for achieving the PELs. CONSAD's conclusion and OSHA's independent findings of the technological feasibility collectively indicated that the measures available to abate employee exposure include: the use of local ventilation systems (to remove the MC vapors emitted from localized or point sources); the use of general dilution ventilation (to reduce MC concentrations resulting from diffused or fugitive sources); the use of magnetic pumps and floating gauges (to eliminate or significantly reduce the leakage from process lines); the use of submerged lances equipped with double concentric jackets (to remove MC vapors during drum filling); the use of in-line quality control sampling techniques, connected directly to analytical equipment (to eliminate manual sampling and its associated workers' exposure); and the use of chilling coils (to reduce the MC temperature and its associated rate of vapor release).

The majority of the above control devices are currently available in virtually leak-proof construction/design (e.g. magnetic pumps) or corrosion resistant design (stainless steel chilling coils using water/glycol cooling media). These improved designs render control equipment to require little or no maintenance during their normal useful lives and under normal operating conditions. OSHA further determined that proper design and implementation of control systems, including consideration of the temperature of MC, size and capacity of process equipment, and volume of MC projected to become airborne (released), are critical to the successful operation/ function of controls and reduction of workers' exposure.

Other measures that can be successfully implemented to lower exposure levels include providing enclosures equipped with activated charcoal beds or similar air cleaning media for operators of mobile equipment; installing fresh air supply islands for fixed workers' stations, supplying down-draft ventilation, whenever workers can be stationed on exhausted grated platforms (e.g. workers in paint stripping whose duties require very limited mobility), and improving the efficiency of vapor recovery systems by increasing the capacity of the heat exchanger to lower the temperature of the cooling media.

OSHA believes that some of the above described control systems may have broader application and could result in higher operating efficiency than LEV systems. Insofar as employers can implement control systems that surpass LEV systems in effectiveness, the Agency anticipates that the need to comply with ancillary provisions, such as those covering regulated areas and medical surveillance, could be eliminated or significantly reduced. Therefore, OSHA requests public comments on this issue. The final standard will reflect the information received in response to this request.

OSHA assessed the technological feasibility of the engineering and work practice controls that are needed to comply with the proposed PELs, without regard to extensive use of respiratory protective equipment. OSHA contemplated the use of respirators, only where the implementation of all feasible engineering and work practice controls would not enable employers to comply with the proposed PELs. The technological feasibility and utility of each of the control technologies is discussed in detail below for each of the industrial segments expected to be impacted by the proposed standard.

A. MC Production

Methylene chloride is produced in an enclosed system using continuous processes, as described in Section IV. Production equipment (tanks, condensation towers, drying towers, pumps, valves, conduits and piping, etc.) is opened only for maintenance and very seldom for sampling quality control specimens.

Most components of production equipment, including storage tanks and loading facilities, are located outdoors. Therefore, leaks from gaskets, pipe couplings, pumps, valves, in-line sampling ports, etc. are diluted and dispersed into the atmosphere. Consequently, exposure of workers to MC is minimized (Ex. 7-209).

In addition, because of the automation of this production process, workers spend very little time in the field (in the vicinity of production equipment) and the majority of their time is spent in the control room, where no exposure to MC exists.

Sources of workers' exposure in the production facilities of MC are limited to leaks from process equipment, (pipes, valves, tanks, towers, and pumps), disassembling process equipment and disconnecting lines for maintenance work, venting vapors from relief valves, loading railroad tanks, truck tanks and drum filling.

The feasible controls which would eliminate and/or minimize workers' exposures from these leak sources are discussed below.

1. Engineering Controls

a. Use of Dual System to Facilitate Purging MC Before Disassembling/Disconnecting Equipment for Maintenance. Because the production of MC employs a continuous and enclosed process, dual production components such as flow control valves and pumps are designed as an integral part of the production process. The use of dual production components is the key to continuous production processes, where bypasses to redirect the flow are used while maintenance is performed on specific components. The redirection of the flow is usually automated and very seldom requires physical contacts to the equipment by process operators. That is, when a signal from the process computer indicating equipment malfunction is received, the pump is automatically blocked off, and another pump is activated to replace the malfunctioning one. This is done by automated valves which employ an air actuator and shut automatically when given a signal from the computer. The employment of dual production equipment, is both a basic necessity for continuous production and contributes significantly to the reduction of workers' exposure. The reduction of workers' exposure is accomplished through the purging of production lines before disconnecting any equipment. This procedure will eliminate the release of any confined MC. The purged effluent is usually vented to flares for instantaneous burning.

Reduction of workers' exposure also depends on workers' training, and their ability to perform the purging process properly. This may entail testing the lines prior to disconnecting them, and disassembling the production components to be repaired.

b. Scheduled Preventive Maintenance and Continuous Monitoring. Scheduled preventive maintenance and prompt repairs have been proven to be feasible controls that limit the extent of workers' exposure. Restricting access to areas where leaks are likely to occur also limits workers' exposure. Regular inspection of equipment and transfer lines where leaks may occur is an additional step that can contribute to the reduction of workers' exposure.

Finally, continuous monitoring with an alarm system connected to the central control room would contribute to the reduction of workers' exposure by alerting workers to the occurrences of leaks.

c. In-line Quality Control Sampling. Sampling for quality control is another source of workers' exposures, if it is performed manually. Unlike manual quality control sampling, the in-line monitoring or sampling technique virtually eliminates workers' exposure to MC. In-line sampling equipment connected to analytical equipment such as gas chromatographs, are currently available and are being used at various production facilities. Further, the in-line sampling technique, not only reduces exposure to sampling technicians, but also significantly reduces exposures to laboratory workers.

d. Equipment Modifications for Drum Filling. Drum filling presents a more serious source of workers' exposure than that encountered during bulk loading (barges and tank truck loading). However, modifications can be made to the filling equipment, in order to reduce workers' exposure to MC. These modifications may include designing an exhaust jacket which surrounds the filling lance, in the form of two concentric pipes. The inner tube is used for filling the drum, while the outer tube functions as an exhaust conduit for the MC vapors. Further, refinement of the drum filling system can be achieved by constructing a drip pan to receive the drippings from the filling lance. The capacity of the exhaust system can be designed to control the vapors which escape from the filling lance, as well as those emitted from the drip pan. The exhaust jacket of the filling lance can be constructed from collapsible material (bellows type) resistant to MC (Ex. 7-209).

e. Equipment Modifications for Bulk Loading. Slip-tube gauges are used to indicate the fluid level in tanks during bulk loading. Reduction of workers' exposure during the bulk loading process can be achieved through the use of magnetic gauges, in lieu of slip-tube gauges. The use of slip-tube gauges is undesirable. When slip-tube gauges are employed within a system, the operators are unnecessarily exposed to MC. Slip-tube gauges release a plume of the MC vapor into the air, when the liquid MC level reaches a predetermined point.

Magnetic gauges operate without the release of vapor into the air. Magnetic gauges function by transmitting the flow of motion by means of a magnetic coupling. A magnetic bond float gauge consists of a hollow magnet-carrying float which rides along a vertical non-magnetic guide tube. The follower magnet which is suspended by tape drives is an indicating dial similar to that on a conventional tape float gauge. The float and guide tube, which come in contact with the measured fluid, are available in a variety of materials for resistance to corrosion, and to withstand high pressures or vacuum. Weighted floats for liquid-liquid interfaces are available. Magnetic coupling is frequently employed in level-sensing electrical switches. The integrated controls which would limit workers' exposures could be achieved when magnetic pumps are coupled with magnetic gauges (Ex. 7-221).

f. Equipment Modifications for Pumps. As indicated before, one of the major sources of workers' exposure is leaks from pumps (seals and glands). Since methylene chloride production is a continuous process, the use of dual equipment constitutes an integral parameter in the design and operational criteria.

Available information gathered during the field visit indicates that simple pumps allow escape of MC around the rotating drive shaft. Simple pumps employ seals consisting of compressed packing in a box around the shaft in the opening to the pump or tank. When the pumped fluid is free of particulates, as it is in the case of MC, mechanical seals can be used. Mechanical seals consist of two precisely machined annular metal faces which are mounted perpendicular to the shaft. One face rotates with the shaft, while the other is stationary. Pressure from the fluid in the pump in conjunction with the spring pressure, press the metal faces together, resulting in a good seal. These mechanical seals are known to be of better performance (less leaking) than pumps with packing. Mechanical seal pumps with dual or tandem seals are better than those with single mechanical seals.

Therefore, reduction of workers' exposure can feasibly be achieved through replacing simple pumps (employing packing) with tandem mechanical seals. Mechanical seal pumps are currently employed within the chemical processing industries. Due to the corrosiveness of MC to seals, the pumps normally require frequent maintenance. Excessive workers' exposure is usually associated with the frequent maintenance required for replacing seals of pumps (Ex. 7-202).

The performance of the magnetic drive pump is based on the complete isolation of the pumped liquid from the rotating shaft. In the design of the magnetic drive pump, the lack of seals and the complete separation between the motor shaft and the pump casing guarantee the total absence of leaks of the pumped fluid. That is, the magnetic drive pump consists of a wet end and a dry end. The wet end includes the pump casing, impeller, shaft and the magnetic drive coupling which is supported with a bearing.

The magnetic driven coupling is the inner carrier which is sealed to the wet end. This sealing is a containment cell which is bolted to a housing with a gasket. The containment cell is made of a material with good electrical characteristics which is compatible with almost any solvent. Over the top of the containment cell is another housing, a secondary container. This secondary container, opens to the atmosphere for safety, through a shaft which is connected to the motor and is also sealed. The dry end consists of a bearing frame that supports a driver magnet carrier, which turns around in the containment cell. This is called the outer drive.

The magnetic drive pump operates with a conventional motor. The magnetic coupling converts the motor to the outer drive. The outer drive also consists of a shaft and standball bearings. This drive (dry end), which consists of outer magnets, excites the inner drive (wet end), and this mechanism provides the spin required for the pump to operate (Ex. 7-215).

The maintenance of magnetic drive pumps is simpler than that of seal pumps, hence making workers' exposure less frequent and of a smaller magnitude. Another advantage of the magnetic pump is its limited number of parts which renders its assembly and disassembly simple for repairs, and a short duration of task performance which affects the extent of workers' exposure. In summary, the unlikelihood of leakage, the low maintenance frequency and short duration of repair tasks, render the use of magnetic drive pumps ideal for the control of workers' exposure.

Finally, although it is not a major source of workers' exposure, leakage from corroded tanks and pipes, can feasibly be controlled. Corrosion protection can be achieved by using protective coatings and cathodic protection or corrosion resistant materials for construction. All of these approaches are technologically feasible, available and proven to be effective for achieving the intended goal.

2. Conclusion

Workers' exposure to MC has been controlled to below 25 ppm in most operations in MC production facilities through the use of the above indicated feasible means. However, information received by OSHA indicated that the highest exposure levels in the MC production sector are obtained from the drum filling process. One facility visited by OSHA previously maintained 50% of the exposure levels below 50 ppm for this process. However, after modifications to the drum filling equipment, exposure levels were lowered to below 25 ppm. Finally, additional modifications to the MC production process such as the replacement of seal pumps with magnetic drive pumps would further reduce workers' exposure levels (Ex. 7-209).

B. Polyurethane Foam Blowing

There are two production stages during which MC is released into the work environment, both of which are sources of workers' exposure. The first stage of production, during which workers are exposed to MC, is pouring. As described in Section IV, all ingredients (including MC and the various additives) are metered and fed into the mixing head through a closed system. The mix is then released into a trough which overflows onto a conveyor which is housed in a partially enclosed and ventilated tunnel. Foam production involves an exothermic reaction, and the water content in the mix affects the reaction temperature proportionally (more water results in higher heat output). If the heat output of the exothermic reaction is not properly controlled, a potential for a fire hazard in the pouring tunnel may become imminent (Ex. 7-207).

The second stage of production, during which workers are exposed to MC, is cooling/curing. In addition to MC's unique characteristics as a blowing agent, it is used as a cooling agent for dissipating the heat output that results from the exothermic reaction. The foam temperature, with the aid of the cooling effects of MC, can reach 300-330oF. The percentage of MC in the mix that accomplishes both functions (blowing and cooling) ranges from 10-15% by weight for super soft foam and 2-3% for the firm foam. The control of workers' exposure in this industrial segment is discussed below.

1. Engineering Modifications

a. Pouring area. During the first stage of production (pouring), approximately 50% of MC is released into the pouring tunnel. This amount of MC is exhausted through a mechanical ventilation system which consists of three blowers located in the ceiling of the pouring tunnel (Ex. 7-217).

The design and configuration of the exhaust system are of a simple type. Based on the information gathered during the site visit, OSHA has determined that if the design parameters of the exhaust system are calculated and integrated properly, the MC concentration could feasibly be controlled to or below a 25 ppm exposure level (Ex. 7-217).

To verify and demonstrate the technological feasibility of controlling workers' exposure to MC vapors emitted in the tunnel during pouring, the following simple calculations are performed:

Annual Consumption of MC (pounds/year/facility) (Based on 750,000

pounds/8 facilities) = 93,750

Hourly Consumption (Based on 252 workdays per year and 4 hour work

shifts per day) = 93 pounds/hour

50% Loss Rate during Pouring in the tunnel = 46.5 pounds/hour OR (0.775 pound/minute)

The volume of air required to dilute the MC in the tunnel so that the concentration does not exceed the 25 ppm level (assuming least efficient/dilution system)

(0.775 lb/min x 456 g/lb x 24.5 L/mole x 10(6) ppm)/(84.9 g/mole

x 28.37 L/ft(3) x 25 ppm) = 143,789 CFM

Based on the prevailing exposure levels, and since the specific operation visited had an exhaust system design capacity of 44,000 CFM, the system can be regarded as properly rated and designed to achieve approximately 81 ppm. Since existing available exposure data indicates that workers' exposure is centered around 75-90 ppm, it would be reasonable to regard the existing system as properly functioning according to its design criteria. However, if the system was designed to achieve the 25 ppm level, then it can be regarded as underrated by 69% of the appropriate capacity (assuming that the system is still functioning at its design capacity).

Several exposure levels collected over a number of years were provided by the firm which was visited by OSHA. Some of these exposure levels are difficult to assess for the unknown conditions under which the samples were collected. However, other exposure data provided are associated with a reasonable amount of information, which was considered during this technological feasibility assessment. These are listed as:

1. Breathing zone sample yielded an estimated 8 hour TWA exposure--(9/24/85 plant 1)--Range from 40-70 ppm.

2. Employee breathing zone sample collected before, during and

after pouring, 8 hour TWAs were estimated, based on sample results and estimates of pre-pour, pour and post-pour--(4/14/87 plant 1)-- Range from 9-28 ppm.

3. Employee breathing zone sample collected before, during and after pouring. Most employee eight hour TWA was estimated to be less than 50 ppm. Utility man and cut-off saw--(3/16/88 plant)--Range from 50-75 ppm.

4. Employee breathing zone sample--(5/18/87 plant 5)--

Range from 4-38 ppm.

5. Employee breathing zone sample yields an estimated 8 hour TWA exposure of less than 100 ppm--(8/7/86 plant 6).

Average Range of the Above Representative Samples: 26-62 ppm (Ex. 7-207).

In this assessment, 20% was added to the above calculated range of exposures, so that the calculated levels resulting from the proposed modifications would be regarded as reasonable projections.

Since the tunnel has two open sides, each with approximately 12 x 6 ft (a total of 144 ft(2)), that allow make up air to exhaust the MC vapor, the face velocity at each open side of the tunnel should be approximately 1000 ft/minute, if the system is handling the 143,789 CFM. For the existing system which handles 44,000 CFM, the face velocity should be about 305 FPM.

It should be noted that the above calculation, demonstrates the technological feasibility of achieving the desired 25 ppm concentration of MC. This calculation was based on dilution ventilation which is the least efficient ventilation system. With the existing capacity of the system (44,000 CFM), the 25 ppm level can be achieved through minor modifications of the exhaust system inlets. Such modifications may include lowering the ceiling and/or changing the configuration and the location of the exhaust inlets (e.g. using a slot exhaust at the inner perimeter of the tunnel).

Another feasible control measure that would contribute to increasing the efficiency of the tunnel's exhaust system is the implementation of appropriate work practices. Because the temperature inside the tunnel is higher than that of the outside, and because the MC vapor density is almost 3 times that of the air, it is imperative that all access openings along the side of the tunnel are kept closed when they are not in use. This type of work practice would reduce or eliminate the dispersion and escape of the MC vapors outside the tunnel confinement, as well as maintain the drawing efficiency of the makeup air through the two openings (entrance and exit) of the tunnel. This work practice would also contribute to the reduction of exposures of workers who are stationed outside the tunnel.

During the site visit, it was observed that the operation of the cutoff saw released excessive MC vapor as a result of rupturing of the closed cells. A feasible control measure needed to reduce the exposure to the saw operator is to provide a slot exhaust system mounted on the guide tracks of the saw. This slot exhaust system would be connected to the exhaust conduit with a flexible hose to allow for the movement of the saw.

Another feasible alternative control measure for the cutoff saw operator and for the "paper pull" operator is to provide fresh air islands with a higher velocity and pressure than the remainder of the tunnel. Unless the air velocity of the fresh air island at the workers' breathing zone exceeds the MC contaminated air velocity inside the tunnel, the fresh air islands will be ineffective.

The control of MC inside the tunnel should be regarded as the principal approach for controlling workers' exposure in the remainder of the work stations (outside the tunnel).This assessment is based on the fact that 50% of the consumed MC is emitted in the tunnel within a 2-3 minute duration; while the other 50% of the consumed MC is emitted during 2-3 hours (rate of release of less than 1/100th of that in the tunnel).

b. Curing and cooling stage. After the foam (bun) moves outside the tunnel, a vacuum test is performed to determine the adequacy of the porosity needed to meet the customers' desired specification. The operator of the vacuum equipment is exposed to MC at a lower concentration than those operators who are required to perform their duties inside the tunnel.

Since the heat generation inside the bun (exothermic reaction) continues for almost 2-3 hours, cooling the bun (heat dissipation) is accomplished through a single layer stacking of the buns. Heat dissipation is accomplished through air movements between and surrounding the single layer buns. It was observed that no mechanical ventilation was provided in the building that was used for cooling the buns. Also, the building relied only on natural drafts from an opening approximately 80 ft wide which allows accessibility to the forklift. To control workers' exposure, the building should be provided with a mechanical dilution ventilation system having the same capacity as the tunnel's exhaust system. The following reflect the basis for the above system rating. The 50% of the MC consumed which is released during the curing and cooling stage (average 2.0 hours) is equivalent to 3.1 pounds per bun, or 11.8 grams per bun per minute. Assuming a homogeneous rate of release during the entire 120 minutes cooling/curing time, the maximum rate of MC release during the time approaching the middle of the pouring duration (30 buns released from the tunnel) is 353 grams per minute. The volume of air per minute (air flowrate) required to dilute the 353 gm of MC to achieve the desired 25 ppm is:

(353 g/minute x 24.5 L/mole x 106 ppm)/(84.9 g/mole x 25 ppm x 28.37 L/ft(3)) = 143,789 CFM

The locations of the exhaust fans needed to exhaust the building should be distributed in a pattern compatible with the layout of the single layer bun, so that no stagnant air pockets would be created.

Since the two principal workers in the cooling/curing building are the crane and forklift operators, an alternative to providing a mechanical dilution ventilation for the entire cooling/curing building would be to equip the forklift and the crane with a ventilated enclosure provided with air cleaning devices. This alternative may be regarded as the preferred feasible control measure. This type of an enclosure is available and proven to be effective for a multitude of other contaminants. Without accurate and representative exposure data for the crane and forklift operators, a judgement cannot be made as to whether the building mechanical ventilation or equipment (forklift and crane) enclosures would be the preferred control method. However, either of these approaches is a technologically feasible control measure.

2. Substitution

MC is used in the production of flexible foam as an auxiliary blowing agent for the control of the foam's density. MC and Freon are comparable auxiliary blowing agents. From the production technology point of view, both MC and Freon would result in a faster foam rise, and hence produce a lighter or lower density foam. Currently, because of the ozone depletion phenomena, although Freon and MC are technologically comparable, MC is regarded as the environmentally preferred auxiliary blowing agent.

During OSHA's meeting with officials from the visited foam producer, it was indicated that the State of California is contemplating the adoption of Rule 1175 which compels the foam producer to totally eliminate the use of both auxiliary blowing agents (MC and Freon) by the year 1994. Further, this rule would require reduction of 40% of the MC emission by the end of 1990.

As a part of the plan to comply with Rule 1175 (if it becomes effective), the technological feasibility of chemical substitutes is currently being investigated by foam producers. One of the chemicals being considered for substitution is Aerolite AG (methyl chloroform) produced by DOW Chemical. Information on current foam production technology indicates that methyl chloroform can be regarded as a partial substitute or partial replacement for MC. Research is currently in progress to achieve the goal of total substitution.

Among other substitutes (partial) are Ortegal (produced by Goldshmidt Chemical), Geolite (produced by Union Carbide) and formic acid. Information gathered during the field visit indicates that Ortegal is regarded as a softening agent which results in reducing the volume of MC required to achieve the desired density. Geolite is only at the laboratory stage, and no information is currently available on its feasibility as a partial or total substitute.

The use of xylene in combination with an inert gas is regarded as another feasible substitute for MC. However, there are concerns for the technological limitations related to the release of unreacted TDI when the foam is crushed to open the closed cells. This crushing process is required for the production of more resilient foam (Ex. 7-207). Although no total substitute for MC is currently available, partial substitutes will reduce both the MC volume and its associated exposure levels proportionally.

3. Conclusion

Workers' exposure in the foam production facilities could be controlled through the use of available and feasible control systems. Although it is technologically feasible to provide dilution ventilation for the protection of the workers in the pouring tunnel, providing fresh air islands for each of the three tunnel workers (mixing head operator, cutoff saw and paper pull operator) may be regarded as the preferred control method.

Similarly, instead of mechanically exhausting/ventilating the cooling/curing building, providing a ventilated enclosure equipped with air cleaning devices may be regarded as the preferred choice for the control of the crane and forklift operators' exposures.

Both approaches are technologically feasible, however, no decision can be made with regard to the preferred control method for a particular facility without reliable, elaborate and representative exposure data. Since partial substitution is feasible, it is reasonable to project that both the volume of MC consumed and its associated exposure levels will be reduced proportionally.

C. Aerosols

Methylene chloride is used as a solvent, co-solvent and vapor pressure suppressant in the aerosol manufacture. The advantages of using MC are included in the production technology section (IV). As mentioned previously, the feasibility of engineering controls for the reduction of workers' exposure depends mainly on the physical and chemical characteristics of the substance and its associated production or process technologies.

In the manufacture of aerosols there is only one major source of MC vapor emission which contributes significantly to workers' exposure to MC in this industrial sector. MC vapor is released when charging aerosol cans with liquid MC, using a metered injection pump. The injection tip is lowered into the can and the metered MC volume is then added to the paint mix in the can. The extent and magnitude of workers' exposure to MC during the can charging is a function of the area of the can's charging hole, the temperature of liquid MC, the time required to charge the can, and the capacity and efficiency of the exhaust system.Since the parameters influencing the extent and magnitude of workers' exposure are difficult to modify, with the exception of the MC temperature and the exhaust system's capacity, the assessment of technological feasibility will be focused on these two elements.

1. Engineering Modifications

a. Chilling MC. For all practical purposes for this particular operation, MC concentration (workers' exposure to MC) is dependent on its vapor pressure (VP) which varies with temperature. At room temperature (20 deg C/68 deg F) the VP of MC is 355 mm Hg. With a slight rise in MC temperature (e.g. 5 deg C), the vapor pressure increases to 450 mm Hg. Therefore, it is reasonable to predict that workers' exposure can increase by 27% as a result of increasing the MC temperature 5 deg C (from 20 deg C to 25 deg C).

Since the freezing point of MC is -142 deg F (-97 deg C), controlling workers' exposure, through lowering the vapor pressure (cooling or chilling the liquid MC) before charging the can, extends over an 100 deg F temperature range. An incremental or slight decrease in the temperature of MC will result in a proportional decrease in workers' exposure to MC vapors.

The vapor pressures associated with lower temperatures clearly demonstrate the extent of reduction in workers' exposure (provided that all other variables remain unchanged). For example, at 77, 68, 20, -8 and -28 deg F, the vapor pressure is 450, 355, 100, 40 and 20 mm Hg, respectively. It is clear that a moderate chilling effect (lowering the MC temperature from room temperature of 77 deg F to 20 deg F) will result in lowering its vapor pressure by 75% (to less than 25% of its VP value at the room temperature). That is, it is reasonable to project that a reduction of workers' exposure equivalent to 75% will be achieved as a result of passing the liquid MC through a chilling coil designed to attain 20oF before charging the can.

The chilling coil can be incorporated within a heat exchanger, where both the coil and the exchanger are made of a non corrosive material (i.e stainless steel). In such a process, the MC will flow through the coil and be chilled within the heat exchanger, where the "reservoir" of the heat exchanger is a separate unit, namely a chiller. The chiller can be made out of aluminum since it only contains a glycol-water chilling solution which will be pumped into the heat exchanger to allow chilling of the MC vapors that flow through the stainless steel coil. This process of chilling the MC vapors is technologically feasible.

Certain chillers are designed to meet a wide range of capacities on an instant demand from zero to 100% capacity. This flexibility can be accomplished by a means of incorporating a dual pump arrangement and storage reservoir which is standard on a variety of chillers. At maximum demand, (100% capacity) the chiller fluid flows from the storage reservoir, to the system pump, to the load and back through the recirculating pump, then through the chiller evaporator and into the reservoir. On a zero load, the fluid bypasses the cooling load system, short circuits through the bypass check valve which opens on a change in pressure differential, and then flows through the recirculating pump, the chiller evaporator and into the storage reservoir.

Evidence in the record, Exhibits (7-204 and 7-214), indicated that chilling systems for lowering liquid MC temperature are technologically feasible and available. A chilling coil having the capacity of lowering the MC temperature from 77 to 20 deg F, at a rate of 220 g/s, (approximately 30,000 BTU/hr)1 will result in lowering the MC vapor pressure and its associated exposure levels, by more than 75%.

Since field gathered information indicates that the majority of current exposure levels range from 11 to 67 ppm (with the exception of non-detectables and outliers2), with the use of a chilling coil to lower the MC temperature to 20oF, workers' exposure levels can be expected to decrease proportionally by 75% (exposure levels will range from about 3 to 17 ppm). This reduction in current exposure levels is based solely on lowering the temperature from approximately 80 deg F to 20 deg F. That is, further reduction in MC temperature, coupled with improvement in the capacity and configuration of the exhaust system, will result in much lower exposure levels.

b. Exhaust system modification. In addition to the chilling approach, workers' exposure can also feasibly be controlled through minor modifications or improvement in the capacity of the current exhaust system.

Information gathered during the field visit indicated that currently, each of the three injection pumps of the three operating charging conveyors, is provided with an exhaust system consisting of a slot hood with an area of approximately 2" high x 6" wide (0.083 sq ft). Since the current exposure levels, as indicated before, range from 11 to 67 ppm, simple extrapolation indicates that increasing the volume of air currently exhausted will result in a proportionate reduction of the prevailing workers' exposure levels. In other words, if the volume of air is increased to 3.5 times that of the current exhaust volume, the current exposure level is expected to decrease proportionally, to below 25 ppm.

Since the area of each slot is only 0.083 sq.ft. (total of less than 0.25 sq ft for the 3 slot hoods), the required amount of exhaust air can not be regarded as significant. Based on field experience and professional judgement, the face or slot velocity was not even close to 50 fpm, when the exposure level ranged from 11 to 67 ppm. Therefore, achieving a predetermined exposure level can be proportionally extrapolated. Using the upper range of the exposure level of 67 ppm, increasing the exhaust volume of air by 3 times, will reduce workers' exposure to below 25 ppm. The volume of air required to achieve the above intended reduction can be quantified to equal 3 x 0.25 sq ft x 100 fpm = 75.0 CFM, a minimal increase in air flow.

Further modifications can be made to the configuration of the slot exhaust system, such as but not limited to, enlarging the dimensions of the slot so that a larger area (surrounding the can being charged with MC) can be exhausted. This modification would increase both the volume and velocity of the exhaust air. It is noteworthy to mention that direct drive exhaust fans are more efficient because they are not subject to belt slippage.

c. Enclosing the conveyor. All of the components used for charging and filling the aerosol cans are assembled on a conveyor (approximately 15 ft long and 2 ft wide). The height of the equipment used for valve assembling, crimping and injection pumps (for the paint or MC) is approximately 3 feet. A simple enclosure for the conveyor can be installed and exhausted through a downdraft plenum to be located before the explosion-proof room. This is a feasible means for lowering workers' exposure to MC.

The volume of air required to exhaust the conveyor enclosure is 4500 CFM (assuming homogenous MC concentration in the conveyor enclosure (15 x 2 x 3 ft), and having 50 air changes per minute). Since workers' easy accessibility to the injection equipment is highly desirable, the enclosure can be made of overlapping flexible plastic strips. The same overlapping flexible plastic strips can be used at both the entrance and exit sides of the conveyor provided that an allowance or an opening for the can movement is incorporated. It is needless to indicate that this simple control approach will not only provide for workers' protection against excessive MC exposure, but will also provide protection against exposures to other volatile substances contained in the paint formulation. Additionally, the flexible plastic strips will result in reducing workers' exposure to noise generated by the conveyor, injection pump and other assembly equipment.

2. Substitution

Another feasible method of controlling workers' exposure to MC is substitution. A non MC combination (methyl chloroform, acetone, a hydrocarbon propellent and pigment solvent) is currently available and in use. However, research is still in progress to achieve more technologically efficient non-MC substitutes.

3. Conclusion

The above assessment demonstrates the availability and feasibility of engineering controls that would limit workers' exposure to MC vapors during the aerosol manufacturing process.

D. Polycarbonate Resin

MC is used as a process solvent in the production of polycarbonate resin. It is a true process solvent and it does not enter into the reaction. Out of a 1,700 person workforce, only 60 workers are exposed to MC.

Polycarbonate resin is produced in an enclosed system using a continuous process as described in the process description section. Most components of the production equipment are located outdoors. Therefore, leaks from gaskets, pipe couplings, pumps, valves, sampling ports, etc. are diluted and dispersed into the atmosphere. Consequently, exposure of workers to MC is minimized, as documented in the record, Exhibit 7-203. The mean concentration levels of MC in 1988 and 1989 (16.0 and 18.3 ppm, respectively) are the result of implementing several feasible control measures such as, column dryer technology, upgrading the solvent recovery system, installing MC rupture disk alarms, substituting standard seals with Teflon seals, upgrading the ventilation system of analytical facilities, installing magnetic relief valves, and upgrading the automated instrumentation to allow off-site (control room) observation of the Lexan production.

Because of the automation of this production system, workers spend very little time in the field (in the vicinity of production equipment) and the majority of their time is spent in the control room where no exposure to MC exists.

As indicated before, sources of workers' exposure to MC in the production facilities of polycarbonate resin are limited to leaks from processing equipment, piping, valves, tanks, towers, and pumps. However, the two main sources of occupational exposure to MC are quality control sampling and scheduled/unscheduled maintenance, which includes the changing of filters (Ex. 7-203).

In the production of polycarbonate resin, most quality control sampling is done by opening valves and draining the viscous solution to flush the line before samples are taken. There are approximately fifty discrete points of sampling. Quality control sampling is performed manually because available automated or in- line sampling devices have only the capability of monitoring chemical characteristics and not physical properties. Polycarbonate quality control samples must undergo physical property testing such as optical density.

Currently sampling ports are equipped with open top buckets to capture the flushing solution that must be drained before the quality control specimens are sampled. This method permits the operator to observe and monitor the flushing of the sampling lines. The buckets are also used to capture any dripping or leaks from valves after sampling is completed.

The second source of worker exposure is during filter change, which is regarded as routine or scheduled maintenance.

1. Engineering Controls

a. Quality Control. Reduction of workers' exposure can be achieved by installing in-line sampling equipment at the various locations of the production facilities. This method of control will limit the number of times that sampling is done in one day. Information gathered during the field visit indicates that the number of manual sampling times per shift will be reduced from 25 to only 1 time which is necessary for testing the optical properties of the polycarbonate resin.

Reduction of workers' exposure during the manual sampling, which is required for testing the optical properties, can be achieved by providing a cover for buckets equipped with a receiving funnel having an elbow in the stem. After sampling, a small aliquot of water can be used to provide vapor blockage at the elbow. If water is added to the bucket and is used to flush the funnel and fill in the elbow, MC vapors will be confined, and workers' exposure would be extensively reduced. This type of modification is simple, can be designed and built on site, and requires no mechanical ventilation.

b. Waste transport. Workers' exposure during waste transport is the result of flushing fluid in buckets used for manual sampling. This exposure can feasibly be reduced through the use of portable and enclosed waste tanks. These portable and enclosed waste tanks could be mounted on dollies, and equipped with funnels having an elbow trap in the stem, similar to the one described above. These portable waste tanks could also be provided with a port to pump the contents to the formulation tank through a closed system, in lieu of the current open dumping practice.

2. Maintenance

a. Unscheduled maintenance. Several pieces of equipment are available to significantly reduce the frequency of performing unscheduled maintenance tasks, and consequently, reduce workers' exposure. These include sealless pumps and magnetic valves which can be employed within the polycarbonate resin operation. These pumps and valves do not require frequent maintenance, and consequently limit workers' exposure to MC. Reduction in maintenance frequency will not only contribute to the reduction of workers' exposure to MC, but will also reduce exposures to other chemicals associated with the production of polycarbonates.

A sealless pump that can be employed is the magnetic drive pump. OSHA realizes some of the limitations on the use of the magnetic drive pumps. Polycarbonate resin production involves pumping high volumes (e.g. 150 gpm) of viscous fluid and at high pressures (e.g. 450 psi). Current technology indicates that no magnetic drive pump is available that has a capacity to move a viscous solution with a pressure of 400 psi and a flowrate of 150 gpm. However, the magnetic drive pumps can be used for several operations involving lower pressures and/or flow rates than those indicated above.

Scheduled preventive maintenance and prompt repairs, restricting access to areas where leaks are likely to occur and regular inspection of equipment where leaks may occur are additional feasible steps that can contribute to the reduction of workers' exposures.

b. Filter replacement (scheduled maintenance). Another source of workers' exposure to MC occurs during the replacement of vacuum filters. The current practice is to purge the vacuum filters before they are replaced in order to remove any MC and thereby limit workers' exposure. Although the purging technique is effective, additional reduction of workers' exposure can be achieved through designing a portable canister that can confine the spent filter components. The current practice of leaving the spent filters exposed during the installation of the new filters can not be regarded as an acceptable practice. This canister, since it does not incorporate any sophisticated engineering design or mechanical ventilation, is a technologically feasible control technology.

3. Conclusion

Although available information indicates that workers' exposure is far below the proposed 25 ppm limit, further reduction could be achieved through the implementation of available and technologically feasible control measures. Workers' exposure during quality control sampling could be reduced through the design and use of covered waste containers provided with a water filled elbow as a vapor trap. The same principles could be used for designing waste transport containers along with a facility to pump the waste directly to process tanks, instead of the direct dumping practice. During scheduled filter replacement, the use of a closed canister to confine the vapor being emitted from the spent filter would contribute to the reduction of workers' exposure. Since prevailing exposure levels are currently below the 25 ppm proposed limit, no modification of engineering controls would be necessary for the promulgation of the 25 ppm limit. Data gathered during the field visit indicated that exposure levels achieved within the last 3 years ranged from 16.0 to 4.5 ppm, with 4.5 ppm being the prevailing level during 1990. OSHA is confident of this assessment since exposure data were measured by two independent methods.(2a)

Finally, although substitute solvents, such as ethylene dichloride, are available for the production of polycarbonate resin, they are not desirable because of their flammability characteristics. Therefore, it is not necessary to assess the feasibility of substitutes at this time (Ex. 7-203).

Based on this assessment, OSHA determined that there would be no additional engineering controls or modifications needed for the purpose of complying with the proposed standard, since current exposure levels are below 25 ppm.

E. Pharmaceuticals

The use of MC in the pharmaceutical industry started in the 1970's at which time it was used as a substitute for isopropyl alcohol and carbon tetrachloride. MC was the choice solvent in pill coating because of its good solvency properties, fast rate of drying (evaporation) and safe handling. Because of the recent health concerns of MC, the pharmaceutical industry has already developed an aqueous coating formula. However, MC is expected to be used in pill coating for several years until all of the necessary data required for obtaining the approval of the Federal Regulatory Agency (i.e. FDA) are secured (Ex. 7-229).

In pill coating, there are five production stages during which MC is released into the air, thus contributing to workers' exposure. The first stage is the coating media formulation which consists of two successive steps, mixing the ingredients and preparing the homogenizer. Workers' exposure during the first step is caused by the addition of MC, into an 1000 gallon mixing tank which contains the various ingredients of the coating formula. The mixing tank is provided with a feeding port approximately 2 feet in diameter. A half circle portable exhaust slot (2 inches x 18 inches) equipped with a flexible hose connected to the main exhaust blower is used to control the MC emission during the feeding of the coating ingredients into the mixing tank.

Workers' exposure during the second step is caused by the stirring of MC during the preparation of the homogenizer formula. The ingredients of the homogenizer formula (titanium dioxide and talc powder) are slowly and manually added to a pan containing MC. The mix in the pan is mechanically stirred. The addition of the homogenizer components and the stirring process takes place in an open face hood (5 sided hood) equipped with a 4 inch exhaust takeoff. The exhaust port is located at the back of the hood. The two 1000 gallon mixing tanks and the homogenizer hood are interconnected and exhausted by one blower.

This exhaust blower operates at 800-2,500 CFM depending on the number of tanks being used during one time. That is, if one mixing tank is used, the exhaust volume would be rated at 2,500 CFM. On the other hand, if both mixing tanks and the homogenizer hood are operated simultaneously, the exhaust volume at each of these three pieces of equipment would be rated at approximately 800 CFM.

Normally, the above two steps are performed successively. However, exposure data are compiled together without indication as to whether one or more of the three pieces were in simultaneous operation. Therefore, differentiation between the independent contribution of each source could not be made. The combined exposure levels during the performance of these two steps were ranging from 4 ppm to 124 ppm, with an arithmetic mean of 54 ppm. It is worth mentioning that the exposure levels prevailing before the installation of the above described exhaust system ranged from 7 to 218 ppm, with an arithmetic mean of 67 ppm (Ex. 7-228).

The second stage of the pill coating operations consists of the gravity filling of the 40 gallon drum with the already mixed and homogenized coating formula, which is contained in the 1,000 gallon mixing tank. The current drum filling technique relies on the operator's attention in watching the movement of the float's stem. Without concerted efforts on the operator's part, overfilling the drum is apt to occur, unnecessarily exposing the operator and other workers, who are stationed in the vicinity of the drum filling station, to MC vapors.

The third stage of the pill coating operation consists of two successive steps. During the first step, the filled drum is stirred to ensure complete homogenization of the coating media. Currently, the stirring is performed without using exposure control measures. This practice requires the unsealing of the drum by removing the tape and the drum cover, and substituting the cover with another cover. The latter cover is provided with a notch to permit the insertion of the mixer.

The second step consists of pumping the coating media to a 5 gallon bucket.Following the completion of the stirring process, the coating media is pumped to a 5 gallon bucket which has a loose lid. This bucket, also, is not provided with any ventilation or control system. The combined emission from both steps (i.e. stirring the drum contents and filling the bucket) results in exposure levels ranging from 1.7 to 2.4 ppm, with an arithmetic mean of 2 ppm.

The fourth stage is the actual spraying of the coating media inside the coating pan. This stage is regarded as a closed system and has insignificant contribution to workers' exposure.

The fifth stage consists of flushing and purging the transfer lines and the pneumatic pumps with MC. This stage is regarded as the most significant source of workers' exposure. During the performance of this stage, workers are exposed to 138 ppm of MC.

1. Engineering Controls.

a. Mixing process--i. Addition of main ingredients. As indicated above, exposure levels before the implementation of the current local exhaust system were ranging from 7 to 218 ppm with an arithmetic mean of 67 ppm. After the implementation of the current exhaust system, the range of prevailing exposure levels were lowered to about 1/2 the old levels (4-124 ppm) with an arithmetic mean of 54 ppm. The current exhaust system is equipped with one blower which is interconnected to the three pieces of equipment (i.e. 2 mixing tanks and the homogenizer hood), having an exhaust capacity ranging from 800-2,500 CFM. Reduction of the prevailing exposure levels can be accomplished by three various means (Ex. 7-228).

The first option is to implement strict and appropriate work practices prohibiting the operation of the three pieces of equipment simultaneously. This will result in dedicating the total system capacity (2,500 CFM) to the one piece of equipment, hence the prevailing exposure level would be expected to be reduced to 1/3 of its current value (i.e. 1/3 of 54 ppm or 17 ppm).

The second option is recommended in case the production protocols call for the necessary operation of the 3 pieces of equipment simultaneously. In this case, each of the two mixing tanks and the homogenization hood would need to be exhausted separately, by independent blowers. Therefore, two additional blowers of the same capacity (i.e. 2500 CFM) would need to be added. This modification would result in having an independent blower for each of the two mixing tanks and the homogenization hood. Therefore, the prevailing exposure levels are expected to be lowered to 1/3 of their current values if these equipment are operated simultaneously.

The third option is to modify the chiller's cooling capacity of the water jacket that surrounds the mixing tank. Currently, the chiller has a capacity of lowering the temperature of the water in the cooling jacket to 40oF. If the cooling water temperature is lowered to 20 deg F, the vapor pressure (VP) of MC will decrease by 59% (from 220 mm Hg to 89 mm Hg). This will result in an approximate proportional decrease of the MC concentration (i.e. from 54 to 22 ppm).

ii. Addition of Homogenization Ingredients. In addition to the above indicated approaches of providing an independent exhaust blower to the homogenization hood, and/or avoiding its simultaneous operation along with the mixing tanks, further reduction of MC vapors released during the homogenization process can be achieved through simple and minor modification to the current five sided open hood. This modification may include providing the front side of the hood with a curtain made of flexible strips, (disposable material), or can be made of a sliding glass (sterilizable material) door to provide the needed accessibility to the homogenization pan. The above modification will increase the face velocity of the hood and reduce its exposed surface area, and therefore, increase the exhaust efficiency of the homogenization hood.

b. Drum Filling. Modifications to the current technique of gravity filling of the drums can be achieved using modern filling devices equipped with automatic shutoff valves. In addition, the current drum filling technique uses a notched drum lid which acts as an open source of MC vapor release from the drum during the filling stage. Examples of these modern filling devices are described in detail in the section on "MC Production". If a modern filling device is used, the current need for the tape sealing of the drum lid will be eliminated. OSHA realizes that minor modifications to the filling port of the drum lid will be needed. These modifications will be needed to accommodate the insertion of the mixer's blades that are required for the stirring of the drum contents (before transferring the coating media to the coating pans). These modifications will not only reduce or eliminate the potential for overfilling the drum, but will also eliminate the need for the operator to stand at a close proximity to the drum being filled.

OSHA realizes that even with the deficiencies described above, the exposure levels were ranging from 13-14 ppm. If these levels are representative of workers' exposure during all times, none of the above technologically feasible control approaches would need to be implemented. However, the above feasibility determination is intended as a broad approach for reducing prevailing exposure levels to the maximum technologically feasible extent.

c. Stirring and transferring coating media. As indicated above, in the coating department there are two potential sources of exposure. The first source is the result of stirring the drum contents to ensure the complete homogenization of its contents. The second source is the result of pumping a predetermined aliquot of the coating media from the drum to the five gallon bucket. Current exposure levels resulting from the combined two sources do not represent potential concerns because they are ranging from 1.7 to 2.4 ppm with an arithmetic mean of 2 ppm. However, the techniques employed during these two steps result in unnecessary exposures, although they appear to be of insignificant magnitude.

d. Spraying the coating media. The potential source of workers' exposure during this stage is the result of spraying the coating media inside the coating pan. The total consumption is 104 pounds of the coating media, which contains 67.7% MC, per hour, or 70.4 lbs MC per hour. This amount is consumed/sprayed in five pill coating pans, yielding 31 liters of MC vapor /min per pan. The exhaust system of each pill coating pan is rated at 1,150 CFM and operates at 4" H2O negative pressure, yielding a concentration of approximately 950 ppm in the exhaust effluent.3 This negative pressure is judged to be of a magnitude which is sufficient to prevent leakage from the pan into the work environment. Therefore, it is not reasonable to recommend increasing the air volume of the current exhaust system.

In summary, exposure levels measured in the vicinity of the coating pans are expected to be generated primarily during the flushing of the transfer lines and the associated pneumatic pumps, and secondarily during the mixing of the coating formula while in the drum (before transfer to the 5 gallon container). An additional and insignificant contributing exposure source is generated during the injection cycle from the loosely covered 5 gallon containers. Since the coating pan is equipped with an exhaust system having a rating of 1,100 CFM input and 1,150 CFM output and operating at 4" H2O negative pressure, OSHA believes that these operating conditions would not result in any appreciable contribution to workers' exposure. Therefore, no engineering modifications are recommended (Ex. 7-228).

e. Flushing transfer lines and pneumatic pumps. The most significant source contributing to workers' exposure is the flushing of both the transfer lines and the pneumatic pumps. Exposure levels measured were 138 ppm. Currently, flushing the transfer lines and the pumps takes place in the coating room with no exhaust system provided to confine the vapors of MC. Therefore, providing an enclosure to house the flushing system and the containers holding the flushing solvent (MC) would be the appropriate and technologically feasible control. The enclosure could be of a simple design such as a 5-sided hood provided with a blower having a capacity of 500 CFM. The blower can be connected with a flexible or rigid duct to the downstream side of the existing coating pan blower.

The 500 CFM blower rating would maintain a minimum face velocity of 80 fpm in a hood having approximately a 2 x 3 ft face opening. This size of the hood's face would be sufficient to accommodate the equipment to be flushed as well as housing the 40 gallon drum, although exposures from this latter source as discussed above, were determined to be of an insignificant magnitude.

Further, the 80 fpm face velocity, is sufficient to exhaust the vapors emitted during the flushing cycle and expected to yield exposure levels below 25 ppm. OSHA realizes that makeup air passes through HEPA filters, and engineering discretion should be exercised to maintain the exhausted air volume to a minimum. However, since the flushing cycle takes place very infrequently and for a very short duration of approximately 19 minutes/shift, OSHA does not expect that the exhaust blower will be operating for any extended duration beyond the necessary time. That is, the 500 CFM blower will be operated for approximately 15-30 minutes per shift totaling a maximum of 15,000 ft3 per shift. Consequently the current volume of makeup air, that is being provided through the HEPA filter, needs to be supplemented by 15000 ft(3) per shift.

2. Conclusion

Achieving exposure levels of 25 ppm or below has been demonstrated to be technologically feasible in this industrial segment. There are two operations that need to be modified by the above described feasible engineering and work practice controls. The first operation is the mixing of ingredients (i.e. adding the formula ingredients in the main mixing tank and adding the homogenization ingredients in the pan). Achieving 25 ppm for these combined operations could be accomplished by two feasible options.

The first option is to implement strict work practice procedures to prohibit simultaneous operation of mixing equipment. That is, dedicating the available exhaust volume of 2,500 CFM to one piece of equipment at any one time. To achieve this objective, the system should be provided with gates to redirect the exhaust flow to the desired piece of equipment.

The second option is to provide two additional blowers to ensure that each piece of equipment (two mixing tanks and homogenization hood) will have its own independent exhaust blower in case that production protocols require simultaneous operation of more than one piece of equipment.

The second operation requiring engineering modification is the flushing of the transfer lines and the pneumatic pumps. Exposure control was determined to be technologically feasible through providing an enclosure equipped with an exhaust blower rated at 500 CFM.

F. Manufacturing of Paint and Paint Removers/Strippers

The main solvents currently used in paint formulations consist of mineral spirits (petroleum naphtha products). Mineral spirits are not used for the purpose of removing paint or as paint/varnish removers due to their inability to penetrate the cured layer of paint efficiently. That is, once a coat of paint is applied, it reacts with oxygen and forms a cross-linking mechanism. The paint then becomes a much tougher polymer, and so the same solvent used to formulate the paint (e.g. mineral spirits), can not be used to remove the paint (Ex. 7-219).

Currently, MC is not used as a solvent in the manufacturing of paint because of its undesirable lifting properties. That is, if MC is used in the formulation of paint and fresh paint is applied over an old coating, the MC in the fresh paint would lift up or "remove" the old coating. This is due to the immense solvent potency of MC. The resulting coat of paint would be undesirable in terms of texture and static appearance. Therefore, MC is currently being used more frequently as a paint/varnish remover (Ex. 7-219).

MC is used as a solvent in the varnish remover formulation and paint remover (stripper) formulation because it has the ability to separate the substrate from the coating system. The paint and varnish remover formulations are similar in terms of MC content since both consist of approximately 70% MC in their formulations. Methyl chloroform, CFC and any combination of dibasic esters are regarded as substitutes for MC, but none possess the desirable penetration characteristics of MC (Ex. 7-219).

Two production methods, the single batch manual mix and the multiple ingredient mix, are used to prepare paint varnish removers and paint stripping formulas. The following is a description of the controls that are currently used for each production method. The first method (i.e.single batch manual mix) is used for the manufacture of paint varnish removers. The second method (i.e. multiple ingredient mix) is used for the manufacture of paint stripping formulas. This second method involves the pumping of multiple ingredients through a piping system designed to eliminate the manual handling of the ingredients. Ingredients are stored in tanks located outdoors and are equipped with mixing platforms and steam cleaning lines (Ex. 7-219, 7-218).

1. Engineering Controls

a. Single batch mix method. As indicated previously, the production method for varnish removers is a single batch mix process, in which the components or the ingredients are normally added manually to the mixing tank with the exception of MC which is pumped and metered directly into the tank.

The mixing tank is usually located in a partially open area (3 sided canopy). The tank is provided with a 2 x 2 ft opening with a hinged cover. The workers' exposure duration is limited to the time required to manually add the ingredients into the tank (e.g. cellosic thickener). However, since no worker is required to be stationed at a close proximity to the mixing tank, appropriate work practices are determined to be of critical importance. Leaving the tank opening uncovered during the mixing process creates an unnecessary source of exposure. It was indicated, during the OSHA site visit, that exposures at this location as measured by a 3M organic vapor monitor revealed 89 ppm (TWA) when a 70% MC formulation was being processed.

Workers' exposure in this paint varnish remover formulation facility is limited to two sources. The first source is generated during the manual addition of ingredients into the mixing tank. The second source is generated during packaging (filling the cans) on the conveyor.

In order to reduce workers' exposure from the first source (mixing tank), local exhaust in the form of a two sided slot hood needs to be installed to trap the MC emission from the feed opening of the mixing tank. An alternative to this is to provide a ventilation system in the form of a fresh air island, at the platform on which the tank operator stands. This system would reduce workers' exposure when the tank is opened for adding ingredients or performing other tasks. In either case, strict adherence to good work practices should be maintained.

Good work practices may include, but are not limited to, keeping the tank cover closed during mixing, and instructing the operators not to lean over the tank when ingredients are being added (Ex.7- 219).

A double sided slot hood is a technologically feasible method for controlling workers' exposure at the platform of the mixing tank. The current reliance on wind effects (dilution or dispersion of MC emission) as a control practice can not be regarded as an acceptable method for limiting workers' exposure. The feasibility of controlling workers' exposure through providing mechanical ventilation (e.g. a double sided slot exhaust hood) can be demonstrated through calculating the volume of exhaust air required to achieve the desired reduction in workers' exposure.

Q = 3.7 x 4 ft (length of slot) x 100 FPM (V) x 1 ft (centerline

for 2 ft tank opening) or 1,500 CFM total

Workers' exposure at the can filling conveyor can be controlled by installing an enclosure in the form of a canopy made of flexible plastic strips so that workers maintain their accessibility to the can's filling equipment. Since the filling of the can takes place on an open conveyor which is approximately 15 ft long by 2 ft wide, and the height of the filling pump is less than 3 ft high, and since the MC vapor is approximately three times heavier than air, a simple enclosure for the conveyor can be installed and exhausted through a downdraft plenum. This is a technologically feasible means for lowering workers' exposure to MC at this location.

The volume of air required to exhaust the conveyor enclosure (assuming homogenous MC concentration along the total length of the conveyor) can be approximated by Q = 15 ft x 2 ft x 3 ft x 50 air changes per minute = 4,500 CFM. As indicated before, to accommodate workers' easy accessibility to the filling pump, the enclosure can be made of overlapping flexible plastic strips. These strips can be used at both the entrance and the exit sides of the conveyor provided that an allowance or an opening for the can movement is incorporated. This flexible and simple enclosure will not only provide for worker protection against excessive MC exposure, but will also provide protection against exposure to other volatile substances contained in the paint remover formulation. Additionally, the flexible plastic strips will result in reducing workers' exposure to noise generated by the conveyor, filling pump and can sealing equipment.

b. Multiple ingredients mix method. As indicated previously this second method is used to manufacture paint stripping formulas. In this method, the mixed formula is prepared by simultaneous pumping of the various ingredients. After mixing is completed, the mixed formula is pumped into an open tank which is located indoors. The filling tank, which was observed by OSHA during this site visit, is currently not provided with any controls or a cover. One of the reasons indicated for not covering the tank is the need for the operator to continue monitoring the level of the fluid (paint stripping media) to ensure a continuous supply to the filling lances (Ex.7-218).

Reduction in workers' exposure, resulting from MC vapor escaping from the open tank, can be achieved by providing the tank with a valve and a flotation device. These devices are to be connected in a series with the main pump. Whenever the fluid drops below a certain level, the valve will open, and replenish the consumed fluid. These simple devices will eliminate the need for the operator to physically monitor the fluid level in the tank. Consequently, there will be no need to maintain the tank uncovered.

Further reduction of workers' exposure, especially during the hot weather, can be achieved by providing the tank with a heat exchanger and a chilling coil. OSHA realizes that the tank temperature cannot be lowered extensively, since lowering the temperature will result in increasing the fluid viscosity. This may render the fluid to be too viscous to be pumped. However, in the summer months where the temperature can exceed 100oF, chilling the tank to 68oF will result in significant reduction of MC evaporation rate. Reduction of the temperature from 100oF to 68oF will be associated with reduction of MC vapor pressure from approximately 690 mm Hg to 350 mm Hg. Consequently, this will result in the proportional reduction of workers' exposure (i.e. approximately 50%) without affecting the ability to pump the fluid.

2. Conclusion

The above assessment for both production methods reflects the availability and technological feasibility of engineering controls that would limit workers' exposure to MC vapors during both steps (i.e. mixing and canning).

G. Paint Stripping

Three methods are used in the furniture stripping industry, the flow-on system, the hand application, and dip tank method. Each method has unique characteristics, and therefore, workers' exposure and their associated controls vary significantly.

1. Engineering Controls

a. Flow-on system. The standard size of the MC tank for the flow-on operation is 10' x 4', with a slight decline to allow stripping fluids to be channeled through a drainage trough back into a storage container for reuse. Usually, ventilation is achieved through a local exhaust system provided with four slots, one located at each side of the tank (Ex. 7-231).

Stripping fluid (72% MC) contains paraffin wax added as a retardant to lower the evaporation rate of MC (Ex. 7-231). As observed by OSHA during the site visit, workers' exposures occur during the performance of the following successive tasks.

During the first task, stripping fluid is pumped from a 55 gallon drum to a four gallon holding can, by placing the applicator brush into the drum and pumping the fluid into the can. The fluid is then pumped from the four gallon can to a brush applicator. After applying the fluid with the brush applicator, a few seconds are allotted for solvent penetration and blistering of the paint.

During the second task, the operator uses a putty knife to scrape the paint or varnish from the furniture. Some stubborn paint may require the use of additional coats of stripping fluid and/or the use of a wire brush or steel wool to expose the wood grain.

During the third task, the operator uses a squeegee to push the excess stripper and the waste that was removed, down through the drainage port in the tank and into the trough, where it is collected back into the four gallon can for recirculation. Through the recirculation, the stripping fluid is continually used, until it reaches a heavy consistency that renders its usefulness for the removal of paint or varnishes obsolete. The consumed stripping fluid is stored in unsealed containers provided with a large hole cut out of the top to allow the stripping fluid to drain into it. The stripping fluid that was previously used for varnishes is reused to strip painted furniture. At any one time there may be as many as three or four such containers being stored under the stripping tank at a close proximity to the worker (Ex. 7-231).

At one of the facilities visited by OSHA, a 10' x 4' table was provided with an exhaust system with a capacity of 1,500 CFM. According to established and published engineering design criteria, this exhaust system handles approximately 1/3 to 1/4 of the appropriate capacity (if the 125 CFM/ft2 is used as recommended in the design criteria). This design criteria yields 67 fpm capture velocity, which is very close to the minimum velocity required for operations releasing vapors with practically no velocity. OSHA's assessment is based on published data indicating that 50 fpm is the minimal capture velocity for vapors in lateral hoods in undisturbed locations. It would be reasonable to consider the movement of the operator at the table as a source of a slight draft, for which an additional 10 - 25 fpm increase in the capture velocity would be desired. Therefore, 60 - 75 fpm capture velocity is needed for this type of system. Clearly, the system currently in use in this facility is underrated, and needs to be upgraded by increasing its capacity from 1,500 CFM to 5,000 CFM, an increase of 3,500 CFM.

The above described engineering modifications would increase the capacity by 3.33 times the current volume. Therefore, it is reasonable to predict that the modified system will reduce prevailing exposure levels by the same factor. That is, technologically feasible controls would result in reducing MC concentration from the current prevailing exposure level of 70 ppm to 21 ppm. This reduction in workers' exposure is the product of implementing simple engineering modifications required to upgrade the system so that the minimum design criteria can be met.

Further reduction could be achieved through implementing other modifications as well as employing appropriate work practices as discussed below. For example, the open face cans contribute significantly to workers' exposure. Cans could be designed in a manner, such that, they are connected to the table, so that the vapors that come off are directed up into the trough where the exhaust slot will capture them. Further, cans should be capped off while they are not in use. An alternative exposure control method would be to provide a turntable to be mounted inside the stripping tank, where furniture pieces can be placed on the turntable and rotated. The turntable inside the stripping tank will allow operators to maintain their position at a fixed location. This approach will facilitate providing a fresh air supply at the workers' fixed location. Providing an exhausted grated floor upon which workers can be stationed, when performing their tasks, would further contribute to achieving the desired reduction in workers' exposure.

b. Hand stripping. Although the majority of the work is performed using the flow-on system, hand stripping may become necessary for specific pieces of furniture having complex details that render the earlier method ineffective. In the hand stripping, the stripping fluid is applied with a brush and allowed to penetrate for a while. The loosened paint coat is scraped off using a wire brush or putty knife. The waste material removed, including the stripper, is then placed into another can to be disposed of later. The stripping fluid is only applied to small areas at a time. While the stripping fluid is penetrating one area, the operator begins coating a second area. Once this second area is coated, the first area is then scraped. Care is taken not to be leaning over the area of first coverage while covering the second area.

This operation takes place in the same room as the flow-on system, and occasionally just outside of the room. At the site visited by OSHA, there was no ventilation available for this operation. A typical operation will take anywhere from 45 minutes to an hour. Hand stripping consumes approximately 33.3 gallons/year (Ex. 7-231). Assuming a homogeneous daily consumption, the maximum evaporative loss of MC is 0.017 gallon/hour. This is equivalent to 18.9 liters/hour4 of MC vapors. This volume of MC vapors generated in a 24 x 30 x 9 ft work room5 will result in approximately 20 ppm, if 5 air changes per hour are provided. This technological feasibility determination is based on using dilution ventilation which is known to be the least effective control system. This dilution ventilation system would require only one fan having a capacity of 550 CFM.

c. Dip tanks. The dip tank system is commonly used for stripping old paint from metal parts. Although MC is the dominant paint stripping media currently in use, there are several substitutes available, all of which have the same effectiveness as MC. Examples of these substitutes are methanol, acetone, and toluene. Even with theeffectiveness and low volatility of these substitutes, their use is not common and is undesirable because of their high flammability rate. Most dipping tanks are not provided with proper ventilation systems. Control of workers' exposure is limited only to providing hinged covers for the tank to confine the vapors during blistering of the paint.

Exposure data indicating the extent and magnitude of the problem are not extensive. However, available information indicates that a typical dipping tank having dimensions of 10 x 4 x 4 ft. is located in a 30 x 40 x 15 ft room (500 m3). Depending on the type of objects being stripped and the "stubbornness" of the paint layers desired to be removed, an average of 5 gallons is lost through evaporation daily (per 8 hour shift). This volume of MC loss indicates that the use of dilution ventilation would not be a technologically feasible means of control for workers' exposure. The infeasibility of dilution ventilation is due to the need for an extremely high volume of air. The 682 liters/hour of MC vapors released in a 500 m3 room with 15 air changes will result in a final concentration of 90.9 ppm. In order to achieve a level of 25 ppm, approximately 60 air changes per hour will be required. Therefore, it is evident from the above calculation, that local exhaust ventilation should be regarded as the preferred control method. Further, the efficiency of the local exhaust method could be substantially increased by implementing minor modifications such as electrical switches. Electrical switches can be used to activate the exhaust system whenever the tank covers are removed. The design of this system is more efficient since operators are not stationed in the vicinity of the dipping tank all of the time. Also, during the blistering duration, the hinged covers are kept closed, hence there is no need to operate the exhaust system.

2. Conclusion

Engineering modifications to current control systems are technologically feasible for all of the three types of paint stripping operations. The technological feasibility of implementing engineering controls to reduce workers' exposure from the current standard to the proposed level of 25 ppm is further demonstrated by increasing the capacity of an existing exhaust system, and implementing modifications to work practices and equipment layout. These modifications in engineering and work practice controls, and equipment layout resulted in lowering workers' exposure to MC from 340-1726 ppm (average 812 ppm) to 22- 35 ppm (8 hr. TWA averages 18 ppm). At one furniture stripping facility, the feasibility of achieving the proposed 25 ppm through engineering and work practice controls was further emphasized by the statement, ". . . exposures can be further reduced by improving the design of the rinse area and by limiting the workers' access to the drum containing the stripping solution (Ex. 7-247).

H. Degreasing and Metal Cleaning

Exposures from vapor degreasing originate from vapors rising past condensation coils (most likely due to underrated capacities of condensation coils). The vapors are emitted from parts that may contain liquid MC in, or on them, upon removal from the degreasing tank (trapped condensed vapors), from spraying liquid MC onto parts with a spray lance (splattering), from leakage of pipes and pumps that carry the solvent, during cleaning of tanks, and/or from implementing improper techniques and work practices.

Workers' exposures could be controlled through the implementation of the following technologically feasible engineering and work practice controls. Local exhaust is the primary engineering control for reducing exposures to MC vapors. Depending on the size of the tank and it's associated exposed area of the liquid MC, either of two types of slotted hoods can be used. The first is the one sided slotted hood and the second is a multiple sided (including full perimeter) slotted hood. Either of these two types of hoods should be provided with make up air in the form of a sweeping apron or push pull system, so that the exhaust efficiency of the system can be maximized and maintained throughout the operational duration. Design criteria for these types of control systems are readily available, and their implementation has proven to be effective for the reduction of workers' exposure to MC.

1. Engineering Controls

a. Mechanical ventilation. The ventilation system observed on an open top vapor degreaser, at the facility visited by OSHA, was a down draft system with a slotted hood, located around the perimeter of the tank. The degreasing tank has dimensions of 10' x 5' x 12' (length x width x depth) and was equipped with a slotted hood having a 13,000 CFM design capacity (Ex. 7-233).

Evaluating the current capacity of the system indicates that the system is underrated by a factor of 2.85.6 The prevailing exposure level of approximately 80 ppm reveals that engineering modifications to the system to meet the proper design criteria are expected to reduce these prevailing levels proportionally (i.e. reduce exposure levels to 28 ppm).7 The appropriate design criteria that yields a system capacity of 37,000 CFM is based on the assumption that all system components (e.g. condensation coils and refrigerated free board) are designed, rated, and functioning properly.

b. Condensation and refrigerated freeboard coils. Condensation coils are the most important component on a vapor degreaser. When coils are properly functioning, they confine MC vapors below the freeboard by condensing hot vapors on their cool surfaces. Further reduction in emissions can be achieved when a refrigerated coil is attached at the freeboard above the condensation coils. These devices assist in reducing solvent loss and workers' exposure, and are not meant to be used alone to control the vapor level, but in conjunction with condensation coils to help reduce the vapor release into the work environment (Ex. 7-234). Using only condensation coils, resulted in exposures ranging from 179 to 219 ppm (Ex. 7-233).

With a refrigerated coil attached to the freeboard, the MC concentration was lowered by 55%, yielding exposure levels ranging from 80 to 100 ppm. The cooling water temperature of this system was not properly conditioned, (i.e. inlet and outlet water temperatures were 68oF and 100oF, respectively). Further reduction in exposure levels can be achieved through lowering the cooling water temperature (Ex 7-233).

One of the major problems responsible for the excessive workers' exposure is the lack of the understanding of the chemical and physical characteristics of MC. When water at ambient temperature (68 deg F) enters condensing coils and then exits at 100 deg F, (nearly the boiling temperature of the solvent), the condensation efficiency of the coils will be extremely reduced, and consequently high levels of exposures will prevail. Simple extrapolation, considering the MC vapor pressure at 100 deg F, indicates that by feeding a chilled fluid (e.g. brine or water and glycol mix) at 20 deg F and exiting at 60 deg F, the relative vapor pressure of MC would decrease by 67%(8), yielding an exposure level of approximately 26 ppm. That is, incorporation of this technologically feasible modification, without upgrading the mechanical exhaust system previously discussed, will result in reducing the current prevailing exposure of 80 ppm to 26 ppm. When combined engineering modifications, (i.e. upgrading the exhaust system capacity and implementing the chilled water system), are incorporated, the prevailing exposure level will be reduced to approximately 9.1 ppm ((80 x 0.325)/2.85).

The above indicated feasible reduction in exposure levels (i.e. through modifications to the exhaust system, incorporating a refrigerated coil, and using a chilled solution in the condensation coil), can only be maintained if an appropriate preventive maintenance program and work practices are properly implemented.

c. Maintenance. Preventive maintenance is critical for efficient operation of exhaust systems. The system should be checked regularly for proper operation of the fan (e.g. belt tension, direction of blade rotation, unbalanced blades...etc.). Loose belts on drive systems can cause extreme reduction in fan speed, which consequently results in decreasing the volume of exhaust air, as well as wear and tear on both the fan and the motor. Proper functioning of fans can be checked through measuring slot velocities against the design criteria. Further, checking and repairing leaks, collapsed piping, and blockage are the main components of good maintenance practices which are essential for reduction of workers' exposure.

2. Work Practices

If automatic nozzles are not available and manually operated spray lances are used, spraying should be performed below the vapor level. Spraying above the vapor level will cause turbulence and will result in excessive exposure in the work area. If the pressure on spray nozzles is not properly adjusted and maintained to provide adequate rinsing action, splattering and consequently excessive and unnecessary exposure will result. Overloading baskets in open top vapor degreasers should be prohibited. The basket which enters the tank with the parts should be carefully lowered, so that the basket does not act like a piston which will force MC vapors out. Workers should be trained to arrange the parts appropriately, so that vapors are not trapped in and between parts. If this is not possible due to the shape of the parts, then drain holes, instead of the tilting practice, should be incorporated in the design of the parts to allow any liquid MC to drain off before the removal of the basket from the tank. If tilting is necessary, it should be done below the vapor level. The speed of raising and lowering of the basket should not exceed 11 ft/min (Ex. 7-234).

3. Alternative and Supplemental Control Measures

a. Isolation. Isolation is a technologically feasible approach for the control of workers' exposure. The use of a monorail degreaser lends itself to the desired isolation and achieves significant reduction of workers' exposure. In this system, parts are carried in and out by conveyor hooks through small openings in the wall of the building. The employees load and unload parts onto the hooks approximately 15 to 20 feet away from the degreaser. To demonstrate the effectiveness of this isolation approach, a vapor degreaser that uses water at ambient temperature in the condensation coils (from the same source as the open top batch vapor degreaser previously discussed), coupled with a refrigerated coil device results in workers' exposure in the range of 10 to 11 ppm. That is, the simple isolation of the degreaser resulted in low exposures without the aid of any mechanical ventilation system. Exhaust systems are necessary to provide workers with protection during periods of time spent in the degreasing room for the removal of parts that have fallen off the hooks, emergency situations, or during the cleaning and maintenance of the degreaser (Ex. 7-233).

b. Vapor confinement. The biggest problem for the exhaust system is the disturbance of air from in and around the tank. To help eliminate poor capture efficiency due to disturbances of the air flow pattern, an enclosure could be designed for the open top vapor degreaser. A canopy with a telescopic or flexible duct can be attached to the chain hoist that lowers the basket of parts into the tank. When the basket is lowered into the tank, the canopy will be lowered simultaneously, such that, when the basket is in the tank the canopy will cover the tank, hence preventing vapors from escaping to the workers' breathing zone. The canopy can be made of a clear material allowing operators to observe the basket in the tank. Glove ports can be attached to the canopy, so that operators will be able to insert their hands through the canopy into MC-resistant rubber gloves, to facilitate rinsing the parts with the spray lance. The canopy will not only reduce workers' exposure through the confinement of MC vapors within the tank, but will also reduce exposure of workers who are stationed in the vicinity of the tank. It should be noted that sufficient clearance between the canopy and the tank should be maintained to allow for air to enter the exhaust system, otherwise excessive negative pressure will develop and render the exhaust system ineffective. This canopy will also keep operators from leaning into the tank unnecessarily and exposing themselves unnecessarily to excessive MC concentrations.

4. Substitution

Aqueous cleaning as a substitute process is currently available and in use in some facilities. However, there are some limitations on the degree of the parts' cleanliness which affects the acceptance of their subsequent processing (e.g. painting, soldering, welding). Research is in progress to develop a detergent that will sufficiently clean parts for painting. However, environmental consideration for water purification deserves special attention. Although aqueous cleaning may not be suitable/proper for all types of degreasing, it is technologically feasible for various degreasing operations, such as printed circuit boards (Ex. 7-233).

5. Conclusion

A feasible engineering modification of the current capacity of the exhaust system has been demonstrated to result in extensive exposure reductions. Supplemental engineering controls (i.e. using a refrigerated coil and chilled solution) have been demonstrated to result in further reduction of exposure levels. The combined modifications would yield approximately 90% reduction in the current exposure levels (from 80 ppm to 9 ppm). Further, appropriate work practice controls and implementation of preventive maintenance should be incorporated as an integral part of the feasible control measures, so that the system's effectiveness can be maintained.

I. Cellulose Triacetate Fiber and Film Base Production

1. Cellulose Triacetate Fiber.

The technological feasibility assessment is limited to controls applicable to the manufacturing of cellulose triacetate film base. Since only one manufacturer of triacetate fibers currently uses MC, OSHA regards this as evidence of the feasibility of MC substitution in this industrial application. Therefore, no engineering determination is needed since other producers have successfully converted their production processes to be compatible with the substitute.

2. Cellulose Triacetate Photographic Film Base.

a. Production processes and exposure levels. Methylene Chloride (MC) is used as a solvent to dissolve cellulose triacetate pellets for making photographic film base. MC is used because of its low flammability as well as its low order of chemical reactivity and fast evaporation rate. There are two main processes in the making of the cellulose triacetate film base. These processes are dope preparation and roll coating (Ex. 7-235).

i. Dope preparation. MC is used to dissolve the cellulose triacetate pellets. The solution is conditioned with plasticizers and other solvents to produce the dope. Impurities in the dope are removed by several successive filtration processes (i.e. continuous screen filter, continuous wash press, transfer and multipress filters). The dissolution of the triacetate pellets and the successive filtration processes are carried out in a closed system. The filtered dope contains 60% to 65% MC by weight (Ex. 7-235).

Workers' exposure during dope production occurs during preparation of crude dope (dissolving cellulose triacetate pellets in MC), dressing filters (changing), unscheduled/scheduled maintenance and leaks from pumps and transfer lines. Exposure levels measured during crude (unfiltered) dope preparation ranged from 6 to 75 ppm (geometric means) with 38% of the samples below 25 ppm (Ex. 7-235).

The filtration process starts by passing the freshly prepared crude dope through a continuous screen filter. The cleaning of the screen is performed through reverse flow or back flushing. The flushing solvent which carries the coarse contaminants (that are being released from the screen during the back flushing cycle), is pumped to the solvent recovery operation. The continuous screen filter is a permanent and sealed filter and therefore, its contribution to workers' exposure is very limited (Ex. 7-235).

The dope, after passing through the continuous screen filter, to remove fiber contaminants, is piped to the continuous wash press filter. The wash press filter consists of a cartridge frame holding the filter plates on which the filter pads are mounted. The total wash press filter assembly (cartridge frame, filter mounting plates and filter pads) are housed in a cylindrical filter shell (Ex. 7-235).

Workers' exposures to MC occur during the dressing of the wash press filter (removing the old filter pads from the plates and replacing them with new pads). There are three tasks performed during filter dressing which result in MC vapor release and contribute to workers' exposure. Currently, these tasks are performed without purging the filter housing, hence all confined MC vapors are released to the work environment. The first task is unbolting and removing the cover of the cylindrical filter shell/housing. The second task is lifting out the MC saturated filter cartridge from the filter shell with a hoist, and allowing the excess MC liquid to drip. This is the most serious source of workers' exposure, since there are no controls in place to confine the MC drippings and their associated vapor release. The third task is the removal of the old filter pads from the mounting plates. Workers' exposures occur as the result of MC evaporation from the wet pads. Removal of the old pads must be performed while the pads are still wet, because if dried, the pads will adhere to the mounting plates and their removal will be difficult and time consuming. The combined exposure level that prevails as a result of performing the continuous wash press filter dressing is 160 ppm (geometric mean).

The filtered dope from the continuous wash press filter undergoes two additional stages of purification, transfer and multipress filtration. Although there are some variations in the size, configuration, methods of disassembling, assembling and compressing the filter pad as well as the purpose of the filtration process, sources of workers' exposure during the performance of these tasks are similar to those described above (i.e. continuous wash press filter dressing). Exposures measured during changing the transfer filters and multipress filters were 200 and 120 ppm (geometric mean values), respectively (Ex.7-235).

ii. Roll coating. Workers' exposures to MC vapors in the roll coating process occur at two operations, the casting of the film base and solvent recovery operation.

(A) Casting of film base. In the film base casting operation, the filtered dope is piped to the receiving hopper of the coating machine. The dope is then spread across a rotating polished metal wheel. As the coating wheel rotates, MC and other solvents are evaporated from the dope inside the casting machine enclosure. At the completion of one turn, the formed film base is stripped off the wheel and conveyed through the curing station for further solvent evaporation by hot recycled air with a temperature of 121-138 deg C. The cured film base is wound onto a core and is moved to another section for inspection, packaging and further processing to produce photographic products. The roll coating process is housed in an enclosure maintained under a slightly positive pressure to prevent contaminant intrusion into the machine housing (Ex.7-235).

The major source of employee exposure to MC vapors in the roll coating operation is the evaporation of MC inside the coating machine enclosure, and the subsequent MC vapor release when access doors and windows are opened during routine maintenance (scheduled/unscheduled and product rescue activities). The maintenance activities include wheel and dope hopper cleaning and trouble shooting. The rescue activities include tie-on sheets to the threading strap, trimming edge and performing other miscellaneous adjustments. These activities are performed through access doors and windows. Workers' exposure occurs as a result of MC vapor release from the machine enclosure which is maintained under positive pressure (Ex.7-235).

(B) Solvent recovery. In the solvent recovery operation, vapors of MC and other solvents are recovered (condensed and purified) for reuse in the dope preparation (dissolving cellulose triacetate pellets). The evaporated solvents are ducted from the film casting machine enclosure to the heat exchanger in the solvent recovery section by two air handling systems. These are housed in the film base casting section. The condensed solvents are purified by distillation. The effluent containing the uncondensed MC (about 3% of the total consumption) is withdrawn from this recovery section, and returned to the film base casting machine enclosure for the purpose of maintaining the desired positive pressure inside the film casting enclosure (Ex.7-235).

Employee exposure in the solvent recovery section is caused by leaks of the effluent containing uncondensed MC. The combined effects of MC release in both the casting of film base and the solvent recovery result in exposures from 20-50 ppm with 63% of the samples being below 25 ppm (Ex.7-235).

b. Engineering controls. Current control strategies for reducing workers' exposure include machine and enclosure retrofit, upgrading ventilation systems to direct solvent vapors away from the workers' breathing zones and to provide fresh makeup air, providing permanent or portable local exhaust systems during the performance of high exposure tasks (e.g. filter dressing and maintenance activities), and upgrading solvent recovery capacity to reduce the release of uncondensed MC vapors. Air-supplied respirators are used to reduce peak exposure during filter dressing operations. Since current engineering controls do not sufficiently reduce workers' exposure to MC vapors, the dressing of the transfer filter occurs in a nearby enclosed dressing station. This station is equipped with a temperature controlled air supply and exhaust system, which directs the air flow downward and away from workers' breathing zones. The dressing of multipress filters is done on a movable table equipped with a local exhaust system. Employees are required to use air-supplied respirators for additional protection while handling spent filter pads. At the completion of filter dressing, spent filter pads are placed in fiber drums for incineration (Ex. 7-235).

Most maintenance activities involve exposure to the process equipment, often in hard to reach spaces, where conventional exhaust systems would not fit. A portable ventilation unit was designed and placed in service in the production building. Table 3 summarized the engineering controls and protective equipment used in dressing operations (Ex.7-235).

TABLE 3.--ENGINEERING CONTROLS&PROTECTIVE EQUIPMENT
_____________________________________________________________________
    Dressing
| Engineering Controls And
  | Protective Equipment
_____________________________________ | _____________________________
    Continuous and
| Portable 5,000 CFM ventilation;
    Wash Press
| operation performed outside;
    Filters.
| cartridge respirator available
  | but their use is not mandatory.
    Transfer Filters
| 5,000 CFM down draft ventilation
  | at work area; air-supplied respi-
  | rator worn at worker discretion.
    Multipress
| 6,000 CFM down draft ventilation
    Filters.
| at work bench; air-supplied res-
  | pirators are available for some
  | tasks.
_____________________________________ | _____________________________

i. Leaks from transfer lines, pumps and air-MC effluent conduits. Control of workers' exposures that result from leaks from transfer lines, pumps and air-MC effluent conduits can feasibly be achieved through several means. Replacement of seal-pumps with magnetic drive pumps will result in substantial reduction of repair frequency and most likely elimination of leaks. Leaks from seams (connected joints) in air-MC effluent conduits can be feasibly eliminated, or at least reduced by welding the joints or sealing the leak sources using plastic-silicon caulking. Further reduction in exposure levels due to leaks can be feasibly achieved through early leak detection. Helium leak detection devices are available and can be used to determine the amount and the source of leakage.

ii. Dope production, dressing of filters.--(A)Use of Mobile Confinement Canisters. Currently, the filter dressing is performed in the field without appropriate purging of the filter canister/ housing before its opening. Decreasing the time during which the top of the filter canister remains open will also result in substantial reduction of workers' exposure. In order to reduce the amount of MC vapor released during filter changing, the filter canister should be purged with air or an inert gas. The purged effluent should be directed or ducted to the MC recovery system. Providing a half circle exhaust slot, connected to the exhaust blower by a means of a flexible hose, will enable the worker to unbolt the filter canister top under controlled conditions. Design criteria for determining the exhaust system capacity are available, and have proven to be effective for controlling emission or vapor release from similar operations.

The current technique of lifting the spent filter cartridge and allowing it to drip in the work area, and replacing the filter pads at the site, should be discontinued. Workers' exposure resulting from performing these tasks can be controlled through confining the MC emission in a portable filter canister that can be mounted on casters for easy mobility. Upon lifting the spent filter cartridge, it can be set or placed inside the portable canisters, and the canister top can immediately be positioned to cover or confine any MC vapors that can be potentially released into the work environment. During the replacement of the spent filter pads, the use of a preassembled filter cartridge, to be inserted in the filter shell would eliminate the need for the workers to perform their duties in an uncontrolled field environment. This would only require the purchase of a spare filter frame and filter plates. The mounting of the fresh filter pads on the spare filter plates, and assembling them on the filter frame can be safely performed in "an office like" environment with no need for control systems, since the potential for exposure to MC is non-existent.

The removal of the spent dry filter pads from the mounting plates can be feasibly achieved, without subjecting the workers to unnecessary exposure, through one of two means (dry and wet method). In the dry method, the dry filter pads are subjected to a hot air stream to soften and loosen the filter pads for their easy removal. If the hot air stream method is proven to be ineffective to loosen the dry spent filter pads, the wet method can be used. In this method, MC or preferably other safer solvents can be used to wash out the dry dope from the spent filter pads. The addition of the solvent can be performed in the portable canister which already houses the spent filter cartridge. Further, the portable canister would be provided with feed and discharge ports, so that the wash-out solvent can be pumped, (under closed system conditions), to the distillation operation for recovery. In this case, a waste drum equipped with self closing covers, would be needed to confine the release of solvent vapors from the spent filter pads which are removed from the mounting plates. Purging the mobile canister with an inert gas/air, after completing the pumping of the wash-out solvent, must be performed before opening the canister for removing the spent filter pads. No information on the possibility of using a disposable filter cartridge assembly is currently available.

(B) Modification to the filter dressing room. Technologically feasible modifications to the design of the exhaust and makeup air systems of the filter dressing room can also achieve the desired reduction of exposure levels. If the dressing room is provided with an exhaust system in the form of a grated floor, and makeup air slots are distributed uniformly and in a manner that maintains a vertical direction of air, then the released vapor will be exhausted at the floor level, while a continuous fresh air flow will be available at the workers' breathing zone.

The current available exhaust system of 5,300 CFM is sufficient to provide 166 air changes per hour (dressing room volume 12 x 20 x 8 ft). However, because of the inefficiency of the fresh air supply distribution, the inability to maintain the shortest distance to the exhaust slot, and the ineffectiveness of maintaining high velocity make-up air to overcome or force the MC vapors downward, the current workers' exposure levels are excessive, and need to be reduced through the implementation of the above indicated technologically feasible control approaches.

Assuming an evaporation loss of 2 gallons, or approximately 15 pounds per hour, when filter dressing is performed, and assuming that the available 5,300 CFM function is dilution ventilation, (which the least efficient control system), prevailing exposure levels would be approximately 288 ppm.9 It should be noted that this concentration results from homogeneous dilution which is unrealistic. In other words, there is a likelihood that the concentration at workers' breathing zones exceeds the calculated 288 ppm level.

A downdraft exhaust system with an overhead high velocity of fresh makeup air yields a minimum efficiency rate of approximately 20 times that of dilution ventilation. Therefore, the current available 5,300 CFM would be sufficient to reduce the MC concentration to approximately 15 ppm when the above modifications are implemented properly. If the actual evaporation loss of MC exceeds the above assumed 2 gallons or 15 pounds per hour, then the exhaust system should be proportionally rated. For example, if the actual evaporation loss is 4 gallons or 30 pounds per hour, the exhaust system capacity should be rated at 10,600 CFM.

The selection of any of the above mentioned technologically feasible control methods depends on the frequency and duration of the filter dressing, the size and configuration of the filter cartridge, and the type of equipment used to complete the filter dressing task. Further, certain modifications to the grated exhaust floor may become necessary. If this design is used for dressing tasks, and the possibility of releasing liquid MC (that is trapped between the plates) exists, a drip pan placed below the grated floor (receiving container) equipped with an elbow trap (smallest diameter possible) should be incorporated in the system design. The elbow trap is necessary to limit the surface area from which liquid MC may be lost through evaporation.

iii. Roll coating.--(A) Film base casting. Exposure to MC in the film base casting operation result from MC vapor releases during the opening of access windows and doors of the casting machine, for the purpose of performing repairs. As indicated previously, the casting equipment are housed in an enclosure that is maintained under positive pressure to prevent contaminant intrusion. Therefore, when access windows and doors are opened to perform maintenance and rescue tasks, workers are exposed to excessive MC levels.

The technological feasibility assessment of engineering controls for this operation is based on assuming a worst case scenario. Since the total consumption of MC is rated at 200 x 106 pounds per year (Ex. 7-146), and the recovery efficiency is currently rated at 97%, it would be reasonable to quantify the MC loss to about 6 x 106 pounds per year.

The worst case scenario assumes that all unrecovered MC, (6,000,000 pounds per year), escapes to the work environment surrounding the film casting equipment. Under this assumption, the exposure level in the work environment that surrounds the film casting equipment is not expected to exceed 118 ppm.10 Since the prevailing exposure levels range from 20 to 50 ppm, an average of 35 ppm, it would be reasonable to assume that approximately 70% of the 6,000,000 pounds of unrecovered MC is lost to the outdoors environment, and only 30% of the 6,000,000 pounds escapes to the work environment.

The 30% of unrecovered MC that escapes to the work environment during the performance of routine maintenance and through gasket leaks around access doors and windows, can be quantified as 3.42 lb/min(11). This amount of MC loss yields approximately 16.00 ft(3)/min(12) of MC vapor. Therefore, dilution ventilation cannot be regarded as a realistic engineering approach for achieving the desired reduction of workers' exposure, when maintenance through the access doors is performed. Three viable options to achieve the needed reduction of workers' exposure are described below.

The first option is to erect a partition along the access doors and windows so that air locks are generated, hence confining MC vapors within air locks. Providing air locks will not only facilitate the installation of an efficient exhaust system for the access doors and windows, but will also reduce the diffusion and escape of MC vapors to the surrounding work environment. Currently, workers who are not directly involved in performing the maintenance or rescue tasks are unnecessarily exposed to fugitive MC concentrations ranging from 20 to 50 ppm. A portable local exhaust system with fresh make-up air, being supplied at a sufficient high velocity to overcome the thermal rise of effluent containing MC vapors, will result in redirecting the MC effluent vapor downward, and/or away from the breathing zone of the operators. Exhaust slots are to be incorporated along the perimeter of the film casting enclosure inside the confinement of the air lock. A properly rated portable exhaust blower, provided with a filter to eliminate potential contaminants from entrainment inside the casting enclosure, is expected to provide the needed protection for the workforce without resorting to the use of air supplied respirators.

The number of portable exhaust systems should be compatible with the maximum number of access doors/windows that are to be potentially opened at any one time. That is, if a maximum of 5 access windows/doors are expected to be the maximum number to be opened for performing the required maintenance work, a maximum of 5 portable exhaust blowers must be available at the work site.

The second option is to design a portable enclosure mounted on casters and provided with an independent and recyclable fresh air supply. The recyclable fresh air supply requires equipping the enclosure with a carbon adsorption bed, or other similar media. This will remove MC from the exhaust effluent before its recirculation as a fresh air supply. An alternative to providing a carbon adsorption bed is to provide feed ports in the casting enclosure, so that the fresh air supply can be continuously exhausted from the portable enclosure and fed into the casting enclosure. The portable enclosure can be rolled from one location to another, in accordance to the work demand. The advantage of this approach is to overcome any space limitation that may occur if a partition is set up to create an air lock.

The third option is to increase the capacity of the air handling units that duct the air-MC effluent to the solvent recovery system. Increasing the capacity of the air handling units will result in maintaining the casting machine's enclosure under negative pressure, hence the escape of MC vapors through the access doors/windows will be eliminated. There are concerns regarding potential contamination of the environment inside the casting enclosure. If the enclosure is maintained under negative pressure, a portable enclosure similar to that described under the second option should be designed. If this enclosure is equipped with a filtered make-up air supply, then the concerns of contamination will be eliminated. One of the advantages of this approach (i.e. maintaining the casting enclosure under a slight negative pressure) is that there will be no need for any additional modifications (e.g., the need to retrofit the doors and windows with new latches and to replace the leaking gaskets).

(B) Solvent recovery. Improving the chilling capacity of the system is expected to result in a better recovery rate of MC and hence reduce the MC concentration in the recycled effluent. Further, the air-MC effluent leaking from the access windows/door would contain a lower concentration of MC. This would be of significant importance if the enclosure of the casting operation is maintained under positive pressure.

c. Conclusion

Reduction of workers' exposure could be achieved through a variety of alternative engineering controls. Providing a spare filter assembly frame and a mobile filter canister to house the spent filters would contribute significantly to the reduction of workers' exposure during filter dressing. Further, modifying the floor of the current filter dressing room to accommodate a grated exhaust system, and providing high velocity overhead make-up air is expected to significantly reduce workers' exposure. Increasing the capacity of the chilling system in the solvent recovery operation would result in decreasing the MC concentration in the return air- MC effluent. Further, air-MC effluent escaping from access windows and door gaskets would be significantly reduced if the casting machine housing is maintained under slightly negative pressure.

J. Electronics In assessing the use of MC in the electronics industry, OSHA determined that MC application in this sector is closely allied to that in cold degreasing. Engineering controls previously described in degreasing operations are applicable for this industrial application. Therefore, OSHA determined that there is no need for repeating the technological feasibility assessment described in the degreasing section.

K. Miscellaneous Uses

1. Food Extraction

In the past, as indicated in Section IV, MC was used in a variety of food extraction processes. These processes included decaffeination of coffee, extraction of hops and manufacture of oleoresins. However, information from the trade association (HSIA) indicates that MC is no longer being used for these purposes. Specifically, the largest use, decaffeination of coffee beans, has been voluntarily discontinued. Therefore, OSHA determined that there was no need to conduct an engineering feasibility assessment for this industrial use. OSHA is seeking information on any current uses of MC in food extraction.

2. Pesticide Formulation

Current information indicates that in response to an EPA mandatory call-in-announcement, no pesticide user/formulator has reported the use of MC in pesticides. Accordingly, OSHA believes that MC usage in pesticides either has already been, or soon will be phased out. However, there is an indication that MC is currently used during the process of manufacturing pesticides, (e.g. for ancillary purposes other than formulations). Therefore, OSHA solicits public comment on the extent, if any, to which MC is used in the process of manufacturing pesticides.

3. Solvent Recovery

The technological feasibility of achieving the new proposed PEL has been described in detail in the section of solvent recovery (cellulose triacetate). OSHA determined that similar engineering control methods are applicable to this industrial sector, and therefore, there is no need for its repetition. OSHA acknowledges that minor modifications may be required. However, the same engineering design criteria would be employed.

4. Ink Manufacture

In the past, as indicated in Section IV, MC was used in ink manufacture. However, current information indicates that due to health concerns regarding MC usage, ink manufacturers are no longer using MC in their formulations. In this regard, OSHA believes that ink manufacturers have already substituted away from MC, and it is no longer being considered as a critical solvent in this industrial segment.

Since the solvency properties of MC are no longer regarded as essential by ink manufacturers, OSHA believes that substitutes are also available for MC use in blanket wash (cleaning of the printing plates). However, there is an indication that MC is still being used by some printing industry for blanket wash. OSHA is requesting comments on the extent and the magnitude of current usage, if any, in blanket wash.

FOOTNOTES (1) 200 g/s x 60 s/min x 60 min/hr x 0.29 cal/goC x 33.34 T deg C (251.996 cal/BTU)

(2) When all samples are considered (i.e. non-detectable and outliers included) the current average concentration of 23.56 ppm will be reduced to less than 6 ppm upon the incorporation of chillin coil within the engineering controls.

(2a) One method is the measuring of exposures by using a 3M-3500 organic vapor monitor. The second method is the measuring of exposures using the current NIOSH method of the 150 mg charcoal tube. Samples collected in charcoal tubes are more reliable since they are processed and analyzed in an on-site laboratory. This method produces reliable data since there is no need for implementing any sampling preservation procedure before analysis (Ex. 7-216).

(3) [70.4 lb/hr x 456 g/lb x 24.45 L/mol x 10(6) ppm]/ [84.5 g/mol x 60 min/hr x 28.37 L/ft3 x 1150 ft3/min x 5 pans]

(4) 33.3 gal/yr x .80 MC x yr/250 days x day/8 hr x 128 oz/gal x 29.5 cc/oz x 1.3g/cc x 24.5 L/mol x mol/85 g = 18.4 L/hr

(5) Furniture stripping occurs in a room that is 24'x 30'x 9', isolated from the general working area of the 90'x 108'x 18' building, but sharing a common air space due to the lack of a roof. The concentration of MC (fugitive) in the general area is approximately 10 ppm (Ex. 7-231). If the paint stripping room where furniture is stripped is fully partitioned by providing a ceiling, this unnecessary workers' exposure in the general surrounding area would be eliminated.

(6) Q(1)/Q (2) = (3.7 x 5 ft.)x(200 fpm)x( 5 x 2 ft.)/13,000 = 37,000 = 2.85.

(7) 80 ppm/2.85 = 28 pp

(8) C2 = VP(2)(out)--VP(2)(in)/ VP(1)(out)-VP(1)(in) x C(1).

C2 = VP(60 deg F)--VP(20 deg)/VP)100 deg F)--VP(68 deg F) x [80 ppm] = 0.325 x 80 = 26.4 ppm

(9) 15 lb/hr x 456 cc/lb x 24.5 L/MW x 10(6) x 1.3 g/cc/28.37 L/ft(3) x 84 g/MW x 5,300 cu ft/min x 60 min/hr = 288 ppm.

(10) 6,000,000 lb/yr x 456 g/lb x 24.5 L/mo.vol x yr/365 d x 10(6) ppm/2hr/d x 60 min/hr x 450,000 ft(3)/m x 84.5 g/mol x 28.37 L/ft(3) = 118 ppm.

(11) 6,000,000 lb/yr x 30% /365 d/yr x 24 hr/d x 60 min/hr = 3.42 lb/min.

(12) 3.42 lb/min x 456 g/lb x 24.45 L/mol/84.5 g/mol x 28.37 L/ft(3) = 16 ft3/min.

VII. Health Effects

A. Introduction

Until the rodent studies conducted by the National Toxicology Program (NTP), the Dow Chemical Company and the National Coffee Association were completed, little was known about the adverse health effects potentially associated with chronic exposure to MC. Health-based standards recommendations were based on prevention of irritation and injury to the neurological system.

The rodent bioassays now indicate that MC is carcinogenic to rats and mice. Based on two epidemiologic studies, OSHA preliminarily concludes that there is suggestive evidence of increased cancer risks in MC-related worker populations. The epidemiological evidence is consistent with findings of excess cancer in the experimental animal studies. OSHA concludes from these data that MC is a suspect or probable human carcinogen. NIOSH has reached a similar conclusion and regards MC as a potential occupational carcinogen. The International Agency for Research on Cancer (IARC) has classified MC as an animal carcinogen.

Much research has also been conducted on the metabolism and toxicity of MC in recent years. Although the current exposure limits were set to prevent neurological damage, recent research findings suggest that MC can be toxic to the central nervous system (CNS) at concentrations much lower than previously suspected. Research on metabolism of MC has identified CO as a human metabolite of MC, leading to consideration of the toxic effects of CO on the heart and CNS. In addition, OSHA will evaluate indications that MC and CO interact synergistically (Exs. 7-182, 7-175), and will consider if it is necessary to address combined exposure through this rulemaking.

B. Disposition and metabolism of MC

1. Absorption and distribution of MC

MC vaporizes readily at room temperature and is well absorbed through the lipid barriers of cell membranes in the lungs, intestine and placenta in rats and humans (Exs. 4-5, 7-16). MC has been detected in the kidney (Ex. 7-17), liver and brain (Ex. 7-18). In addition, trace amounts of MC have also been found in body fluids, such as human milk (Ex. 7-16) and the urine of dogs and humans (Exs. 7-14, 7-15). Exposure to MC leads to wide distribution of this compound in the body and, potentially, depending largely on dose, makes MC and its metabolites available for toxic interaction with tissues throughout the body.

Inhalation is the most significant route of entry for MC in occupational settings. The quantity of MC taken into the body depends on inspired air MC concentration, pulmonary ventilation rate, duration of exposure to MC, rates of MC diffusion into blood and tissues and solubility of MC in blood and tissues. The concentration of MC in alveolar air upon initial exposure increases rapidly, approaching the concentration of MC in the inspired air until the concentration of MC in alveolar air is almost equal to that in ambient air. After total body equilibrium is attained during exposure, uptake is balanced by elimination of MC (primarily through the lungs) and metabolism (Exs. 7-15, 7-115).

The uptake and elimination of MC has been well described in human and animal studies (Exs. 7-156, 7-157, 7-174). The solubility of MC in both water and lipid suggests that it distributes with the body water as well as in various tissues. High concentrations of MC have been localized in the adipose tissue of animals and humans. The adipose tissue MC concentration equilibrates very slowly to ambient exposure levels. MC is released very slowly from adipose tissue, providing a continuing dose of MC for metabolism after exposure has been terminated (Exs. 7-156, 7-158, 7-120).

Dermal absorption of MC is a relatively slow process. In 1964, Stewart et al. (Ex. 7-13) measured the rate of dermal MC absorption in volunteers who immersed a thumb into liquid MC. It was determined that, although MC is lipophilic, the rate of dermal MC absorption is not significant when compared to absorption of MC resulting from inhalation exposure. In order to contribute significantly to body burden of MC by the dermal route of exposure, it would be necessary to immerse the hands and forearms in liquid MC for an extended period of time. Stewart has also reported that contact with liquid MC is accompanied by an intense burning sensation after a few minutes. The pain associated with direct contact and the slow rate of absorption would tend to limit systemic exposure via this route.

The investigation by Stewart et al. looked at the effect of dermal exposure to pure MC solutions. In paint strippers and other MC formulations, thickeners and other agents are generally added to the MC. These agents may influence the rate of dermal MC absorption and evaporation of MC from the skin. An example of this is a paint stripper to which paraffin has been added to retard evaporation of MC from the stripping surface. The paint stripper will not quickly evaporate from the surface of the skin. This prolonged skin contact with MC may cause irritation and skin burns and increased absorption of MC through the skin, leading to increased toxicity at other organ sites.

Absorption of MC through the oral route is rapid and virtually complete. However, this route is not an important source of occupational exposure to MC (Ex. 7-170).

2. Metabolism of MC

It has been established by Kubic and Anders (Ex. 7-167) and Ahmed and Anders (Ex. 7-25) that MC is metabolized by rat liver enzymes in vitro by two distinct pathways. The first pathway is the mixed function oxidase system (MFO) associated with the microsomal cell fraction and the second is the glutathione dependent pathway localized primarily in the cytoplasm. The MFO pathway yields CO as the final end product. There is some evidence that significant amounts of CO2 may also be produced in this pathway. The glutathione dependent pathway is mediated by glutathione-S-transferase (GST) and yields CO2 as the end product and formaldehyde as a metabolic intermediate. Both pathways have the potential to produce reactive intermediates during metabolism which may subsequently interact with cellular constituents such as DNA, RNA, proteins and lipids. The liver is the most active site of MC metabolism by both pathways in all species examined.

Animal data indicates that the MFO pathway is saturated at relatively low levels of exposure (less than 500 ppm), while the GST pathway remains linear throughout the exposure levels examined (Exs. 7-161, 7-171). Saturation of the MFO pathway in humans has been estimated to occur at a level which is within the range of the animal data (estimates range from 200 to 1000 ppm MC) (7-114, 7-115, 8-32). The GST pathway is not thought to be saturated for any species at any of the doses examined.

The saturation of the MFO pathway has been used as evidence that the carcinogenic metabolite of MC, if one exists, is generated in the GST route of metabolism (Exs. 7-125, 8-32, 14b). This conclusion is supported by the correlation between the carcinogenic response and the increasing level of GST metabolite produced with increasing dose of MC. This association occurs at MC concentrations above which the MFO pathway is believed to be saturated.

C. Carcinogenicity

1. Animal Studies

The evidence for the carcinogenic potential of MC is primarily based upon chronic studies in rodent species. Table 4 contains a summary of the major bioassays conducted thus far. These bioassays have been conducted in three rodent species (rat, mouse and hamster) using two routes of administration (oral and inhalation) and a wide range of doses (from 5 mg/kg/d, oral to 4000 ppm inhaled).

a. Mouse studies. Two chronic studies of the carcinogenicity of MC in the mouse have been completed. Investigators in the National Toxicology Program (NTP) study (Ex. 7-8) exposed male and female mice to inhalation concentrations of MC. The National Coffee Association (NCA) sponsored study (Ex. 7-179) looked at the response of mice which received MC by oral administration.

TABLE 4.--METHYLENE CHLORIDE LIFETIME BIOASSAYS
__________________________________________________________________________
REFERENCE | SPECIES/ | ROUTE&DOSING | DOSAGE (No.Animals) | COMMENTS
  | STRAIN | SCEDULE |   |  
__________ | _________ | _______________ | ___________________ | ______________
  |   |   |   |  
NTP (1985) | B6C3F(1) | Inhalation | 0, 2000, 4000 ppm | Lung&Liver 
  | mouse | 6 hr/day, | (50 mice/sex/dose) | tumors both 
  |   | 5 days/week |   | sexes, both
  |   |   |   | doses 
  |   |   |   |  
Serota | B6C3F(1) | Daily in Water | 0 (125M,100F) 60 | No tumors.
(NCA) | mouse |   | (200M,100F), 125 |  
(1986) |   |   | (100M,50F), 185 |  
  |   |   | (100M,50F), and |  
  |   |   | 250 (125M,50F)mg/kg |  
  |   |   |   |  
NTP | Fischer | Inhalation | 0, 1000, 2000, and | Mammary and
(1985) | 344 rat | 6 hr/day, | 4000 ppm (50 rats/ | integumentary
  |   | 5 days/week | sex/dose). | fibromas and
  |   |   |   | fibrosarcomas ;
  |   |   |   | in both sexes
  |   |   |   |  
Burek | Sprague- | Inhalation | 0, 500, 1500, and | Malignant
(DOW) | Dawley | 6 hr/day, | 3500 ppm (95 rats/ | salivary
(1980) | rat | 5 days/week | sex/dose). | gland tumors
  |   |   |   | at 3500 ppm,
  |   |   |   | dose-related
  |   |   |   | increase in
  |   |   |   | mammary 
  |   |   |   | tumors
  |   |   |   |  
Nitschke | Sprague- | Inhalation | 0, 50, 200, and | No tumors
(DOW) | Dawley | 6 hr/day, | 500 ppm (70 rats/ |  
(1982) | rat | 5 days/week | sex/dose). |  
  |   |   |   |  
Serota | Fisher | Daily in water | 0, 5, 50, 125, and | No tumors
(NCA) | 344 rat |   | 250 mg/kg/d (135/ |  
(1986) |   |   | sex at 0, 85/sex/ |  
  |   |   | dose) |  
Burek | Syrian | Inhalation | 0, 500, 1500, and | No tumors
(DOW) | Golden | 6 hr/day, | 3500 ppm (90 |  
(1980) | hamster | 5 days/week | hamsters/sex/dose). |  
__________ | _________ | _______________ | ___________________ | ______________

F = Female
M = Male
NTP = National Toxicology Program
NCA = National Coffee Association
DOW = DOW Chemical Company

i. The NTP study. In the NTP study (Ex. 7-8), groups of 50 male and 50 female B6C3F1 mice were exposed to 0, 2000 or 4000 ppm MC, 6 hr/day, 5 days/week for 102 weeks. All animals were necropsied and examined histopathologically.

(A) Lung tumors. In treated male and female mice, the incidences of alveolar or bronchiolar adenomas were increased as compared with control. Both sexes of mice were also found to have a dose-related increased incidence of carcinomas of the alveolar/bronchiolar regions. In addition, there was an increased number of lung tumors per tumor-bearing animal (multiplicity of tumors) with increasing dose of MC.

(B) Liver tumors. In the liver, the toxic effects of MC were expressed as cytologic degeneration in male and female mice which was not present in the controls. An increased incidence of hepatocellular adenomas and carcinomas (combined) was observed in male mice. The incidence of hepatocellular carcinomas in male mice was statistically significantly increased at 4000 ppm. Female mice also experienced dose-related increases in the incidences of hepatocellular adenomas and carcinomas. As described in the lung tumor data, an increased multiplicity of liver tumors was found in both male and female mice.

The increases in tumor incidences presented here were observed when the treated groups were compared with concurrent and with historical control groups. The tumor rates for male mouse liver tumors and rat mammary tumors (especially in females) are normally high in control animals of these species. This sometimes makes it difficult to discern a true dose response for a treatment group when concurrent control animals are used for comparison. When comparing tumors which have relatively high or variable background rates, the NTP has determined that it is appropriate to compare the tumor incidence of a treated group, not only to concurrent control animals, but also to historical controls. Historical control animals are defined as those animals of the same species and strain which have been used in previous chronic bioassays in the same laboratory. This practice provides a larger control group and increases the statistical stability of the tumor rates with variable background incidences. The increases in tumor rates observed in these studies were statistically significant when compared to historical or concurrent control animals.

The dose-related increase in the incidence of lung and liver tumors in mice, and the increased multiplicity of these tumors, present the strongest evidence for the carcinogenicity of MC. NTP concluded that based on the evidence from these lung and liver tumors, that there was clear evidence of the carcinogenicity of MC in both male and female mice.

ii. The NCA study. Serota et al. (Ex. 7-179) exposed male and female B6C3F1 mice to target levels of 0, 60, 125, 185 or 250 mg MC/kg body weight/day in drinking water for 24 months. Females developed a statistically significantly increased trend toward survival in the treatment groups as compared to controls. No treatment related effects were noted on survival rates of the males in any exposure group. Both male and female mice were found to have an increased fatty liver at 250 mg/kg/day. In the treated male mice, there was a marginally increased incidence of proliferative hepatocellular lesions. Incidences are presented in Table 5. These lesions did not increase among treated females. The incidence of hepatocellular carcinoma in the high dose males was statistically significantly increased over the first control group, but when compared with all of the control animals (control groups 1 and 2), the difference disappeared. The authors also reported that the incidences of hepatocellular carcinomas and of adenomas or carcinomas (combined) were within the range of historical controls. This study did not demonstrate a clear relationship between MC exposure and carcinogenesis.

b. Rat studies.--i. The NTP study. NTP conducted a two-year bioassay examining the effects of inhalation of MC at 0, 1000, 2000 and 4000 ppm in F344 rats (Ex. 7-8). Body weights of all exposure groups were comparable. The highest dose female rats experienced reduced survival after 100 weeks of exposure.

(A) Mammary tumors. Incidence of mammary fibroadenomas alone and combined incidence of fibroadenomas and adenomas in male and female rats occurred with statistically significant positive trends (see table 6). The incidence in the high dose group in both sexes was statistically significantly higher than controls (concurrent and historical). When subcutaneous fibromas or sarcomas in the male rat, which were believed to have originated in the mammary chain, were included in comparisons, differences between control and exposed animals were even greater.


TABLE 5. - INCIDENCE OF TUMORS IN MICE INDUCED BY METHYLENE CHLORIDE
__________________________________________________________________________
NTP mouse study
__________________________________________________________________________
Dose (ppm) | Alveolar/ | Alveolar/ | Alveolar/
  | Bronchiolar | Bronchiolar | Bronchiolar
  | adenoma | carcinoma | adenoma or
  |   |   | carcinoma
_____________________ | ________________ | ________________ | ________________
Male Mice: |   |   |  
     0 | 3/50 | 2/50 | 5/50
     2000 | *19/50 | *10/50 | *27/50
     4000 | *24/50 | *28/50 | *40/50
_____________________ | ________________ | ________________ | ________________
  | Hepatocellular | Hepatocellular | Hepatocellular
  |   adenoma |   carcinoma |  adenoma or
  |   |   | carcinoma
_____________________ | ________________ | ________________ | ________________
Male Mice: |   |   |  
     0 | 10/50 | 13/50 | 22/50
     2000 | 14/49 | 15/49 | 24/49
     4000 | 14/49 | *26/49 | *33/49
_____________________ | ________________ | ________________ | ________________
  | Alveolar/ | Alveolar/ | Alveolar/
Dose (ppm) | Bronchiolar | Bronchiolar | Bronchiolar
  | adenoma | carcinoma | adenoma or
  |   |   | carcinoma
_____________________ | ________________ | ________________ | ________________
Female Mice |   |   |  
     0 | 2/50 | 1/50 | 3/50
     2000 | *23/48 | *13/48 | *30/48
     4000 | *28/48 | *29/48 | *41/48
_____________________ | ________________ | ________________ | ________________
  | Hepatocellular | Hepatocellular | Hepatocellular
  |   adenoma |   carcinoma |  adenoma or
  |   |   |   carcinoma
_____________________ | ________________ | ________________ | ________________
Female Mice |   |   |  
     0 | 2/50 | 1/50 | 3/50
     2000 | 6/48 | *11/50 | *16/48
     4000 | *22/48 | *32/48 | *40/48
_____________________ | ________________ | ________________ | ________________
  | Alveolar/Bronchiolar or |  
Dose (ppm) | hepatocellular adenoma or |  
  | carcinoma |  
_____________________ | ________________ _ ________________ | ________________
  | Male | Female |  
_____________________ | ________________ | ________________ | ________________
Combined Tumors: |   |   |  
     0 | 27/50 | 5/50 |  
     2000 | 34/49 | *36/48 |  
     4000 | *45/49 | *45/47 |  
___________________________________________________________________________
  | Serota mouse study - NCA
  | ____________________________________________________
Dose (mg/kg) | Hepatocellular | Hepatocellular | Hepatocellular
  | adenoma | carcinoma | adenoma or
  |   |   | carcinoma
_____________________ | ________________ | ________________ | ________________
Male Mice: |   |   |  
     0 | 10/125 | 14/125 | 24/125
     60 | 20/200 | 33/200 | 51/200
     125 | 14/100 | 18/100 | 30/100
     185 | 14/99  | 17/99  | 31/99 
     250 | 15/125 | 23/125 | 35/125
__________________________________________________________________________

1. For inhalation studies, adjusted dose was calculated as d(mg/kg/day) = d (ppm) X (1.2 x mol. wt./mol. wt. of air) x breathing rate x hrs. of exposure/24 x days of exposure/7 * body wt.

2. Incidence expressed as number of animals with response per number of animals examined for the response.

* Statistically significant, using Fischer's Exact Test and a Bonferroni correction, at the .05/r level, where r is the number of test doses. For data sets 22-26 a Chisquare approximation of the Fischer Exact Test is used due to large sample size.

TABLE 6. - INCIDENCE OF TUMORS IN RATS AND HAMSTERS INDUCED BY METHYLENE                    CHLORIDE
__________________________________________________________________________
NTP rat study
__________________________________________________________________________
Dose (ppm) |   | Mammary or |  
  | Mammary | subcutaneous |  
  | adenoma or | adenoma, |  
  | fibroadenoma | fibroadenoma |  
  |   | or fibroma |  
_____________________ | ________________ | ________________ | ________________
Male Rats: |   |   |  
    0 | 0/50 | 1/50 |  
    1000 | 0/50 | 1/50 |  
    2000 | 2/50 | 4/50 |  
    4000 | *5/50 | *9/50 |  
_____________________ | ________________ | ________________ | ________________
Dose (ppm) |   | Neoplastic |  
  | Mammary | nodules or |  
  | adenoma or | hepatocellular |  
  | fibroadenoma | carcinoma |  
_____________________ | ________________ | ________________ | ________________
Female Rats: |   |   |  
    0 | 5/50 | 2/50 |  
    1000 | 11/50 | 1/50 |  
    2000 | 13/50 | 4/50 |  
    4000 | *23/50 | 5/50 |  
_____________________ | ________________ | ________________ | ________________
Burek rat study - DOW
___________________________________________________________________________
Dose (ppm) |   |   | Mammary tumors per
  | Salivary gland | Mammary | tumor-bearing rat
  | sarcomas | tumors | (multiplicity)
_____________________ | ________________ | ________________ | ________________
Male Rats: |   |   |  
    0... | 1/92 | 7/92 | 1.1
    500. | 0/95 | 3/95 | 2.0
    1500 | 5/95 | 7/95 | 1.6
    3500 | *11/97 | 14/97 | 1.2
_____________________ | ________________ | ________________ | ________________
Dose (ppm) | | Mammary Tumors |  
  | Mammary | per tumor- |  
  | tumors | bearing rat |  
  | | (multiplicity) |  
_____________________ | ________________ | ________________ | ________________
Female Rats: |   |   |  
    0... | 79/96 | 2.1 |  
    500. | 81/95 | 2.7 |  
    1500 | 80/96 | 3.1 |  
    3500 | 83/97 | 3.5 |  
_____________________ | ________________ | ________________ | ________________
Nitschke rat study - DOW
__________________________________________________________________________
Dose (ppm) |   |   | Mammary tumors per
  | Salivary gland | Mammary | tumor-bearing rat
  | sarcomas | tumors | (multiplicity)
_____________________ | ________________ | ________________ | ________________
Female Rats: |   |   |  
    0... | 52/70 | 52/70 | 2.0
    50 . | 58/70 | 58/70 | 2.3
    200 | 61/70 | 61/70 | 2.2
    500 | 55/70 | 55/70 | 2.7
_____________________ | ________________ | ________________ | ________________
Serota rat study - NCA
__________________________________________________________________________
  | Neoplastic | Historical control incidence
Dose (mg/kg) | nodules or | __________________________________
  | hepatocellular | Neoplastic | Hepatocellular
  | carcinomas | nodules | carcinomas
_____________________ | ________________ | ________________ | ________________
Female Rats: |   |   |  
    0... | 0/135 |   |  
    5... | 1/85 | range = 0-13% | 0-3%
    50.. | 4/83 |   |  
    125. | 1/85 | mean = 6.3% | 1.7%
    250. | *8/110 |   |  
_____________________ | ________________ | ________________ | ________________
Burek hamster study - DOW
__________________________________________________________________________
Dose (ppm) | Lymphsarcoma |   |  
_____________________ | ________________ | ________________ | ________________
Female Rats: |   |   |  
    0... | 1/91 |   |  
    500. | 6/92 |   |  
    1500 | 3/91 |   |  
    3500 | 8/91 |   |  
_____________________ | ________________ | ________________ | ________________

1. For inhalation studies, adjusted dose was calculated as d(mg/kg /day) = d (ppm) X (1.2 x mol. wt./mol. wt. of air) x breathing rate x hrs. of exposure/24 x days of exposure/7 divided by body wt.

2. Incidence expressed as number of animals with response per number of animals examined for the response.

* Statistically significant, using Fischer's Exact Test and a Bonferroni correction, at the .05/r level, where r is the number of test doses. For data sets 22-26 a Chi-square approximation of the Fischer Exact Test is used due to large sample size.

(B) Liver effects. Liver toxicity was characterized by hemosiderosis, hepatocytomegaly, cytoplasmic vacuolization and necrosis in exposed male and female rats. Neoplastic nodules alone and combined incidence of neoplastic nodules and hepatocellular carcinomas in female rats occurred with significant positive trends by the life table test (see table 6). Pair-wise comparisons did not indicate any statistically significant effects at any one dose. Although this is suggestive of a carcinogenic response in the female rat liver, NTP did not use this response in their determination of the carcinogenicity of MC.

NTP based its determination of the carcinogenicity of MC in the rat on the mammary tumor data described above. NTP has concluded that the increased incidences of mammary gland tumors in the female rats provided clear evidence of carcinogenicity and in the male rats, some evidence of carcinogenicity.

ii. The high dose DOW study. Burek et al. (Ex. 7-151) exposed male and female Sprague-Dawley rats to inhalation concentrations of 0, 500, 1500 and 3500 ppm MC, 6 hr/day, 5 days/week for 2 years. Female rats exposed to 3500 ppm had statistically significantly reduced survival during the final 6 months of exposure.

(A) Mammary tumors. The number of female rats with mammary tumors in this study did not increase with dose of MC. However, the number of tumors per tumor-bearing rat increased in a dose-related manner. Therefore, there was a statistically significant increase in total mammary tumors in the female rat due to MC administration (see table 6). This increase in total mammary tumors was also noted in the male rats exposed to MC, although the increases were not as pronounced as in the female rats.

(B) Salivary gland tumors. At 3500 ppm, male rats also exhibited a statistically significant increase in salivary gland sarcomas. The authors noted a high incidence of sialodacryoadenitis (a viral infection of the salivary gland) in all exposure groups and both sexes during the first two months of the study. The authors believed that the salivary gland sarcomas were related to the presence of the virus, or perhaps a combination of the virus and MC exposure, since the incidence increased in a dose-related manner (see table 6). Female rats did not show an increase in salivary gland sarcomas even though they were also infected with the virus. Because of the confounding presence of the sialodacryoadenitis virus, and the apparent sensitivity of the males of the species, the biological significance of the salivary gland tumor is unclear. OSHA feels that because similar increases in these sarcomas were not observed in other rat bioassays (Exs. 7-8, 7-173, 7-180), in which the sialodacryoadenitis was not a factor, it is unclear whether the sarcoma incidence observed in the male rats should be used to quantify the carcinogenic response of the rats to MC.

iii. The low dose DOW study. Nitschke et al. (Ex. 7-173) exposed male and female Sprague-Dawley rats to much lower concentrations of MC than used in the Burek study. In the Nitschke study, rats were exposed by inhalation to 0, 50, 200 or 500 ppm MC, 6 hr/day, 5 days/week for 2 years. The mortality experience for the exposed animals was equivalent to that of controls. A statistically significant increase in liver toxicity, characterized by cytoplasmic vacuolization and increases in the number of multinucleated hepatocytes, was observed in female rats at 500 ppm (see table 6). There was no increase in number of rats with tumors, but, consistent with the Burek study, the number of mammary gland tumors per tumor-bearing rat was increased in female rats exposed to 500 ppm MC. No statistically significant differences in tumor numbers or distribution were observed in male rats. Salivary gland sarcomas were noted in only two rats, one female at 50 ppm and one male at 500 ppm. These were not considered to be compound related.

iv. The NCA study. In a study sponsored by the National Coffee Association (Ex. 7-180), Serota et al. exposed male and female Fischer F344 rats to 0, 5, 50, 125 and 250 mg MC/kg body weight/day in drinking water for 2 years. Animals which received 125 and 250 mg/kg/day had lower body weights and a decreased food and water intake. Significant dose-related changes were observed in the livers of both sexes were observed at 50, 125 and 250 mg/kg/day. These changes were characterized by increased number of foci or areas of cellular alteration and increased fatty liver. Increased incidences of neoplastic nodules and hepatocellular carcinoma were identified in females receiving 50 or 250 mg/kg/day (see table 6). However, the authors felt that these apparent increases were due to the unusually low incidences of neoplastic nodules and hepatocellular carcinoma in the concurrent control animals. When compared to historical controls, the differences between treated and control animals disappeared. The NTP has determined that it is appropriate to compare tumor incidence to the historical incidence in control animals in previous chronic bioassays in a particular laboratory. Even though there was a statistically significant dose-related trend observed when concurrent control animals were used, only one occurrence of neoplastic nodules was found at 125 mg/kg/day and the incidences in the 50 and 250 mg/kg/day groups were within the range of historical controls. OSHA believes that the data presented here are suggestive (but not conclusive) of a carcinogenic effect induced by MC.

c. Hamster study. In conjunction with the study on the chronic effects of MC in rats, Burek et al. (Ex. 7-151) examined the effects of MC inhalation in hamsters. Syrian golden hamsters received inhalation concentrations of 0, 50, 1500 or 3500 ppm MC 6 hr/day, 5 days/week for 2 years. The total number of benign tumors and the number of lymphosarcomas in the female group at 3500 ppm was increased when compared to control. This phenomenon is believed by the authors to be related to the significantly decreased mortality among the high dose female hamsters as compared with controls. Hamsters treated with MC experienced a dose-related decrease in the incidence and severity of amyloid deposits (thought to be a normal consequence of aging). The biological significance of this effect is unclear. No compound related toxicity or tumor was identified in this study.

d. Summary of animal studies. In summary, NTP found dose-related increases in lung and liver tumor incidences and multiplicity. These data were used to support the conclusion by NTP that the lung and liver tumor data in mice indicate clear evidence of carcinogenicity of MC. OSHA agrees with this conclusion. The mouse study of Serota et al. (Ex. 7-179) was conducted at exposure levels approximately an order of magnitude below those of NTP (Ex. 7-8). Because of the low doses employed, it is not surprising that Serota et al. could not detect a carcinogenic response in mice.

The rat studies described here (Exs. 7-8, 7-151, 7-173, 7-180) showed a clear pattern of liver toxicity and increased multiplicity of mammary tumors in female and male rats in both the Burek study (Ex. 7-151) and the NTP study (Ex. 7-8). The increased incidence of salivary gland sarcomas indicated in the Burek study were not repeated in other studies and are of questionable value in assessing carcinogenic response to MC because of the involvement of the sialodacryoadenitis virus. OSHA agrees with the determination of NTP that the rat data presented above indicate, in the female rats, clear evidence and, in the male rats, some evidence of carcinogenicity of MC.

In the Burek study (Ex. 7-151), hamsters showed no carcinogenic response due to MC exposure. The highest does used in a chronic bioassay to determine carcinogenicity in a species should represent the maximum tolerated dose for that species. No evidence was presented to support the contention that 3500 ppm MC was the maximum tolerated dose for hamsters. In fact, the toxicity data seem to suggest that the hamsters (especially the females) do not suffer toxic effects 3500 ppm MC. The maximum tolerated dose generally produces signs of toxicity during a lifetime bioassay. In order to evaluate the carcinogenic potential of MC in the hamster during a lifetime bioassay, it is necessary to administer the compound at the maximum tolerated dose.

There has been some discussion of the appropriateness of using an increase in benign tumors (rat mammary tumors) as an indication of a carcinogenic response. OSHA agrees with NTP's contention that the increase in incidence or multiplicity of these benign tumors indicates clear evidence of carcinogenicity in the female rats. When the evidence for the carcinogenicity of MC derived from rat studies is combined with the data from the NTP mouse study, OSHA believes that the weight of evidence supports the conclusion that MC is an animal carcinogen and, therefore, a suspect human carcinogen.

2. Epidemiologic Studies OSHA has reviewed epidemiologic studies of three industrial processes for which MC was the primary chemical exposure. Ott et al. (Ex. 7-76) and Lanes et al. (Ex. 7-260) examined the relationship between MC exposure and mortality among workers in a cellulose triacetate (CTA) fiber production plant. Friedlander et al. (Ex. 4-27) and Hearne et al. (Exs. 7-122, 7-163) investigated the mortality experience of a cohort of workers exposed to MC during the production of photographic film. The National Paint and Coatings Association (NPCA) sponsored an epidemiologic study by SRI which looked at employees exposed to MC during paint and varnish manufacturing (Ex. 10-29b).

a. Studies of fiber production workers. Ott el al. (Ex. 7-76) studied the mortality of 1248 men and 971 women who worked for at least 3 months in the preparation and extrusion areas in one of two fiber production plants at any time between January 1, 1954 and January 1, 1977. The "exposed" cohort consisted of 1271 workers (551 men and 720 women) in a plant in Rock Hill, S.C. in which MC was the primary chemical exposure. Other exposures included methanol (at approximately 1/10 of the MC concentration), acetone (100 to 1000 ppm, lower concentrations in areas with higher MC exposures), and oil mists. MC TWAs for work stations in this plant ranged from 140 ppm MC to 475 ppm MC. These exposure concentrations were measured in 1977 and 1978 and assumed by the authors to be representative of ambient concentrations of MC throughout the history of the plant. Vital status for the exposed cohort could not be confirmed for 226 (18%) of these workers. There were 54 deaths recorded for the exposed cohort during the study period.

The reference plant, located in Narrows, VA, produced acetate fibers. No methylene chloride was used in this plant, and the primary chemical exposure was acetone. Of the 697 men and 251 women in this reference cohort, the vital status could be confirmed for all but 112 (12%) of the workers. Twenty-seven deaths were reported from this cohort.

Expected death rates for the two plants were calculated using U.S. general population statistics, and the mortality of the exposed cohort compared to the referent cohort. Among white males, statistically significant differences (p less than 0.05) in risk were observed for all causes of death (risk ratio (RR) = 2.2), for diseases of the circulatory system (RR = 2.2), and for all external causes of death (RR = 2.5). The risk ratio for malignant neoplasms in white males in exposed versus the referent group was not statistically significant (RR = 1.2). Females in the exposed group showed no statistically significant increases in mortality, but the RR for death by all causes was 1.3.

Although the purpose of choosing the two plants described above was to eliminate all differences in the populations except MC exposure, further examination of the data by the authors led them to conclude that the differences in mortality experienced between the two plants were due primarily to geographical differences (48% rural population in the Rock Hill (exposed) plant, 85% rural in the Narrows (referent) plant). The authors believed these differences in geographical distribution of the populations of interest contributed to differences in death rates observed in this study and that these factors accounted for a greater proportion of the differences in death rates than MC exposure.

Although no increases in mortality from malignant neoplasms were observed in the MC exposed cohort, the authors noted that this study had little power to detect small to moderate increases in cancer rates. Also, the latency period for development of cancer in this study was relatively short, so that further follow-up studies would be necessary to examine any causal relationship between MC exposure and the development of cancer.

Lanes et al. (Ex. 7-260) extended the follow-up period for this cohort nine additional years, through September 1986. Therefore, this investigation increased the latency period during which cancer could develop and be detected. The statistical power to detect changes in chronic disease rates was also increased. To ensure comparability with the original study, Lanes et al. calculated the death rates for the exposed cohort through 1977. The close agreement of their results with those of Ott et al. (Ex. 7-76) verified that the methods of analysis of the two studies were similar. No attempt was made to extend the analysis of the referent group in the Narrows, VA plant. Death rate comparisons were based on U.S. general population statistics and death rates for York County, S.C. (in which 95% of the MC exposed cohort resided). Cohort members made up less than 4% of the total York County population.

When comparing disease occurrence between workers and the general population, the "healthy worker effect" must be considered; that is, workers, especially those in demanding or strenuous jobs, must have and maintain a degree of good health in order to perform and keep their jobs. Considering that the overall health of these workers is generally better than the overall health of the general population, a significantly elevated SMR for a worker population, when compared to the general population, is that much more compelling. Therefore, OSHA looks with particular interest at SMR data which show a significant excess of deaths in worker populations when compared to general population rates.

The total number of deaths increased from 54 in 1977 to 123 in 1986. Expected mortality was 121.4 (based on U.S. mortality rates, SMR = 1.01) and 140.8 (based on mortality in York County, SMR = 0.87). Total deaths from malignant neoplasms reached 28 (33 expected, US and York County comparisons). Four deaths due to cancer of the liver and biliary passages were reported in the MC-exposed cohort. This was significantly different from the expected values of 0.53 deaths (based on U.S. statistics, SMR = 2.40) and 0.86 deaths (based on York County data, SMR = 2.32). The authors noted that all deaths occurred in workers who had been employed in the plant for more than 10 years and who died at least 20 years after they were hired. No deaths from these types of cancers were observed in the initial study. These results suggested that the latency period for these cancers may have been longer than the observation period in the initial study, and that cancers associated with MC exposure became observable during the follow-up study. This idea was further supported in that, in this relatively young population, only 9.68% of the cohort had died by the time of the analysis (4.25% in the original study), so that chronic effects, which are more likely to be observed in later life may not have had sufficient time to develop. Further follow-ups of the mortality experience of this cohort are necessary in order to confirm the increases in biliary/liver cancer described above and to identify any other chronic health effects due to MC exposure, especially neoplastic diseases.

The increase in liver and biliary cancer deaths is significant particularly in light of the fact that the liver was identified as a target site in the NTP rodent oncogenicity study. Also, three of these liver/biliary cancers were identified in individuals with apparently long durations of exposure and in all four of these employees, there was a long period between first hire and death from cancer. Although it must be taken into consideration that only a small number of cases of cancer have been identified in this study, that individual exposures to MC in this plant have not been well characterized, and that the effects of concurrent exposures to other chemicals (methanol, acetone, oil mists) have not been evaluated, OSHA believes that this study can be regarded as preliminary evidence of a positive human carcinogenic response to MC exposure.

OSHA is aware that additional epidemiological data are being collected from a MC-exposed cohort of cellulose acetate fiber workers. The plant (closed since 1982) is located in Cumberland, MD, and was similar in operation and exposures to the Rock Hill, S.C. plant. It is the Agency's understanding that the same methodology will be used as employed in the previous study. OSHA will closely follow the progress of this study and evaluate any results which may become available during the rulemaking process.

b. Studies of film production workers. Friedlander et al. (Ex. 4-27) and Hearne et al. (Exs. 7-122, 7-163) have studied the mortality experience in the film coatings operations of a Kodak film production plant in Rochester, NY. The cohort studied consisted of 1013 men employed for at least one year in the roll coating division at any time between January 1964 and December 1970. Cohort members were followed through 1988.

The comparison groups consisted of the male population of New York state outside of New York City, and an industrial control group of 40,000 men employed at Kodak Park in Rochester, but not working in the roll coating division. This industrial control group was useful in correcting for the healthy worker effect discussed previously. This effect can mask small increases in mortality due to occupational factors when comparisons are made to general population mortality.

Exposure characterizations for each job site were made through extensive personal and ambient air sampling. The mean TWA for the cohort described was 26 ppm. The mean tenure in the roll coating division was 23.1 years. Employment history and exposure profile was constructed for each employee. The latest follow-up study (Ex. 7-163) accumulated 22,006 person-years of follow-up. The total number of deaths was 238 (23.5% of the cohort) and determination of vital status was greater than 99%.

In the latest update (Ex. 7-163), no statistically significant increases in cause-specific or total mortality was associated with MC exposure. The cohort was analyzed by lifetime MC exposure (dose) and latency (time from first exposure). No dose-related or latency-related trends were identified for cause-specific death rates. In earlier updates of the original study (Ex. 7-122), an elevated number of pancreatic cancers were reported in the MC exposed cohort. The excess pancreatic cancers did not meet the statistical criteria for significance set by the authors for non-hypothesized causes of death. Hypothesized causes of death were based on the metabolism of MC to CO and subsequent cardiac stress (ischemic heart disease) and cancer target sites identified in the NTP rodent bioassay (liver, lung and breast). Death rates from hypothesized causes were required to meet a one-tailed p less than 0.05 to be statistically significant, while non-hypothesized causes of death were required to meet a two-tailed p less than 0.01 to be significant. The purpose of this increased stringency for non-hypothesized causes of death was to reduce the probability that a difference in death rates would be determined to be significant when it was a chance occurrence. As the number of outcomes examined (cause-specific deaths) is increased, the probability that a death rate will be elevated or depressed by chance alone, increases. The suggestive increases in the rates of pancreatic cancers observed in the earlier studies has become less statistically significant with time. In the latest update the SMR for pancreatic cancer was 1.9 (8 cancers observed versus 4.2 expected (NYS and Kodak Park comparators), p = 0.13). No additional pancreatic cancers have been observed since the previous update in 1984 (3 expected). This lends further credence to the contention that the suggestive elevation in pancreatic cancers was not due to MC exposure.

The overall mortality of this cohort was statistically significantly less than both comparison groups (SMR = 0.72 based on NYS statistics and SMR = 0.80 based on Kodak Park data). The explanation for this deficit in mortality among MC exposed workers has not been explained.

c. Study of workers in paint and varnish manufacturing. The NPCA submitted an epidemiological study by SRI (Ex. 10-29b) that examined 16,243 employees who worked for at least one year in the manufacture of paint or varnish. MC exposure was not measured for the cohort studies, however, the authors stated that typical exposure to MC was below 100 ppm. The overall mortality for this cohort compared favorably with U.S. general population death rates. This "healthy worker effect" is described above in the discussion of the cellulose acetate fiber workers. No statistically significant excess cancers were identified in the exposed cohort; however, marginally elevated SMRs were identified for cancer of the skin, lung, colon/rectum and liver. The authors felt that these were sufficiently elevated to warrant further study. Because of the multiple exposures in these workers, lack of individual exposure data and lack of statistically significant excesses of specific cancers, there is no evidence of an association between MC exposure and cancer in this cohort.

OSHA believes that while all workers in the study were potentially exposed to MC, the subcohort of workers who cleaned tubs and tanks had the greatest exposure. This subcohort numbered only 238 of the 16,243 total workers. Although there are limited data available for this subcohort and none of the SMRs achieve statistical significance, the Agency notes that there were 4 malignant neoplasms of the pancreas (1.93 expected) and 15 malignant neoplasms of digestive organs and peritoneum (10.66 expected).

In summary, there is no evidence of statistically significant excess of cancers in the study of workers in paint and varnish manufacture and no evidence for an association of MC exposure and cancer for this industry. This study does point out, however, the need for follow-up investigations of this cohort, including documentation of exposures (to all chemical agents) and identification of confounding factors.

d. Summary of epidemiological studies. OSHA preliminarily believes that the Kodak and NPCA studies indicate no increase in mortality associated with MC exposure. This result is not inconsistent with the findings of Cohen (Ex. 7-75) because of the much greater MC exposures likely to have been experienced in the fiber production workers than described for the film production workers or workers in paint and varnish manufacture. The low average exposure levels in the Friedlander and Hearne and NPCA studies and relatively small population with higher exposures to MC limit the power of these studies to detect small to moderate increases in cancer rates.

In summary, an epidemiological study of fiber production workers has shown an increased incidence of liver/biliary cancer subsequent to relatively high MC exposures (140-475 ppm TWA). A second epidemiologic study of workers in a film production plant showed no increase in any cause specific death rates. These workers were exposed to much lower MC concentrations (26 ppm TWA). A third study of workers in paint and varnish manufacture also showed no increase in any cause specific death rates associated with MC exposure. OSHA notes that individual MC exposures were not documented and that workers in this study were likely exposed to other chemical agents. OSHA preliminarily concludes that based on the increased incidence of liver/biliary cancers in the fiber production workers, there may be an increased risk of cancer in these worker populations causally related to MC exposure.

3. Mutagenicity Studies

Mutagenicity and genotoxicity studies are useful in describing the possible carcinogenic mechanism of action of MC. Evidence for the interaction of MC or MC metabolites with DNA (producing mutations or toxicity) supports a genotoxic mechanism for the carcinogenic action of MC, rather than a non-genotoxic action (i.e., by acting as a promoter, increasing cell turnover). EPA has reviewed the literature concerning the mutagenic potential of MC in their Health Assessment Document for Dichloromethane (Methylene Chloride) (HAD) (Ex. 4-5) and the studies conducted by ECETOC in the Technical Analysis of New Methods and Data Regarding Dichloromethane Hazard Assessments (Ex. 7-129). OSHA agrees with EPA's assessment of the various studies, the results of which are summarized below.

a. Bacterial studies. Investigations of the induction of mutagenicity by MC were performed using the Salmonella typhimurium histidine reversion assay. MC tested positive for mutagenesis in all of the studies using Salmonella TA100, TA1535 or TA98 with and without mammalian metabolic activation of MC, when assays were performed in sealed, gas tight exposure chambers (Ex. 4-5). In studies which presented sufficient data for analysis, clear dose responses were apparent. A 10-fold or greater increase in revertants was observed at the highest doses compared to negative controls. Barber et al. (Ex. 7-190) conducted their tests in a chemically inert, closed incubation system and analyzed concentrations of MC in the vapor phase and the aqueous phase of a test plate. Based on this quantitative determination of the MC dose (115 ?mol/plate), MC was considered to be a weak mutagen for Salmonella under the conditions of the test.

The relevance of the mutagenicity data derived from Salmonella has been questioned. However, bacterial metabolism of MC is very similar to that of mammalian systems (Salmonella metabolizes MC to CO2 and CO, apparently by pathways similar to those in mammals). Because of the reactivity of the metabolic intermediates of these pathways (formaldehyde, formal chloride and S-chloromethylglutathione), and the proximity of the bacterial DNA to the cytoplasmic enzymes, it has been suggested (Ex. 10-18) that bacteria may be more susceptible to mutagenicity than more complex organisms, which would be protected by sequestration of the DNA in the nucleus of the cells. The highly reactive metabolites would then be more likely to react with other cellular constituents before they could cross the nuclear membrane to interact with DNA.

b. Yeast and Drosophila studies. In yeast, two studies were conducted, one by Simmon (Ex. 7-241) on the mitotic recombination potential of yeast after exposure to MC and one by Jongen (Ex. 7-191) on the potential for gene conversion, reverse mutations and mitotic recombination in yeast. The former study was judged by the authors to show no mutagenic potential of MC in yeast. The latter study produced positive evidence of the mutagenicity of MC. The EPA felt that differences in the results of these two studies were most likely due to different yeast strains used, differences in exposure times and differences in incubation temperature. It is interesting to note that the mutagenic potential of MC correlated with the cytochrome P450 metabolic ability of each yeast strain (Ex. 4-5).

In 1981, Gocke et al. (Ex. 7-193) tested the mutagenicity of MC by examining induction of sex-linked recessive lethal mutations in Drosophila. MC was administered in solutions of 2% DMSO and 5% saccharose. The highest dose was thought to be close to the LD50. A dose-related incidence of lethal mutations was reported. This study demonstrated that MC was mutagenic to sperm in Drosophila.

c. Studies in mammalian cells. MC has been tested for mutagenicity in several mammalian cell culture test systems. In 1980, Jongen et al. (Ex. 7-49) incubated CHO and V79 cells with concentrations of MC up to 5%. After exposure to MC, cells were selected for expression of the HGPRT gene locus (a forward mutation). MC did not increase the mutation frequency of either cell line. EPA suggested that, in order to evaluate the mutagenic potential of MC in this system, the test dose should be higher than that used in the study, because minimal cytotoxicity was observed in the cells at all of the doses given. Cell survival was decreased only 20% by the highest dose of MC.

Several investigators have studied the potential for MC to induce chromosomal aberrations. In an experiment conducted by Thilagar and Kumaroo (Ex. 7-192), MC induced a dose-related increase in chromosome aberrations in CHO cells. This response was not altered by the presence of an exogenous metabolic activation system (S-9 mix from Aroclor-induced rat livers).

Burek et al. (Ex. 7-151) examined the bone marrow of rats exposed to concentrations of 0, 500, 1500 or 3500 ppm MC 6 hr/day 5 days/week for 6 months. No increases in the frequency of abnormal cells or in the frequency of any specific aberration were reported in treated animals compared to the controls. However, in this experimental protocol it is necessary for the active metabolite of MC to reach bone marrow and interact with the DNA. There is no evidence that bone marrow is a target for MC, that MC is metabolized in bone marrow, or that metabolites produced in distant sites are stable enough to be transported to the bone marrow to exert a toxic effect. Therefore, it is predictable that MC would not exhibit a genotoxic effect in this assay.

Two studies of the ability of MC to cause micronuclei in polychromatic erythrocytes (PCE) (a measure of the genotoxicity of a compound) were evaluated. Gocke et al. (Ex. 7-193) examined the effects of three dose levels of MC (850, 1700, and 3400 mg/kg in 2 i.p. injections 24 hours apart). An increase in PCEs with micronuclei was observed at the two highest doses, but a dose-response relationship was not demonstrated. Also, the highest response observed was not greater than two times the control values. EPA considered these results inconclusive, but suggestive of a positive response. In 1986, Sheldon et al. (Ex. 8-30) also evaluated the potential for MC to induce micronuclei in PCEs. This study was determined to be negative for MC. These studies required MC-induced toxicity in the bone marrow (the site of erythrocyte formation), which has not been identified as a target tissue for MC toxicity. The mouse micronucleus assay may not be a sensitive indicator of the genotoxic potential of MC because, as indicated above, there is no evidence that bone marrow is a target for MC toxicity and the concentration of MC metabolites formed in other organs such as lung and liver which do reach the bone marrow, may not be in sufficient quantities to elicit a positive response in this assay.

Three studies have examined the effects of MC on the induction of sister chromatid exchanges in the DNA of mammalian cells in culture. MC was shown to induce SCEs in V79 cells by Jongen et al. (Ex. 7-49). This induction was dose-related and statistically significant at p less than 0.001. In a similar study, Thilagar and Kumaroo (Ex. 7-192) judged their study of MC induction of SCEs in CHO cells to be negative. However, slight dose-related increases in SCEs were reported. These increases did not achieve statistical significance, but were suggestive of a positive response. The doses used in this study were lower than in the study by Jongen et al. In a study by McCarroll et al. (Ex. 7-237), dose-related increases in the SCEs in CHO cells were reported at higher doses (up to 7% atmosphere) than used in the Thilagar and Kumaroo experiments (Ex. 7-192). Based on the evidence from these three studies, MC has been determined to cause DNA damage resulting in SCEs in cultured mammalian cells.

Several studies were conducted to determine the potential for MC to induce DNA repair, expressed as unscheduled DNA synthesis (UDS). Jongen et al. (Ex. 7-49) measured UDS and inhibition of DNA synthesis in V79 cells and primary human fibroblasts in vitro. MC had no detectable effect on UDS in either cell line. Inhibition of DNA synthesis was detected, but this effect was demonstrated to be a toxic effect of MC on the metabolism of MC and not a direct action of MC on DNA synthesis. In 1981, Perocco and Prodi (Ex. 7-189) also found no differences in in vitro DNA repair rates between MC-treated and control human lymphocytes.

Trueman et al. (Ex. 8-16) examined the effects of MC on UDS in vitro and in vivo. In the in vitro study, rat and mouse primary hepatocytes were exposed to 500, 1000, 2000 or 4000 ppm MC for 2 or 6 hours, and evaluated for UDS. The authors judged this study to be negative because, although the data is suggestive of a dose response, the results did not achieve statistical significance. The results may have had greater statistical power if higher doses were used. The study can be criticized on the grounds of dose selection because appropriate doses in in vitro UDS experiments are generally chosen as fractions of a dose which produces profound cytotoxic effects. The very limited cytotoxicity described in this study indicates that the doses used should most likely have been much higher. This study had little power to predict MC effects on UDS.

In the in vivo UDS experiments, rats and mice were exposed for 2 or 6 hours to 2000 or 4000 ppm MC. Hepatocytes were isolated from these animals and the DNA repair rates evaluated by measuring UDS. The results of this study show no effect of MC on DNA repair rates. However, the appropriateness of this protocol in the assessment of MC genotoxicity has been called into question by the EPA (Ex. 7-128). EPA states that the study of UDS in vivo is only justified when metabolism of a toxic agent is thought to occur outside the liver and the resulting metabolites are stable enough to be transported to the liver where they can interact with the DNA and cause genotoxic damage. The evidence accumulated concerning the metabolism of MC, on the other hand, suggests that MC is metabolized in the liver and lung, and that the toxic metabolites are very short-lived (too short-lived to be transported outside the metabolizing organ). In addition, the doses used in this study, as in the in vitro work, were too low. The basis for choosing these doses was the NTP chronic bioassay. Doses in the NTP study were designed to be administered to animals 6 hr/day for two years. Doses appropriate in a chronic study are generally too low to elicit detectable genetic changes in a short-term genotoxicity assay.

Lefevre and Ashby (Ex. 8-31) examined the effects of MC on the induction of cell replication by measuring the induction of S-phase hepatocytes by exposure to MC in vivo. Mice were exposed to 4000 ppm MC for 2 hours. This exposure was followed by in vivo radiolabelling of DNA and autoradiography of isolated hepatocytes. In two of three experimental protocols small, but statistically significant, increases in replicating hepatocytes were observed. The authors alluded to the possibility that the carcinogenic action of MC is the result of a non-genotoxic event which increases cell turnover, and therefore, tumorigenicity. However, the low dose used (4000 ppm is appropriate for a chronic bioassay, but not in short term studies) and the small effect observed gave this study little power to discriminate between weakly genotoxic and non-genotoxic activity.

The ability of a compound to bind covalently with DNA is one measure of its potential for genotoxicity. Although it is not necessary for a compound to bind to DNA to cause mutation, there are many examples of compounds which act in this manner. Green et al. (Ex. 8-16d) described experiments which test the ability of MC to bind covalently with DNA in vivo. Mice were exposed to 4000 ppm 14C-labelled MC and the liver DNA was examined for alkylated bases. A confounding factor in this protocol was that MC is metabolized to one-carbon compounds which may then enter the normal metabolic pathways for DNA. This results in radioactivity from labelled MC associated with all of the normal DNA bases as well as with any alkylation products. This problem was assessed by a second protocol in which DNA was labelled with 14C-formate (which labels all normal DNA bases except cytosine) and then the animals were exposed to 4000 ppm unlabelled MC. No alkylated bases resulting from MC exposure were detected in this study.

The sensitivity of these experiments was questioned because of the low dose of MC used (one dose of 4000 ppm), but also because of the apparent insensitivity of the analytical methods. In these experiments, no 5-methylcytosine was detected. This normally-occurring base is labeled at the 5-methyl position by 14C-formate and comprises approximately 3% of the normal DNA cytosines. Using the exposure protocol outlined by the authors, alkylated bases would be expected to occur at much lower frequencies than 5-methylcytosine in the DNA, especially if MC is believed to be a weak alkylating agent. If a normal minor base such as 5-methylcytosine cannot be detected by the methods used, the presence of any alkylated bases, especially from a weakly genotoxic agent, could not possibly be detected. OSHA disagrees with the authors findings that this study presents evidence of the lack of covalent binding of MC to DNA.

d. Summary of mutagenicity studies. In summary, OSHA believes that the evidence reported above indicates that MC is mutagenic in bacterial and lower eukaryotic systems, and has been shown to be weakly genotoxic in some mammalian systems. OSHA disagrees with the conclusion of Broome et al. (Ex. 4-65) that "the genetic rationale for a carcinogen risk assessment for DCM (MC) is inappropriate." Negative findings in several of the studies described here have been explained by inappropriate dosing or inappropriate protocol. The documentation of positive responses in the production of mutations in bacteria, yeast and Drosophila, chromosomal aberrations in CHO cells and SCEs in CHO and V79 cells and equivocal responses in other systems, indicate the potential genotoxicity of MC. These results support the rationale for development of a cancer risk assessment based on the genotoxic mechanism of action of MC.

D. Other Toxic Responses

1. CNS Toxicity

a. Animal studies. There is little data available describing behavioral or neurological effects of MC in animals other than the induction of anesthesia at high doses (greater than 1000 ppm). The data base describing the behavioral and neurological effects in humans from experimental and occupational exposures to MC is fairly large. Therefore, the value of additional behavioral data for rodents (measured as increased sleeping time or decreased running time) in assessing human risk from exposure to MC is questionable. Studies of biochemical changes in the brains of rodents exposed to MC, on the other hand, could be very important in determining the mechanism of action of MC neurotoxicity and the reversibility of chronic effects of MC exposure.

In a study by Savolainen et al. (Ex. 7-178), increased levels of acid proteinase in rat brains, but no change in brain RNA levels, were reported at 3 and 4 hours on the fifth day of exposure to 500 ppm MC, 6 hours/day. The authors suggest that the increase in acid proteinase may be due to increased levels of CO from metabolism of MC. The induction of a measurable change in the biochemistry of the brain after a relatively low concentration of MC (the current PEL) and the short duration of exposure suggests that human exposures to these levels may similarly induce biochemical CNS changes. More research in these areas is necessary to assess the biological significance of these findings.

In a study of long term exposure to MC, Rosengren et al. (Ex. 7-56) looked at the effects of MC on glial cell marker proteins and DNA concentrations in gerbil brains. Animals were exposed continuously to 210, 350 or 700 ppm MC. Because of high mortality in the 2 higher doses, no data was collected at 700 ppm and exposure was terminated after 10 weeks at 350 ppm. Exposure to 210 ppm was continued for three months. Exposure to MC was followed by four months of no exposure before animals were examined for irreversible CNS effects. The authors found increased levels of glial cell marker proteins in the frontal cerebral cortex and sensory motor cortex after exposure to 350 ppm MC. These findings are consistent with glial cell hypertrophy or glial cell proliferation. Levels of DNA were decreased in the hippocampus of gerbils exposed to both 210 and 350 ppm and in the cerebellar hemispheres after 350 ppm MC. Decreased DNA concentrations indicate decreased cell density resulting from cell death or inhibition of DNA synthesis.

The neurotoxic mechanism of action of MC in gerbil brains is not understood. However, since the metabolism of MC to CO was determined to be saturated at both 210 and 350 ppm (COHb levels were equivalent at both exposure concentrations), the toxic effect of MC was attributed to either the parent compound or metabolism by a second pathway (e.g. the GST pathway). It would be interesting to examine the effects of MC on these parameters using a daily exposure protocol instead of continuous exposure to determine if the irreversible effects observed would be diminished. It is not known at the present time whether a daily "recovery period" would increase the reversibility of these effects or not. Also, replication of these effects in other species is important, in order to establish that this effect is not specific to the gerbil (in which no other MC toxicity studies have been conducted).

In summary, OSHA believes that this evidence is highly suggestive of the susceptibility of the CNS to reversible and irreversible effects due to MC exposure. Biochemical studies of this nature are critical in elucidating the mechanism of action of MC on a biochemical level, and extrapolation of these effects to human exposures.

b. Human studies. The CNS depressant effects of MC have been well described in the literature (Exs. 7-4, 7-153, 7-154, 7-160, 7-175, 7-182, 7-183, 7-184). In the early part of this century, MC was used as an inhalation anesthetic, but abandoned because of the excitatory responses at doses required for anesthesia and the narrow margin between induction of anesthesia and death.

Accidental human overexposures to MC (Exs. 7-18, 7-19) have indicated that acute, high exposures (greater than 10,000 ppm) can result in narcosis and death. Inhalation of much lower concentrations of MC are associated with less severe CNS effects. In humans, CNS effects have been noted after experimental exposures to as low as 200 ppm (Ex. 7-175) and occupational exposures to as low as 175 ppm (Ex. 7-153).

i. Experimental studies. Putz (Ex. 7-175) described CNS deactivation, decreased eye/hand coordination and decreased vigilance, speed and precision during exposure to 200 ppm MC for 4 hours. Deficits in eye/hand coordination and dual task performance were larger than those produced by exposure to 70 ppm CO alone. The COHb resulting from these two exposures was approximately equal, leading to the conclusion that the CNS effects produced by MC were the result of the direct toxicity of MC in addition to the toxicity due to COHb.

Stewart (Ex. 7-4) found increased lightheadedness and changes in visual evoked response (a measure of CNS activation) after the first hour of a two hour exposure to 986 ppm and the same types of changes after 1 hour exposure to 514 ppm followed by approximately 15 minutes of a second 1 hour exposure to 868 ppm. In 1973, after exposure to a complex schedule of doses from 1 hour per day at 50 ppm to 7.5 hours per day at 500 ppm, Stewart (Ex. 7-5-R0327) demonstrated changes in the visual evoked response that were dose-related, but no effects on reaction times or performance of various tasks.

Gamberale et al. (Ex. 7-160) exposed 14 subjects to four 30 minute intervals, of increasing MC concentration increments from 250 to 1000 ppm (total exposure duration of 2 hours). The authors found a favorable change in mood, decreased heart rate and an increased variability in reaction time only at 1000 ppm. They found no statistically significant dose-response trend. However, since each dose was only experienced for one 30 minute interval, the power of this study to detect dose-related changes was low.

In contrast to the reported negative findings of Gamberale et al., Winneke (Ex. 7-184) performed a series of experiments on male and female volunteers which demonstrated a CNS depression after exposure to 300 and 800 ppm. This depression was manifested as decreased vigilance and decreased critical flicker fusion at both doses, after approximately 1.5 hours of a 3 hour exposure to 300 ppm MC. Decreased vigilance, psychomotor speed and reaction times were also measured during a 4 hour exposure to 800 ppm. A second study by Winneke (Ex. 7-182) compared the effects of MC at 300, 500 and 800 ppm to those effects produced by 50 and 100 ppm CO. These doses of CO produced a COHb level in the range of that produced by the MC doses. COHb was not measured in these experiments, but estimated to be equivalent whether exposure was to CO or MC. Winneke described increased deficits during MC exposure as compared with CO exposure. The authors concluded that MC produced greater toxicity than could be explained by metabolism to CO alone. Although this conclusion is the same as that forwarded by Putz (Ex. 7-175), the study is weakened by the fact that actual COHb levels were not measured.

These experimental studies show that there are definite signs of CNS depression as low as 200 ppm for 4 hours and 300 ppm at 1.5 hours of exposure. In the experiments which were sensitive enough to detect subtle CNS effects, a no observed effect level was not determined, because the lowest experimental concentration used (200 ppm) elicited CNS changes. It is reasonable to suggest that MC may cause CNS effects similar to those observed at 200 ppm, at lower exposures or after exposure for shorter durations, but OSHA has is not aware of any experimental study of this type which has investigated the CNS effects of MC at these levels.

ii. Occupational exposure studies. Kuzelova et al. (Ex. 7-26) examined workers in a film production plant who were exposed to MC at concentrations from 29 to 4899 ppm. There were cases of frank intoxication and large numbers of workers with neurological symptoms of MC toxicity. The mechanism for controlling exposure to these high industrial levels was removal of the affected employee to fresh air until he or she had recovered sufficiently to resume working. The effects described in this study were thought to be completely reversible, even after intoxication. No other toxicity associated with MC exposure was observed.

Cherry et al. (Ex. 7-154) studied the effects of occupational exposure to much lower concentrations of MC in two populations exposed to MC. In the 1981 study, the authors found a marginal increase in self-reported neurological symptoms among exposed workers. This increase disappeared when an appropriate reference group was used for comparison. However, in a similar study in 1983, Cherry (Ex. 7-153) showed statistically significant increases in tiredness and deficits in reaction time and digit symbol substitution which correlated to MC in blood. Exposures for this population ranged from 28 to 175 ppm for the full shift. This study demonstrated CNS effects due to occupational MC exposures below 200 ppm (the lowest dose which was administered in the experimental studies).

All of the CNS effects described above are currently thought to be completely reversible; however, there are some reports of a neuropathy associated with chronic occupational exposure to various solvents. Hanke (Ex. 7-195) and Weiss (Ex. 7-196) have described a diffuse toxic brain damage which is associated with chronic exposure to MC. Weiss (Ex. 7-196) described the case of a 39 year old chemist who worked for 5 years with airborne concentrations of MC as high as 660 ppm to 3600 ppm in a room with poor ventilation. After 3 years of exposure, the worker developed neurological symptoms, characterized by restlessness, palpitations, forgetfulness, poor concentration, sleep disorders, and finally, acoustical delusions and optical hallucinations. No hepatic damage or cardiac toxicity was found. At the first appearance of symptoms, cessation of exposure produced an immediate cessation of symptoms. Later, longer and longer periods were required after termination of exposure in order to alleviate the symptoms. The increasing persistence of symptoms is consistent with a diagnosis of toxic encephalosis.

Hanke et al. (Ex. 7-195) examined 32 floor tile setters who were exposed primarily to MC at concentrations from 400 to 5300 ppm for an average tenure of 7.7 years. Clinical examination of 14 of the workers who had neurological symptoms (headache, vertigo, sleep disturbance, digestive complaints and lapses in concentration and memory) revealed changes in the EEG patterns of the exposed workers which persisted over a weekend pause in exposure. These EEG changes were characteristic of a toxic encephalosis produced by chronic intoxication with a halogenated solvent (MC). The persistence of the EEG changes over the weekend break excluded an acute effect of MC exposure on EEG patterns. (Additional changes in the EEG found during exposure could be attributed to an acute effect of MC). Although these studies represent a small number of cases with very high chronic exposures, the evidence is suggestive of a relationship between chronic MC exposure and toxic encephalosis.

In a case study report, Barrowcliff et al. (Ex. 7-123) attributed cerebral damage in a case study to CO poisoning caused by exposure to MC. Axelson (Ex. 7-150) has described an increased number of neuropsychiatric disorders among occupations with high solvent exposures. These studies, coupled with the limited animal data on the irreversible effects of MC, provide suggestive evidence of a permanent toxicity which may be the result of chronic exposure to MC.

c. Summary of CNS toxicity studies. The primary concern surrounding the CNS toxicity of MC is the CNS deactivation that has been described in humans as low as 175 ppm (8 hour TWA). This depression in CNS activity can be expressed as increased tiredness, decreased alertness and decreased vigilance. These effects could compromise worker safety by leading to an increased likelihood of accidents during MC exposure. A second concern is the potential for development of irreversible brain damage as described by Hanke and Weiss (Ex. 7-195, 7-196). In these studies, the case numbers are small, the exposures to MC very high and more work is necessary to adequately describe the mechanistic relationship of the toxic encephalosis to MC exposure. However, the evidence that solvent-associated neuropathy exists justifies OSHA's action for reevaluating the adverse health effects of MC.

2. Cardiac Toxicity

Since MC is metabolized in vivo (in animals and humans) to CO and CO2, it is reasonable to suspect that cardiovascular stress known to occur from CO exposure may occur with exposure to MC as well (Ex. 7-73, 4-33). Carbon monoxide successfully competes with oxygen and blocks the oxygen binding site on hemoglobin, effectively reducing the delivery of oxygen to the tissues. Hemoglobin has an affinity for CO that is 240 times its affinity for oxygen. This means that even at low ambient CO concentrations, CO can outcompete oxygen for the hemoglobin binding sites. The most severe result of this binding is the reduction of oxygen supply to the heart itself, which can result in myocardial infarction (heart attack) (Ex. 4-033).

a. Animal studies. In the acute and chronic animal studies conducted to date, there is no evidence of a direct effect of MC on the heart. In lethal doses of MC, death is primarily the result of CNS and respiratory depression (Exs. 7-27, 7-28). Chronic studies (in which COHb levels have been maintained at 10% and higher) (Exs. 7-3, 7-8, 7-14, 7-130, 7-151) have also shown no direct cardiotoxicity of MC.

Chlorinated solvents have been shown to sensitize the cardiac tissue to epinephrine-induced fatal cardiac arrhythmias (Ex. 7-226). However, the evidence concerning MC is limited because the animals were susceptible to the narcotic effects of MC at a dose below which cardiac sensitivity was initiated. This suggests that this finding is of limited usefulness in occupational settings, because MC concentrations high enough to produce narcosis would be intolerable in a work environment.

b. Human studies. Because of the large numbers of American workers with silent or symptomatic heart disease, human populations may be more susceptible to the cardiac toxicity of MC than laboratory animals. Elevated COHb has been measured in humans experimentally and occupationally exposed to MC (Exs. 7-4, 7-5-R0327, 7-102, 7-115, 7-157, 7-159, 7-169, 7-174, 7-176). The effect of elevated CO exposure on the heart has been well established. Atkins and Baker (Ex. 7-198) described two cases of myocardial infarction in workers subsequent to CO exposure. COHb was measured at 30% and 24% in these individuals. While lower levels of COHb (3-10%) (levels which may result from occupational exposure to CO or MC) have not been associated with frank morbidity or mortality, COHb at these levels has been correlated with decreased exercise tolerance and increased anginal pain in individuals with coronary artery disease (Ex. 7-198).

Stewart et al. (Ex. 7-102) described a case of a 66 year old man who experienced three separate myocardial infarctions (the last one was fatal), each one after a 2 to 3 hour session of furniture stripping using a commercial paint remover formulation. Although the MC exposure and COHb levels were not measured, this case is highly suggestive of an association between MC exposure and cardiac stress. Welch (Ex. 7-73) described 144 case reports of clinical disease associated with MC exposure. Three of the cases were of cardiac symptoms which worsened upon exposure to MC; one was a myocardial infarction. MC exposure levels were not reliably measured in these cases, but these cases also suggest an association between MC exposure and cardiac stress.

DiVincenzo and Kaplan (Ex. 7-222) described the effects of smoking and exercise on the uptake, metabolism and excretion of MC. They found that exercise increases MC uptake and, subsequently, blood COHb levels through the metabolism of MC. The COHb levels due to smoking were found to be additive to the COHb produced by MC metabolism. This means that smokers or individuals engaged in physical exertion (as in a workplace), may be at increased risk from CO-induced toxicity from MC exposure. This is particularly true for individuals with silent or symptomatic cardiac disease who may be susceptible to the effects of CO at levels as low as 3%.

The two major epidemiological studies (in film coating and fiber production workers) (Exs. 7-75, 7-76, 7-122, 7-163) reported no increased cardiac mortality due to occupational exposure to MC. In the original study of the fiber production workers, Ott (Ex. 7-76) compared mortality from the MC exposed plant in South Carolina to a reference plant in Virginia. An increased risk ratio for ischemic heart disease was observed in the MC exposed workers compared to the reference population. The authors explained this disparity by examining geographical variability in the incidence of ischemic heart disease. The reference plant was found to have an unusually low (and unexplained) death rate due to ischemic heart disease. In an update of the study (Ex. 7-75), this contention was further supported when the exposed population was compared to the surrounding York County, S.C. population. No difference in ischemic heart disease rates was detected between exposed workers and controls. The SMR was 0.94 (32 observed, 34.2 expected).

Further examination of the fiber production workers by Ott in 1977 (Ex. 4-33d) provided information on the cardiac response of 24 male workers during occupational exposures to MC. The workers were monitored using continuous ambulatory electrocardiographic (ECG) recorders (Holter monitors) for 24 hours during a work day. The authors found no effects of MC on the ECG tracings of any of the men observed, even when COHb was measured at levels in which adverse effects were observed in angina patients under controlled laboratory conditions. The usefulness of the study is limited because, although efforts were made to include men with heart disease, only 3 of the 24 monitored were known to have heart disease. Also, the day to day variability of ECG responses within an individual is very high. Much more data must be collected to establish the existence or absence of a cardiac response to MC among individuals with silent or symptomatic heart disease.

c. Summary of cardiac toxicity. In summary, although the animal studies and epidemiological data are non-positive for a cardiac effect due to MC exposure, the collected case reports are highly suggestive of an effect of MC on the subpopulation with symptomatic or silent heart disease. The special susceptibility of this subpopulation to cardiac stress resulting from the metabolism of MC to CO would be very difficult to detect in an epidemiological study unless very large populations were used or the segment of the population with heart disease was identified. OSHA feels that there is sufficient evidence of cardiac toxicity from exposure to MC and/or its metabolites that OSHA should protect the population at risk from COHb levels due to MC metabolism as low as 3%.

3. Hepatic Toxicity

a. Animal studies.--i. Acute studies. Acute studies of MC exposure and liver toxicity have failed to demonstrate severe liver toxicity even at lethal or near-lethal doses. Kutob et al. (Ex. 7-27) and Klaassen et al. (Ex. 7-28) conducted investigations into the relationship between narcosis produced by single exposures to halogenated methanes and hepatotoxicity. In both cases MC was determined to be the least hepatotoxic of the halogenated methanes examined. In fact, MC produced no hepatotoxic effects by the parameters measured in the studies (bromsulfophthalein retention, SGPT activity and histopathologic changes). The only injury described was a mild inflammatory response associated with lethal MC concentrations.

Short-term, nonlethal exposures to MC also seem to elicit minimal liver toxicity. A study by Weinstein et al. (Ex. 7-181) examined the effects of continuous inhalation exposures of female mice to MC for up to 7 days. Mild, nonlethal injury to the livers was noted by the authors, characterized by balloon degeneration of the rough endoplasmic reticulum (RER), transient severe triglyceride accumulation (fatty liver), partial inhibition of protein synthesis and breakdown of polysomes into individual ribosomes. The injury is similar to a mild form of carbon tetrachloride toxicity (a structural analog of MC) and suggests that although the toxicity due to MC is not as severe as that produced by carbon tetrachloride, the mechanism of toxicity may be similar. An interesting aspect to this study is that by seven days the animals appeared to be adapting to the exposure conditions: the fatty accumulation and ballooning RER was largely reversed and the animals were more active, more like control animals than at the start of the experiment.

ii. Subchronic studies. Subchronic exposures to MC produce more defined hepatic injury than that described as resulting from acute exposure to MC. MacEwen et al. (Ex. 7-14) studied the effects of continuous exposure of mice, rats, dogs and rhesus monkeys to 1000 and 5000 ppm MC for up to 14 weeks. Fatty liver, icterus, elevated SGPT and ICDH were reported in dogs at both concentrations, these effects appeared at 6-7 weeks of exposure to 1000 ppm MC and at 3 weeks of exposure to 5000 ppm. Monkeys were less sensitive to hepatic injury, presenting no changes in liver enzymes and only mild to moderate liver changes at 5000 ppm MC. No liver alterations were detectable in monkeys exposed to 1000 ppm MC. Mice and rats developed liver toxicity at both exposure levels, characterized by increased hemosiderin pigment, cytoplasmic vacuolization, nuclear degeneration and changes in cellular organization.

iii. Chronic studies. Chronic hepatic effects associated with MC exposure were observed in lifetime bioassays in three rodent species. In the NTP, Burek, and Nitschke studies (Exs. 7-8, 7-151, 7-173), rats were exposed to inhalation concentrations of MC from 50 ppm to 4000 ppm. Hepatic effects were noted after chronic exposure to as low as 500 ppm. Hepatic injury in rats was characterized by increased fatty liver, cytoplasmic vacuolization and an increased number of multinucleated hepatocytes. At the higher doses (greater than 1500 ppm), increased numbers of altered foci and hepatocellular necrosis became apparent. Serota et al. (Ex. 7-180) administered 5 to 250 mg MC/kg body weight in the drinking water. Hepatic toxicity similar to that found in the inhalation studies was reported at doses from 50 to 250 mg/kg.

The chronic hepatic effects of MC in mice were investigated in two bioassays: NTP (Ex. 7-8) and Serota et al. (Ex. 7-179). The NTP study exposed mice to inhaled MC concentrations of 2000 and 4000 ppm. MC produced cytologic degeneration in both male and female mice and increased incidence of hepatocellular adenomas and carcinomas. The carcinogenic effects of MC are described in greater detail in the section on carcinogenicity. In mice exposed to 50 to 250 mg/kg/d MC in drinking water, Serota et al. found treatment-related increases in the fat content of the liver. Although some proliferative hepatocellular lesions were identified in this study, they were distributed across all exposure groups. Hepatocellular tumor incidences were not elevated above historical control incidences.

In the hamster, Burek et al. (Ex. 7-151) found very minimal treatment related changes in the livers of the MC exposed animals after exposure to 500, 1500 or 3500 ppm MC. A dose-related increase in hemosiderin was found in male hamsters at 6 months and at 3500 ppm at 12 months. No other changes in liver physiology were reported.

iv. Summary of animal studies of hepatotoxicity. In summary, the acute effects of MC exposure on the livers of experimental animals in these studies were slight and appear to be reversible. However, long term exposure to MC, as in the chronic bioassays, lead to more severe and more permanent changes in liver physiology. In the case of mice in the NTP study, these changes included carcinogenesis. The studies described above demonstrate the susceptibility of the liver as a target organ for MC, especially after chronic administration.

b. Human studies.--i. Epidemiological studies. In a cross-sectional analysis of the health of workers in an acetate fiber production plant in which workers were exposed to 140 to 475 ppm MC, Ott et al. (Ex. 4-33c) reported statistically significant increases in serum bilirubin and alanine aminotransferase (ALT) (also known as serum glutamic pyruvic transaminase (SGPT)) when compared with a reference group of industrial workers. The elevation in bilirubin levels showed a dose-response relationship, but the ALT levels were not associated with MC exposure. The authors felt that the increase in ALT in MC-exposed workers could not be attributed to MC because a dose-response relationship was not demonstrated and, therefore, the increase in ALT between the exposed and reference populations could be disregarded as a sign of liver toxicity. The authors concluded that although bilirubin elevation may be interpreted as a sign of liver toxicity, this interpretation was not supported by alterations in other liver parameters. OSHA feels that ALT can not be disregarded as unrelated to MC exposure based on the lack of dose response within the exposure group. The high variability of this parameter and the low numbers of individuals within certain exposure subgroups (e.g. 10 men exposed at 280 ppm), makes a dose-response relationship difficult to ascertain. Although the evidence is not unequivocal, OSHA believes that the elevated bilirubin coupled with the elevated ALT values indicate suggestive evidence of a hepatotoxic response to MC exposure in this worker population.

In an update to the study described above, Cohen et al. (Ex. 7-75) found 4 cases of liver/biliary duct cancer in workers with more than 10 years of exposure to MC and after 20 years from first hire. Further description of this study can be found in the section on carcinogenicity.

In a 1968 study, Kuzelova et al. (Ex. 7-26) found no liver abnormalities in workers exposed to MC concentrations from 29 ppm to 4899 ppm, even when cases of acute neurotoxicity were identified. However, in a study aimed primarily at detecting neurological changes due to MC exposure, Hanke et al. (Ex. 7-195) identified hepatic toxicity in 4 of 14 floor tile setters examined. These workers were chronically exposed to MC at concentrations as high as 400 to 5300 ppm. The average tenure of employment of these workers was 7.7 years.

ii. Case reports. In addition to the cross-sectional analyses of worker morbidity described above (Exs. 4-33c and 7-26), the relationship of MC exposure and hepatotoxicity has been studied by analysis of case reports. Welch (Ex. 7-73) collected 144 case reports of clinical disease reported subsequent to occupational MC exposure. Quantitative exposure estimates for individuals were unreliable, but the presence of MC in the work environment was ascertained for each employee. The most prevalent findings in these case reports were CNS symptoms, upper respiratory syndrome and alterations in liver enzymes. The alterations in liver enzymes were not consistent among individuals, but may be suggestive of a MC-associated hepatotoxic effect. One case of hepatitis of unknown etiology was identified. The case physician felt that the hepatitis was secondary to solvent exposure. The solvents to which this employee was exposed included MC, xylene and methylethyl ketone.

Analysis of cases of fatal and near-fatal human exposures (Exs. 7-18, 7-19), indicated no apparent alterations of liver function. Acute concentrations of MC which caused narcosis and even death were not associated with changes in liver enzymes. The primary cause of death in MC-induced fatalities appeared to be CNS depression, not hepatotoxicity.

c. Summary of human hepatotoxicity. In summary, the toxicity data from the animal studies and the limited data from human MC exposures appear to coincide. Acute, high doses (even fatal doses) of MC do not noticeably impair liver function, while chronic, lower exposures are associated with mild to moderate hepatotoxicity, well described in rodent studies and suggested by analysis of human data. MC also induces liver tumor formation in rodents. Further, there is suggestive evidence that liver and biliary tumors may be produced after chronic MC exposure in humans, as well.

4. Reproductive Toxicity

It is difficult to determine the potential adverse teratogenic or reproductive effects due to MC exposure because of the limited availability of human and animal data. Studies (Ex. 4-5) using chicken embryos have indicated that MC disrupts embryogenesis in a dose-related manner. Since the application of MC to the air space of chicken embryos is not comparable to MC administration to animals with a placenta, the exposure effect seen in the chick embryos can only be considered as suggestive evidence that an effect may also occur in mammalian systems. The limited rodent data which have been collected do not demonstrate teratogenic effects as the result of maternal MC exposure.

Information on the effects of MC on human reproduction, gathered through case studies and limited epidemiological investigations, suggests that MC may be associated with decreased male fertility and increased spontaneous abortions among exposed females. These studies are limited by lack of exposure information and some deficits in study design, so that the reproductive, teratogenic or developmental toxicity of MC to humans is still unclear.

a. Animal studies. The teratogenicity of inhaled MC has been studied in rats and mice. Although the studies showed that MC was not teratogenic in either rodent species, some maternal toxicity and minor skeletal defects and post-natal behavioral effects among offspring were observed (Exs. 7-20, 7-21, 7-22).

i. Mouse study. In 1975, Schwetz et al. (Ex. 7-21) conducted a study on Swiss Webster mice. Mice inhaled 1250 ppm MC for 7 hours/day, on days 6-15 of gestation. On day 18 of gestation, Caesarian sectioning of dams was performed. A statistically significant increase in mean maternal body weight (11-15%) was observed in dams exposed to 1250 ppm MC; however, food consumption was not measured. The only effect on fetal development associated with MC exposure was a statistically significant increase in the number of fetuses which contained a single extra center of ossification in the sternum. The incidence of gross anomalies observed in the MC-exposed fetuses was not significantly different from the control litters. Maternal COHb level during exposure reached 12.6%; however, 24 hours after the last exposure, COHb returned to control levels.

ii. Rat studies. In the same study by Schwetz et al. (Ex. 7-21), Sprague-Dawley rats were exposed to 1250 ppm MC via inhalation for 7 hours daily on days 6-15 of gestation. No MC-associated effects were observed in food consumption or maternal body weight. Among litters from MC-exposed dams, the incidence of lumbar ribs or spurs was significantly decreased when compared to controls, while the incidence of delayed ossification of sternebrae was significantly increased compared to controls. No increased incidence of gross anomalies were observed in the fetuses from exposed rats compared to fetuses from control litters. No MC-associated effects were observed on the average number of implantation sites per litter, litter size, the incidence of fetal resorptions, fetal sex ratios or fetal body measurements, in the 19 litters that were evaluated. As observed in the MC-exposed mice, there was significant elevation of the COHb level in the dams, but the level returned to control values within 24 hours of cessation of exposure.

In 1980, Hardin and Manson (Ex. 7-22) evaluated the effect of MC exposure in Long-Evans rats after inhalation of 4500 ppm for 6 hours/day, 7 days/week prior to and during gestation. Four exposure groups were described. The first group was exposed to MC for 12 to 14 days prior to gestation and during the first 17 days of pregnancy. The second group was exposed to MC only during the 12 to 14 days prior to gestation. The third group was exposed to MC only during the first 17 days of pregnancy. The fourth group (control group) was exposed only to filtered air. The purpose of this study was to test whether MC exposure prior to and/or during gestation was more detrimental to reproductive outcome in female rats than exposure during gestation alone.

In rats exposed to MC during gestation, there were signs of maternal toxicity, characterized by a statistically significant increase in maternal liver weights. The only fetal MC effects observed were statistically significant decreases in mean fetal body weights. No significantly increased incidence of skeletal or soft tissue anomalies was observed in the offspring.

In 1980, Bornschein et al. (Ex. 7-224) tested some of the offspring of the Long-Evans rats from Hardin and Manson's study described above. All four treatment groups were used to assess the postnatal toxicity of MC exposure at 4500 ppm. The general activity measurements of groups of 5-day old pups showed no exposure-related effects. At 10-days of age, however, significant MC-associated effects were observed in both sexes in the general activity test. These effects were still apparent in male rats at 150-days of age. This study showed that maternal exposure to MC prior to and/or during pregnancy altered the manner in which the offspring react and adapt to novel test environments at up to 150-days of age. These effects suggest that MC exposure prior to, or during pregnancy may influence the processes of orientation, reactivity, and/or behavioral habituation. No changes in growth rate, long-term food and water consumption, wheel running activity or avoidance learning were reported.

b. Human studies. Limited data have been collected on the reproductive effects of MC in male workers. In a study reported in the Occupational Safety and Health Reporter (Ex. 7-43), a greater risk of male sterility was found in male workers exposed to MC. In 1988, Kelly (Ex. 7-165) reported 4 cases of oligospermia in MC-exposed workers. The individuals involved in this study were employed at an automobile paint and body shop, and were part of a group of 86 workers who were interviewed for possible health effects resulting from MC exposure. Between Dec. 7, 1984 and June, 1986, 34 men with MC exposure and some health problems, were evaluated. The most prevalent complaints from these men were associated with CNS dysfunction. Eight of the 34 men complained of genital pain. Four of these eight men consented to semen evaluation. The occupational exposure to MC for the four cases involved dipping auto parts into an open container of MC without the use of protective gloves. None of these men were found to have a motile sperm count greater that 20 million/ml.

Eight weeks following the cessation of MC exposure, the individual with the highest sperm count showed some improvement. However, the number of motile sperm was still below 20 million. In two of the men examined, the sperm count had declined over a period of several months. It was also noted that none of the 4 individuals tested had had children since occupational exposure to MC had begun, although none of the men were using contraceptives. These findings are based on a very small number of cases and more research is necessary before conclusions can be drawn about the human male reproductive toxicity of MC.

The reproductive and developmental effects of MC due to exposure in female workers have also been studied. According to information reported by Vozovaya et al. (Ex. 7-16), detectable levels of MC were found in the blood, milk, embryonal, fetal and placental tissues of nursing women exposed to MC in a rubber product plant. In a different study, by Taskinen et al. (Ex. 7-199), increased rates of spontaneous abortions were observed in female pharmaceutical workers exposed to MC. Exposure data were not reported in this study and it is unclear what confounding factors or other chemical exposures were present. OSHA believes that more research is necessary in order to evaluate the potential effect of MC on pregnancy outcomes.

Other studies have documented the adverse reproductive effects of human exposures to the MC metabolite, CO. The EPA has reviewed the literature on the effects of maternal CO exposure on the development of the fetus in the Air Quality Criteria for Carbon Monoxide (Ex. 7-201). Very high maternal CO exposures have resulted in fetal or infant death or severe neurological impairment of the offspring. CO reduces the amount of oxygen available to the tissues. The developing fetus is very sensitive to these effects. According to Fechter et al. (Ex. 7-200), low levels of CO exposure in animals have been shown to adversely affect the fetus, producing CNS damage or reduced fetal growth. These effects suggest that pregnant women may be especially sensitive to the toxic effects of MC through its metabolism to CO.

c. Summary of reproductive effects. Results obtained from studies using the chick embryo are suggestive that embryotoxic and teratogenic effects may occur in mammals, but these results cannot be directly applied to mammalian systems. The rodent studies described here have not demonstrated that MC is embryolethal or teratogenic. Minor skeletal defects and postnatal behavioral effects have been noted in these studies, but the significance of these effects in assessing human risk of reproductive hazards is unclear. The case studies showing oligospermia and the increased incidence of spontaneous abortion in MC-exposed female pharmaceutical workers is suggestive evidence that human exposure to MC may cause adverse reproductive health effects. There is also some concern that pregnant women exposed to MC may suffer from adverse reproductive effects associated with increased COHb, due to MC metabolism.

Currently it is not possible to quantify the reproductive and developmental effects of MC. Each of the animal studies only observed effects at a single exposure level and a no adverse effect level was not identified. The human studies do not contain enough information on exposure levels or confounding variables to permit generation of a reproductive or developmental risk assessment. Since the developmental effects observed in mice and rats were mild and occurred at exposures from 1250 to 4500 ppm, it is OSHA's belief that a 25 ppm PEL, developed on the basis of carcinogenic effects, would also be protective against the reproductive health effects described in these studies.

E. Conclusion

OSHA's determination that MC is a potential occupational carcinogen was based primarily on the positive findings of chronic inhalation bioassays in rodents. MC was carcinogenic to mice of both sexes, producing lung and liver neoplasms. In rats, MC produced dose-related increases in mammary tumors and increases in the number of tumors per tumor-bearing rat. The evidence in rodents is supported by epidemiologic findings from cellulose triacetate fiber production workers. This epidemiologic study suggests an association between liver and biliary cancer and long term (greater than 10 years) exposure to MC. This evidence is further supported by the observation of liver toxicity in animals and humans subsequent to chronic exposure to MC (suggesting the liver as a target organ for MC) and the findings of genotoxic activity of MC in bacterial and mammalian cell systems.

Acute neurotoxicity has been demonstrated in humans and animals at relatively low inhalation concentrations of MC. There is preliminary evidence in case reports of humans with chronic occupational exposure to MC and in experimental research in gerbils that chronic exposure to MC may cause an irreversible neurotoxicity.

Because of the metabolism of MC to CO, there is a concern about the potential for cardiac toxicity, especially in sensitive populations, such as smokers, persons with silent or symptomatic heart disease and pregnant women. OSHA believes that it is important to limit MC exposure so that COHb production does not exceed 3% for these workers.

In summary, findings in humans and experimental animals exposed to MC are indicative of damage to the genetic material (DNA). Evidence from in vivo studies in animals and humans shows that genotoxicity may be expressed as increased incidence of cancer in the adult. Other adverse health effects from MC exposure, suggested by existing evidence, are hepatotoxicity, potentially irreversible neurotoxicity and increased cardiac stress.

VIII. Preliminary Quantitative Risk Assessment

A. Introduction

The United States Supreme Court, in the "benzene" decision, (Industrial Union Department, AFL-CIO v. American Petroleum Institute, 448 U.S. 607 (1980)) has ruled that the OSH Act requires that, prior to the issuance of a new standard, a determination must be made that there is a significant risk of health impairment at existing permissible exposure levels and that issuance of a new standard will substantially reduce or eliminate that risk. The Court stated that "before he can promulgate any permanent health or safety standard, the Secretary is required to make a threshold finding that a place of employment is unsafe in the sense that significant risks are present and can be eliminated or lessened by a change in practices" [488 U. S. 642]. The Court also stated "that the Act does limit the Secretary's power to requiring the elimination of significant risks" [488 U.S. 644].

Although the Court in the Cotton Dust case (American Textile Manufacturers Institute v. Donovan, 452 U.S. 490 (1981)) rejected the use of cost-benefit analysis in setting OSHA standards, it reaffirmed its previous position in "benzene" that a risk assessment is not only appropriate, but also required to identify significant health risk in workers and to determine if a proposed standard will achieve a reduction in that risk. Although the court did not require OSHA to perform a quantitative risk assessment in every case, the Court implied, and OSHA as a matter of policy agrees, that assessments should be put into quantitative terms to the extent possible.

B. Choice of Data Base

The determining factor in the decision to perform a quantitative risk assessment is the availability of suitable data for use in such an assessment. In the case of MC, OSHA has determined that data are available to quantify the cancer risk. OSHA's approach for this risk assessment was, as a first step, to perform a critical review of the health studies associating MC exposure and cancer. The purpose of such a critical evaluation is to determine whether exposure to the substance has caused cancer. The critical review also enables OSHA to select those studies that have potential for use in a quantitative risk assessment. OSHA has reviewed risk assessments performed by scientists outside of OSHA to determine if they are relevant to the occupational situation (EPA, Exs. 4-6 and 7-129; CPSC, Exs. 5-2 and 7-126; FDA, Ex. 6-1;ECETOC Ex. 10-39; Reitz and Anderson, Ex. 7-125). In order to obtain additional professional opinion on how the MC data should be used for quantitative risk assessment, OSHA contracted with K.S. Crump and Company through Meridian Research Inc. to perform an independent quantitative risk assessment (Exs. 12 and 7-127). OSHA has evaluated these risk assessments and has made its own preliminary estimates of cancer risk associated with MC exposure to workers. OSHA extrapolated the data from the two-year inhalation study on rats and mice performed by the National Toxicology Program (NTP) (Ex. 4-35) in an effort to quantify the lifetime excess risk of cancer to humans. OSHA chose lifetime exposure levels of 1, 10, 25, 50, 100 and 500 ppm as possible scenarios to examine. The following discussion summarizes the data and conclusions of OSHA's preliminary quantitative risk assessment.

C. Selection Of The Most Appropriate Studies

OSHA examined several studies in order to select the most appropriate data for performing a quantitative risk assessment. These include studies in which the route of exposure was inhalation (Burek et al., Ex. 4-25, Nitschke et al., Ex. 7-29, and the NTP, Ex. 4-35) and two studies in which the route of exposure was drinking water (National Coffee Association, Exs. 7-30, 7-31). Data sets selected from these studies are listed in table 7. In order to ensure complete analysis of the data, all data sets which showed an elevated incidence of tumors in a MC-exposed group, compared to controls, were analyzed, whether or not the elevation of tumor response was statistically significant.

TABLE 7. - INCIDENCE OF TUMORS IN MICE AND RATS INDUCED BY METHYLENE
            CHLORIDE
__________________________________________________________________________
  |      Doses |  
  | _________________________ | Tumor
Data Set | Experimental | Adjusted | Incidence(2)
  | (ppm) | (m/kg/day) |  
___________________________________ | _____________ | ___________ | ____________
  | | |  
1. NTP -Male Rats; Mammary | 0 | 0 | 0/50
Adenoma or Fibroadenoma | 1000 | 406.7 | 0/50
  | 2000 | 813.5 | 2/50
  | 4000 | 1627.0 | 5/50
  | | |  
2. NTP - Male Rats; Mammary or | 0 | 0 | 1/50
Subcutaneous Adenoma, Fibro- | 1000 | 406.7 | 1/50
adenoma, or fibroma | 2000 | 813.5 | 4/50
  | 4000 | 1627.0 | *9/50
  | | |  
3. NTP - Female Rats; Mammary | 0 | 0 | 5/50
Adenoma or Fibroadenoma | 1000 | 623.1 | 11/50
  | 2000 | 1246.1 | 13/50
  | 4000 | 2492.3 | *23/50
  | | |  
4. NTP - Male Mice; Alveolar/ | 0 | 0 | 3/50
Bronchiolar Adenoma | 2000 | 1857.9 | *19/50
  | 4000 | 3715.9 | *24/50
  | | |  
5. NTP - Male Mice; Alveolar/ | 0 | 0 | 2/50
Bronchiolar Carcinoma | 2000 | 1857.9 | *10/50
  | 4000 | 3715.9 | *28/50
  | | |  
6. NTP - Male Mice; Alveolar/ | 0 | 0 | 5/50
Bronchiolar Adenoma or | 2000 | 1857.9 | *27/50
Carcinoma | 4000 | 3715.9 | *40/50
  | | |  
7. NTP - Male Mice; | 0 | 0 | 10/50
Hepatocellular Adenoma | 2000 | 1857.9 | 14/49
  | 4000 | 3715.9 | 14/49
  | | |  
8. NTP - Male Mice; | 0 | 0 | 13/50
Hepatocellular Carcinoma | 2000 | 1857.9 | 15/49
  | 4000 | 3715.9 | *26/49
  | | |  
9. NTP - Male Mice; | 0 | 0 | 22/50
Hepatocellular Adnoma or | 2000 | 1857.9 | 24/49
Carcina | 4000 | 3715.9 | *33/49
  | | |  
10. NTP - Male Mice; | 0 | 0 | 15/50
Alveolar/Bronchiolar or | 2000 | 1857.9 | 21/49
Hepatocellular Carcinoma | 4000 | 3715.9 | *39/49
  | | |  
11. NTP - Male Mice; | 0 | 0 | 27/50
Alveolar/Bronchiolar | 2000 | 1857.9 | 34/49
or Hepatocellular | 4000 | 3715.9 | *45/49
Adenoma or Carcnoma | | |  
  | | |  
12. NTP - Female Mice; | 0 | 0 | 2/50
Alveolar/Bronchiolar | 2000 | 2051.0 | *23/48
Adenoma | 4000 | 4101.9 | *28/48
  | | |  
13. NTP - Female Mice; | 0 | 0 | 1/50
Alveolar/Bronchiolar | 2000 | 2051.0 | *13/48
Carcinoma | 4000 | 4101.9 | *29/48
  | | |  
14. NTP - Female Mice; | 0 | 0 | 3/50
Alveolar/Bronchiolar | 2000 | 2051.0 | *30/48
Adenoma or Carcinoma | 4000 | 4101.9 | *41/48
  | | |  
15. NTP - Female Mice; | 0 | 0 | 2/50
Hepatocellular Adenoma | 2000 | 2051.0 | 6/48
  | 4000 | 4101.9 | *22/48
  | | |  
16. NTP - Female Mice; | 0 | 0 | 1/50
Hepatocellular Carcinoma | 2000 | 2051.0 | *11/48
  | 4000 | 4101.9 | *32/48
  | | |  
17. NTP - Female Mice; | 0 | 0 | 3/50
Hepatocellular Adenoma or | 2000 | 2051.0 | *16/48
Carcinoma | 4000 | 4101.9 | *40/48
  | | |  
18. NTP - Female Mice; | 0 | 0 | 1/50
Alveolar/Bronchiolar or | 2000 | 2051.0 | *21/48
Hepatocellular Carcinoma | 4000 | 4101.9 | *43/47
  | | |  
19. NTP - Female Mice; | 0 | 0 | 5/50
Alveolar/Bronchiolar | 2000 | 2051.0 | *36/48
or Hepatocellular | 4000 | 4101.9 | *46/47
Adenoma or Carcinoma | | |  
  | | |  
20. Burek - Male Rats; Salivary | 0 | 0 | 1/95
Gland Region Sarcoma | 500 | 147.4 | 0/95
  | 1500 | 442.3 | 5/95
  | 3500 | 1032.0 | *11/97
  | | |  
21. Burek - Female Hamster; | 0 | 0 | 1/91
Lymphosarcoma | 500 | 97.4 | 6/92
  | 1500 | 292.2 | 3/91
  | 3500 | 681.7 | 8/91
  | | |  
22. Nitschke - Female Rats | 0 | 0 | 52/70
Mammary Adenoma, | 50 | 22.6 | 58/70
Fibroadenoma or Fibroma | 200 | 90.2 | 61/70
  | 500 | 225.6 | 55/70
  | | |  
23. NCA - Female Rats; | | 0 | 0/98
Neoplastic Nodules | | 6.5 | 1/48
  | | 58.3 | 2/49
  | | 135.6 | 1/49
  | | 262.8 | *3/47
  | | |  
24. NCA - Female Rats; | | 0 | 38/98
Pituitary Adenoma | | 6.5 | 16/48
  | | 58.3 | 11/49
  | | 135.6 | 11/49
  | | 262.8 | 28/47
  | | |  
25. NCA - Male Mice; | | 0 | 0/125
Hepatocellular Hemangioma | | 60.6 | 1/200
  | | 123.6 | 2/100
  | | 177.4 | 4/99
  | | 234.3 | 0/125
  | | |  
26. NCA - Male Mice; | | 0 | 24/125
Hepatocellular Adenoma or | | 60.6 | 51/200
Carcinoma | | 123.6 | 30/100
  | | 177.4 | 31/99
  | | 234.3 | 35/125
___________________________________ | _____________ | ___________ | ____________

FOOTNOTE (1): For inhalation studies, adjusted dose was calculated as d(mg/kg/day) = d (ppm) X (1.2 x mol. wt./mol. wt. of air) x breathing rate x hrs. of exposure/24 x days of exposure/7 * body wt.

FOOTNOTE (2): Incidence expressed as number of animals with response per number of animals examined for the response.

* Statistically significant, using Fischer's Exact Test and a Bonferroni correction, at the .05/r level, where r is the number of test doses. For data sets 22-26 a Chi-square approximation of the Fischer Exact Test is used due to large sample size.

In a bioassay performed by the NTP (Ex. 4-35), eight-week old F344/N rats and nine-week old B6C3F1 mice were exposed by inhalation to various concentrations of MC. Groups of 50 rats of each sex were exposed to MC at concentrations of 0, 1000, 2000, or 4000 ppm, while groups of 50 mice of each sex were exposed to concentrations of 0, 2000, or 4000 ppm MC. The inhalation exposures were administered 6 hours a day, 5 days a week for 102 weeks. Food was provided to the animals ad libitum except during the exposure periods, while water was available at all times via an automatic watering system. All animals were observed twice a day for mortality and moribund animals were sacrificed. Clinical examinations were performed once a week for 3.5 months, then twice a month for 4.5 months, and once a month thereafter. Each animal was also weighed weekly for 12 weeks, then monthly until the conclusion of the study at 104 weeks. All animals were necropsied and histologically examined. Three different neoplastic lesions were observed to have significantly increased incidence over the controls: mammary gland fibroadenomas and fibromas in male and female rats, adenomas and carcinomas of the lung in male and female mice, and adenomas and carcinomas of the liver in male and female mice.

In a two-year inhalation study by Burek et al. (Ex. 4-25), Sprague-Dawley rats and Syrian Golden hamsters were exposed to MC six hours a day, five days per week for the length of the experiment. All animals were approximately eight weeks old at the start of the experiment. For the chronic toxicity and oncogenicity portion of the study, approximately 95 animals per sex of each species were assigned to each dose group. Dosage levels administered were 0, 500, 1500 or 3500 ppm MC. Additional animals were used for cytogenetic studies and interim sacrifices. Interim sacrifices occurred at 6, 12, 15, and 18 months with 5 to 10 animals of each sex sacrificed per dose group. Food was provided to the animals ad libitum only during non-exposure periods, while water was provided ad libitum at all times.

All animals were observed five days per week for general health, signs of toxicity, and mortality. Animals were sacrificed when moribund. Beginning in the third month of the study, all rats and hamsters were examined monthly for palpable masses. This procedure was continued for the duration of the study.

The final sacrifice was performed 24 months after the first exposure. All animals were necropsied and tissues were fixed in 10% formalin. The authors state that "conventional methods" were used for sectioning and staining "representative organs and tissues."

The only significantly increased response observed was the incidence of sarcomas in the salivary gland region in high-dose male rats. This tumor response was not observed in other rat bioassays using the Fischer 344 rat at similar doses or the Sprague-Dawley rat at lower doses. The authors state that the salivary gland tumors may have been affected by the presence of a common viral disease, sialodacryoadenitis, which primarily affects the salivary glands. However it should be noted that no sarcomas were detected in females similarly affected with this virus. Female hamsters showed an increase in lymphosarcomas in the lymphoreticular system. However, high dose females had greater survival than controls, such that after correcting for this difference the authors did not feel this response was significant.

In a two-year inhalation study, by Nitschke et al., (Ex. 7-29) male and female Sprague-Dawley rats were exposed to 0, 50, 200, or 500 ppm MC for 6 hours/day, 5 days/week for 20 months for male rats and 24 months for female. One group of female rats was exposed to 500 ppm MC for the first 12 months of the study only, while another group of female rats was exposed to 500 ppm for the last 12 months of the study (designated 500:0 and 0:500, respectively). Animals were distributed into groups of 185 animals per sex per group for the 0 and 500 ppm dose groups and 90 animals per sex per group for the 50 and 200 ppm dose groups. The 500:0 and 0:500 ppm dose groups consisted of 30 female rats each. Eighteen additional female rats were included in each exposure group for determining the rate of DNA synthesis in the liver. Five rats from each sex/dose group were sacrificed after 6, 12, 15, and 18 months of exposure.

Food and water were provided to the animals ad libitum except during exposure periods. Body weights were determined at the initiation of the study, twice a month for the first three months, and monthly thereafter. Animals were observed daily after the exposures for signs of toxicity and changes in appearance, and dead and moribund animals were removed.

The authors state that, "conventional methods" were used for processing representative sections of organs and tissues that were histologically examined. All animals from the interim and terminal sacrifices were subjected to complete examinations. Some of the animals that died spontaneously or were sacrificed when moribund did not receive complete examinations. The only significantly increased response in this study was the increased incidence of benign mammary tumors in the female rats at the 200 ppm dose.

In a study sponsored by the National Coffee Association (NCA) (Serota et al.; Exs. 7-30 and 7-180), MC was administered to eight-week old Fischer 344 rats via the drinking water. MC was added to deionized water to provide target doses of 5, 50, 125, or 250 mg MC/kg body weight/day. Rats were randomly assigned to treatment groups with 85 animals in each treated group, while the controls consisted of 135 animals. An additional treatment group ("recovery" group) of 25 animals received a target dose of 250 mg/kg/day for the first 78 weeks of the experiment, and then received deionized water alone until terminal sacrifice. Actual doses received by the rats were measured (by measuring water consumption) and the mean daily consumption of MC was reported for each dose group. The male rats received average daily doses of 5.85, 52.28, 125.04, 235.00 or 232.13 mg/kg/day. The female rats consumed an average of 6.47, 58.32, 135.59, 262.81, or 268.72 mg/kg/day.

Food and water were provided to the animals ad libitum. Observations for mortality and signs of moribundity were performed twice daily for the first 52 weeks. Thereafter, a third observation was performed five days a week in addition to the twice daily observations. All animals that were found moribund were sacrificed. Body weight, clinical signs, and food consumption were measured weekly, while water consumption was measured twice weekly. Interim sacrifices were performed on 5, 10, or 20 animals per group at 26, 52, and 78 weeks. These animals were excluded from subsequent analysis, as were the recovery groups. All surviving animals were sacrificed after 104 weeks on the study. A complete necropsy was performed on every animal, whether found dead, sacrificed when moribund, or sacrificed at the end of the study.

For the male rats, the incidence of tumors (of any type) in the treatment groups at any dose level was not significantly increased over the controls. The female treated rats showed a marginally significant increased incidence of neoplastic nodules and pituitary adenomas when compared to the controls. Increased incidence of mammary tumors in female rats were not observed in this study. The dosages were, however, 10-fold less than those in the NTP study.

In the second 24-month oncogenicity study by the NCA (Serota et al.; Exs. 7-31 and 7-179), MC was administered to eight-week-old B6C3F1 mice in the drinking water. The mice were divided into four dose groups and two control groups of various sizes. (Since the control groups were treated identically, data for the two groups were combined.) MC was mixed with drinking water to provide doses of 60 mg/kg/day (200 males and 100 females), 125 mg/kg/day (100 males and 50 females), 185 mg/kg/day (100 males and 50 females), and 250 mg/kg/day (125 males and 50 females). The control groups consisted of 125 males and 100 females. Actual doses received by the mice were measured and the mean daily consumption of MC was reported for each group. The male mice received average daily doses of 60.55, 123.61, 177.45, or 234.29 mg/kg/day. The female mice received average daily doses of 59.46, 118.19, 172.41, or 237.76 mg/kg/day.

Food and water were provided to the animals ad libitum. Observation for mortality and signs of moribundity were performed twice daily for the first 52 weeks. All animals that were found moribund were killed. Body weights, clinical signs, and food consumption were measured weekly, while water consumption was measured twice weekly. All surviving animals were sacrificed after 104 weeks on the study. A complete necropsy was performed on every animal, whether found dead, sacrificed when moribund, or sacrificed at the end of the study. Histopathological examination of the livers, eyes and palpable or suspected neoplasms were performed on the low- and mid-dose groups. Animals in the control and high-dose groups received complete histopathological examinations.

For the female mice, the incidence of tumors (of any type) in the treatment groups was not significantly increased over the controls at any dose level. In male mice, the incidence of hemangioma of the liver and hepatocellular adenoma or carcinoma were significantly increased over the incidence in controls for the 185 mg/kg/day dose group only. Incidence in the high dose group for either response was not significantly different from controls.

Of the animal studies evaluated, the Crump report concludes that the NTP study provides the clearest evidence of the carcinogenicity of MC from both a toxicological and statistical standpoint. The report states that, in the NTP study, MC induced significant increases in benign mammary tumors in male and female rats and alveolar/bronchiolar and hepatocellular neoplasms in male and female mice. In contrast, the increases in the incidences of salivary gland sarcomas in rats and lymphosarcomas in hamsters observed in the Burek study were of questionable significance and the statistically significant responses observed in the Nitschke study were observed only at a mid-level dose group. No dose-related effect on the incidence of liver tumors in female mice or of lung tumors in either sex was observed in the NCA study. However, the highest dose tested in the NCA study was more than ten times less than that administered in the NTP study; therefore, the delivered dose to the tissue sites was lower. These lower doses administered in the drinking water may have been further reduced by biotransformation during first passage through the liver or elimination before reaching the target tissues, especially the lungs. Lower doses result in fewer tumors and lower statistical power of the study. In addition, the oral route of exposure in the NCA studies differs from the route of exposure typical to workers in the occupational setting.

The EPA, the CPSC and the FDA have also chosen the NTP study as the most appropriate data for their quantitative risk assessments because of the quality and clear positive responses observed in the bioassay. OSHA agrees with these reasonings and supports the use of the NTP bioassay for the best estimate of risk.

OSHA has also reviewed three human studies (Exs. 8-14c, 7-75, 4-33 and 7-163) which examined the possible relationship between MC exposure and cancer. Friedlander et al. studied mortality in the film coatings operations of a Kodak film plant using a cohort of 1,013 men employed in film coating operations at any time between January, 1964 and December, 1970 and who had at least one year of employment in that department. Cohort members were followed through 1988. The control groups were defined as the male population of New York State living outside New York City (NYS) and an industrial control group of 40,000 male employees (not employed in the roll coating division) of Kodak Park, Rochester, New York (KP). These groups were used to calculate expected numbers of deaths. A total of 55 malignant neoplasms were observed in the cohort versus 79 and 75 expected in the NYS and KP comparison groups, respectively. Eighteen lung cancers were observed whereas 25.6 (NYS) and 22.8 (KP) were expected; 18 digestive system neoplasms occurred (22.6 (NYS) and 21.7 (KP) expected) and 8 pancreatic cancers occurred (4.2 expected in both NYS and KP control groups). In previous analyses of this cohort, the authors stated that the observed pancreatic cancers were suggestive of an increase in malignancy, although the p value was not considered statistically significant for a non-hypothesized cause of death. However, in the latest update (Ex. 7-163), which followed the cohort through 1988, the incidence of pancreatic cancer no longer approached statistical significance when compared with control values (p = 0.13). The authors believe, and OSHA agrees, that this evidence does not indicate an association between pancreatic cancer and MC exposure. However, future updates of this cohort will be assessed for effects on the pancreas, as well as other organs.

Ott et al. (Ex. 4-33) identified a plant which had used MC as a solvent in the production of cellulose triacetate fibers since 1954 and a second plant that had similar production characteristics but did not use MC. The cohort studied consisted of employees who worked at least three months in the preparation or extrusion areas of either plant between 1954 and 1977. A total of 1271 MC-exposed and 948 control workers were identified. Follow-up extended through June 1977. Among the white male or female employees, 7 malignant neoplasms were observed in the exposed group (11.5 expected on the basis of U.S. national rates) and 7 were found in the control group (12.3 expected). There was no discussion by the authors of the types of malignancies observed and the associated expected numbers of such deaths, because of the small numbers of malignancies identified in this cohort. MC-exposed and control workers came into contact with acetone and had other minor chemical exposures.

An update of this study by Cohen et al. (Ex. 8-14c) extended the follow-up for this population through September 1986. Twenty-eight deaths from malignant neoplasms were observed versus 33 expected (US general population and York County, S.C. death rates were used as the comparison). The most significant results were the four deaths from liver/biliary cancers reported versus 0.53 and 0.86 cancers expected (US and York County statistics, respectively). Seven cancers were found in the digestive organs, versus 7.05 (US) and 6.76 (York County) expected. One cancer of the pancreas was reported compared to 1.4 (US) and 1.53 (York County) expected. In cancers of the respiratory system, 8 were found versus 9.56 and 10.37 expected (US, York County).

In addition, the National Paint and Coatings Association has submitted an epidemiological study by SRI (Ex. 10-29b) of 16,243 workers in paint and varnish manufacture. No statistically significant excess cause-specific mortality was identified in this cohort or the subcohort of 238 tub and tank cleaners presumed to have the highest MC exposures. There was no documentation of individual or job category exposure data, although typical exposure to MC was described as less than 100 ppm. In addition, workers in this study were exposed to multiple chemicals in the production of paint and varnish. Overall, because of the lack of exposure data and possible confounding exposures, this study had little power to identify an association between MC exposure and cause-specific mortality.

The Ott, Friedlander and NPCA studies have been interpreted as non-positive. However, the Cohen update is suggestive of a positive carcinogenic response to MC exposure. The data from the Cohen update and that from the Friedlander study can be used to derive upper confidence limits on human risk. The use of non-positive epidemiological studies is supported by the Office of Science Technology and Policy (OSTP) which states that "The lack of evidence of a hazard from an epidemiological investigation can also be useful in that within the scope of the study, a likely range can be determined for estimates of risk " (50 FR 10371). The EPA and K.S. Crump and Company also use this approach in their risk assessments. Therefore, since the use of these studies may provide additional information as to the range of possible human risk, OSHA feels it is reasonable and appropriate to include analysis of this type in the preliminary quantitative risk assessment.

D. Selection of Data Sets

Data sets from the animal studies selected in the Crump report (Ex. 12) for subsequent quantitative analysis are listed in table 7. These data sets represent positive responses observed in the various studies. From these studies, as stated previously, the NTP study was selected as the most appropriate study for quantitative analysis. From the NTP study certain data sets are considered more appropriate than others. For example, results from mouse alveolar/bronchiolar adenomas or carcinomas in male or female mice were chosen in the Crump report as the most appropriate data sets for the following reasons:

1. Alveolar/bronchiolar tissues appear to be more sensitive to the carcinogenic effects of MC than other mouse tissues;

2. Males and females show a consistent response, with females slightly more sensitive;

3. Mice have a relatively low background incidence of alveolar/bronchiolar neoplasms in either sex; and

4. The relevance of mouse liver tumors in assessing carcinogenic risk to humans has been questioned by some investigators.

The EPA, the CPSC and the FDA chose to use the data sets for combined responses of adenomas and carcinomas of the lung and liver. Specifically, the EPA placed emphasis on the experimental species and sex group showing the highest risk: lung/liver adenomas or carcinomas in female mice. The CPSC used mammary, lung and liver benign and malignant responses and averages male and female estimates and lung and liver estimates to derive combined response risk estimates. The FDA used benign and malignant responses of female mice. The Crump report noted that it may be reasonable to combine lung and liver responses to give an indication of MC's potency, due to the fact that metabolism of MC occurs by the same pathway in both lung and liver and thus results in the same ultimate metabolites. However, the report adds that since both tissues have different background responses, combining responses may tend to affect risk estimates. The results from combining responses are discussed later.

At this time OSHA believes it may be more appropriate to consider different tissue sites separately rather than combining them and to focus on alveolar/bronchiolar tumors, as this appears to be the more sensitive site.

The adenomas are included in the quantitative analysis because OSHA holds that the presence of benign tumors should be interpreted as representing a potentially carcinogenic response for this case. This belief is supported by the OSTP's views on chemical carcinogenesis (50 Fr 10371). They state that at certain tissue sites, such as the lung, most tumors diagnosed as benign really represent a stage in the progression to malignancy. Therefore, it is appropriate and sometimes necessary to combine certain benign tumors with malignant ones occurring in the same tissue and the same organ site. They also state that "the judgement of the pathologist as to whether the lesion is an adenoma or an adenocarcinoma is so subjective that it is essential they be combined for statistical purposes." (50 FR 10371). Additionally, the EPA, the CPSC and the FDA have also included benign responses in their assessments.

E. Statistical Methods and Predictions

1. Choice of Model

Because of the complexity of the carcinogenic process and the fact that so little is understood about the pathogenesis of cancer, there is uncertainty in describing the shape of the dose response curve for carcinogens when data from high doses are used to predict risk at low dose. In general, there are usually no data points in the low dose region to aid in defining the curve. Hence investigators often turn to mathematical models in an attempt to describe the relationship between dose and response at low doses.

There are several types of models generally employed, among which are the one-hit, probit, multi-hit, Weibull and multistage models. OSHA has consistently shown a preference for the multistage model of carcinogenesis. This model is based on the theory that carcinogens induce cancer through a series of stages. EPA, in its guidelines for carcinogen risk assessment (51 FR 33992), also stated a preference for the multistage model due to the fact that it incorporates the current scientific opinion on carcinogenesis. Specifically, for MC, the EPA and the CPSC used the multistage model in their quantitative risk assessments. EPA stated that, in addition to the biological plausibility of the multistage model, the preliminary mutagenic data support the use of a linear low dose model. The CPSC justified its use of the multistage model based on their observations that other models have shown no more than a 3-fold variation in risk estimates for MC and they provide little refinement in predicted risks compared to the multistage model. Likewise K.S. Crump and Company, in their risk assessment for OSHA, used an updated version of GLOBAL82, a computer program based on the multistage model, to produce risk estimates for cancer. Additional analyses of the use of other models and the incorporation of pharmacokinetic modeling and the effect on the predicted risk are discussed later.

2. Species to Species Extrapolation

Using animal data to estimate human risk requires extrapolation between species. The best agreement between observed and predicted human cancer risk is often obtained when experimental doses are scaled to " human equivalent doses " using either ppm in air, mg/kg/day or mg/m2/day (OSTP, 50 FR 10371). A ppm in air dosage scale is generally used when site-of-contact tumors are involved, which is not the case for MC. The lung in this case is not considered a site-of-contact tumor because it is believed that in the lung, as in the liver, carcinogenicity may be a result of metabolism of MC. For non-site-of-contact tumors there is no conclusive evidence as to whether it is more appropriate to use a body weight basis (mg/kg/day) or a surface area basis (mg/m2/day) to calculate dose equivalency. The dosage scale used will affect the magnitude of the projected risk. For example, calculating dose equivalency on a body weight basis rather than a surface area basis can reduce the estimated human risk by approximately 6-fold when rat data are used for modeling human response and up to 14-fold for mouse data.

The EPA chooses the more conservative basis for extrapolation, the relative surface area. Likewise, the CPSC uses the mg/m2/day due to the theoretical basis that chemicals are more slowly metabolized and eliminated on a weight basis in larger species. However, K.S. Crump and Company and the FDA use mg/kg/day dose equivalency in their risk assessments.

Based on the lack of information to support one dosage scale over another and the fact that OSHA has used the mg/kg/day in other risk assessments (i.e. ethylene oxide), OSHA has used the mg/kg/day dosage scale for MC.

3. Prediction of Risk

K.S. Crump and Company's predictions of risk for cancer, based on selected data sets from the NTP bioassay, are presented in table 8. The predictions of risk are based on a worker's lifetime exposure scenario of 8 hours per day, 5 days per week, 50 weeks per year for 1 and 45 years. Predictions of risk from the selected data sets are listed separately, and can be used to formulate a range of predicted risk. As shown in table 8, the multistage model predicts a lifetime excess risk MLE of cancer from occupational exposure to MC at the current PEL of 500 ppm as 33.2 per 1000 workers, based on the male mice lungs tumors. The female mice data predict an excess risk MLE of 45.5 per 1000 workers at 500 ppm for 45 years. OSHA has used these data to formulate a range of predicted excess risk of 33.2 to 45.5 per 1000 at 500 ppm for 45 years. The 95% upper confidence limits associated with the MLE's for this exposure level are 49.9 to 57.7 deaths per 1000 workers. Upper confidence limits are useful in assessing the amount of statistical variation found in the data being used for the quantitative risk assessment. The excess risk of cancer from an occupational exposure of 25 ppm ranges from 1.67 to 2.32 per 1000 workers with upper confidence limits of 2.56 to 2.97 per 1000 workers. A reduction in the PEL from 500 ppm to 25 ppm would constitute a 95% reduction in the estimated risk. Chi-squared goodness of fit test results are given in order to judge the fit of a given model to the data. The closer the p-value associated with a chi-square goodness of fit statistic is to one, the better the fit.

TABLE 8. - ESTIMATES OF EXTRA RISK PER 1000 WORKERS BASED ON INHALATION
          DATA SETS, BY INTENSITY AND DURATION OF EXPOSURE(1)
_____________________________________________________________________________
  | Methylene | MLE(3) years | 95% Upper limit
  | chloride | of exposure | years of exposure
  | concen- | ____________________ | __________________
Data set | tration |   |   |   |  
  | __________ | 1 | 45 | 1 | 45
  | (ppm) |   |   |   |  
_______________________ | __________ | _________ | _________ | __________ | _______
  | |   |   |   |  
NTP - Male Mice;(2) | 1 |   0.00149 |   0.0669 | 0.00228 |   0.109
Alveolar/Bronchiolar | 10 |   0.0149 |   0.669 | 0.0228 |   1.09
Adenoma or Carcinoma | 25 |   0.0372 |   1.67 | 0.0569 |   2.56
  | 50 |   0.0743 |   3.34 | 0.114 |   5.11
  | 100 |   0.149 |   6.68 | 0.228 | 10.2
  | 500 |   0.743 | 33.2 | 1.14 | 49.9
  | |   |   |   |  
NTP - Female Mice;(2) | 1 |   0.00207 |   0.0930 | 0.00264 |   0.119
Alveolar/Bronchiolar | 10 |   0.0207 |   0.930 | 0.0264 |   1.19
Adenoma or Carcinoma | 25 |   0.0517 |   2.32 | 0.0660 |   2.97
  | 50 |   0.103 |   4.64 | 0.132 |   5.92
  | 100 |   0.207 |   9.26 | 0.264 | 11.8
  | 500 |   1.03 | 45.5 | 1.21 | 57.7
________________________ | __________ | __________ | _________ | __________ | _______

(1) From multistage model. Extra risk [PE=(P(d)-P(o))/1-P(o)], Adjusted doses were used. (2) Chi square goodness of fit and associated p-value is .0001 and 1.00 respectively. (3) Maximum likelihood estimate. F. Other Models.

In addition to the multistage model, K.S. Crump and Company also implemented the multistage-Weibull time-to-tumor model to analyze the selected data sets. This extension of the multistage model estimates the probability of occurrence of a tumor by the time selected rather than the probability of death from tumor. The model was implemented by using the computer program WEIBULL82. In these analyses, tumors are assumed to be incidental and time is set equal to the length of the experiment.

Table 9 compares predicted average daily dose of MC which would give a fixed risk of 1 per 1000, based on the results of the multistage-Weibull time-to-tumor model and the multistage model. In each case, the estimates in the multistage-Weibull model are similar to those predicted by the multistage model, differing by less than an order of magnitude. The results derived from the multistage-Weibull model are not consistently lower than those from the multistage model, and in several cases, result in lower bound estimates of dose that are higher than the multistage model estimates.

TABLE 9 - ESTIMATES OF AVERAGE DAILY DOSES OF METHYLENE CHLORIDE
         (MG/KG/DAY) CORRESPONDING TO AN EXTRA RISK OF 10-(3) FOR
         INHALATION DATA SETS(a), BY MODEL
____________________________________________________________________________
  |  
  | Model
  | _____________________________________
  | Multistage | Multistage-
  | Model | Weibull(b)
Data set | _________________ | ________________
  | 95% |   | 95% |  
  | Lower | MLE | Lower | MLE
  | limit(c) |   | limit(c) |  
_____________________________________ | _________ | _______ | _________ | ______
  |   |   |   |  
NTP - Male Mice; Alveolar/ |   |   |   |  
Bronchiolar Carcinoma | 6.60 | 13.4 | 6.46 | 92.4
  |   |   |   |  
NTP - Female Mice; Alveolar/ |   |   |   |  
Bronchiolar Carcinoma | 4.41 | 14.7 | 4.97 | 10.3
  |   |   |   |  
NTP - Male Mice; Alveolar/Bronch- |   |   |   |  
iolar Adenoma or Carcinoma |   2.06 | 3.15 | 1.56 | 53.6
  |   |   |   |  
NTP - Female Mice; Alveolar/Bronch- |   |   |   |  
iolar Adenoma or Carcinoma | 1.77 | 2.26 | 1.31 | 11.1
  |   |   |   |  
NTP - Male Mice; Alveolar/Bronchiolar |   |   |   |  
or Hepatocellular Adenoma or |   |   |   |  
Carcinoma | 2.16 | 89.7 | 1.27 | 54.4
  |   |   |   |  
NTP - Female Mice; Alveolar/Bronch- |   |   |   |  
iolar or Hepatocellular Adenoma |   |   |   |  
or Carcinoma | 1.18 | 2.97 | 1.37 | 46.0
  |   |   |   |  
NTP - Male Rats; Mammary Adenoma or |   |   |   |  
Fibroadenoma | 13.1 | 154 | 5.95 | 119
  |   |   |   |  
NTP - Male Rats; Mammary or Subcutan- |   |   |   |  
eous Adenoma, Fibroadenoma |   |   |   |  
or Fibroma | 7.53 | 106 | 18.4 | 171
  |   |   |   |  
NTP - Female Rats; Mammary Adenoma |   |   |   |  
or Fibroadenoma | 3.66 | 5.95 | 2.29 | 4.05
_____________________________________ | _________ | _______ | _________ | _______

Data sets for alveolar/bronchiolar carcinoma in male and female mice, presented in Table 9, show the effect of combining benign and malignant tumors in the risk models. For alveolar/bronchiolar carcinomas and for alveolar/bronchiolar adenomas or carcinomas the average daily doses differ by less than an order of magnitude. Similarly, the estimates from combining alveolar/bronchiolar and hepatocellular adenomas or carcinomas differ little between models and data sets. Also shown are data sets for benign mammary neoplasms in male and female rats. The lower limits derived from the rat bioassay data are consistent with the range of lower limits estimated from the mouse data sets.

In general, estimates of risk from the Weibull time-to-tumor model agreed with those from the multistage model. Thus, the estimates from the multistage model generally represent the level of risk predicted by both models. The multistage model has an added advantage in that no assumption must be made as to whether tumors are incidental or fatal as is the case when using the time-to-tumor model with the NTP data, where no information on incidental or fatal tumor type was provided. Therefore, the multistage model is preferred for purposes of this risk assessment.

The predictions of risk for cancer based on the epidemiologic studies were estimated by K.S Crump and Company who used a relative risk model and a life table approach. It was assumed that the observed cancers in dose group i, 0i, were distributed as a Poisson random variable with mean Ei(1 + Bdi). Here Ei was the expected, background number of cancers and di was the cumulative exposure in group i. The potency parameter B and its 95% one-sided statistical confidence limits were estimated by likelihood methods. These parameters were used to estimate risk for different patterns of exposure. From the two occupational cohorts, in the Friedlander and Cohen studies, the 95% upper confidence limits on potency parameter estimates for lung cancers and total malignancies were all positive. Thus, despite the generally non-positive evidence provided by these studies, they were consistent with some positive effect of MC. In fact, the number of extra cancers expected from these upper bound estimates could be substantial. Using the Friedlander and Ott studies, in the case of total malignancies, for a 500 ppm exposure for 45 years, 241 to 334 extra cancer deaths per 1000 workers is estimated. Using the Friedlander study only, where data was included for lung cancer incidence, 179 extra lung cancers per 1000 workers exposed at 500 ppm over 45 years were estimated. It was estimated that 5 extra lung cancers would be expected per 1000 workers for a 25 ppm, 45 year occupational exposure to MC.

Thus, the epidemiological data were not inconsistent with the results from the bioassay analyses. This is true in the sense that the range of risks predicted on the basis of the epidemiology includes the risks extrapolated from the animal data. The animal results, specifically the lung and liver tumors, provided an estimate of the potency of MC for causing cancer and should not be understood to imply that lung and liver tumors are the only tumors that should be of concern in humans. Differences in metabolism, storage, and elimination between humans and rodents may entail different sites of action, but have no effect on the potency of the chemical. The direct human evidence is consistent with the potency estimates derived from the animal bioassay data.

G. Other Risk Assessments

The EPA Carcinogen Assessment Group (CAG) (Ex. 4-6) has presented a risk assessment for MC based on evidence from the NTP bioassays. CAG reported that the NTP study produced significant exposure-related increases in tumor incidences, with the strongest evidence of carcinogenicity provided by mammary and subcutaneous tumors in rats and lung and liver tumors in mice. Data on these endpoints were analyzed by fitting the multistage model with one less stage than the number of doses, and by fitting the time-to-tumor response model. Risk was measured by extra risk and doses expressed in terms of mg/body-surface-area/day were assumed to be equivalent across species. For purposes of comparison, EPA also fit four Weibull and probit models and two other configurations of the multistage model to the data. EPA has also recently modified its risk assessment to incorporate pharmacokinetic considerations. Their approach as well as their criticisms of the pharmacokinetic model will be discussed later.

EPA concluded that the multistage model provided an adequate fit, that for rats the largest upper confidence limit on risk was produced by the data for mammary tumors in females, and that for mice the largest confidence limit was for females with either adenomas or carcinomas of the lung and/or liver. The EPA pointed out that there was high mortality in the mouse and female rat high dose groups, which may have resulted in underestimation of risks. Male rats experienced high mortality in all dose groups. NTP reported that the high mortality might be due to the frequent occurrence of leukemia in all groups. The largest risks were estimated for the combined carcinomas and adenomas of the lung and/or liver in female mice, so these data received emphasis in the analyses.

To adjust the data for early mortality, EPA eliminated from the data all deaths before the first observed tumor (week 61 of the study) and refit the multistage model. This did not result in large changes in upper confidence limits on extra risk, but did, in some cases, have a great effect on maximum likelihood estimates (not an uncommon phenomenon).

In their time-to-tumor analysis, EPA made assumptions as to whether tumors were fatal or incidental. The NTP pathologists did not provide information on whether specific tumors caused death. EPA analyzed the data for both incidental and fatal tumors and compared the results of the two time-to-response analyses with the quantal analysis. The slopes for the confidence limits of the quantal multistage model were all between or near the slopes for the confidence limits of the time-to-response models, and the analysis assuming that the tumors were incidental produced higher slopes (and therefore risks) than the analysis assuming that the tumors were fatal.

Because time-to-response models have been less widely used, and because they require that assumptions be made as to the cause of death, EPA chose to use the quantal model for the final risk assessments.

EPA also fit the multistage model to data from the studies conducted by Burek, Nitshchke and the NCA and compared the resulting risk estimates to those derived using the NTP experiments. Similar tissue sites were used in both cases. Upper limits on risk were generally in the same range as those produced by the NTP study data.

To estimate human risks from the NTP animal data, EPA used upper confidence limits on risk for female mice lung or liver adenomas or carcinomas. Using this information EPA additionally applied correction factors to account for differences in surface area and to correct for differences in dosing regimens between species in order to convert animal doses to equivalent human doses.

Based upon the female mice data, EPA predicted the extra risk to a human exposed to 1 ppm continuously for a lifetime as 0.014 (14 excess cancer cases per 1000 exposed). In this case, lifetime cancer risk was calculated assuming humans are exposed continuously over the entire course of their life. It was also assumed that humans breathe 20 m3/day. This approach is similar to that taken by the CPSC but differs from OSHA's approach, in which cancer risk is calculated based on a working lifetime and an inhalation rate of 9.8 m3/8-hour workday.

Using the upper confidence limits from the NTP female mice (liver and lung tumors), EPA calculated that in the non-positive epidemiological studies by Friedlander (Ex. 4-30), MC would cause an expected excess of 2.8 to 11.3 deaths in a cohort of 252 exposed workers. According to the EPA, the power of the study to detect 2.8 excess deaths was only 7%, and to detect 11.3 excess deaths was 51%. The EPA concluded that this study did not have the power to rule out an overall cancer risk and therefore the non-positive result of this epidemiological study is not inconsistent with the positive result of the NTP animal bioassay. Hearne et al. (Ex. 4-96a), in response to EPA's analysis, calculated the upper confidence limits of risk for their cohort using improved MC exposure data and EPA's original risk assessment. Hearne et al. stated that the excess deaths expected in this cohort were 11 in the high exposure subcohort of 252 and 35 deaths in the total cohort. Because of differences in the statistical analyses and refinement of the exposure data, the authors have determined that their epidemiological data had 81% and 91% power to detect the lung and liver excess cancers predicted by the animal model.

Tollefson et al. (Ex. 7-249), from the FDA, also compared the cancer risks predicted from the NTP bioassay with the Hearne epidemiologic evidence. The risk assessments used for comparison were those performed by EPA and FDA. Tollefson et al. concluded that the power of the Hearne study to predict excess lung and liver cancer deaths for the most recent update of the study cohort were 50% for the EPA upper 95% confidence limit lifetime potency and 10% if FDA's lifetime potency value was used. These values correspond to a relative risk of 1.4 for the EPA assessment and 1.01 for the FDA assessment. Since OSHA's estimate of risk is most similar to that calculated by FDA, it is clear that the expected increase in mortality in the total cohort from lung and liver cancer was unlikely to be detected in the cohort described by Hearne. Tollefson went on to calculate the expected increase in mortality from lung and liver cancer in this cohort if they were followed until the entire cohort had died. The risk assessment produced by EPA would predict that there would be 35.5 excess cancer deaths, yielding a 95% power to detect the excess. The FDA risk assessment, however, would only predict 1.1 excess deaths from lung and liver cancer in this cohort, or 10% power to detect the excess.

The CPSC has also performed a MC risk assessment (Ex. 5-2). CPSC used the NTP bioassay as its choice for the data on which to base its risk estimates. As with the EPA, the CPSC has also recently incorporated pharmacokinetics into their risk assessment and this will be discussed later. The endpoints selected for the final analyses were rat mammary fibroadenomas, mouse hepatocellular and alveolar/bronchiolar carcinomas and mouse hepatocellular and alveolar/bronchiolar adenomas and carcinomas. Data on these endpoints were analyzed using a variety of models to produce maximum likelihood estimates and lower confidence limits for the dose corresponding to a risk of 1 x 10-5. In particular, the multistage model (with the number of stages not restricted by the number of doses), was selected over other models, maximum likelihood estimates were used rather than upper confidence limits and male and female estimates were averaged rather than using the more sensitive; in each case the choice was justified by pointing out that the alternative would change the estimates by a factor of only about 2.

To extrapolate estimated risks from rodents to humans, the risk estimates from the multistage model, based on rodent data were multiplied by two correction factors, (mg/kg/day of MC inhaled by humans * mg/kg/day of MC inhaled by rodents and (weight human/weight animal)1/3), to account for dose equivalency on a mg/m2-body-surface-area/ day basis. Values were further adjusted to correct for the proportion of lifetime exposed; 6 hours a day at 5 days a week for 24 months. Risks at the combined sites were estimated by adding the risk estimates calculated independently at the two sites.

The final estimates derived for lifetime human continuous inhaled concentrations, producing a risk of 10-5, based upon benign responses in rats, malignant responses in mice and malignant plus benign responses in mice were, respectively, 0.012 ppm, 0.0033 ppm and 0.0012 ppm. For a lifetime inhalation of 1 ppm, the estimated lifetime human carcinogenic risks are .830 per 1000, 3 per 1000, and 8.3 per 1000, respectively.

Similar to the EPA and the CPSC, the FDA also used the NTP bioassay to estimate risks (Ex. 6-1). However a straight line extrapolation method was used instead of more complex low-dose extrapolation models. To make direct comparisons between mice exposed to 2000 ppm MC by inhalation in the NTP study and potential human exposure at different exposure levels and time intervals, time weighted average air concentrations were calculated. These averages represent the concentration of MC that individuals are exposed to on a continuous daily basis. For a consumer with an assumed exposure of 50 ppm MC in air for 5 minutes per day, 7 days a week, FDA calculated a time weighted average exposure of 0.174 ppm. Using similar calculations the average exposure for hair care specialists was 1.74 ppm. For a mouse in the NTP study exposed to 2000 ppm for 6 hours a day, five days a week the time weighted average was 357 ppm.

FDA assumed a linear dose-response model from zero dose to the experimental level of 2000 ppm (357 ppm time weighted exposure). Extrapolating from the incidence of benign and malignant neoplasms in female mice exposed at 357 ppm to average human exposures of 0.174 ppm (for consumers) and 1.74 ppm (for hair care specialists), FDA estimated a lifetime cancer risk for consumers of 1 per 1000 to 0.1 per 1000 (depending on whether the animal-to-human dose comparison is based on mg/kg/day or ppm, respectively) and a lifetime cancer for hair care specialists of 10 per 1000 to 1 per 1000.

OSHA calculated risks employing the FDA approach for an industrial worker exposed 8 hours a day 5 days a week at OSHA's current PEL of 500 ppm. In this case the time weighted average for continuous exposure is 119 ppm. Using this value and extrapolating from the linear dose-response model results in a lifetime cancer risk ranging from 666 per 1000 to 66.6 per 1000 (based on mg/kg/day and ppm, respectively).

H. Pharmacokinetics

In the quantitative risk assessments previously described, the NTP bioassay was the primary study used to estimate the cancer risk for humans exposed to MC. The NTP bioassay provided data on statistically significant dose-response relationships which were deemed suitable for estimating human risks at expected human doses. In most cases an applied dose multistage procedure was used. However, OSHA has received several comments and studies which indicate that use of the applied dose risk assessment approach may be inappropriate because it does not account for the metabolic and pharmacokinetic differences between mice and humans (Exs. 8-14d, 8-16c, 8-16d, 8-16e, 8-30, 8-31, 8-32, 8-33, 10-6-A, 14a, 14b, 14c, 10-39). In particular, it has been hypothesized that the carcinogenicity of MC results from a metabolite produced by only one of the pathways that metabolizes MC, the glutathione-S-transferase (GST) pathway. Under this theory, the GST pathway, rather than the mixed function oxidase (MFO) pathway, is the carcinogenic pathway. Proponents of this theory also believe that the GST pathway is active only at high doses (greater than the saturation of the MFO pathway, approximately 500 ppm), and that the GST pathway is more active in mice than in humans. These comments and studies indicate that metabolism by the GST pathway, unlike metabolism by the MFO pathway, correlates well with observed lung and liver tumors in mice and that the carcinogenic response observed in mice does not occur in humans exposed at low doses. DOW Chemical Company and the European Council of Chemical Manufacturers' Federations (CEFIC) have been especially active in studying the metabolism of MC (Exs. 7-225, 8-14d, 8-32, 8-33, 14a, 14b, 14c).

The carcinogenic mechanism of action of MC has not been elucidated with anything approaching certainty. However, the evidence suggests that the GST pathway may have been the primary pathway which produced the observed carcinogenic response. OSHA also notes that, while the carcinogenic response in mice correlated with the dose of the parent compound (Ex. 7-8), the lack of reactivity of the parent compound and the lack of interspecies correlation of blood levels of MC and carcinogenic response (i.e., rat blood levels of MC are higher than mouse levels for equivalent doses, but mice are more susceptible to carcinogenic effects than rats), suggest that the parent compound did not have a primary role in carcinogenesis.

Some researchers have suggested that the potentially reactive metabolites of MC (produced by either metabolic pathway) are not long-lived enough to interact with DNA (Ex. 10-18). They suggest that MC may act by a non-genotoxic mechanism, such as cytotoxicity, to produce cancer in the mouse (Ex. 8-31). This hypothesis raises questions about the possibility of a threshold response (indicating that there is an exposure level below which MC would not act as a carcinogen) and regarding applicability of the NTP mouse data when assessing human cancer risk. OSHA feels that, although there is no conclusive proof regarding how MC causes cancer, there is suggestive evidence supporting the genotoxicity of MC.

OSHA does not discount the possibility that the parent compound or the products of the MFO metabolic pathway contribute to the carcinogenicity of MC. Also, it is possible that some MC metabolites may exert a genotoxic effect while the parent compound or other metabolites may act by other, non-genotoxic mechanisms which promote carcinogenicity. These possibilities raise questions as to the sensitivity of the pharmacokinetic models to the carcinogenic contributions of these factors.

Dow Chemical submitted documentation of a physiologically-based pharmacokinetic model (Exs. 8-14d and 10-6a), developed for MC by Reitz and Anderson, which described the rates of metabolism of the MFO and GST pathways and the levels of MC and its metabolites in various tissues of rats, mice, hamsters and humans. The model was presented as a basis for converting an applied (external) dose of MC to an internal dose of active metabolite in the lung and liver in various species under various MC exposure scenarios.

A series of differential equations was used to model the mass balance of MC and its metabolites in various physiologically defined compartments, including the lung, liver, richly perfused tissue, slowly perfused tissue, and fat. Metabolism via the MFO pathway was described by saturable Michaelis-Menton kinetics whereas GST metabolism was assumed to be first-order nonsaturable. The rate constants for the system of equations were estimated on the basis of measurement of partition coefficients, allometric approximations of physiological constants (e.g., lung weight), and estimated biochemical constants (e.g., Michaelis-Menton constants).

From the model's predictions, Reitz and Anderson concluded that the metabolites formed by the GST pathway were responsible for the lung and liver tumors observed in the NTP mouse bioassays. They based their conclusion on the observation that the model's predictions of the concentrations of MFO metabolites did not correlate with the mouse lung and liver tumor incidences observed in the NTP study, whereas the predicted GST metabolite concentrations in the lung and liver did correlate with the observed incidence of liver and lung tumors. That is, in bioassays, mice developed tumors at sites known to metabolize MC by the GST pathway at relatively high levels, whereas rats, which showed no evidence of lung or liver tumors, had low levels of GST activity in the lung and liver. However, this model cannot explain the increased incidence in mammary tumors observed in rats in the NTP study. Reitz and Anderson also suggested that the parent compound, MC, was not the carcinogenic agent because it is not sufficiently reactive and has not been shown to enhance mutagenicity in bacteria in the absence of GST enzymes. Thus, they concluded that the GST metabolites were most likely responsible for the observed carcinogenicity.

Reitz et al. (Ex. 7-225) have supported their model with measurements of the biochemical constants (Km and Vmax) in vitro for the GST and the MFO metabolic pathways using MC as a substrate. Enzyme activities were determined by measuring the conversion of 36Cl-labeled MC to water-soluble products. Biochemical constants were then compared across species (mouse, rat, hamster and human). In the liver, the MFO activity was highest in the hamster, followed by the mouse, human and rat. Human values were much more variable than those of the rodent species. Human Vmax for the liver MFO pathway ranged approximately an order of magnitude and human Km varied approximately three-fold. GST activity in liver was determined for mouse and human tissues only. Mouse liver had approximately 18-fold greater activity than human liver, but the human tissue had about a three-fold greater affinity (Km) for MC than the mouse.

In the lung, the activity of the MFO and GST enzymes was determined for a single substrate concentration. For the MFO pathway, mouse tissue had the highest activity, followed by hamster and rat. No MFO activity specific for MC was detected in the human lung tissue, although other MFO isozymes were demonstrated to be active in the tissue. For the GST pathway in lung, mouse tissue was the most active, followed by rat and human. No GST activity was detected in the hamster lung.

Reitz and Anderson stated that the model's predictions of the concentration of the GST metabolite in humans exposed to low doses of MC resulted in risks which were 140-170 fold lower than would be expected using EPA's applied dose risk assessment methods. Thus, Reitz and Anderson concluded that risk assessments which do not utilize pharmacokinetics may be subject to substantial error and may overestimate the risk in humans exposed to low concentrations of MC.

Metabolic studies submitted by CEFIC supported the conclusions of Reitz and Anderson. In one study (Ex. 8-32), the metabolism of MC was compared in vitro using rat, mouse and hamster lung and liver tissue as well as tissue from four human livers. The activity of the MFO pathway was determined by measuring the conversion of MC to carbon monoxide and the GST pathway activity was determined by measuring formaldehyde formation. In this study the most active tissue for metabolizing MC by the MFO pathway was the hamster liver, with similar rates observed in the mouse liver and lower rates observed in rat and human liver. In lung tissue, lower rates of MFO activity were observed for rat lung compared to rates in the mouse and hamster. Human lung tissue was not available so no results were presented for human lung. For the GST pathway, rates in the mouse liver were higher than in any other tissues. Low rates were observed in the mouse lung tissue but no activity was detected in either the hamster or human liver or the rat or hamster lung. GST activity in these tissues was further examined using 36Cl-labeled MC (Ex. 14b). In this in vitro study, GST activity was found in all tissue samples. Mice continued to show higher levels of activity but the human tissue also showed some low activity, whereas previously this activity had not been detected.

In a second metabolic study (Ex. 8-33) by CEFIC, the metabolism of MC was assessed in vivo using F344 rats and B6C3F1 mice, exposed by inhalation to 500, 1000, 2000 and 4000 ppm MC for 6 hours. From this study it was observed that the MFO pathway saturated at concentrations of 500 ppm or higher in both species, as measured by COHb levels. In rats, after saturation of the MFO pathway, there was a linear increase in the parent compound, MC, in the blood with corresponding increases in dose, indicating that little further metabolism of MC occurred by other pathways. However in mice, there was a non-linear relationship between dose increases and the level of MC in the blood after saturation of the MFO pathway, indicating that further metabolism might be occurring by another pathway. At high dose levels, the mouse also showed a 10-fold higher elimination rate of C02 than the rat. This finding was interpreted as further evidence that the GST pathway was more active in the mouse.

EPA has criticized (Ex. 7-128) the CEFIC metabolic studies (Exs. 8-32 and 8-33). Some of their criticisms addressed the methodologies used to detect MFO and GST activity in animals and in humans. In particular, the use of formaldehyde as a measure of GST activity was considered to be an insensitive measure of GST activity at low dose levels. The use of CO2 as a marker for GST activity was also considered inappropriate, due to the fact that the MFO pathway may also generate CO2. Furthermore, EPA noted that few samples of human liver tissue and no samples of lung tissue were available to estimate GST activity. In the case of human liver tissue, it was questioned if four samples from accident victims provided an adequate basis upon which to assess human enzyme activity in general. Generally, when human tissue is used for in vitro enzyme measurements, small numbers of samples are available, and the medical history of the donors and the state of the tissue at the time of death are unknown. These factors make it difficult to extrapolate data collected from human tissue in vitro to the general population in vivo. In the case of the lung, CEFIC has implied (Ex. 10-39) that enzyme activity would be very low in human tissue because the measured human liver tissue activity was low compared to mouse liver. Due to the fact that tissues may vary in enzymatic activity, it was questioned whether or not low liver activity would necessarily imply low lung activity.

In addition to metabolic studies of MC, CEFIC submitted studies concerning the cellular toxicity and genotoxicity of MC. In a ten-day inhalation toxicity study (Ex. 8-16c) CEFIC investigated the toxic effects of MC on mouse and rat lung and liver cells. After exposure to 2000 or 4000 ppm MC, the only toxic effect observed histologically was toxicity to the Clara cells of the mouse lung. Clara cells are believed by the authors to have a high potential for GST activity. It was concluded that the specific toxicity for Clara cells in the mouse, with no observed effect in the rat, suggested that there was a species difference in metabolic capacity. This interspecies difference in metabolic capacity, in turn, might account for the differences observed between species in tumor development. Clara cell toxicity was further examined in mice exposed to 4000 ppm MC 6 hours/day for 10 days (Ex. 14c). In the Clara cells, MFO enzymes were reduced by almost half; however, the GST enzymes were unaffected. This study supported an hypothesis generated by CEFIC (Ex. 8-16c) suggesting higher GST activity in these specialized cells, compared to GST activity in the whole lung. This higher activity in Clara cells may help to explain the lung tumor response observed in mice, which was higher than would be predicted on the basis of overall GST metabolism in the lung.

Other studies submitted by CEFIC suggested that MC induces carcinogenicity by a non-genotoxic mechanism, which most likely operates primarily at high doses. In a mouse micronucleus test (Ex. 8-30), mice exposed to single intragastric doses of MC did not show a significant increase in micronuclei in their erythrocytes. Micronuclei are formed as a result of chromosomal damage induced by test compounds and are easily measured in erythrocytes. In this test, since no significant increases in micronuclei were detected, the authors concluded that MC was not genotoxic to the mouse.

This study has been criticized because the micronucleus tests for genotoxicity require the reactive metabolites of MC to be produced in bone marrow or to be stable enough to reach the bone marrow. There is no evidence at this time that MC metabolites produced in the liver or other organ sites are stable enough to reach the bone marrow or that the bone marrow has any metabolic capability for MC. Also, bone marrow has not been described as a target for MC toxicity.

In another study to test for genotoxicity, CEFIC examined the in vivo interaction of MC and its metabolites with rat and mouse lung and liver DNA after inhalation exposure to 4000 ppm 14C-MC (Ex. 8-16d). In this experiment, no MC-induced DNA adducts were detected after MC exposure and it was concluded by the authors that MC or its metabolites did not react with the DNA and, therefore, MC was not genotoxic.

The detection limits of these experiments to determine whether MC caused DNA adducts (DNA alkylation) were questioned by the EPA. When the negative DNA adduct data was presented, the investigators' data did not show the detection of 5-methylcytosine (a normal minor base in DNA which comprises approximately 3% of the cytosines). This base is not a DNA adduct, but is labeled by 14C-formate in the protocol used in this experiment and should have been easily detected. The concentration of DNA adducts from exposure to a potent DNA-adduct forming chemical would be expected to be much lower than 3% (the concentration of 5-methylcytosine in untreated DNA). Since apparently no 5-methylcytosine was detected by the methods described in this experiment, there is doubt as to the sensitivity of the assay for detecting DNA adducts produced by a genotoxic compound, particularly a weakly genotoxic compound. In a related issue, no in vivo positive control for DNA-adduct formation was included in the protocol. This positive control is important to determine the levels at which DNA adducts can be detected, and to ensure that the assay is working properly. A further criticism of this experimental protocol was that the dose used (4000 ppm) was too low to detect short-term DNA adduct formation. (4000 ppm was the highest dose used by the NTP chronic bioassay and was designed to elicit minimal toxicity over a 2-year exposure period. This dose would be too low for the purpose of detecting short-term genotoxic effects.)

To further test for genotoxicity, CEFIC conducted an in vivo and in vitro study to determine if MC induced unscheduled DNA synthesis (UDS) (Ex.8-16e). UDS is an indication of DNA replication and repair in response to chromosomal damage. In the in vivo study, mice and rats were exposed by inhalation to 2000 or 4000 ppm, for 2 or 6 hours. In the in vitro study, isolated hepatocytes of rats and mice were exposed to 500, 1000, 2000, and 4000 ppm of gaseous MC for 8 hours. No UDS was detected in either species, in either study, indicating that no detectable DNA damage occurred using these protocols.

Studies of UDS in vivo are of questionable value because these protocols are primarily used when extra-hepatic metabolism of MC is suspected. The MC metabolites (produced in a site outside the liver) then must be stable enough to reach the liver and interact with liver DNA in order to be measured as in vivo UDS in this assay. There is currently no evidence that metabolites of MC are produced in large enough quantities at extra hepatic sites or that the metabolites are stable enough to be transported from the site of metabolism to the liver to attack DNA. Negative responses in the two assays described above do little to confir action for MC and limit the usefulness of this data in the interpretation of the genotoxicity of MC.

As with the DNA alkylation study discussed above, the doses used here in the in vitro and in vivo genotoxicity studies were too low for researchers to be confident of detecting measurable effects. In order to accurately characterize the genotoxic potential of MC, these studies would need to be repeated at higher doses.

In order to determine if a non-genotoxic mechanism, such as increased cell turnover, was responsible for the carcinogenicity observed in mouse bioassays, CEFIC exposed mice by inhalation to 4000 ppm MC and then examined the mice for increased scheduled DNA synthesis (Ex. 8-31). Scheduled DNA synthesis represents cell replication, and not DNA repair. Chemicals which are cytotoxic at high doses may induce increased cell division and thus enhance the background levels of tumors. In the case of mouse hepatocarcinogenicity, such a cell division increase can be measured by an increased incidence of S-phase hepatocytes. In this study a statistically significant but small increase in S-phase hepatocytes was observed. It was concluded that this response suggested only a tentative correlation between increased cell proliferation and hepatocarcinogenicity in the mouse.

In this study, as in those cited above, the dose used was the same as the highest dose from the NTP chronic bioassay. In order to determine if MC increases cell turnover and acts as a non-genotoxic carcinogen, it would be necessary to repeat the short-term experiments with higher doses of MC, or to examine the effects of chronic administration of lower doses of MC on cell replication.

OSHA has determined that the information from the CEFIC studies is insufficient to conclude that MC is non-genotoxic. For example, the negative responses from the mouse micronucleus (Ex. 8-30), UDS (Ex. 8-16e) and DNA interaction tests (Ex. 8-16d), which were interpreted as evidence that MC is non-genotoxic, might also be interpreted as evidence that MC is a weak mutagen (e.g., a weak mutagen might evoke a response below the level of detection of the assay). Also, the S-phase hepatocyte study (Ex. 8-31), conducted to determine the possibility of cytotoxicity rather than genotoxicity as a cause of carcinogenic response, showed a small positive response, but the response was interpreted by the authors as unclear evidence of cytotoxicity. Therefore, OSHA continues to seek evidence regarding the extent to which MC acts by a genotoxic mechanism during carcinogenesis.

In general, although pharmacokinetic models, when properly defined, can be used to estimate the internal doses for various chemicals in various organs, they do not provide information on (1) which chemical or metabolite is the carcinogen, (2) the differences in sensitivities of target tissues to concentrations of chemicals or (3) whether the site of carcinogenic response is the same from one species to the next.

In addition, methods have not been developed for quantifying the uncertainty of the internal dose estimates. Potentially quantifiable uncertainty in any pharmacokinetic model arises from two major sources of statistical variability: inherent biological variability between members of the same species; and experimental error in estimating average values for model parameters (due to technological limitations and to sampling error in those quantities which have appreciable biological variability). Physiological parameters (such as ventilation rates and organ and body weights) may be expected to evidence considerable variability, which may cause large variations in internal doses within members of a single species. Biochemical parameters (such as metabolic parameters and partition coefficients representing the relative affinities of the chemical for air, blood, and various organ tissues) may be subject to less inherent variability, but these must be estimated (sometimes indirectly) from experimental data.

In the specific case of MC, the model developed by Reitz and Anderson, appears to provide a plausible description of the absorption, distribution and elimination of MC. However, the model's description applies only to the lung and liver. In rats, an excess of mammary tumors was observed that was not explained by the Reitz and Andersen model. In humans, other sites may metabolize MC and be vulnerable to the toxic or carcinogenic effects of MC.

In the preliminary draft of its Update to the HAD for MC (Ex. 7-128), EPA has also made a number of criticisms specific to the pharmacokinetic model developed by Reitz and Anderson. This draft document has been approved by the Scientific Advisory Board (SAB) and the risk estimates based on this document have been accepted by the Carcinogen Risk Assessment Verification Endeavor (CRAVE) for inclusion in the Integrated Risk Information System as the official interim stance of the EPA concerning MC. The citation in the IRIS data base contains a note explaining that the risk estimate comes from a draft document which has been approved by the SAB and the CRAVE. Criticisms contained in this document primarily come from critical analyses performed by the Hazard/Risk Assessment Committee of the Integrated Chlorinated Solvents Project. This committee, chaired by EPA and comprised of representatives from CPSC, FDA, and OSHA, has been reviewing and evaluating the models and metabolic studies in order to determine their use/effect in estimating risk to humans.

Overall the model structure was considered by EPA to be a plausible description of MC metabolism. The major uncertainties were felt to be chiefly from the input data for the model, some of which might contribute a source of error that might influence the calculation of internal doses of GST metabolites. For example, EPA observed that the model does not take into account the fact that MC may become sequestered in the lipid rich regions of various tissues. Over time the sequestering into the lipid areas could affect the disposition and metabolism of MC. Such an effect, unless taken into account, could alter the model's ability to correctly predict the GST metabolite concentrations. Also it was noted that the tissue/air partition coefficients input for the model were measured using homogenized tissue rather than intact tissue. In homogenizing tissues, the structure of the tissue is destroyed and thus the tissues may not adequately portray the processes occurring in vivo that determine partitioning. With regard to breathing rate input data, EPA observed that the authors of the model used a higher breathing rate for mice and a lower breathing rate for humans than those standardly employed by EPA. In particular Reitz and Andersen's model used breathing rates for humans at rest. This value may not accurately reflect the rate at which humans may breathe MC in the occupational setting. EPA, in its analysis of the pharmacokinetic data, used an average daily breathing rate of 20 m3/24 hour day (as compared with OSHA's estimated breathing rate of 9.8 m3/8 hour workshift of exposure). Choice of breathing rate would, in turn, alter the model's prediction of GST metabolites in humans after MC exposures (i.e., humans exposed to MC during physical exertion would take in more MC than a sedentary individual exposed to the same MC concentration).

EPA also pointed out that the metabolic rates for each pathway were calculated by mathematical optimization rather than by experimentation. By this process values were selected which optimized the model's ability to predict the loss of MC from a closed inhalation chamber as the compound was inhaled and metabolized by animals. EPA noted that many alternative metabolic rates could be used to optimize the experimental data. Some of these alternate rates could change the model's prediction of internal dose. Furthermore, in order to calculate the relative amount of activity of each pathway in the liver and the lung, surrogate substrates were used in place of MC. EPA feels that this may be an inappropriate method because the enzyme activity not only varies from species to species but also from tissue to tissue, such that each tissue may have its own array of enzymes. These surrogates may not be an appropriate measure of these pathways' activities for MC.

Despite the above-noted uncertainties, EPA has concluded that the Reitz and Anderson model is a reasonable method for describing and predicting the disposition of MC and its metabolites in human tissues. As the model is further refined, these uncertainties may be reduced. However, even with refinement of the pharmacokinetic model a major question remains: What is the appropriate way to use internal doses calculated from the model to estimate the risk to humans?

In the draft Update of its HAD (Ex. 7-129), EPA proposed a method to incorporate the pharmacokinetic model to develop estimates of risk. In this approach the pharmacokinetic model was used to estimate the internal dose in mice at exposure levels tested in the NTP bioassay. Using these doses and the tumor responses in the NTP bioassay, a dose-response curve was constructed using the multistage procedure. Liver data were fitted by a two stage model and lung data were fitted by a one stage model. Next the pharmacokinetic model was used to calculate the internal dose of GST metabolite in human liver and lung.

These doses were then scaled by the surface area correction factor and from these corrected doses the risks were calculated according to the dose-response curve. EPA felt that the surface area correction factor should continue to be applied to internal doses in the same manner as it has been used with applied doses. This is based on EPA's belief that, as reflected in its previous risk assessments, the surface area correction factor was applied to correct for metabolic differences between species and to correct for the differences in a chemical's potency between species. Differences in potency reflect many factors in addition to metabolism (e.g., differences in responsiveness to a given internal dose, number of cells exposed, immunosurveillance, DNA repair capability, species longevity, and basal cell division rate). EPA has indicated that, because one cannot determine the magnitude of the effect that any one factor may have on species sensitivity, that Agency would continue to apply a surface area correction factor on dose.

Using the procedure outlined above, EPA calculated a revised lifetime risk estimate of 0.47 per million for a continuous exposure to 1 ug/m3. This constitutes an approximate nine-fold reduction from its previous lifetime risk estimate of 4.1 per million in which applied doses were used.

EPA calculated its risk estimates based on continuous lifetime exposure to extremely low ambient concentrations of MC (1 ug/m3 = 0.000288 ppm) compared to OSHA's risks calculated at occupational exposures of 25 ppm (= 86,750 ug/m3). The risk assessment developed by OSHA, which was based on applied dose methods, was extrapolated from the calculated occupational risks at 25 ppm to lifetime continuous exposure at 1 ug/m3, so that the OSHA numbers were comparable to those produced in the EPA assessment. OSHA's assessment predicted a risk of 0.18 per million after lifetime continuous exposure to 1 ug/m3. This value is close to that calculated by EPA after incorporation of the pharmacokinetic data and is 23-fold lower than the EPA applied dose estimate.

Based on these estimates, EPA noted that "In view of the uncertainties involved, the changes in DCM's carcinogenic potency that results from different uses of the available pharmacokinetic information are not, in practical terms, very distinct" (Ex. 7-128). OSHA notes that EPA has a mandate to protect the general public from low level environmental hazards, which enables that Agency to regulate hazards when the population risk is 1 per million to 1 per ten thousand. In this case, EPA's incorporation of pharmacokinetics was not a critical factor in that Agency's decision regarding the regulation of MC. On the other hand, as discussed above, OSHA's mandate to regulate MC hinges on the determination that the population risk for occupational exposure at a particular exposure level is approximately 1 per thousand or greater. Accordingly, considering the risk numbers which OSHA generated using the applied dose multistage procedure, any change in the risk estimates prompted, for example, by the incorporation of pharmacokinetic data, will directly impact OSHA's decision regarding permissible exposure limits for MC. For this reason, OSHA believes it is necessary to carefully evaluate the pharmacokinetic and mechanistic data and assess the impacts of the uncertainties in the pharmacokinetic data before incorporating that data into its risk assessment for MC.

The CPSC has incorporated pharmacokinetics to update its previous risk estimates by a different method than used by the EPA (Ex. 7-126). The CPSC felt that it was premature to extrapolate from species to species based on pharmacokinetic information and therefore the pharmacokinetic information was used to extrapolate only from high to low doses within each species. As a first step the animal doses tested in the NTP bioassay were corrected by a surface area correction factor. These doses were modified by dividing the doses by a high-to-low dose extrapolation factor derived from output from the pharmacokinetic model. This factor is used to describe the nonlinear aspect of the dose-response curve associated with the metabolism of MC. These modified doses and the tumor responses from the NTP bioassay were put into the multistage model to construct the dose-response curve. The human doses were corrected by the same high-to-low dose correction factor and were then used to calculate risks according to the dose-response curve. CPSC calculated a maximum likelihood estimate (MLE) lifetime risk of 2.3 per thousand for continuous exposure to 1 mg/kg/day based on carcinomas alone and a lifetime risk of 5.2 per thousand per mg/kg/day based on carcinomas and adenomas. (As in its previous risk assessment, estimates for male and female mice were averaged for the lung and liver separately and then the lung and liver estimates were added together). This represents approximately a factor of two reduction from CPSC's applied dose risk estimates.

In a preliminary investigation, K.S. Crump and Company have also compared the difference between applied and internal dose risk estimates (Ex. 7-127). Using Reitz and Anderson's pharmacokinetic model, Crump and Company calculated human risk estimates for the same data sets analyzed previously in their quantitative risk assessment using external doses. Data sets were analyzed using a one-hit model, with parameters estimated from the experimental tumor data, and the internal doses derived from the pharmacokinetic model. Internal doses were expressed as either the concentration of MC in target tissue, the concentration of MC in arterial blood or the concentration of GST metabolite in target tissue. For a given data set the risk estimates were similar for each measure of internal and external adjusted dose. For example, at an exposure of 500 ppm, the 95% upper limit of human risk based on female mouse lung adenomas or carcinomas and the GST metabolite was 9.12 per thousand. This represents an approximate six-fold reduction from the 95% upper limit on human risk estimated previously without pharmacokinetic data (57.7 per thousand). For the same data set, an estimate of extra risk corresponding to an occupational exposure of 1 ppm was 10.8 per million compared to an extra risk of 119 per million without pharmacokinetic data, an approximate eleven-fold reduction. The differences in reduction of risk at high and low doses of MC reflect the nonlinearity of the pharmacokinetic model for MC.

Two additional risk assessments incorporating pharmacokinetics have been submitted by Reitz et al. (Ex. 7-225) and ECETOC (Ex. 10-39). Reitz et al. used the Reitz and Anderson pharmacokinetic model and internal doses were calculated from the model in a manner similar to that described by EPA, except that no surface area corrections were made to internal doses. Species were assumed to be equally sensitive to equal internal doses of GST metabolites. The internal doses were calculated for female mice at exposure levels tested in the NTP bioassay and these doses were used in four different dose-response models: the linearized multistage, the Probit, the Weibull and the Logit. The authors reported that each model fit the data equally well. However, the predicted upper bound risk estimates differed by 5 to 15 orders of magnitude. Based on female mouse lung adenomas and carcinomas the multistage model estimated a lifetime unit risk of 0.037 per million for continuous exposure to 1 ug/m3 which is two orders of magnitude lower than the unit risk of 4.1 per million calculated by EPA without pharmacokinetics and one order of magnitude lower than the unit risk of 0.47 per million calculated by EPA using pharmacokinetics. For an occupational dose of 50 ppm the multistage model predicted an upper bound risk of lung tumor of 14 per million. This value is approximately two orders of magnitude lower than the upper bound risk estimate of 592 per million calculated by Crump without the use of pharmacokinetics.

ECETOC, using data obtained through the CEFIC/ECETOC research program, modified the pharmacokinetic model developed by Reitz and Anderson and used the internal doses calculated from this modified model to conduct their risk assessment. Internal doses were calculated for the GST metabolite for female mice at exposure levels tested in the NTP bioassay. These doses and the corresponding observed tumor incidences were used in three different dose-response extrapolation models: the multistage, "one-hit" and Weibull. The modified pharmacokinetic model was also used to calculate human internal doses of GST metabolites. These doses were adjusted to a lifetime average daily dose and run in the risk models. The authors stated that the one-hit model provided a poor fit to the data and thus did not report those results. For both the quadratic multistage and Weibull models, the risks were calculated for both the lung and the liver and also for both organs combined. From the multistage model, at 10 ppm, the MLE of risk for lung tumor was 0.00612 per million. This value was approximately five orders of magnitude lower than the MLE risk estimate of 934 per million calculated by Crump without the use of pharmacokinetics and four orders of magnitude lower than the MLE risk of 109 per million calculated by Crump using pharmacokinetics. At 500 ppm the MLE risk estimate for lung tumors from the multistage model was 17.5 per million. This value was three orders of magnitude lower than the MLE risks calculated by Crump at 500 ppm without pharmacokinetics (45.5 per thousand), and two orders of magnitude lower than the risk estimates using pharmacokinetics, 7.3 per thousand.

The above risk assessments indicate that the incorporation of information from the pharmacokinetic model for MC can reduce previous risk estimates derived using applied dose methods. In some cases the risk estimates were reduced by a factor of two while in other cases there was up to five orders of magnitude difference. The larger differences generally occurred in those cases in which internal doses predicted from the pharmacokinetic model were used in quantitative risk models without any corrections for differences in species sensitivity (e.g. a surface area correction factor).

At this time, OSHA feels that use of pharmacokinetic parameters to adjust internal dose of MC may be premature. The primary reason for this is that a major assumption must be made that the GST pathway is the only carcinogenic pathway, and that there is no contribution to the carcinogenic process by metabolites from other pathways or by the parent compound itself. If it is determined that MC or MC metabolites from the MFO pathway contribute to the carcinogenicity of MC, the pharmacokinetic model would not provide an accurate estimate of risk.

Another disadvantage of the model is that it does not account for the possibility of MC metabolism or carcinogenesis at sites other than the lung or liver. In order to account for species differences in potency, CPSC has limited its use of pharmacokinetics to high-to-low dose extrapolation within species whereas EPA corrected internal doses by a surface area correction factor to extrapolate both from high to low doses and from species to species. These reduced risk estimates are a result of incorporating pharmacokinetic information specific to the lung and liver. The model does not provide information for other potentially active sites in the body (for example, it does not address the excess tumors identified in the mammary glands of rats exposed to MC). Because metabolic activity may vary from tissue to tissue within a species and also because one cannot be sure whether the site of carcinogenic response is the same from one species to the next, it may not be appropriate to base reductions in risk estimates solely on pharmacokinetic information from two tissues.

The pharmacokinetic model also has little ability to differentiate differences in tissue sensitivity between species to a given dose of MC. The EPA and the CPSC have used correction factors based on body weight or surface area in part to account for these differences. OSHA agrees with the application of these correction factors in cases where pharmacokinetic data is used. If analysis of the evidence collected in the record indicates that pharmacokinetic data should be used to adjust the internal MC dose for use in occupational risk estimates, OSHA feels these correction factors should continue to be applied.

Other uncertainties surrounding pharmacokinetic models and their use for risk assessment are the validity of using data extrapolated from human and animal tissue in vitro to predict human risk during occupational exposures, and the validity of estimated pharmacokinetic parameters, such as partition coefficients in the model.

At this time, OSHA feels it is most prudent to continue to use the applied dose methods in its assessment of risk. Serious consideration is being given to pharmacokinetics and OSHA invites comment (see Issue 6 for specific questions) on the appropriateness of the pharmacokinetic data for assessment of occupational exposures, on the choice of risk model and how the risk model is affected by pharmacokinetic data, and on the sensitivity of the pharmacokinetic model parameters to errors or refinements in their estimation. OSHA will evaluate the utility of pharmacokinetic models to predict human risk from occupational exposure to MC and consider the uncertainties associated with these models during the rulemaking process.

I. Conclusions

Based on its evaluation of the studies and its review of quantitative risk assessments performed outside the Agency, OSHA believes that there is an excess risk of cancer death from exposure to MC. OSHA endorses K.S. Crump and Company's approach to the MC quantitative risk assessment, and concludes that risk estimates based on the NTP mouse lung tumor data will be used in making the preliminary determination of risk.

OSHA believes that the multistage model, at this time, is the most appropriate model for the prediction of excess risk from exposure to MC. The curve shows good fit to the observed data and was employed in almost all quantitative risk assessments submitted to the record.

OSHA also believes that, despite the fact that the some of the epidemiological data has been interpreted as non-positive, the human studies can be used to calculate upper confidence limits on human risk. These upper limits demonstrate the reasonableness of the animal data, insofar as the risk estimates derived from the animal data are within the range of the estimates based on the epidemiological data.

Although the metabolism of MC has been extensively studied and plausible models of the mechanism of action of MC have been generated, there is still substantial uncertainty as to the carcinogenic mechanism of action of MC. The uncertainty surrounding the possible contributions of the parent compound or metabolites from the MFO pathway to the carcinogenic process remains the single most critical factor for validating the usefulness of the pharmacokinetic modeling approach. Other areas of uncertainty include the organ specificity of the model (excluding the possibility of metabolism or carcinogenesis at sites other than the lung or liver) and the extrapolation of human enzyme activity from in vitro data.

The quantitative risk assessment produced using the NTP bioassay is intended to assess some measure of the carcinogenic potency of MC. It is not designed for or limited to the identification of a specific target site in humans. The pharmacokinetic and metabolic studies to date have concentrated on specific sites such as the liver and lung tissue and have not examined other tissues. From this approach it is not clear that the risk of cancer at sites other than the liver and the lung can be excluded. Due to the limitations of the model described above and the associated uncertainties, OSHA does not feel that it is appropriate at this time to incorporate the pharmacokinetic model, as submitted, into its preliminary quantitative risk assessment for MC.

Thus, at this time, OSHA concludes that the lifetime estimate of risk from exposure to MC at the current 8-hour TWA of 500 ppm is 33 to 45 excess deaths per thousand (95% confidence limits of 50 to 58 excess deaths per thousand). Such risks warrant OSHA regulatory action to reduce occupational exposure to MC.

In determining the level to which the permissible exposure limit should be lowered, several alternative 8-hour TWA's (100, 50, 25, 10, and 1) were considered by the Agency, as shown in Table 10. OSHA believes that compliance with the proposed 25 ppm TWA is technologically and economically feasible based on the Agency's knowledge of available control technology and on the Agency's awareness that several industries or industry segments are presently controlling exposures to or very near this level. OSHA's preliminary analysis of technological and economic feasibility of the proposal is discussed in the following section of the preamble.

TABLE 10. - ESTIMATES OF EXCESS CANCER DEATHS PER 1000
WORKERS EXPOSED TO METHYLENE CHLORIDE*
_________________________________________________________
  |   |  
  |   |  
Exposure (ppm) | Excess Cancer | Cancer Death
  | deaths | reduction
_______________ | ____________________ | _______________
500 | 33.2-45.5 |  
100 | 6.68-9.26 | 79%
50 | 3.34-4.64 | 90%
25 | 1.67-2.32 | 95%
10 | 0.67-0.93 | 98%
1 | 0.067-0.093 | 99%
__________________ | ____________________ | ________________
* Occupational Exposures of 45 years without consideration
of Pharmacokinetic data in risk estimates.

IX. Significance of Risk

In the 1980 benzene decision, the Supreme Court, in its discussion of the level of risk that Congress authorized OSHA to regulate, indicated when a reasonable person might consider the risk significant and take steps to decrease or eliminate it. The Court stated:

It is the Agency's responsibility to determine in the first instance what it considers to be a "significant" risk. Some risks are plainly acceptable and others are plainly unacceptable. If for example, the odds are one in a billion that a person will die from cancer by taking a drink of chlorinated water, the risk clearly could not be considered significant. On the other hand, if the odds are one in a thousand that regular inhalation of gasoline vapors that are 2 percent benzene will be fatal, a reasonable person might well consider the risk significant and take the appropriate steps to decrease or eliminate it. (I.U.D. v. A.P.I., 448 U.S. 607, 655).

The Court further stated that "while the Agency must support its findings that a certain level of risk exists with substantial evidence, we recognize that its determination that a particular level of risk is significant will be based largely on policy considerations." The Court added that the significant risk determination required by the OSH Act is "not a mathematical straightjacket," and that "OSHA is not required to support its findings with anything approaching scientific certainty." The Court ruled that "a reviewing court [is] to give OSHA some leeway where its findings must be made on the frontiers of scientific knowledge [and that] *** the Agency is free to use conservative assumptions in interpreting the data with respect to carcinogens, risking error on the side of overprotection rather than underprotection" (448 U.S. at 655, 656).

OSHA's overall analytic approach to regulating occupational exposure to particular substances is a four-step process consistent with recent court interpretations of the OSH Act, such as the benzene decision, and rational, objective policy formulation. In the first step, OSHA quantifies the pertinent health risks, to the extent possible, performing quantitative risk assessments. The Agency considers a number of factors to determine whether the substance to be regulated poses a significant risk to workers. These factors include the type of risk presented, the quality of the underlying data, the reasonableness of the risk assessment, the statistical significance of the findings and the significance of risk [48 FR 1864, January 14, 1983]. In the second step, OSHA considers which, if any, of the regulatory provisions being considered will substantially reduce the identified risks. In the third step, OSHA looks at the best available data to set permissible exposure limits that, to the extent possible, both protect employees from significant risks and are technologically and economically feasible. In the fourth and final step, OSHA considers the most cost-effective way to fulfill its statutory mandate.

The current OSHA standard for MC was designed to prevent irritation and injury to the neurological system of the employees exposed to MC. In 1985, the National Toxicology Program (NTP) released the results of their MC rodent lifetime bioassays. Those results indicated that MC is carcinogenic to rats and mice. As discussed in the Events Leading to the Proposed Standard section, based on the NTP findings, EPA now considers MC a probable human carcinogen, and NIOSH regards MC as a potential occupational carcinogen and recommends controlling the exposure to MC to the lowest feasible level. In 1988, ACGIH classified MC as an industrial substance suspected of carcinogenic potential for man. As discussed in the Health Effects section, OSHA has determined, based on the NTP data, that MC is a potential occupational carcinogen. Having determined, as discussed in the Preliminary Quantitative Risk Assessment section, that the NTP study provided suitable data for quantitative analysis, OSHA performed quantitative risk assessments to determine if MC presents a significant risk at the current PELs.

OSHA prefers to use the multistage model of carcinogenesis in quantitative risk assessment. The multistage model is a mechanistic model based on the biological assumption that cancer is induced by carcinogens through a series of stages. The model generally is considered conservative, in the sense that it risks error on the side of overprotection rather than underprotection, because it assumes no threshold for carcinogenesis and because it is approximately linear at low doses. The Agency believes that this model conforms most closely to what we know of the etiology of cancer. OSHA believes that the use of such a model is prudent public health practice. OSHA's preference is consistent with the position of the Office of Science and Technology Policy which recommends that "when data and information are limited, and when much uncertainty exists regarding the mechanisms of carcinogenic action, models or procedures that incorporate low-dose linearity are preferred when compatible with limited information (Ex. 7-227).

Several comments and studies, submitted to OSHA have suggested that the current applied dose approach for risk assessment should be replaced by assessments using the delivered dose of MC (Exs. 8-14d, 8-16c, 8-16d, 8-16e, 8-30, 8-31, 8-32, 8,33, 10-6-A, 14a, 14b, 14c, 10-39). The delivered dose is described by pharmacokinetic models of MC fate and metabolism, which may account for metabolic and pharmacokinetic differences between rodents and humans. While OSHA is interested in receiving and evaluating risk assessments produced using pharmacokinetic models, serious questions remain concerning the application of these models in the risk assessments prepared by OSHA. Specifically, the Agency is concerned that the pharmacokinetic model 1) assumes that the only carcinogenic metabolite is produced by the GST pathway; 2) relies on in vitro data to supply many of the biochemical constants; 3) extrapolates from a very small database of human metabolic data (especially for the lung); and 4) assumes that the lung and liver are the only target sites for carcinogenesis across all species. The Agency notes that the NTP and the Chemical Industry Institute of Toxicology are continuing investigations of the mechanisms by which MC produces cancer in rodents. OSHA will carefully evaluate the results of those studies, as they become available.

Other concerns with the use of pharmacokinetic models include the lack of quantification of the reduction in uncertainty in the risk assessment process that should follow from using a model which predicts risk based on delivered dose rather than applied dose. Also, even when pharmacokinetic data have been used in risk assessments, there has been no consensus as to how the data should be incorporated, or how that incorporation affects use of the multistage model of cancer risk. OSHA has determined that it is not appropriate at this time to incorporate pharmacokinetic models in the MC cancer risk assessment. OSHA is soliciting information through an issue included in this proposed rule to address various concerns about the pharmacokinetic models and the risk assessment process (see Issue 6 for specific questions).

As discussed in the Health Effects and Preliminary Quantitative Risk Assessment sections, OSHA has evaluated four MC rodent bioassays (Exs. 4-35, 4-25, 7-29, 7-30, 7-31) to select the most appropriate bioassay as the basis for a quantitative risk assessment. These bioassays have been conducted in three rodent species (rat, mouse, and hamster) using two routes of administration (oral and inhalation). The NTP study (rat and mouse, inhalation) was chosen for a quantitative risk assessment because it provides the clearest evidence of the carcinogenicity of MC from both a toxicological and statistical standpoint (Exs. 12, 7-127). In the NTP study, MC induced significant increases both in incidence and multiplicity of alveolar/bronchiolar and hepatocellular neoplasms in male and female mice.

Once the incidences of alveolar/bronchiolar and hepatocellular neoplasms in male and female mice were chosen as the most appropriate data sets, the multistage model of carcinogenesis was used to predict a lifetime excess risk of cancer from occupational exposure to MC at several concentration levels. OSHA's best estimate of excess cancer risks at the current PEL of 500 ppm (8-hour TWA) are 33 to 45 per 1000 and at the proposed PEL of 25 ppm are 1.67 to 2.32 per 1,000 employees for 45 years of exposure.

As discussed in more detail in the Health Effects Section, above, human data concerning the carcinogenicity of MC was presented in three epidemiology studies. In a study of cellulose triacetate fiber production (MC used as solvent) workers, marginally increased incidence of liver/biliary cancer (Ex. 7-260) was noted. Although the case numbers were small and the exposure information limited, this epidemiological evidence is consistent with findings from animal studies and indicates that there may be an association between human cancer risk and MC exposure. A study of workers in photographic film production was non-positive (7-163). However, the exposures experienced by these workers may have been much less than in the cellulose triacetate fiber plant. The study of workers in paint and varnish manufacture was also non-positive (Ex. 10-29b). Exposures in these plants were not documented and workers were exposed to multiple chemicals during their employment.

The proposed STEL of 125 ppm for 15 minutes is primarily designed to protect against non-cancer risks, although there is evidence that reducing the GST metabolite production by reducing short term exposure to high concentrations of MC may also lower the cancer risk. As discussed in the Health Effects section, there are substantial risks of CNS effects and cardiac toxicity resulting from acute exposure to MC and its metabolites. CNS effects have been demonstrated at concentrations as low as 175 ppm. A STEL of 125 ppm for 15 minutes would be protective against the CNS effects described. Metabolism of MC to CO increases the body burden of COHb in exposed workers. Levels of COHb above 3% COHb may exacerbate angina symptoms and reduce exercise tolerance in workers with silent or symptomatic heart disease. Smokers are at higher risk for these effects because of the already increased COHb associated with smoking (COHb ranges from 2 to 8% in most smokers). Limiting short term exposure to 125 ppm for 15 minutes will keep COHb levels due to MC exposure below the 3% level, protecting the subpopulation of workers with silent or symptomatic heart disease and also limiting the additional COHb burden in smokers.

Further guidance for the Agency in evaluating significant risk is provided by an examination of occupational risk rates, legislative intent, and decisions of the Supreme Court. For example, in the high risk occupations of mining and quarrying (Division B), the average risk of death from an occupational injury or an acute occupationally-related illness over a lifetime of employment (45 years) is 15.1 per 1,000 workers. Typical occupational risks of deaths for all manufacturing (Division D) are 1.98 per 1,000. Typical lifetime occupational risk of death in an occupation of relatively low risk, like retail trade, is 0.82 per 1,000 (Division G). (These rates are averages derived from 1984-1986 Bureau of Labor Statistics data for employers with 11 or more employees, adjusted to 45 years of employment, for 50 weeks per year).

There are relatively few data on risk rates for occupational cancer, as distinguished from occupational injury and acute illness. The estimated cancer fatality rate from the maximum permissible occupational exposure to ionizing radiation is 17 to 29 per 1,000 (47 years at 5 rems; Committee on Biological Effects of Ionizing Radiation (BEIR) III predictions). However, most radiation standards require that exposure limits be reduced to the lowest level reasonably achievable below the exposure limit (the ALARA principle). Consequently, approximately 95% of radiation workers have exposures less than one-tenth the maximum permitted level. The risk at one-tenth the permitted level is 1.7 to 2.9 per 1,000 exposed employees.

Congress passed the Occupational Safety and Health Act of 1970 because of a determination that occupational safety and health risks were too high. Congress therefore gave OSHA authority to reduce above-average or average risks when feasible. Within this context, OSHA's preliminary best estimates of risk from occupational exposure to MC at the current 8-hour TWA PELs are substantially higher than other risks that OSHA has concluded are significant, are substantially higher than the risk of fatality in high-risk occupations, and are substantially higher than the example presented by the Supreme Court. Consequently, OSHA preliminarily concludes that its best estimate of risk, 33-45 cancer deaths per 1,000 workers, associated with the current 8-hour TWA PEL of 500 ppm presents a significant risk. OSHA's estimate of risk, derived from the same data and model, shows that, at the proposed exposure level of 25 ppm, the risk is 1.67-2.32 per thousand, which would also be significant based on the above reasoning.

Because of the feasibility limitations discussed in the Summary of Preliminary Regulatory Impact and Regulatory Flexibility section, OSHA integrated other protective provisions into the proposed standard to further reduce the risk of developing cancer among employees exposed to MC. Employees exposed to MC at the proposed 8-hour TWA PEL limit without the supplementary provisions would remain at risk of developing adverse health effects, so that inclusion of other protective provisions, such as medical surveillance and employee training, is both necessary and appropriate. For workers exposed over the action level, illness and injury may be identified at an early enough stage to prevent irreversible damage. Consequently, the programs triggered by the action level will further decrease the incidence of disease beyond the predicted reductions attributable merely to a lower PEL. As a result, OSHA preliminarily concludes that its proposed 8-hour TWA PEL of 25 ppm and associated action level (12.5 ppm) and STEL (125 ppm) will protect employees and that employers who comply with the provisions of the standard will be taking reasonable steps to protect their employees from the hazards of MC.

X. Summary of Preliminary Regulatory Impact and Regulatory Flexibility Analysis

The objective of this analysis is to measure the regulatory impact of changing the MC PEL to an 8 hour time-weighted average (TWA) of either 50 ppm or 25 ppm, together with associated action levels, short-term exposure limits (STELs) and ancillary requirements. The primary sources of information for this analysis are studies conducted for OSHA by CONSAD Research Corporation, Economic Analysis of OSHA's Proposed Standards for Methylene Chloride, 1990 (Ex. 15), and Economic Analysis of OSHA's Proposed Standards for Methylene Chloride in the Construction and Shipbuilding Industries, 1991, (Ex. 15C).

Based on production and process technology data collected from a literature search and during site visits to industrial facilities, OSHA believes it is technologically feasible to achieve the proposed PEL of 25 ppm through implementation of traditional and conventional engineering controls. However, OSHA's contractor chose a conservative model and projected that a portion of exposed workers, within certain industrial segments covered by the standard, would incur costs associated with compliance protocols (e.g., respiratory protection) including some of the ancillary provisions (e.g., medical surveillance, regulated areas).

OSHA has tentatively agreed with the contractor's conservative assessment, which resulted in higher respirator usage than would have been projected if the engineering feasibility assessments which were based on information gathered during OSHA's site visits had been solely relied on. Therefore, OSHA is requesting public comments on the appropriateness of using the contractor's assumptions and estimates. The costs of compliance in the final standard will reflect the information to be received in response to this request.

A. Methodology.

OSHA's contractor carried out two major data collection activities. The first was intended to gather pertinent secondary data and to help structure the sample frame, and the second was intended to collect primary data from firms which produce or could potentially use or distribute methylene chloride.

Primary data collection was required to determine current industry practices with regard to control procedures, substitution possibilities, and impacts of the proposed regulation. Primary data were collected from almost 1,300 respondents to a survey questionnaire in 1987. The sample was stratified on the basis of MC application for purposes of survey control and subsequent analysis.

To establish baseline levels of exposure to methylene chloride, CONSAD's subcontractor, PEI Associates, Inc., reviewed inspection or evaluation reports prepared by OSHA, NIOSH, EPA, and the U.S. Air Force (for an EPA survey) in which the use of MC was documented. These reports were analyzed and grouped according to the application-related taxonomy created for the survey. Exposure data and abstracts of the reports are in the appendices to CONSAD's reports(1).

B. Industry Profile

CONSAD Research Corporation delineated 25 application groups in order to distinguish the different circumstances and processes in which methylene chloride is used. These groups are identified in Table 11. The largest group, cold cleaning, includes 22,652 establishments with 90,293 directly exposed employees. The processes employed by this group include wiping with a rag, use of a cold cleaning degreaser, and use of an immersion cleaner. There are also other incidental exposures to methylene chloride. The employees in this group have an estimated arithmetic mean exposure of 26.9 ppm (8-hour TWA). The next largest group, printers, use a solvent (referred to as blanket wash) to clean printing plates and blankets between printing "runs". This group consists of an estimated 10,482 establishments with 34,868 exposed employees. MC-based solvents are used by workers in this group to clean other graphic arts equipment as well. The estimated arithmetic mean exposure for this group is 24.2 ppm (8-hour TWA).

The third largest group, construction, contains 9,504 establishments with 24,896 exposed workers who would be subject to the proposed standards. The major construction uses of MC are in paint stripping, cleaning of foam heads and equipment, traffic paint, epoxy paint, and adhesives. The estimated arithmetic mean exposure for construction is 57.7 ppm (8-hour TWA).

TABLE 11. - METHYLENE CHLORIDE APPLICATION GROUPS
___________________________________________________________________________
  |   |   |   | Estimated |  
  | Estimated |   | Estimated | arithmetic | MC
  | number of | Estimated | number of | mean of | handled
  | estab- | total | exposed | current | (mill-
  | lishments | employment | workers | exposures | ions)of
  | ** | ** | ** | (PPM) | pounds)
____________________ | _________ | __________ | _________ | __________ | _______
Manufacture of MC | 6 | 2,496 | 124 | 9.1 | 467
Distribution/Formulation |   |   |   |   |  
  of Solvents | 422 | 110,902 | 2,245 | 40.2 | 250
Metal Cleaning: |   |   |   |   |  
 Cold Degreasing and |   |   |   |   |  
  Other Cold Cleaning | 22,652 | 860,776 | 90,293 | 26.9 | 31
 Open Top Vapor |   |   |   |   |  
  Degreasing | 124 | 12,090 | 271 | 115.7 | 7
 Conveyorized Vapor |   |   |   |   |  
  Degreasing | 107 | 6,942 | 177 | 115.7 | 3
Aerosol Packing | 217 | 17,388 | 2,182 | 143.3 | 106
Paint&Paint Remover |   |   |   |   |  
 Formulation: |   |   |   |   |  
   Paint Remover |   |   |   |   |  
   Formulation | 293 | 22,464 | 760 | 23.3 | 155
   Paint Manufacturing | 390 | 70,446 | 1,808 | 11.7 | 28
Paint Stripping (PS): |   |   |   |   |  
   PS-Large Aircraft Firms. | 75 | 255,000 | 1,671 | 58.1 | 10
   PS-Small Aircraft Firms. | 225 | 11,826 | 799 | 58.1 | 3
   PS-Furniture | 4,000 | 21,440 | 5,720 | 126.2 | 14
   PS-Industrial . | 1,930 | 534,803 | 6,942 | 70.4 | 25
Electronics: |   |   |   |   |  
   Semiconductors | 666 | 608,558 | 3,888 | 46.9 | 1
   Printed Circuit Boards | 393 | 216,908 | 832 | 46.9 | 39
Foam Blowing/Plastics: |   |   |   |   |  
   Foam Blowing | 180 | 18,720 | 1,169 | 30.1 | 54
   Other Plastics/ |   |   |   |   |  
     Adhesives | 847 | 288,099 | 2,546 | 29.5 | 10
Ink Use (Printing): |   |   |   |   |  
   Ink Solvent Manufact | 37 | 4,899 | 143 | 40.2 | 9
   Ink Solvent Use |   |   |   |   |  
     (Blanket Wash) | 10,482 | 174,528 | 34,868 | 24.2 | 9
Pesticide Formulation | 60 | 1,440 | "90" | 40.2 | 10
Pharmaceuticals | 76 | 49,400 | 1,007 | 154.9 | 28
Solvent Recovery | 40 | 1,096 | 161 | 3.8 | 37
Film Base | 2 | 46,080 | 700 | 35.8 | 11
Polycarbonates | 4 | 1,898 | 67 | 3.9 | 7
Construction | 9,504 | 63,115 | 24,896 | 57.7 | 2
Shipyards | 25 | 85,212 | 3,040 | 139.7 | *
Total, all application |   |   |   |   |  
    groups | 52,757 | 3,486,526 | 186,429 | 40.2 | ***497
____________________ | _________ | __________ | _________ | __________ | _______

* More than zero, but less than 0.5 million.
** Estimated number of establishments in each application group was based
on volume flows of methylene chloride in 1985. Estimated number of
establishments was multiplied by total employees per establishment and
exposed employees per establishment, as reported in CONSAD's survey.
*** Netting out rehandling, estimated total consumption equals 467 million
pounds manufactured, minus 7 million pounds exported, plus 37 million
pounds recovered from used solvent.
Source: CONSAD.

The fourth and fifth largest groups use MC-based solvents for paint removal. The paint stripping - industrial group (1,930 establishments, 6,942 exposed workers) includes paint removal from various surfaces and equipment. This group has a wide variety of alternative paint remover solvents and methods available for metal surfaces. The paint stripping - furniture group (4,000 establishments, 5,720 exposed workers) strips wood and has few, if any, substitutes available which could do the job as quickly or thoroughly or with as little fire hazard as MC. Industrial paint strippers have an estimated arithmetic mean exposure of 70.4 ppm (8-hour TWA). Furniture paint strippers have an estimated arithmetic mean exposure of 126.2 ppm (8- hour TWA) This is the fourth highest among all of the application groups.

While the above groups constitute the largest in terms of number of establishments, two others are also of special interest: pharmaceuticals and aerosol packing. The pharmaceutical group, with 76 firms and 1,007 exposed workers, has the highest estimated exposure level (154.9 ppm) of any group. The aerosol group has the second highest estimated average exposure level, 143.3 ppm. Activities here include packing of aerosol cans and preparation of batch chemicals. An estimated 217 firms and 2,182 exposed workers are involved.

C. Technological Feasibility

OSHA has preliminarily determined that both a 50 ppm and a 25 ppm standard are technologically feasible. They can be achieved primarily through the use of engineering controls, supplemented when necessary by air-supplied respirators (ASRs). Local exhaust ventilation (LEV) is the most typical engineering control; ASRs are the simplest type of respirator which will protect against MC. OSHA notes that NIOSH has determined that MC can break through a cartridge respirator in 30 to 45 minutes at 15 ppm.

The assessment of technological feasibility addresses engineering controls as the first step to reduce exposure levels. The primary engineering control for most application groups is local exhaust ventilation. According to PEI Associates, the LEV used in OSHA's model represents good engineering practice for a typical facility in the application group. New LEV can reduce exposures by 80% and incremental LEV (i.e., modifications to existing LEV) can reduce exposures by either 5%, 15%, or 20%, according to the age and design of the original LEV systems in the application groups. The same reduction factors are used in this model for all other types of new and incremental engineering controls, such as general ventilation and booths -- with the exception of 50% in printing (because of difficulty in installing LEV on presses) and 50% in construction and shipyards (where portable exhaust or blower units must be used.)

The implementation of LEV and other engineering controls would enable most establishments to reduce the arithmetic mean exposures (AM's) of their exposed workers to or below a target level of one-half of the proposed PELs. Within these establishments, almost all individual exposures would fall below the PELs.

However, in establishments with predicted AMs above the target level after implementation of engineering controls, some workers would need personal respiratory protection in order to comply with the proposed regulations. OSHA's model adds ASRs for those workers whose exposures cannot be reduced below the PEL with engineering controls. These situations exist for a limited number of establishments in most application groups, even if the predicted AM for the application group is low. PEI has estimated that the ASRs will substantially reduce exposures for those workers who wear them. In order to meet a PEL of 25 ppm, as contrasted to 50 ppm, more workers would have to wear ASRs and the average exposure level under the lower PEL would be lower. Tables 12 and 13 show exposure reductions at the proposed standards.

The technological feasibility analysis shows that in solvent recovery and polycarbonates, engineering controls would not be needed to meet standards of 50 ppm or 25 ppm. In manufacture of MC, controls would be needed for the 25 ppm standard, in order to avoid costs of monitoring. In all other application groups, in order to meet either standard, controls would have to be implemented. In 19 groups for the 50 ppm standard and in 21 groups for the 25 ppm standard, ASRs would be needed for a generally small portion of workers whose exposures could not be brought below the PEL by controls alone.

Tables 14 and 15 show, by application group, the numbers and percents of exposed workers who would be required to wear ASRs in order to meet the proposed standards.

TABLE 12. - EXPOSURE REDUCTIONS AT 50 PPM STANDARD
__________________________________________________________________________
  |   |   |   | Average
  |   |   | Average | Exposures
  |   |   | Exposures | after Regulation
  |   |   | before | ________________
  | Total |   | Regu- |   | Eng'g
  | Exposed | Reduction Factors | lation |   | Contrls
  | Workers in | ________________ | (Arith- |   | Plus
  | Complying | New | Incre- | metic | Eng'g | Some
  | Establish- | Eng'g | mental | mean | Controls | Use of-
Application | ments | Controls | Controls | PPM) | Only | Respir-
  Group |   |   |   |   |   | ators
_______________ | _________ | ______ | ________ | ________ | _______ | _______
  |   |   |   |   |   |
Manufacture of MC | 124 | n.a. | n.a. | 9.14 | 9.14 | 9.14
  |   |   |   |   |   |
Distribution/ |   |   |   |   |   |
  Formulation of |   |   |   |   |   |
  Solvents | 2,021 | 0.8 | 0.05 | 40.18 | 22.81 | 21.09
  |   |   |   |   |   |
Metal Cleaning: |   |   |   |   |   |
  Cold Degreasing |   |   |   |   |   |
  and Other Cold |   |   |   |   |   |
  Cleaning | 45,147 | 0.8 | 0.15 | 26.88 | 12.42 | 12.38
  |   |   |   |   |   |
  Open Top Vapor |   |   |   |   |   |
  Degreasing | 244 | 0.8 | 0.15 | 115.70 | 92.14 | 49.77
  |   |   |   |   |   |
  Conveyorized |   |   |   |   |   |
  Vapor Degreasing | 159 | 0.8 | 0.15 | 115.70 | 56.52 | 36.69
  |   |   |   |   |   |
Aerosol Packing | 1,964 | 0.8 | 0.20 | 143.34 | 93.35 | 32.79
  |   |   |   |   |   |
Paint and |   |   |   |   |   |
Paint Remover |   |   |   |   |   |
Formulation: |   |   |   |   |   |
  Paint Remover |   |   |   |   |   |
  Formulation | 684 | 0.8 | 0.20 | 23.34 | 18.81 | 18.08
  |   |   |   |   |   |
  Paint Manufacturg | 904 | 0.8 | 0.15 | 11.67 | 11.34 | 11.34
  |   |   |   |   |   |
Paint Stripping |   |   |   |   |   |
(PS) |   |   |   |   |   |
  PS-Large Air- |   |   |   |   |   |
       craft Firms | 836 | 0.8 | 0.15 | 58.13 | 41.64 | 29.82
  PS-Small Air- |   |   |   |   |   |
       craft Firms | 400 | 0.8 | 0.15 | 58.13 | 24.50 | 16.73
  PS-Furniture | 5,148 | 0.8 | 0.20 | 126.17 | 56.58 | 29.53
  PS-Industrial | 3,471 | 0.8 | 0.20 | 70.35 | 32.85 | 26.96
  |   |   |   |   |   |
Electronics |   |   |   |   |   |
  Semiconductors | 3,888 | 0.8 | 0.05 | 46.89 | 41.59 | 19.21
  Printed Circuit |   |   |   |   |   |
  Boards | 832 | 0.8 | 0.05 | 46.89 | 31.91 | 20.51
  |   |   |   |   |   |
Foam Blowing/ |   |   |   |   |   |
Plastics |   |   |   |   |   |
  Foam Blowing | 1,169 | 0.8 | 0.15 | 30.10 | 22.41 | 18.56
  Other Plastics/ |   |   |   |   |   |
  Adhesives | 2,291 | 0.8 | 0.15 | 29.51 | 22.13 | 17.03
  |   |   |   |   |   |
Ink Use (Printing) |   |   |   |   |   |
  Ink Solvent Mfg. | 14 | 0.8 | 0.05 | 40.18 | 22.25 | 20.72
  Ink Solvent Use |   |   |   |   |   |
    (Blanket Wash) | 3,487 | 0.5 | 0.15 | 24.17 | 16.66 | 13.44
  |   |   |   |   |   |
Pesticide Formu- |   |   |   |   |   |
  lation | 120 | 0.8 | 0.20 | 40.18 | 30.41 | 19.86
  |   |   |   |   |   |
Pharmaceuticals | 1,007 | 0.8 | 0.15 | 154.87 | 121.68 | 40.78
  |   |   |   |   |   |
Solvent Recovery | 161 | n.a. | n.a. | 3.83 | 3.83 | 3.83
  |   |   |   |   |   |
Film Base | 700 | * | * | 35.80 | * | 29.60
  |   |   |   |   |   |
Polycarbonates | 67 | n.a. | n.a. | 3.88 | 3.88 | 3.88
  |   |   |   |   |   |
Construction | 19,917 | 0.8 | n.a. | 57.68 | 32.54 | 17.24
  |   |   |   |   |   |
Shipyards | 2,432 | 0.8 | n.a | 139.65 | 119.49 | 7.26
  |   |   |   |   |   |
TOTAL, ALL |   |   |   |   |   |
APPLICATION GROUPS | 97,187 |   |   | 40.25 | 27.83 | 21.52
________________ | _________ | ______ | ________ | ________ | _______ | _______

* Exposure reduction for film base was estimated from site visit and establishment data.

TABLE 13. - EXPOSURE REDUCTIONS AT 25 PPM STANDARD
__________________________________________________________________________
  |   |   |   | Average
  |   |   | Average | Exposures
  |   |   | Exposures | after Regulation
  |   |   | before | ________________
  | Total |   | Regu- |   | Eng'g
  | Exposed | Reduction Factors | lation |   | Contrls
  | Workers in | ________________ | (Arith- |   | Plus
  | Complying | New | Incre- | metic | Eng'g | Some
  | Establish- | Eng'g | mental | mean | Controls | Use of-
Application | ments | Controls | Controls | PPM) | Only | Respir-
  Group |   |   |   |   |   | ators
__________________ | _________ | ______ | ________ | ________ | _______ | _______
  | | | | | |
Manufacture of MC | 124 | 0.8 | 0.05 | 9.14 | 1.75 |  
  1.75 | | | | | |
Distribution/ | | | | | |
  Formulation of | | | | | |
  Solvents | 2,021 | 0.8 | 0.05 | 40.18 | 21.72 | 10.36
  | | | | | |
Metal Cleaning: | | | | | |
  Cold Degreasing | | | | | |
  and Other Cold | | | | | |
  Cleaning | 45,147 | 0.8 | 0.15 | 26.88 | 8.67 |
  6.47 |   | | | | |
  | | | | | |
  Open Top Vapor | | | | | |
  Degreasing | 244 | 0.8 | 0.15 | 115.70 | 91.15 |
  4.77 |   | | | | |
  | | | | | |
  Conveyorized | | | | | |
  Vapor Degreasing | 159 | 0.8 | 0.15 | 115.70 | 54.03 | 12.15
  | | | | | |
Aerosol Packing | 1,964 | 0.8 | 0.20 | 143.34 | 93.35 |
  6.32 |   | | | | |
  | | | | | |
Paint and | | | | | |
Paint Remover | | | | | |
Formulation: | | | | | |
  Paint Remover | | | | | |
  Formulation | 684 | 0.8 | 0.20 | 23.34 | 16.19 |
  4.04 |   | | | | |
  | | | | | |
  Paint Manufacturg | 904 | 0.8 | 0.15 | 11.67 | 9.27 |
  4.01 |   | | | | |
  | | | | | |
Paint Stripping | | | | | |
(PS) | | | | | |
  PS-Large Air- | | | | | |
        craft Firms | 836 | 0.8 | 0.15 | 58.13 | 40.50 |
  9.57 |   | | | | |
  PS-Small Air- | | | | | |
        craft Firms | 400 | 0.8 | 0.15 | 58.13 | 22.18 | 14.03
  PS-Furniture | 5,148 | 0.8 | 0.20 | 126.17 | 55.61 |
  8.40 |   | | | | |
  PS-Industrial | 3,471 | 0.8 | 0.20 | 70.35 | 31.13 |
  7.72 |   | | | | |
  | | | | | |
Electronics | | | | | |
  Semiconductors | 3,888 | 0.8 | 0.05 | 46.89 | 41.12 |
  2.60 |   | | | | |
  Printed Circuit | | | | | |
  Boards | 832 | 0.8 | 0.05 | 46.89 | 30.70 |
  6.64 |   | | | | |
  | | | | | |
Foam Blowing/ | | | | | |
Plastics | | | | | |
  Foam Blowing | 1,169 | 0.8 | 0.15 | 30.10 | 21.86 |
  5.47 |   | | | | |
  Other Plastics/ | | | | | |
  Adhesives | 2,291 | 0.8 | 0.15 | 29.51 | 21.22 |
  4.37 |   | | | | |
  | | | | | |
Ink Use (Printing) | | | | | |
  Ink Solvent Mfg. | 14 | 0.8 | 0.05 | 40.18 | 21.10 | 10.43
  Ink Solvent Use | | | | | |
    (Blanket Wash) | 3,487 | 0.5 | 0.15 | 24.17 | 13.82 |
  4.29 |   | | | | |
  | | | | | |
Pesticide Formu- | | | | | |
  lation | 120 | 0.8 | 0.20 | 40.18 | 39.81 |
  2.78 |   | | | | |
  |   | | | | |
Pharmaceuticals | 1,007 | 0.8 | 0.15 | 154.87 | 121.68 |
  4.54 |   | | | | |
  |   | | | | |
Solvent Recovery | 161 | n.a. | n.a. | 3.83 | 3.83 |
  3.83 |   | | | | |
  |   | | | | |
Film Base | 700 | * | * | 35.80 | * | 21.54
  |   | | | | |
Polycarbonates | 67 | n.a. | n.a. | 3.88 | 3.88 |
  3.88 |   | | | | |
  |   | | | | |
Construction | 19,917 | 0.8 | n.a. | 57.68 | 32.13 |
  5.91 |   | | | | |
  |   | | | | |
Shipyards | 2,432 | 0.8 | n.a | 139.65 | 119.41 |
  2.22 |   | | | | |
  |   | | | | |
TOTAL, ALL |   | | | | |
APPLICATION GROUPS | 97,187 | | | 40.25 | 25.62 |
  8.15 |   | | | | |
__________________ | _________ | ______ | ________ | ________ | ______ | ______

* Exposure reduction for film base was estimated from site visit and establishment data.

TABLE 14. - RESPIRATOR USE AT 50 PPM STANDARD
 
NOTE: Because of its width, this Table has been split into two parts. The
          final 3 columns are included as a separate table, immediately below
          this Table.
__________________________________________________________________________
  | | | Number of | Percent
  | | Baseline | Workers in ASRs | of
  | | Estimatd | Due to Standard | Affected
  | | Group | _________________ | Workers
  | Total | Arith- | Due | Due | | in ASRs
  | Affected | metic | to | to | | Due to
Application Group | Workers | Mean PPM | PEL | STEL | TOTAL | Standard
______________________ | _______ | _________ | ______ | ____ | ______ | ________
  | | | | | |
Manufacture of MC | 124 | 9.14 | 0 | 0 | 0 | 0.0%
  | | | | | |
Distribution/Formulation | | | | | |
    of Solvents | 2,021 | 40.18 | 131 | 0 | 131 | 6.5%
  | | | | | |
Metal Cleaning: | | | | | |
    Cold Degreasing and Other | | | | | |
     Cold Cleaning | 45,147 | 26.88 | 145 | 1 | 146 | 0.3%
    Open Top Vapor Degreasing | 244 | 115.70 | 49 | 0 | 49 | 20.0%
    Conveyorized Vapor | | | | | |
     Degreasing | 159 | 115.70 | 25 | 0 | 25 | 16.0%
  | | | | | |
Aerosol Packing | 1,964 | 143.34 | 666 | 0 | 667 | 34.0%
  | | | | | |
Paint and Paint Remover | | | | | |
Formulation: | | | | | |
    Paint Remover Formulation | 684 | 23.34 | 20 | 0 | 20 | 2.9%
    Paint Manufacturg | 904 | 11.67 | 0 | 0 | 0 | 0.0%
  | | | | | |
Paint Stripping (PS) | | | | | |
    PS -Large Aircraft Firms | 836 | 58.13 | 57 | 0 | 57 | 6.8%
    PS -Small Aircraft Firms | 400 | 58.13 | 4 | 0 | 4 | 1.1%
    PS -Furniture | 5,148 | 126.17 | 1,464 | 0 | 1,465 | 28.5%
    PS-Industrial | 3,471 | 70.35 | 321 | 1 | 322 | 9.3%
  | | | | | |
Electronics | | | | | |
    Semiconductors | 3,888 | 46.89 | 1,117 | 0 | 1,118 | 28.7%
    Printed Circuit Boards | 832 | 46.89 | 125 | 0 | 125 | 15.0%
  | | | | | |
Foam Blowing/Plastics | | | | | |
    Foam Blowing | 1,169 | 30.10 | 123 | 0 | 123 | 10.5%
    Other Plastics/Adhesives | 2,291 | 29.51 | 174 | 0 | 174 | 7.6%
  | | | | | |
Ink Use (Printing) | | | | | |
    Ink Solvent Manufacturing | 14 | 40.18 | 1 | 0 | 1 | 7.1%
    Ink Solvent Use (Blanket | | | | | |
     Wash) | 3,487 | 24.17 | 158 | 3 | 160 | 4.6%
  | | | | | |
Pesticide Formulation | 120 | 40.18 | 35 | 0 | 35 | 28.8%
  | | | | | |
Pharmaceuticals | 1,007 | 154.87 | 473 | 0 | 473 | 47.0%
  | | | | | |
Solvent Recovery | 161 | 3.83 | 0 | 0 | 0 | 0.0%
  | | | | | |
Film Base | 700 | 35.80 | 0 | 0* | 0* | 0.0%*
  | | | | | |
Polycarbonates | 67 | 3.88 | 0 | 0 | 0 | 0.0%*
  | | | | | |
Construction | 19,917 | 57.68 | 2,668 | 0 | 2,668 | 13.4%
  | | | | | |
Shipyards | 2,432 | 139.65 | 1,769 | 0 | 1,769 | 72.7%
  | | | | | |
TOTAL, ALL APPLICATION | | | | | |
  GROUPS | 97,187 | 40.25 | 9,526 | 6 | 9,532 | 9.8%
______________________ | _______ | _________ | ______ | ____ | ______ | _______
* All exposed workers in film base had ASRs prior to the standard, to deal
    with short-term excursions.
    Source: CONSAD


TABLE 15. - RESPIRATOR USE AT 25 PPM STANDARD
NOTE: Because of its width, this Table has been split into two parts. The
          final 3 columns of the above table are included here, in addition to
          the "Total Affected Workers" column which is also shown on the
          previous table.
__________________________________________________________________________
| | | Full-time | FTE Workers
| | Percent | Equivalent | in ASRs Due
| | of | Workers | to Standard
| Total | Workyear | in ASRs | as Percent of
| Affected | Exposed | Due to | All Affected
Application Group | Workers | to MC | Standard | Workers
_________________________ | _______ | ________ | __________ | ______________
| | | |
Manufacture of MC | 124 | 100% | 0 | 0.0%
| | | |
Distribution/Formulation | | | |
    of Solvents | 2,021 | 45% | 59 | 2.9%
| | | |
Metal Cleaning: | | | |
    Cold Degreasing and Other | | | |
      Cold Cleaning | 45,147 | 30% | 44 | 0.1%
    Open Top Vapor Degreasing | 244 | 14% | 7 | 2.8%
    Conveyorized Vapor | | | |
      Degreasing | 159 | 100% | 25 | 15.7%
| | | |
Aerosol Packing | 1,964 | 100% | 667 | 34.0%
| | | |
Paint and Paint Remover | | | |
Formulation: | | | |
    Paint Remover Formulation | 684 | 36% | 7 | 1.1%
    Paint Manufacturing | 904 | 91% | 0 | 0.0%
| | | |
Paint Stripping (PS) | | | |
    PS -Large Aircraft Firms | 836 | 53% | 30 | 3.6%
    PS -Small Aircraft Firms | 400 | 13% | 1 | 0.1%
    PS -Furniture | 5,148 | 20% | 293 | 5.7%
    PS-Industrial | 3,471 | 20% | 64 | 1.9%
| | | |
Electronics | | | |
    Semiconductors | 3,888 | 42% | 470 | 12.1%
    Printed Circuit Boards | 832 | 30% | 38 | 4.5%
| | | |
Foam Blowing/Plastics | | | |
    Foam Blowing | 1,169 | 43% | 53 | 4.5%
    Other Plastics/Adhesives | 2,291 | 38% | 66 | 2.9%
| | | |
Ink Use (Printing) | | | |
    Ink Solvent Manufacturing | 14 | 13% | 0 | 0.9%
    Ink Solvent Use (Blanket | | | |
      Wash) | 3,487 | 11% | 18 | 0.5%
| | | |
Pesticide Formulation | 120 | 7% | 2 | 2.0%
| | | |
Pharmaceuticals | 1,007 | 100% | 473 | 47.0%
| | | |
Solvent Recovery | 161 | 33% | 0 | 0.0%
| | | |
Film Base | 700 | 100% | 0* | 0.0%*
| | | |
Polycarbonates | 67 | 100% | 0 | 0.0%*
| | | |
Construction | 19,917 | 100% | 2,668 | 13.4%
| | | |
Shipyards | 2,432 | 100% | 1,769 | 72.7%
| | | |
TOTAL, ALL APPLICATION | | | |
 GROUPS | 97,187 | | 6,754 | 6.9%
_________________________ | _______ | ________ | __________ | ______________
* All exposed workers in film base had ASRs prior to the standard, to deal
    with short-term excursions.
    Source: CONSAD

BILLING CODE 4510-26-C

TABLE 15. - RESPIRATOR USE AT 25 PPM STANDARD
NOTE: Because of its width, this Table has been split into two parts. The
          final 3 columns of the above table are included here, in addition to
          the "Total Affected Workers" column which is also shown on the
          previous table.
__________________________________________________________________________
  | | | Full-time | FTE Workers
  | | Percent | Equivalent | in ASRs Due
  | | of | Workers | to Standard
  | Total | Workyear | in ASRs | as Percent of
  | Affected | Exposed | Due to | All Affected
Application Group | Workers | to MC | Standard | Workers
_____________________ ____ | ________ | _________ | ___________ | ____________
  | | | |  
Manufacture of MC | 124 | 100% | 0 | 0.0%
  | | | |  
Distribution/Formulation | | | |  
    of Solvents | 2,021 | 45% | 97 | 4.8%
  | | | |  
Metal Cleaning: | | | |  
    Cold Degreasing and Other | | | |  
     Cold Cleaning | 45,147 | 30% | 143 | 0.3%
    Open Top Vapor Degreasing | 244 | 14% | 10 | 4.1%
    Conveyorized Vapor | | | |  
     Degreasing | 159 | 100% | 38 | 23.9%
  | | | |  
Aerosol Packing | 1,964 | 100% | 1,215 | 61.9%
  | | | |  
Paint and Paint Remover | | | |  
Formulation: | | | |  
    Paint Remover Formulation | 684 | 36% | 73 | 10.6%
    Paint Manufacturing | 904 | 91% | 23 | 2.5%
  | | | |  
Paint Stripping (PS) | | | |  
    PS -Large Aircraft Firms | 836 | 53% | 137 | 16.6%
    PS -Small Aircraft Firms | 400 | 13% | 2 | 0.6%
    PS -Furniture | 5,148 | 20% | 423 | 8.2%
    PS-Industrial | 3,471 | 20% | 224 | 6.4%
  | | | |  
Electronics | | | |  
    Semiconductors | 3,888 | 42% | 843 | 21.7%
    Printed Circuit Boards | 832 | 30% | 89 | 10.7%
  | | | |  
Foam Blowing/Plastics | | | |  
    Foam Blowing | 1,169 | 43% | 180 | 15.4%
    Other Plastics/Adhesives | 2,291 | 38% | 178 | 7.8%
  | | | |  
Ink Use (Printing) | | | |  
    Ink Solvent Manufacturing | 14 | 13% | 0 | 0.9%
    Ink Solvent Use (Blanket | | | |  
     Wash) | 3,487 | 11% | 60 | 1.7%
  | | | |  
Pesticide Formulation | 120 | 7% | 3 | 2.3%
  | | | |  
Pharmaceuticals | 1,007 | 100% | 567 | 56.3%
  | | | |  
Solvent Recovery | 161 | 33% | 0 | 0.0%
  | | | |  
Film Base | 700 | 100% | 0* | 0.0%*
  | | | |  
Polycarbonates | 67 | 100% | 0 | 0.0%
  | | | |  
Construction | 19,917 | 100% | 6,876 | 34.5%
  | | | |  
Shipyards | 2,432 | 100% | 2,196 | 90.3%
  | | | |  
TOTAL, ALL APPLICATION | | | |  
  GROUPS | 97,187 | | 13,376 | 13.8%
__________________________ | ________ | _________ | ___________ | ___________
* All exposed workers in film base had ASRs prior to the standard, to deal
    with short-term excursions.
    Source: CONSAD

The percent of exposed workers in respirators at least part of the time would be above 25% in six application groups at 50 ppm and seven application groups at 25 ppm. These would be shipyards (73% and 90% respectively), pharmaceuticals (47% and 56% respectively), aerosol packing (34% and 62%, respectively), construction (13% and 35%, respectively), semiconductors (29% and 52%, respectively), furniture stripping (29% and 41% respectively), and pesticide formulation (29% and 33%, respectively). In the first four of these groups, exposed workers are estimated to handle MC full-time. In the latter three groups, however, MC is used less than half of the time. On a full-time equivalent (FTE) basis, the percent of exposed workers who would require ASRs drops below 25% in semiconductors, furniture stripping, and pesticides, for either standard.

Overall, under a 50 ppm standard, 9.8% of exposed workers (6.9% FTE) would have to wear respirators. Under a 25 ppm standard, 19.7% of exposed workers (13.8% FTE) would have to wear respirators.

OSHA also considered the technological feasibility of achieving 15-minute short-term exposure limits of five times the proposed PELs-- i.e., a STEL of 250 ppm with the 50 ppm standard and a STEL of 125 ppm with the 25 ppm standard. Again, both proposed standards were technologically feasible with the use of LEV, supplemented when necessary by respirators.

D. Substitution

OSHA also considered that firms might substitute other solvents for methylene chloride or eliminate products or processes as an alternative to complying with a revised standard.

CONSAD, in consultation with PEI and after considering survey responses, site visit reports, and the views of manufacturers, distributors and users of MC, developed estimates of the percentage of establishments which would substitute away from MC in the event of a revised standard. Five points were chosen to represent the possible gradations of substitution activity: none = 0%, minor = 10%, some = 20%, substantial = 50%, near total = 90%.

With adoption of a standard of either 50 ppm or 25 ppm, the estimated numbers of workers exposed to MC would drop from the present 186,429 workers in 52,757 establishments to 97,187 workers in 28,147 establishments. In order to avoid costs of compliance, 24,610 establishments would substitute another solvent or abandon products or processes that require MC. E. Total Costs of Regulation

Annualized costs of regulation (including costs of substitution) total $83 million for all 25 application groups for a 50 ppm standard and $108 million for a 25 ppm standard.

For either standard, the largest expenses are for engineering controls. Annualized costs of engineering controls are $43 million for 50 ppm and $58 million for 25 ppm*. The next most expensive item is clothing and eye protection, with annual costs of $14.9 million for either proposed standard. Exposure monitoring has annual costs of $10.1 million for 50 ppm and $13.4 million for 25 ppm. (See Tables 16 and 17.)


* If not annualized, first year capital costs for engineering controls would be $163 million for 50 ppm and $219 million for 25 ppm.


Furniture paint stripping accounts for the largest share of costs of regulation at either 50 ppm or 25 ppm. These are $19 million in each year for 50 ppm and $22 million in each year for 25 ppm. (There are no costs for polycarbonates, since MC is not capable of being released in airborne concentrations either at or above the action level or in excess of the STEL in this application group.)

F. Benefits Analysis

The benefits of a revised standard for occupational exposure to MC would include reductions in the incidence of cancer and reductions in acute central nervous system and carboxyhemoglobinemia effects.

TABLE 16. - ANNUALIZED COSTS FOR 50 PPM STANDARD, BY REQUIREMENT
______________________________________________________________
        | Annualized
        Requirement | cost
        | ($000)
_________________________________________ | _________________
        |  
Engineering controls: |  
    Install new controls........ | 36,452
    Install incremental controls | 6,717
        | ______
        Subtotal...... | 43,169
Monitoring............................... | 10,101
Air-supplied respirators................. | 5,571
Clothing/eye protection.................. | 14,873
Written compliance program............... | 1,057
Medical surveillance..................... | 3,192
Regulated areas.......................... | 932
Emergency alert device................... | 933
Medical recordkeeping.................... | 42
Exposure recordkeeping................... | 213
        | _______
        Total compliance costs............. | 80,084
Substitution costs....................... | 3,356
        | _______
        Grand total.. | 83,439
______________________________________________________________
  Source: CONSAD.


TABLE 17. - ANNUALIZED COSTS FOR 25 PPM STANDARD, BY REQUIREMENT
_______________________________________________________________
        | Annualized
        Requirement | cost
        | ($000)
_________________________________________ | _____________________
        |  
Engineering controls: |  
    Install new LEV........................ | 47,132
    Install incremental LEV................ | 10,517
        | ______
        Subtotal............................ | 57,649
Monitoring............................... | 13,385
Air-supplied respirators................. | 9,700
Clothing/eye protection.................. | 14,873
Written compliance program............... | 1,916
Medical surveillance..................... | 4,547
Regulated areas.......................... | 1,731
Emergency alert device................... | 933
Medical recordkeeping.................... | 60
Exposure recordkeeping................... | 280
        | _______
        Total compliance costs............. | 105,072
Substitution costs....................... | 3,356
        | _______
        Grand total........................ | 108,428
_______________________________________________________________
  Source: CONSAD.

In order to calculate cancer reductions, OSHA began with a multistage model generated by K.S. Crump and Company from animal data. Crump's model predicted an excess risk of cancer at an occupational exposure of 500 ppm for 250 days per year of 45 per 1000 workers over a 45-year period (based on female mice). If the estimated 186,429 workers directly exposed to MC were exposed at the current PEL of 500 ppm, they would suffer 8,147 excess cancer deaths over 45 years.

However, simply applying Crump's model to the current PEL for MC overstates the current population risk. Current average levels of exposure are far lower than the current PEL of 500 ppm.

In order to reflect actual exposure levels, OSHA entered into Crump's model the arithmetic mean exposures for each application group (these ranged from 3.8 ppm for solvent recovery to 154.9 ppm for pharmaceuticals). An estimated 668 cancer deaths over 45 years are projected at the current exposure levels for the currently exposed population.

With the introduction of a new methylene chloride standard, both the number of exposed workers and their levels of exposure would drop. (See Tables 18 and 19.) OSHA estimates that at a PEL of 50 ppm, cancer deaths would be reduced from 668 to 144 over 45 years. This is a reduction of 525 deaths over 45 years, or about 11.7 deaths per year, compared to current levels. A PEL would further reduce excess cancer deaths to 54 over 45 years, for a total reduction of 614 deaths over 45 years, or about 13.6 deaths per year, compared to current levels.
TABLE 18. - REDUCTIONS IN EXCESS CANCER DEATHS OVER 45 YEARS BY ADOPTING
        50 PPM STANDARD
__________________________________________________________________________
        | | Exposures | | |  
        | | __________ | | |  
        | PELs | Current& | Directly | Expected | Reduc-
     Application group | (PPM) | expected | exposed | excess | tion in
        | | arithmetic | workers | deaths | deaths
        | | mean (PPM) | | |  
_______________________________ | _____ | __________ | ________ | ________ | _______
Manufacture of MC............... | 500 | 9.14 | 124 | 0.10 |  
        | 50 | 9.14 | 124 | 0.10 | 0.00
Distribution/Formulation of | | | | |  
    Solvents...................... | 500 | 40.18 | 2,245 | 8.04 |  
        | 50 | 21.09 | 2,021 | 3.80 | 4.24
Metal Cleaning.................. | | | | |  
    Cold Degreasing and Other Cold | | | | |  
       Cleaning.................... | 500 | 26.88 | 90,293 | 216.52 |  
        | 50 | 12.38 | 45,147 | 49.89 | 166.63
    Open Top Vapor Degreasing..... | 500 | 115.70 | 271 | 2.79 |  
        | 50 | 49.77 | 244 | 1.08 | 1.71
    Conveyorized Vapor Degreasing. | 500 | 115.70 | 177 | 1.82 |  
        | 50 | 36.79 | 159 | 0.52 | 1.30
Aerosol Packing................. | 500 | 143.34 | 2,182 | 27.76 |  
        | 50 | 32.79 | 1,964 | 5.74 | 22.02
Paint&Paint Remover | | | | |  
  Formulation: | | | | |  
    Paint Remover Formulation..... | 500 | 23.34 | 760 | 1.58 |  
        | 50 | 18.08 | 684 | 1.10 | 0.48
    Paint Manufacture............. | 500 | 11.67 | 1,808 | 1.88 |  
        | 50 | 11.34 | 904 | 0.92 | 0.96
Paint Stripping (PS): | | | | |  
    PS - Large Aircraft Firms..... | 500 | 58.13 | 1,671 | 8.65 |  
        | 50 | 29.82 | 836 | 2.22 | 6.43
    PS - Small Aircraft Firms..... | 500 | 58.13 | 799 | 4.14 |  
        | 50 | 16.73 | 400 | 0.60 | 3.54
    PS - Furniture................ | 500 | 126.17 | 5,720 | 64.11 |  
        | 50 | 29.53 | 5,148 | 13.56 | 50.55
    PS - Industrial............... | 500 | 70.35 | 6,942 | 43.49 |  
        | 50 | 26.96 | 3,471 | 8.35 | 35.14
Electronics: | | | | |  
    Semiconductors................ | 500 | 46.89 | 3,888 | 16.25 |  
        | 50 | 19.21 | 3,888 | 6.67 | 9.58
    Printed Circuit Boards........ | 500 | 46.89 | 832 | 3.48 |  
        | 50 | 20.51 | 832 | 1.52 | 1.96
Foam Blowing/Plastics: | | | | |  
    Foam Blowing.................. | 500 | 30.10 | 1,169 | 3.14 |  
        | 50 | 18.56 | 1,169 | 1.94 | 1.20
    Other Plastics/Adhesives...... | 500 | 29.51 | 2,546 | 6.70 |  
        | 50 | 17.03 | 2,292 | 3.48 | 3.22
Ink Use (Printing): | | | | |  
    Ink Solvent Manufacturing..... | 500 | 40.18 | 143 | 0.51 |  
        | 50 | 20.72 | 14 | 0.03 | 0.48
    Ink Solvent Use (Blanket Wash) | 500 | 24.17 | 34,868 | 75.19 |  
        | 50 | 13.44 | 3,487 | 4.18 | 71.01
Pesticide Formulation........... | 500 | 40.18 | 120 | 0.43 |  
        | 50 | 19.86 | 120 | 0.21 | 0.22
Pharmaceuticals................. | 500 | 154.87 | 1,007 | 13.84 |  
        | 50 | 40.78 | 1,007 | 3.66 | 10.18
Solvent Recovery................ | 500 | 3.83 | 161 | 0.06 |  
        | 50 | 3.83 | 161 | 0.06 | 0.00
Film Base....................... | 500 | 35.80 | 700 | 2.23 |  
        | 50 | 29.60 | 700 | 1.85 | 0.38
Polycarbonates.................. | 500 | 3.88 | 67 | 0.02 |  
        | 50 | 3.88 | 67 | 0.02 | 0.00
Construction.................... | 500 | 57.68 | 24,896 | 127.94 |  
        | 50 | 17.24 | 19,917 | 30.64 | 97.30
Shipyards....................... | 500 | 139.65 | 3,040 | 37.69 |  
        | 50 | 7.26 | 2,432 | 1.58 | 36.11
Total, All 25 Application Groups | 500 | 35.75 | 186,429 | 668.36 |  
        | 50 | 16.74 | 97,187 | 143.73 | 524.64
Average Annual Reduction........ | ..... | .......... | ........ | ........ | 11.66
_______________________________ | _____ | __________ | ________ | ________ | _______
    Sources: CONSAD, Crump Report, Office of Regulatory Analysis


TABLE 19. - REDUCTIONS IN EXCESS CANCER DEATHS OVER 45 YEARS BY ADOPTING
        25 PPM STANDARD
_____________________________________________________________________________
        | | Exposures | | |  
        | | __________ | | |  
        | PELs | Current& | Directly | Expected | Reduc-
     Application group | (PPM) | expected | exposed | excess | tion in
        | | arithmetic | workers | deaths | deaths
        | | mean (PPM) | | |  
_______________________________ | _____ | __________ | ________ | ________ | _______
Manufacture of MC............... | 500 | 9.14 | 124 | 0.10 |  
        | 25 | 1.75 | 124 | 0.02 | 0.08
Distribution/Formulation of | | | | |  
    Solvents...................... | 500 | 40.18 | 2,245 | 8.04 |  
        | 25 | 10.36 | 2,021 | 1.87 | 6.17
Metal Cleaning: | | | | |  
    Cold Degreasing and Other Cold | | | | |  
       Cleaning.................... | 500 | 26.88 | 90,293 | 216.52 |  
        | 25 | 6.47 | 45,147 | 26.08 | 190.44
    Open Top Vapor Degreasing..... | 500 | 115.70 | 271 | 2.79 |  
        | 25 | 4.77 | 244 | 0.10 | 2.69
    Conveyorized Vapor Degreasing. | 500 | 115.70 | 177 | 1.82 |  
        | 25 | 12.15 | 159 | 0.17 | 1.65
Aerosol Packing................. | 500 | 143.34 | 2,182 | 27.76 |  
        | 25 | 6.32 | 1,964 | 1.11 | 26.65
Paint&Paint Remover | | | | |  
  Formulation: | | | | |  
    Paint Remover Formulation..... | 500 | 23.34 | 760 | 1.58 |  
        | 25 | 4.04 | 684 | 0.25 | 1.33
    Paint Manufacture............. | 500 | 11.67 | 1,808 | 1.88 |  
        | 25 | 4.01 | 904 | 0.32 | 1.56
Paint Stripping (PS): | | | | |  
    PS - Large Aircraft Firms..... | 500 | 58.13 | 1,671 | 8.65 |  
        | 25 | 9.57 | 836 | 0.71 | 7.94
    PS - Small Aircraft Firms..... | 500 | 58.13 | 799 | 4.14 |  
        | 25 | 14.03 | 400 | 0.50 | 3.64
    PS - Furniture................ | 500 | 126.17 | 5,720 | 64.11 |  
        | 25 | 8.40 | 5,148 | 3.86 | 60.25
    PS - Industrial............... | 500 | 70.35 | 6,942 | 43.49 |  
        | 25 | 7.72 | 3,471 | 2.39 | 41.10
Electronics: | | | | |  
    Semiconductors................ | 500 | 46.89 | 3,888 | 16.25 |  
        | 25 | 2.60 | 3,888 | 0.90 | 15.35
    Printed Circuit Boards........ | 500 | 46.89 | 832 | 3.48 |  
        | 25 | 6.64 | 832 | 0.49 | 2.99
Foam Blowing/Plastics: | | | | |  
    Foam Blowing.................. | 500 | 30.10 | 1,169 | 3.14 |  
        | 25 | 5.47 | 1,169 | 0.57 | 2.57
    Other Plastics/Adhesives...... | 500 | 29.51 | 2,546 | 6.70 |  
        | 25 | 4.37 | 2,292 | 0.89 | 5.81
Ink Use (Printing): | | | | |  
    Ink Solvent Manufacturing..... | 500 | 40.18 | 143 | 0.51 |  
        | 25 | 10.43 | 14 | 0.01 | 0.50
    Ink Solvent Use (Blanket Wash) | 500 | 24.17 | 34,868 | 75.19 |  
        | 25 | 4.29 | 3,487 | 1.34 | 73.85
Pesticide Formulation........... | 500 | 40.18 | 120 | 0.43 |  
        | 25 | 2.78 | 120 | 0.03 | 0.40
Pharmaceuticals................. | 500 | 154.87 | 1,007 | 13.84 |  
        | 25 | 4.54 | 1,007 | 0.41 | 13.43
Solvent Recovery................ | 500 | 3.83 | 161 | 0.06 |  
        | 25 | 3.83 | 161 | 0.06 | 0.00
Film Base....................... | 500 | 35.80 | 700 | 2.23 |  
        | 25 | 21.54 | 700 | 1.35 | 0.88
Polycarbonates.................. | 500 | 3.88 | 67 | 0.02 |  
        | 25 | 3.88 | 67 | 0.02 | 0.00
Construction.................... | 500 | 57.68 | 24,896 | 127.94 |  
        | 25 | 5.91 | 19,917 | 10.51 | 117.43
Shipyards....................... | 500 | 139.65 | 3,040 | 37.69 |  
        | 25 | 2.22 | 2,432 | 0.48 | 37.21
Total, All 25 Application Groups | 500 | 35.75 | 186,429 | 668.36 |  
        | 25 | 6.51 | 97,187 | 54.46 | 613.90
Average Annual Reduction........ | ..... | .......... | ........ | ........ | 13.64
_______________________________ | _____ | __________ | ________ | ________ | _______
    Sources: CONSAD, Crump Report, Office of Regulatory Analysis

G. Economic Impacts

OSHA calculated economic impacts by comparing estimated substitution or compliance costs of the proposed standards with the estimated sales and profits for affected firms. For most application groups, economic impacts would be modest.

Recurring costs of compliance, even at 25 ppm, will amount to far less than one percent of estimated sales in most application groups. Notable impacts could be experienced, however, by 149 large and small firms which strip paint from aircraft, 80 slab stock foam blowers, and 3,600 firms which strip paint from furniture. In furniture stripping, recurring compliance costs at 50 ppm are estimated to equal 6% of sales or 106% of profits; at 25 ppm, they are estimated to equal 7% of sales or 121% of profits. (See Tables 20 through 23). It is expected that firms in this category may elect the option to substitute for MC use and/or to specialize in refinishing and send pieces of furniture elsewhere for stripping.



TABLE 20
ECONOMIC IMPACT OF A 50 PPM STANDARD - FIRST YEAR
NOTE: Because of the width of this table, columns describing the IMPACT OF
        COMPLIANCE follows as a separate table.
_________________________________________________________________________
Impact of Substitution
_________________________________________________________________________
          First Year  
        Number of Substitution First Year
        Estab- Cost per Costs of Substitution
        lishments Substituting _____________________
        Substi- Establish- as Percent as Percent
Application Group tuting ment ($) of Sales of Profit
_________________________________________________________________________
Manufacture of MC 0 - - -
Distribution/Formulation
    of Solvents 42 0 0.00% 0.00%
Metal Cleaning
    Cold Degreasing and
       Other Cold Cleaning 11,326 0 0.00% 0.00%
    Open Top Vapor Degreasing 12 12,009 0.15% 3.26%
    Conveyorized Vapor
     Degreasing 11 18,720 0.24% 5.09%
Aerosol Packing 22 60,000 0.23% 6.30%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 29 40,000 0.82% 34.00%
    Paint Manufacturing 195 6,000 0.12% 5.10%
Paint Remover Use (Stripping)
    Paint Stripping - Large
       Aircraft Firms 38 5,347 0.00% 0.13%
    Paint Stripping -Small
       Aircraft Firms 113 852 0.01% 0.31%
    Paint Stripping - Furniture 400 4,075 4.86% 88.44%
    Paint Stripping - Industrial 965 1,788 0.02% 0.49%
Electronics
    Semiconductors 0 - - -
    Printed Circuit Boards 0 - - -
Foam Blowing/Plastics
    Foam Blowing 0 - - -
    Other Plastics/Adhaesives 85 0 0.00% 0.00%
Ink Use (Printing)
    Ink Solvent Manufacturing 33 0 0.00% 0.00%
    Ink Solvent Use (Blanket
       Wash) 9,434 0 0.00% 0.00%
Pesticide Formulation 0 - -  
Pharmaceuticals 0 - -  
Solvent Recovery 0 - -  
Film Base 0 - -  
Polycarbonates 0 - - -
Construction 1,901 0 0.00% 0.00%
Shipyards 5 0 0.00% 0.00%
 
ALL APPLICATION GROUPS 24,610 311
_________________________________________________________________________
Source: CONSAD


TABLE 20
ECONOMIC IMPACT OF A 50 PPM STANDARD - FIRST YEAR
NOTE: The following table is part of the preceding Table which shows the
Impact of Substitution. The Table has been split because of its width.
__________________________________________________________________________
Impact of Compliance
__________________________________________________________________________
              First Year    
        Number of     Substitution First Year
        Estab-     Cost per Costs of Substitution
        lishments     Substituting _____________________
        Substi-     Establish- as Percent as Percent
Application Group tuting     ment ($) of Sales of Profit
_________________________________________________________________________
Manufacture of MC 6 2,403     0.01% 0.25%
Distribution/Formulation
    of Solvents 380 3,692     0.09% 2.22%
Metal Cleaning
    Cold Degreasing and
        Other Cold Cleaning 11,326 1,246     0.02% 0.34%
    Open Top Vapor Degreasing 112 1,330     0.02% 0.36%
    Conveyorized Vapor
     Degreasing 96 2,087     0.03% 0.57%
Aerosol Packing 195 7,803     0.03% 0.82%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 264 1,702     0.03% 1.45%
    Paint Manufacturing 195 628     0.01% 0.53%
Paint Remover Use (Stripping)
    Paint Stripping - Large
        Aircraft Firms 37 254,902     0.18% 6.21%
    Paint Stripping -Small
        Aircraft Firms 112 44,111    0.73%     16.15%
    Paint Stripping - Furniture 3,600    4,889     5.83%    106.08%
    Paint Stripping - Industrial 965    5,434     0.07%    1.48%
Electronics
    Semiconductors     666     2,661     0.03%     0.68%
    Printed Circuit Boards    393    2,285     0.05%     1.07%
Foam Blowing/Plastics
    Foam Blowing     180     22,369     0.62%     14.42%
    Other Plastics/Adhaesives    762     1,896     0.05%     1.22%
Ink Use (Printing)
    Ink Solvent Manufacturing     4    2,171     0.01%     0.23%
    Ink Solvent Use (Blanket
        Wash)     1,048     637     0.04%    0.81%  
Pesticide Formulation     60     1,474    0.02%    0.61%
Pharmaceuticals     76     8,219    0.02%    0.37%
Solvent Recovery     40     555    0.04%    0.63%
Film Base     2     841,099    0.05%    1.55%
Polycarbonates     4     0    0.00%     0.00%
Construction     7,603     1,921    0.43%    11.83%
Shipyards     20     31,031    0.10%    2.58%
ALL APPLICATION GROUPS     28,147     2,901       
__________________________________________________________________________
Source: CONSAD
 
TABLE 21
ECONOMIC IMPACT OF A 50 PPM STANDARD - SECOND AND FOLLOWING YEARS
NOTE: Because of the width of this table, columns describing the IMPACT OF
          COMPLIANCE follows as a separate table.
__________________________________________________________________________
Impact of Substitution
__________________________________________________________________________
    Recurring  
  Number of Substitution Recurring
  Estab- Cost per Costs of Substitution
  lishments Substituting _____________________
  Substi- Establish- as Percent as Percent
Application Group tuting ment ($) of Sales of Profit
__________________________________________________________________________
Manufacture of MC         0         -         -         -
Distribution/Formulation
    of Solvents         42         0        0.00%         0.00%
Metal Cleaning
    Cold Degreasing and
        Other Cold Cleaning        11,326         0         0.00%        0.00%
    Open Top Vapor Degreasing 12         0         0.00%        0.00%
    Conveyorized Vapor
      Degreasing         11         0         0.00%        0.00%
Aerosol Packing         22         0         0.00%         0.00%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 29         0         0.00%         0.00%
    Paint Manufacturing         195         0         0.00%         0.00%
Paint Remover Use (Stripping)
    Paint Stripping - Large
        Aircraft Firms         38         0         0.00%         0.00%
    Paint Stripping -Small
        Aircraft Firms         113         0         0.00%         0.00%
    Paint Stripping - Furniture 400         4,075         4.86%         88.44%
    Paint Stripping - Industrial 965         1,788         0.02%         0.49%
Electronics
    Semiconductors         0         -         -         -
    Printed Circuit Boards        0         -         -         -
Foam Blowing/Plastics
    Foam Blowing         0         -         -         -
    Other Plastics/Adhaesives 85         0         0.00%         0.00%
Ink Use (Printing)
    Ink Solvent Manufacturing 33         0         0.00%         0.00%
    Ink Solvent Use (Blanket
        Wash)         9,434         0         0.00%        0.00%
Pesticide Formulation         0         -         -         -
Pharmaceuticals         0         -         -         -
Solvent Recovery         0         -         -         -
Film Base         0         -         -         -
Polycarbonates         0         -         -         -
Construction         1,901         0        0.00%         0.00%
Shipyards         5         0        0.00%         0.00%
ALL APPLICATION GROUPS        24,610         136           
__________________________________________________________________________
Source: CONSAD
+++
TABLE 21
ECONOMIC IMPACT OF A 50 PPM STANDARD - SECOND AND FOLLOWING YEARS
NOTE: The following table is part of the preceding Table which shows the
Impact of Substitution. The Table has been split because of its width.
__________________________________________________________________________
Impact of Substitution
__________________________________________________________________________
    Recurring  
  Number of Substitution Recurring
  Estab- Cost per Costs of Substitution
  lishments Substituting _____________________
  Substi- Establish- as Percent as Percent
Application Group tuting ment ($) of Sales of Profit
__________________________________________________________________________
Manufacture of MC 6 2,403 0.01% 0.25%
Distribution/Formulation
    of Solvents 380 3,488 0.09% 2.22%
Metal Cleaning
    Cold Degreasing and
       Other Cold Cleaning 11,326 1,245 0.02% 0.34%
    Open Top Vapor Degreasing 112 1,330 0.02% 0.36%
    Conveyorized Vapor
     Degreasing 96 2,086 0.03% 0.57%
Aerosol Packing 195 7,804 0.03% 0.82%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 264 1,702 0.03% 1.45%
    Paint Manufacturing 195 627 0.01% 0.53%
Paint Remover Use (Stripping)
    Paint Stripping - Large
       Aircraft Firms 37 254,902 0.18% 6.21%
    Paint Stripping -Small
       Aircraft Firms 112 44,111 0.73% 16.15%
    Paint Stripping - Furniture 3,600 4,889 5.83% 106.08%
    Paint Stripping - Industrial 965 5,434 0.07% 1.48%
Electronics
    Semiconductors 666 2,661 0.03% 0.68%
    Printed Circuit Boards 393 2,285 0.05% 1.07%
Foam Blowing/Plastics
    Foam Blowing 180 22,368 0.62% 14.42%
    Other Plastics/Adhaesives 762 1,896 0.05% 1.22%
Ink Use (Printing)
    Ink Solvent Manufacturing 4 2,171 0.01% 0.23%
    Ink Solvent Use (Blanket
       Wash) 1,048 637 0.04% 0.81%
Pesticide Formulation 60 1,474 0.02% 0.61%
Pharmaceuticals 76 8,219 0.02% 0.37%
Solvent Recovery 40 555 0.04% 0.63%
Film Base 2 841,256 0.05% 1.55%
Polycarbonates 4 0 0.00% 0.00%
Construction 7,603 1,728 0.39% 10.65%
Shipyards 20 30,781 0.10% 2.56%
ALL APPLICATION GROUPS 28,147 2,845
__________________________________________________________________________
Source: CONSAD
TABLE 22
ECONOMIC IMPACT OF A 25 PPM STANDARD - FIRST YEAR
NOTE: Because of the width of this table, columns describing the IMPACT OF
          COMPLIANCE follows as a separate table.
__________________________________________________________________________
Impact of Substitution
__________________________________________________________________________
    First Year    
  Number of Substitution First Year
  Estab- Cost per Costs of Substitution
  lishments Substituting _____________________
  Substi- Establish- as Percent as Percent
Application Group tuting ment ($) of Sales of Profit
__________________________________________________________________________
Manufacture of MC 0 - - -
Distribution/Formulation
    of Solvents 42 0 0.00% 0.00%
Metal Cleaning
    Cold Degreasing and
        Other Cold Cleaning 11,326 0 0.00% 0.00%
    Open Top Vapor Degreasing 12 15,339 0.20% 4.17%
    Conveyorized Vapor
      Degreasing 11 21,942 0.28% 5.96%
Aerosol Packing 22 60,000 0.23% 6.30%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 29 40,000 0.82% 34.00%
    Paint Manufacturing 195 6,000 0.12% 5.10%
Paint Remover Use (Stripping)
    Paint Stripping - Large
        Aircraft Firms 38 5,347 0.00% 0.13%
    Paint Stripping -Small
        Aircraft Firms 113 852 0.01% 0.31%
    Paint Stripping - Furniture 400 4,075 4.86% 88.44%
    Paint Stripping - Industrial 965 1,788 0.02% 0.49%
Electronics
    Semiconductors 0 - - -
    Printed Circuit Boards 0 - - -
Foam Blowing/Plastics
    Foam Blowing 0 - - -
    Other Plastics/Adhaesives 85 0 0.00% 0.00%
Ink Use (Printing)
    Ink Solvent Manufacturing 33 0 0.00% 0.00%
    Ink Solvent Use (Blanket
        Wash) 9,434 0 0.00% 0.00%
Pesticide Formulation 0 - - -
Pharmaceuticals 0 - - -
Solvent Recovery 0 - - -
Film Base 0 - - -
Polycarbonates 0 - - -
Construction 1,901 0 0.00% 0.00%
Shipyards 5 0 0.00% 0.00%
ALL APPLICATION GROUPS 24,610 314
__________________________________________________________________________
Source: CONSAD
TABLE 22
ECONOMIC IMPACT OF A 25 PPM STANDARD - FIRST YEAR
NOTE: The following table is part of the preceding Table which shows the
Impact of Substitution. The Table has been split because of its width.
__________________________________________________________________________
Impact of Compliance
__________________________________________________________________________
    First Year    
  Number of Substitution First Year
  Estab- Cost per Costs of Substitution
  lishments Substituting _____________________
  Substi- Establish- as Percent as Percent
Application Group tuting ment ($) of Sales of Profit
__________________________________________________________________________
Manufacture of MC 6 2,636 0.01% 0.28%
Distribution/Formulation
    of Solvents 380 3,968 0.10% 2.53%
Metal Cleaning
    Cold Degreasing and
        Other Cold Cleaning 11,326 1,611 0.02% 0.44%
    Open Top Vapor Degreasing 112 1,699 0.02% 0.46%
    Conveyorized Vapor
     Degreasing 96 2,446 0.03% 0.66%
Aerosol Packing 195 9,954 0.04% 1.04%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 264 2,227 0.05% 1.89%
    Paint Manufacturing 195 1,576 0.03% 1.34%
Paint Remover Use (Stripping)
    Paint Stripping - Large
        Aircraft Firms 37 361,587 0.26% 8.81%
    Paint Stripping -Small
        Aircraft Firms 112 62,618 1.03% 22.93%
    Paint Stripping - Furniture 3,600 5,568 6.64% 120.81%
    Paint Stripping - Industrial 965 6,810 0.09% 1.86%
Electronics
    Semiconductors 666 3,182 0.04% 0.81%
    Printed Circuit Boards 393 2,910 0.07% 1.37%
Foam Blowing/Plastics
    Foam Blowing 180 24,300 0.67% 15.67%
    Other Plastics/Adhaesives 762 2,506 0.07% 1.62%
Ink Use (Printing)
    Ink Solvent Manufacturing 4 2,494 0.01% 0.26%
    Ink Solvent Use (Blanket
        Wash) 1,048 911 0.06% 1.16%
Pesticide Formulation 60 2,020 0.02% 0.83%
Pharmaceuticals 76 8,028 0.02% 0.36%
Solvent Recovery 40 555 0.04% 0.63%
Film Base 2 1,951,862 0.11% 3.60%
Polycarbonates 4 0 0.00% 0.00%
Construction 7,603 2,663 0.60% 16.41%
Shipyards 20 33,824 0.11% 2.81%
ALL APPLICATION GROUPS 28,147 3,770
__________________________________________________________________________
Source: CONSAD


TABLE 23
ECONOMIC IMPACT OF A 25 PPM STANDARD - SECOND AND FOLLOWING YEARS
NOTE: Because of the width of this table, columns describing the IMPACT OF
          COMPLIANCE follows as a separate table.
__________________________________________________________________________
Impact of Substitution
__________________________________________________________________________
    Recurring    
  Number of Substitution Recurring
  Estab- Cost per Costs of Substitution
  lishments Substituting _____________________
  Substi- Establish- as Percent as Percent
Application Group tuting ment ($) of Sales of Profit
__________________________________________________________________________
Manufacture of MC 0 - - -
Distribution/Formulation
    of Solvents 42 0 0.00% 0.00%
Metal Cleaning
    Cold Degreasing and
        Other Cold Cleaning 11,326 0 0.00% 0.00%
    Open Top Vapor Degreasing 12 0 0.00% 0.00%
    Conveyorized Vapor
      Degreasing 11 0 0.00% 0.00%
Aerosol Packing 22 0 0.00% 0.00%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 29 0 0.00% 0.00%
    Paint Manufacturing 195 0 0.00% 0.00%
Paint Remover Use (Stripping)
    Paint Stripping - Large
        Aircraft Firms 38 0 0.00% 0.00%
    Paint Stripping -Small
        Aircraft Firms 113 0 0.00% 0.00%
    Paint Stripping - Furniture 400 4,075 4.86% 88.44%
    Paint Stripping - Industrial 965 1,788 0.02% 0.49%
Electronics
    Semiconductors 0 - - -
    Printed Circuit Boards 0 - - -
Foam Blowing/Plastics
    Foam Blowing 0 - - -
    Other Plastics/Adhaesives 85 0 0.00% 0.00%
Ink Use (Printing)
    Ink Solvent Manufacturing 33 0 0.00% 0.00%
    Ink Solvent Use (Blanket
        Wash) 9,434 0 0.00% 0.00%
Pesticide Formulation 0 - - -
Pharmaceuticals 0 - - -
Solvent Recovery 0 - - -
Film Base 0 - - -
Polycarbonates 0 - - -
Construction 1,901 0 0.00% 0.00%
Shipyards 5 0 0.00% 0.00%
ALL APPLICATION GROUPS 24,610 155 0.00% 0.03%
__________________________________________________________________________
Source: CONSAD
TABLE 23
ECONOMIC IMPACT OF A 25 PPM STANDARD - SECOND AND FOLLOWING YEARS
NOTE: The following table is part of the preceding Table which shows the
Impact of Substitution. The Table has been split because of its width.
__________________________________________________________________________
Impact of Compliance
__________________________________________________________________________
    Recurring    
  Number of Substitution Recurring
  Estab- Cost per Costs of Substitution
  lishments Substituting _____________________
  Substi- Establish- as Percent as Percent
Application Group tuting ment ($) of Sales of Profit
__________________________________________________________________________
Manufacture of MC 6 2,636 0.01% 0.28%
Distribution/Formulation
    of Solvents 380 3,969 0.10% 2.53%
Metal Cleaning
    Cold Degreasing and
        Other Cold Cleaning 11,326 1,612 0.02% 0.44%
    Open Top Vapor Degreasing 112 1,698 0.02% 0.46%
    Conveyorized Vapor
      Degreasing 96 2,446 0.03% 0.66%
Aerosol Packing 195 9,954 0.04% 1.04%
Paint and Paint Remover Formu-
    lation
    Paint Remover Formulation 264 2,227 0.05% 1.89%
    Paint Manufacturing 195 1,577 0.03% 1.34%
Paint Remover Use (Stripping)
    Paint Stripping - Large
        Aircraft Firms 37 361,586 0.26% 8.81%
    Paint Stripping -Small
        Aircraft Firms 112 62,618 1.03% 22.93%
    Paint Stripping - Furniture 3,600 5,568 6.64% 120.82%
    Paint Stripping - Industrial 965 5,434 0.07% 1.48%
Electronics
    Semiconductors 666 3,182 0.04% 0.81%
    Printed Circuit Boards 393 2,910 0.07% 1.37%
Foam Blowing/Plastics
    Foam Blowing 180 24,300 0.67% 15.67%
    Other Plastics/Adhaesives 762 2,506 0.07% 1.62%
Ink Use (Printing)
    Ink Solvent Manufacturing 4 2,495 0.01% 0.26%
    Ink Solvent Use (Blanket
        Wash) 1,048 910 0.06% 1.16%
Pesticide Formulation 60 2,020 0.02% 0.83%
Pharmaceuticals 76 8,028 0.02% 0.36%
Solvent Recovery 40 555 0.04% 0.63%
Film Base 2 1,952,019 0.11% 3.60%
Polycarbonates 4 0 0.00% 0.00%
Construction 7,603 2,524 0.57% 15.56%
Shipyards 20 33,605 0.11% 2.79%
ALL APPLICATION GROUPS 28,147 3,733
__________________________________________________________________________
Source: CONSAD

H. Regulatory Flexibility Analysis

Among the various application groups, only small firms (those with under 20 total employees) involved with stripping of aircraft or with paint stripping of furniture would incur compliance costs that would threaten their profitability. Small aircraft stripping firms may react by substituting away from MC and by performing more of their work outdoors. Small firms engaged in paint stripping of furniture may react by substituting other chemicals for MC and by specialization. Because almost all firms in this application group are small, the effects would be uniform throughout the group. OSHA invites comments on ways to ameliorate the impacts in these sectors.

I. Environmental Impacts

Future environmental releases of methylene chloride resulting from the alternative PELs being considered by OSHA will largely be a function of how these alternative PELs affect the demand for methylene chloride and for its substitutes. The demand for methylene chloride has been declining (e.g., generally, it is no longer being used in formulating hairsprays). Any regulatory action by OSHA is expected to further reduce the demand for MC and, thus, the extent of its environmental releases.

The proposed revision of the MC standard is not expected to influence any users of methylene chloride to turn to chlorofluorocarbons as a substitute.

Generally, it is not expected that any significant environmental impact would result from revision of the methylene chloride standard.

XI. Environmental Impact

This section analyzes the impact on the environment of changing the standard for methylene chloride (MC) to either (1) a 50 parts per million (ppm) eight-hour time weighted average permissible exposure limit (PEL) and 250 ppm 15-minute short-term exposure limit (STEL) or (2) a 25 ppm PEL and 125 ppm STEL. It is based on a study conducted for OSHA by CONSAD Research Corporation and reported in Analysis of Draft Regulatory Standard for Methylene Chloride, 1990 (Ex. 15).

Current uses of methylene chloride involve releases to the air through venting of storage tanks or drums and performance of activities such as paint stripping and solvent recovery outdoors and also possible air, water, or solid waste pollution in the disposal of waste residues. Additional details by application group are presented in CONSAD's report.

Future environmental releases of methylene chloride resulting from the alternative PELs being considered by OSHA will largely be a function of how these alternative PELs affect the demand for methylene chloride and for its substitutes. The demand for methylene chloride has been declining (e.g., generally, it is no longer being used in formulating hairsprays). Any regulatory action by OSHA is expected to further reduce the demand for MC and thus the extent of its environmental releases.

Although it is technically possible to substitute chlorofluorocarbons (CFCs) for methylene chloride in electronics and foam blowing, OSHA does not expect the proposed revisions of MC standards to have any such effect. CFC products are significantly more expensive than MC products and are themselves being phased out because of their effects on the environment.

To the extent that firms might have to use greater quantities of substitute chemicals to get the same effects formerly obtained with MC, waste residues and disposal costs would increase. On the other hand, increases in MC leak prevention and recycling would improve the environment. Generally, it is not expected that any significant environmental impact would result from revision of the methylene chloride standard.

XII. Summary and Explanation of the Proposed Standard

OSHA believes that the proposed requirements set forth in this notice are those which, based on currently available data, are necessary and appropriate to provide adequate protection to employees exposed to MC. In the development of the proposal, OSHA has considered all recommendations received in response to the ANPR as well as numerous reference works, journal articles, and other data accumulated by OSHA since initiation of this rulemaking.

The language of the standard and the order of the various provisions are consistent with drafting in other recent OSHA health standards, such as the formaldehyde and benzene standards. OSHA believes that a similar style should be followed from standard to standard to facilitate uniformity of interpretation of similar provisions. Section 6(b)(5) of the Act states that health standards shall also be based on "experience gained under this and other health and safety laws."

A. Scope and application: Paragraph (a)

This proposed standard would apply to all workplaces in all industries, including those in general industry, construction and shipyards, where MC is produced, released, stored, handled, used, or transported, and over which OSHA has jurisdiction. As indicated in the following discussion, an exemption provision has been provided in the proposal for those employers who obtain objective data which demonstrate that MC cannot be released from the product in question at concentrations above the action level.

OSHA has consulted with its Shipyard Employment Standards Advisory Committee (SESAC) to obtain information on MC use and exposure in shipyards. On May 13, 1991, OSHA provided the SESAC with the draft proposed regulatory text and with a list of questions. The SESAC formed a work group to generate recommendations regarding the draft proposal and to collect information responsive to OSHA's questions. On August 12, 1991, the work group presented its report to the full committee. In particular, the work group urged OSHA to carefully consider 1) the extent to which the non-positive results of human studies offset the positive results of the animal studies used by OSHA to estimate human cancer risk and 2) the appropriateness of requiring that filter-type respirators not be used by MC-exposed shipyard employees. The work group report also contained information on 1) MC-containing products used in shipyards; 2) the number of shipyard employees exposed to MC; 3) the activities during which shipyard employees are exposed to MC; 4) the measures taken to eliminate or control shipyard employee exposure to MC; and 5) MC exposure levels in shipyards. The SESAC adopted the work group report and forwarded it to OSHA as the recommendation of the Committee (SESAC Tr. 2-82, 8-13-91). The SESAC work group report (Ex. 17a) and the pertinent SESAC meeting transcripts (Ex. 17b) are available for review and copying in the OSHA Docket Office.

In addition, the SESAC discussed whether or not OSHA should allow employers whose employees use MC on fewer than 30 days a year to comply with the draft proposed PELs by any mix of engineering, work practices and respiratory protection. Some SESAC members noted that this threshold would allow small shipyards reasonable flexibility in determining how to comply with the PELs. OSHA solicits comments, supported by cost and benefit data, on this issue and other issues pertaining to shipyards in question 26, above.

As indicated by proposed paragraph (a), OSHA has included construction within the scope of this rulemaking. Under section 107 of the Contract Work Hours and Safety Standards Act (40 U.S.C. 333) (the Construction Safety Act) and 29 CFR 1911.10, OSHA consults with the Advisory Committee on Construction Safety and Health (ACCSH) in the formulation of standards that would have a significant impact on construction employment. In general, OSHA has complied with these requirements by 1) providing the ACCSH with copies of any draft proposed rule related to construction, along with any pertinent factual information; 2) convening the ACCSH to elicit recommendations on the draft standard; and 3) incorporating the Advisory Committee's recommendations into the Notice of Proposed Rulemaking (NPRM) published in the Federal Register, as OSHA deems appropriate, either as proposed regulatory text or as part of the preamble discussion.

OSHA has not yet consulted with the ACCSH regarding the proposed rule for MC because the Committee's members, whose terms expired in June 1990, have not yet been replaced. It is uncertain when the process of reconstituting the ACCSH will be completed.

Based on its review of the rulemaking record, the Agency believes that the NPRM for MC provides the necessary rationale for regulatory action and sets out the requirements needed to protect employees in all industries, including construction, from the health hazards associated with occupational exposure to MC. OSHA believes that further deferral of NPRM publication, pending consultation with the ACCSH, would delay Agency efforts to increase protection of MC-exposed employees, of whom the vast majority work in general industry and in shipyards. Accordingly, OSHA has determined that publishing the MC proposal at this time best effectuates the purposes of the OSH Act.

The Agency will consult the ACCSH and obtain its recommendations regarding the regulation of MC as soon as the ACCSH is in a position to provide its input. If OSHA determines, based on its consultation with the ACCSH, that any provision(s) of the proposal should be revised with respect to the construction industry, the Agency will publish these revisions to the proposal. If the Agency determines, based on consultation with the ACCSH, that it is inappropriate to revise the proposal, OSHA will explain the basis for that determination in the hearing notice.

The notice of proposed rulemaking does not schedule hearings on the proposed rule. OSHA expects to issue a hearing notice, if hearings are requested, after the Agency has consulted with the ACCSH and has evaluated the Committee's recommendations. This will enable OSHA to conduct a single set of hearings covering all industry sectors where there is occupational exposure to MC.

This section does not apply to the processing, use, and handling of products containing MC where objective data demonstrate that the product cannot release MC above the action level under foreseeable conditions of processing, use, and handling which will cause the greatest possible release. It is likely, in a number of products made from, containing or treated with MC, that an insignificant residual of MC will be present and from which minimal exposure to MC would be expected. This determination (that air concentrations of MC will not exceed the action level or the STEL) need not be based on data generated by the processor but may, for example, be based upon information provided by the manufacturer. The provision enables fabricators or users of products made from, containing or treated with MC to avoid the burdens of compliance with the standard where exposures are minimal.

It should be noted that where objective data are not available to satisfy the conditions for exemption, the employer is required to perform, at the very least, initial monitoring of employee exposures to MC. If the results of initial monitoring indicate employee exposures are below the action level, the employer may discontinue monitoring for those employees and is relieved of other obligations under the proposal, except for the labelling requirements in paragraph (j). Thus, even if operations are not specifically exempted from the proposal, employers have an incentive to keep exposure levels below the 12.5 ppm "action level". This provision has been incorporated in a number of OSHA standards (acrylonitrile 29 CFR §1910.1045, 43 FR 45809 (1978); arsenic 29 CFR §1910.1018, 43 FR 19624 (1978); ethylene oxide 29 CFR §1910.1047, 49 FR 5796 (1984) and 53 FR 11413 (1988)).

In addition, the Hazard Communication Standard, §1910.1200 (d)(5)(iv), provides that a mixture shall be assumed to pose a health hazard where a component present in the mixture in concentrations of less than one percent (or in the case of carcinogens, less than 0.1 percent) could be released in concentrations which would exceed an established OSHA permissible exposure limit or ACGIH Threshold Limit Value, or could present a health hazard to employees in those concentrations. As noted above, OSHA has determined that MC is a potential occupational carcinogen and that there is no MC exposure level at which employees are safe from cancer risk. Therefore, regardless of exposure level, employers whose employees are exposed to MC are required to comply with the requirements of the Hazard Communication Standard.

B. Definitions: Paragraph (b)

"Action Level"

"Action level" means an airborne concentration of MC at or above 12.5 ppm, measured as an 8-hour time-weighted average. One purpose of the action level is to relieve the burden on employers by providing a cut-off point for virtually all required compliance activities under the proposed standard. In addition, due to the variable nature of employee exposures to airborne concentrations of MC, the concept of an action level provides a means by which the employer may have greater assurance that the employees will not be exposed to MC concentrations above the permissible exposure limits.

The action level also increases the cost-effectiveness and performance orientation of the standard while improving employee protection. Employers who can, in a cost-effective manner, come up with innovative methodology to reduce exposures below the action level, will be encouraged to do so in order to spare themselves the expense of monitoring and medical surveillance. Their employees will be protected because their exposures will be less than half of the permissible exposure limit. When employers do not lower exposures below the action level, employees above the action level will have the protection of medical surveillance, monitoring and other provisions of the standard to give further protection from the effects of MC.

The statistical basis for using an "action level" has been discussed in connection with several other OSHA health standards (see, for example, acrylonitrile (29 CFR §1910.1045 (43 FR 45809, October 3, 1978)). In brief, although all measurements on a given day may fall below the permissible exposure limit, some possibility exists that on unmeasured days the employee's actual exposure may exceed the permissible limit. Where exposure measurements are above the action level, the employer cannot reasonably be confident that the employee may not be overexposed. Therefore, requiring periodic employee exposure measurements to begin at the action level provides the employer with a reasonable degree of confidence in the results of the exposure measurement program (Ex. 7-248). OSHA's specific choice of setting an action level of one-half the PEL is based on its successful experience in utilizing one-half the PEL as the action level in many standards, such as arsenic, ethylene oxide, vinyl chloride and benzene.

The action level provides a way of maximizing employee protection in those instances where exposures are possibly significant, and of minimizing employer obligations by defining the point below which no action, except as required by the Hazard Communication Standard (29 CFR 1910.1200), is necessary. Use of the action level concept will result in the necessary inclusion of employees under the proposed standard, whose exposures are above the action level and for whom further protection is warranted. The action level concept, therefore, provides an objective means of tailoring different sections of the standard to those employees who are at significant risk of developing adverse health effects from exposure to MC.

"Day" is defined as any part of a calendar day. Therefore, if a requirement is applicable for an employee who is exposed to MC for 10 days in a calendar year, that requirement becomes applicable to an employee who is exposed to MC for any part of each of 10 calendar days in a year.

"Emergency"

For the purposes of the standard, an "emergency" is an occurrence such as, but not limited to, equipment failure, rupture of a container, or failure of control equipment which may or does, result in an unexpected significant release of MC. Sections of the proposed standard that include provisions that must be met in case of emergency include Respiratory Protection, Medical Surveillance, Employee Information and Training and Emergency Plan. Every spill or leak does not automatically constitute an emergency situation. The exposure to employees must be high and unexpected. This is a performance-oriented provision which relies on judgment. It is not possible to specify detailed circumstances which constitute an emergency.

"Employee exposure" is defined as that exposure to airborne MC which would occur if the employee were not using respiratory protective equipment. This definition is consistent with OSHA's previous use of the term "employee exposure" in other health standards.

"Methylene chloride" (MC) means an organic compound with chemical formula, CH(2)Cl(2). Its Chemical Abstracts Registry Number is 75-09-2. It is a colorless, volatile, liquid with a chloroform-like odor and is not flammable by standard tests in air, but will burn under extreme conditions. It has molecular weight of 84.94, a boiling point of 39.85 deg C (104 deg F) at standard atmospheric pressure, a lower explosive limit of 12% and an upper explosive limit of 19.5% in air. It is completely miscible with most organic solvents but is sparingly soluble in water (1.3% by weight at room temperature). It has an extensive oil and fat solubility. Decomposition products during combustion or fire include phosgene, hydrochloric acid and carbon monoxide.

"Regulated area" means an area demarcated by the employer where airborne concentrations of MC exceed or can reasonably be expected to exceed the eight-hour TWA or the STEL. The requirements for regulated areas are discussed in relation to proposed paragraph (e), below.

The definitions of "Assistant Secretary", "Authorized Person" and "Director" are consistent with OSHA's previous uses of these terms found in other health standards.

C. Permissible Exposure Limits (PELs): Paragraph (c)

OSHA proposes to set an 8-hour time weighted average (TWA) exposure limit of 25 ppm, because OSHA has determined that occupational exposure to MC at the current 500 ppm 8-hour TWA PEL presents a significant risk of cancer to employees and that compliance with the new standard will substantially reduce that risk.

The basis for the 8-hour permissible exposure limit is discussed above in the sections on significant risk and feasibility. OSHA believes lowering the current PEL to 25 ppm, as an 8-hour TWA, substantially reduces a significant risk and is feasible for industry to achieve.

OSHA is also proposing a short term exposure limit (STEL) of 125 ppm for 15 minutes to protect employees from the acute toxicity of MC and its metabolites, and to complement the protection from MC's carcinogenic effects afforded by compliance with the 8-hour TWA. The acute toxicity of MC is characterized primarily by CNS effects such as, decreased alertness and coordination, headaches and dizziness which may ultimately lead to accidents and further exposure to MC. Without incorporation of a STEL into the MC health standard, an employee can theoretically be exposed to up to 12,000 ppm for one minute, a level which is regarded as immediately dangerous to life (e.g., loss of orientation or loss of consciousness which could lead to life-threatening accidents or further overexposure to MC).

Another acute toxic effect of MC exposure is the increase in carboxyhemoglobin levels. High carboxyhemoglobin levels can interfere with the oxygen carrying capacity of blood and are a particular problem for individuals who smoke, those who have limited oxygen carrying capacity, those with silent or symptomatic heart disease, and pregnant women.

OSHA is also concerned regarding the metabolism of MC to its putative carcinogenic metabolite. Metabolic evidence suggests that the MFO pathway (the pathway not believed to be a major contributor to carcinogenesis) begins to be saturated at approximately 100 ppm and metabolism by the GST pathway (the putative carcinogenic pathway) becomes more quantitatively important. For this reason, it is important to limit short-term exposure to MC in order to limit metabolism by the GST pathway and protect the employee from excessive exposure to carcinogenic metabolites of MC. A 15-minute STEL of 125 ppm will protect against the CNS effects, maintain the COHb levels below 3% and limit the extent to which MC would be metabolized by the putative carcinogenic pathway, further decreasing the cancer risk. The basis for the STEL is discussed further in the Significance of Risk section, above.

The proposed standard allows a 15-minute exposure to 125 ppm as long as the employer complies with the 8-hour TWA of 25 ppm. If the health effects of MC are related to total dose alone, without regard to temporal distribution of that dose, an 8-hour TWA limit on exposures will reduce the risk of those health effects by limiting the total dose received. However, if the effects from exposure can be shown to be greater when the total dose is received in a short period than when it is spread over a longer period, an 8-hour TWA limit alone might not be adequate to reduce the risks. In the event of such a "dose-rate" relationship being established, a STEL might be warranted as a supplement to the 8-hour TWA in order to provide protection against additional risk attributable to concentration of the dose over short periods. This "dose-rate" relationship has been established for the CNS and COHb acute health effects of MC. The MC metabolic data also suggests a dose rate effect for the carcinogenesis of MC. Because of the saturation of the MFO pathway described above, the putative carcinogenic pathway becomes quantitatively more important at exposure levels as low as 125 ppm. For this reason, it is prudent to minimize the duration of exposures to MC at 125 ppm. Therefore, a STEL of 125 ppm for 15 minutes duration has been proposed to protect against the dose rate effects described.

The level of the STEL in this proposal, five times the PEL, is consistent with the standards for other substances, such as formaldehyde, which was recently promulgated by OSHA.

D. Exposure Monitoring: Paragraph (d)

The proposed standard imposes monitoring requirements pursuant to Section 6(b)(7) of the OSH Act (29 U.S.C. § 655) which mandates that any standard promulgated under section 6(b) shall, where appropriate, "provide for monitoring or measuring of employee exposure at such locations and intervals, and in such manner as may be necessary for the protection of employees." The purposes of requiring air sampling for employee exposure to MC include: the prevention of overexposure of employees; the determination of the extent of exposure at the work-site; the identification of the source of exposure to MC; and collection of exposure data by which the employer can select the proper control methods to be used and evaluate the effectiveness of the selected methods. Monitoring enables employers to meet the legal obligation of the standard to assure that their employees are not exposed to MC in excess of the prescribed levels, and to be able to notify employees of their exposure levels, as required by section 8(c)(3) of the Act. In addition, collection of exposure monitoring data enables the examining physician to be informed of employee exposure levels.

Exposure monitoring is also important to determine the level of MC to which employees are exposed. This determines what other requirements of the standard will have to be met. Certain sections of the standard are triggered if an employee is exposed above the action level and are not required if the employee is not.

The exposure monitoring provisions require the employer to determine the exposure for each employee exposed to MC. This does not mean that separate measurements for each employee must be taken but rather that "representative employee exposure" is to be determined. In some cases, that will entail monitoring all exposed employees. In others, the monitoring of "representative" employees suffices. Samples must be taken within the employee's breathing zone (also known as "personal breathing zone samples" or just "personal samples"). The samples used to determine whether the employee is exposed above the action level must represent the employee's exposure to airborne concentrations of MC over an eight-hour period without regard to the use of respirators. Representative 15-minute short-term employee exposures are to be determined on the basis of one or more samples representing 15-minute exposures associated with operations that are most likely to produce exposures above the STEL for each shift for each job classification in each work area. Here, too, respirators cannot be a factor. (See "Employee exposure", as defined in the definitions section). Full-shift sampling must be conducted for each job classification in each work area. These samples must consist of at least one sample representative of the entire shift or of consecutive samples taken over the length of the shift.

Representative exposure sampling is permitted when there are a number of employees performing essentially the same job under the same conditions. For these types of situations, it may be sufficient to monitor a fraction of such employees in order to obtain data that are "representative" of the remaining employees. As permitted in section (d)(1)(iv), representative personal sampling for employees engaged in similar work and exposed to similar MC levels can be achieved by measuring that member of the exposed group reasonably expected to have the highest exposure. This result would then be attributed to the remaining employees of the group.

To eliminate unnecessary monitoring and improve the cost-effectiveness of the standard, paragraph (d)(1)(iv) allows employers who can document that exposure levels are the same for similar operations in different work shifts throughout the work day, to sample only the shift for which the highest exposures are expected to occur. This provision does not apply to initial monitoring requirements. The employer must be able to demonstrate that employees on the shifts who are not monitored, are not likely to have exposures higher than those of the shifts monitored.

Initial monitoring is required (proposed paragraph (d)(2)) of all employers who have a place of employment covered under the scope of this standard. In addition, the proposed standard requires that the initial monitoring be conducted within 120 days of the effective date of the final standard or the introduction of MC to the work place. OSHA believes that within that time employers will be able to either prepare objective data exempting them from monitoring requirements or complete initial monitoring.

To eliminate unneeded requirements, proposed paragraph (d)(2)(ii) provides that if an employer has workplace monitoring data from within one year prior to the effective date which satisfies the proposed rule, those data can be used to satisfy the requirements of the initial monitoring. This provision is designed to make clear that OSHA does not intend to require employers who have recently performed appropriate employee monitoring to conduct "initial" monitoring. The employer would use that monitoring data to determine if periodic monitoring was required. If it was required, the recent monitoring data would indicate the appropriate frequency for that monitoring.

The results of the initial monitoring represent the data which would be used to determine when periodic monitoring would be required. The requirements for periodic monitoring are presented in proposed paragraph (d)(3). If exposures are below the action level, no further monitoring would be required unless processes or products change which are likely to lead to higher exposure. If the initial monitoring results show employee exposures at or above the action level, but at or below the PEL, then the employer must repeat monitoring for these individuals every six months. If exposures are above the PEL, then the employer must remonitor every three months. If the employee's exposure is above the STEL, the employer shall repeat such monitoring at least every three months. If, under the terms of proposed paragraph (d)(3)(iv), in subsequent monitoring, results indicate that an employee's exposure, as determined by two consecutive measurements taken at least seven days apart, falls from above the PEL to between the PEL and action level, then monitoring need only be done every six months, unless production changes may lead to higher exposures. Similarly, when the two consecutive measurements indicate that the exposure has dropped below the action level, further monitoring can be discontinued. OSHA believes those frequencies, which are similar to other OSHA standards such as Ethylene Oxide, are sufficient.

OSHA's proposed monitoring of employees whose exposures are between the action level and the 8-hour TWA every six months is based on several factors. While these employees have been shown to be exposed to levels of MC below the 8-hour TWA, their levels of exposures are not so far below the PEL that monitoring could safely be discontinued. Even minor changes in engineering controls or work practices could result in exposures increasing to levels above the PEL. Remonitoring on a semi-annual basis will enable the employer to be confident that engineering controls are working or, in the event exposures are shown to exceed the 8-hour TWA, alert the employer as to the need for additional controls.

The standard would contain an 8-hour TWA, a STEL and action level. The interrelationship between the 8-hour TWA PEL, the STEL, and the action level at a given workplace would determine the frequency with which employers are obligated to monitor employee exposures under proposed paragraph (d)(3). There would be six possible exposure scenarios, or combinations of 8-hour TWA and short-term exposures, that would determine the frequency of required monitoring. Table 24 below lists these six exposure scenarios, along with their monitoring frequencies. As shown by Table 24, the action level trigger largely determines whether employers must monitor employees exposure to MC. The only exception would be the scenario in which 8-hour TWA exposures are below the action level and short-term exposures are above the STEL. In this particular case, the existence of a STEL would obligate employers to monitor short-term exposures four times per year at those job locations where the STEL was exceeded, but employers would not be obligated to monitor 8-hour TWA exposures at those job locations.

TABLE 24 - SIX EXPOSURE SCENARIOS AND THEIR ASSOCIATED MONITORING
              FREQUENCIES
__________________________________________________________________
    Exposure Scenario | Required Monitoring Activity
_______________________________ | __________________________________
|
Below the action level | No 8-hour TWA or STEL
    and at or below the STEL. | monitoring required.
|
Below the action level and | No 8-hour TWA monitoring
    above the STEL. | required; monitor STEL
| exposures every three
| months.
|
At or above the action level, | Monitor 8-hour TWA exposures
    at or below the TWA, and at | every six months.
    or below the STEL. |
|
At or above the action level, | Monitor 8-hour TWA exposures
    at or below the TWA, and | every six months and monitor
    above the STEL. | STEL exposures every three
| months.
|
Above the TWA and at or | Monitor 8-hour TWA exposures
    below the STEL. | every three months
|
Above the TWA and above the | Monitor 8-hour TWA exposures
    STEL. | and STEL exposures every
| three months.
______________________________ | _____________________________________

OSHA recognizes that exposures in the workplace may fluctuate. In the proposed standard, changes in production or work practices which are likely to increase exposure would trigger the provision for additional monitoring. OSHA is concerned that this provision does not provide sufficient guidance to the employer for situations in which the exposure levels may increase without an identifiable change in process or work practice. Currently, the language in the proposal implies that any increase in exposures from between the action level and PEL to above the PEL or STEL would prompt an increased frequency of monitoring. However, in order to eliminate any confusion over the application of this provision, OSHA is considering the addition of a provision to clarify that a periodic exposure monitoring sample which demonstrates that an employee's exposure has increased from below the PEL and STEL to above the PEL or STEL would trigger an increase in the frequency of required monitoring from 6 months to 3 months. This provision would not impose an additional monitoring burden on the employer, but would serve as a clarification of the current proposed requirements. OSHA is soliciting comment as to whether this provision would be necessary and appropriate in the final rule to clarify the intent of the provisions for changing the frequency of monitoring.

Under the terms of proposed paragraph (d)(4) employers are allowed to forgo periodic monitoring of employees for whom initial monitoring results indicate exposure below the action level. Furthermore, if periodic monitoring results indicate, by at least two consecutive measurements taken at least seven days apart, that employee exposures are below the action level, the employer may discontinue monitoring for these employees. OSHA recognizes that monitoring may be a time-consuming, expensive endeavor and therefore offers employers the incentive of being allowed to discontinue monitoring for employees whose sampling results indicate exposures below the action level. In addition, OSHA anticipates that proposed paragraph (d)(4) will encourage employers to keep exposures to MC below the action level and the STEL in their workplaces. Thus employees would be protected from health hazards and employers could save themselves the time and expense of monitoring and other applicable provisions of the proposed rule as well.

Employees are further protected, even when periodic monitoring has ceased, because additional monitoring is required by paragraph (d)(5)(i) when there has been a process or production change or a change in control equipment, personnel or work practices which may result in new or additional exposures to MC. Additional monitoring is also required when the employer suspects that changes at the workplace will result in new or additional MC exposure. Also, in keeping with Agency policy favoring the use of performance-oriented language, OSHA has proposed the additional monitoring requirement in general terms, instead of trying to define each and every situation where the employer must monitor for new or additional exposures to MC.

Paragraph (d)(5)(ii) specifically requires additional monitoring to be conducted whenever spills, leaks, ruptures or other breakdowns occur. Such occurrences can result in very high exposures. After the clean-up of the spill or repair of the leak employers must again perform the "initial" monitoring provided in proposed paragraph (d)(2) to characterize the exposure for those employees who may be exposed at such areas of their worksites. Such remonitoring provides one method of ascertaining if proper corrective methods have been instituted and if employees' exposures have been significantly altered from what they were prior to the leak or spill.

Under the terms of proposed paragraph (d)(6), the employer is required to use monitoring and analytical methods which have an accuracy (at a confidence level of 95%) of not less than plus or minus 25% for airborne concentrations of MC and within plus or minus 35% over airborne concentrations of MC at the action level. Methods of measurement are presently available to detect MC to this accuracy level at levels of 0.155 ppm. One such method is described in Appendix D. Sampling and analysis may also be performed by portable direct reading instruments, real-time continuous monitoring systems, passive dosimeters or other suitable methods. Employers must select a monitoring method which meets the accuracy and precision requirements of the standard under the unique conditions which exist at the employer's worksite.

Proposed paragraph (d)(7) requires that employers notify affected employees of monitoring results in writing, either individually or by posting of results in an appropriate location accessible to affected employees, within 15 working days after the receipt of the results. In addition, whenever the 8-hour TWA PEL or the STEL has been exceeded, the written notification must contain a description of the corrective action(s) being taken by the employer that will reduce the employee's workplace exposure to or below the PEL and 15 minute STEL. The requirement to inform employees of the corrective actions the employer is going to take to reduce the exposure level to below the PEL is necessary to assure employees that the employer is making efforts to furnish them with a safe and healthful work environment, in accordance with section 8(c)(3) of the Act.

The employer is also required to allow employees or their designated representatives an opportunity to observe the employee exposure monitoring. This provision is required by section 8(c)(3) of the Act (29 U.S.C. 657(c)(3)). It is provided for in paragraph (l) of the proposal, as is discussed in more detail below.

OSHA solicits comment on the proposed frequency of monitoring and any other aspects of the proposed exposure monitoring requirements.

E. Regulated areas: Paragraph (e)

The proposal would require employers to establish a regulated area where airborne exposures to MC exceed either the 8-hour TWA PEL or the STEL. Access to the regulated area would be restricted to authorized persons and the areas themselves are to be designated in a manner that adequately establishes and alerts employees of the boundaries of the regulated areas and minimizes the number of persons exposed to MC within these areas. This provision applies when either the TWA PEL or STEL is likely to be exceeded, but it does not apply to inadvertent releases covered under paragraph (h) (Emergency situations).

The purpose of a regulated area is to ensure that employers make employees aware of the presence of MC at levels above the TWA PEL or STEL in the workplace and to limit MC exposure to as few employees as possible. The establishment of a regulated area is an effective means of limiting the risk of exposure to substances known to have or suspected of having carcinogenic activity in humans. Because of the serious nature of the possible exposure and the need of persons entering the area to be protected by properly fitted personal protective equipment, such as respirators, the number of persons given access to the area should be limited to only those employees needed to do the job.

In keeping with the performance orientation of this proposed standard, OSHA has not specified how employers are to demarcate their regulated areas. Factors that the Agency believes are appropriate for employers to consider in determining how to demarcate their areas include the configuration of the area, whether the regulated area is permanent, the airborne MC concentration, the number of employees in adjacent areas, and the period of time the area is expected to have exposure levels above the PEL. Permitting employers to choose how to identify and limit access to regulated areas is consistent with OSHA's belief that employers are in the best position to make such a determination based on the specific conditions of their workplaces.

OSHA is proposing to require respirators in regulated areas. As a further means of underscoring the importance of keeping hands and mouth clean from contamination with MC, OSHA is soliciting comment on the appropriateness of prohibiting the following activities in regulated areas: smoking, eating, drinking, chewing gum or tobacco and applying cosmetics. Because of the health concerns for the metabolism of MC to CO in the body, and the resulting carboxyhemoglobinemia, OSHA feels it is particularly important to exclude smoking (which also produces CO) from regulated areas. OSHA has prohibited the activities listed above in the proposed rule for cadmium (55 FR 4052).

Paragraph (e)(5) requires that an employer at a multi-employer worksite who establishes a regulated area communicate effectively the location and access restrictions to other employers at the worksite. Such communication would lessen the possibility that unauthorized persons would enter the area or that workers not involved in MC-related operations would be exposed inadvertently. OSHA would require employers whose employees are exposed to MC at concentrations above the PELs to be responsible for coordination of their work with other employers whose employees could suffer excessive exposure because of their proximity to the source of exposure to MC.

The regulated area provision reflects OSHA's concern that the employees at nearby sites be aware of the existence of the hazard and respect the need to remain outside of the perimeters delineated as a regulated area. While this could be accomplished by the employees of the second employer simply reading the signs posted by the first employer, this would not assign accountability. If the second employer is aware of the hazards, then it is the responsibility of the second employer to assure that his employees do not enter the regulated area of the first employer without permission and proper protective equipment.

F. Methods of Compliance: Paragraph (f)

The proposed standard would require the employer to reduce employee exposures to within the permissible limit by use of feasible engineering controls and work practices. Employers would be required to institute engineering controls and work practices to reduce exposures to the lowest feasible level even if these measures, alone, would not reduce the concentration of airborne MC below the PEL. The employer would be required to supplement these controls with respirators to ensure that employees are not exposed to MC at levels above the PEL.

Primary reliance on engineering controls and work practices is consistent with good industrial hygiene practice and with the Agency's traditional adherence to a hierarchy of preferred controls. However, regarding this traditional hierarchy of controls, OSHA published an Advance Notice of Proposed Rulemaking (ANPR) on February 22, 1983 (48 FR 7473) to solicit comments on methods of compliance issues. Among these issues was OSHA's preference for the use of engineering controls over respirators for control of employees' exposures to air contaminants. Many employers have felt the need for increased flexibility in the use of respiratory protection. Based on data received in response to the ANPR, OSHA published a Federal Register notice on June 5, 1989, (54 FR 23991) proposing to incorporate additional flexibility in its methods of compliance requirements by more explicitly setting forth circumstances under which respiratory protection may be used due to the general infeasibility of implementing engineering controls. They are: (1) During the time necessary to install feasible engineering controls; (2) Where feasible engineering controls result in only a negligible reduction in exposures; (3) During emergency, life saving, recovery operations, repair, shutdowns and field situations where there is a lack of utilities for implementing engineering controls; (4) Operations requiring added protection where there is a failure of normal controls; and (5) Entries into unknown atmospheres.

In addition, OSHA requested public comment on other ways of allowing the employer to place greater reliance on the use of respirators to protect workers. Specifically, the Agency asked whether it is necessary to require all feasible engineering controls be installed for maintenance activities; whether respirator use should be permitted for any work situation in which the hazardous exposure is of very brief duration or at any time to achieve compliance with the STEL; and whether respirator use could be allowed in instances where the protection afforded by respirators was equal to, but less costly than, that provided by engineering controls. The proposal also requested information on whether equivalent protection for employees could be achieved by allowing respirator use in lieu of engineering controls for some substances while at the same time requiring employers who choose this option to do something extra, such as submit a written plan to the Agency that demonstrates how respirators provide protection equal to that provided by feasible engineering controls in the given work situation. Finally, OSHA asked for comment on the appropriateness of allowing employers to comply with exposure limits at all times by any method the employer deems advisable, an allowance which would, in effect, abolish OSHA's traditional hierarchy of controls.

In this MC proposal, OSHA would require that employers use engineering controls to comply with the proposed standard, because these controls would reduce exposure hazards in the working environment by removing, at least in part, the contaminant from the air. OSHA has found that employers also generally need to modify their work practices in order to operate engineering controls effectively. OSHA considers the use of respirators to be the least satisfactory approach to exposure control because they provide adequate protection only if employers ensure that respirators are properly fitted and worn. Unlike engineering controls and work practices, respirators are intended to protect only the employees who are wearing them from a hazard, rather than reducing the hazard. Accordingly, OSHA would permit reliance on respirators only insofar as employers can demonstrate that the engineering controls and work practices needed to comply with the PEL are infeasible.

There are certain activities where exposures are intermittent in nature and limited in duration, most often those involving maintenance and repair operations as well as those in emergency situations, where the use of engineering and work practice controls to control exposure to MC is not feasible. Where engineering controls are not feasible, the employer, nevertheless, has the obligation to protect employees. This obligation may require the use of respirators as a primary means of control.

OSHA policy in the past in this matter has been spelled out in the Respiratory Protection Standard, 29 CFR 1910.134(a)(1), which applies to all exposures to airborne toxicants, and in the Air Contaminant Standard 29 CFR 1910.1000(e), which applies to exposures to all substances listed in Table Z-1, Z-2, and Z-3. This policy was inherent in the national consensus standards which were adopted by OSHA in 1971, pursuant to section 6(a) of the OSH Act of 1970. Subsequent additions to Subpart Z, which were developed through section 6(b) rulemaking proceedings also reflect OSHA's determination that employers must control hazards by engineering controls and work practices instead of respirators to the extent feasible.

Under contract to OSHA, CONSAD conducted a study (Ex. 15) that assessed the type and cost of engineering controls that could be used to meet the proposed PEL. CONSAD's suggested compliance strategy, based on a cost-effectiveness approach, relied primarily on local exhaust ventilation, supplemented when necessary with air supplied respirators. OSHA's proposed standard, however, is performance-oriented so that any combination of engineering controls or work practices may be applied to achieve the PEL; and in certain circumstances, firms may find it appropriate to rely on other measures.

OSHA has described control technologies in Section VI, many of which have already been implemented in certain plants where MC is used. These control strategies include magnetic pumps and magnetic floating gauges, exhausted lances for drum filling, inline quality control sampling equipment, chilling coils and dilution and local exhaust ventilation systems. OSHA solicits information and comments regarding the feasibility and effectiveness of these compliance strategies.

Employees' exposures also can be controlled with administrative controls. For example, one method of controlling worker exposures to contaminants is by scheduling operations with the highest exposures at a time when the fewest employees are present. However, another form of administrative control, worker rotation, would be prohibited by OSHA as a compliance strategy. Worker rotation reduces the extent of exposure to individual employees, but increases the number of employees exposed. Since MC has been demonstrated to be carcinogenic in animals and is suspected of being carcinogenic to humans, OSHA would prohibit these practices, or any other practice, which would place more employees at risk. Since no threshold has been demonstrated for the carcinogenic action of MC, it is prudent public health practice to limit the number of workers exposed at any concentration. This policy is consistent with language in other recently proposed OSHA standards, such as 1,3-butadiene (55 FR 32736, August 10, 1990) and cadmium (55 FR 4052, February 6, 1990).

Paragraph (f)(2) requires employers who experience exposure in their work places above the PELs to establish and implement a written compliance program which describes the methodology to be used to reduce employee exposure to or below the PELs within their workplaces. No written compliance program is required if the exposure levels are already below the PELs. The written plan must describe the feasible engineering and work practice controls to be implemented, describe any respiratory protection needed to get exposure below the PELs and include a schedule for implementation. The plan would be furnished upon request for examination and copying to OSHA, NIOSH, and affected employees or their representatives. Once a workplace is in compliance with the standard, the written compliance plan need not be updated. If exposures later increase over the PELs, however, an update must be prepared. The written compliance plans are to be revised as appropriate. Circumstances requiring revision of the compliance plan may include a change in controls or substantially different exposure conditions.

G. Respiratory Protection and Other Protective Clothing and Equipment; Paragraph (g)

Respiratory Protection: When engineering controls and work practices cannot reduce employee exposure to MC to below the PELs, the employer must protect employees' health by the use of respirators. Specifically, respirators must be used while feasible engineering and work practices controls are being installed, in work operations such as maintenance and repair where engineering and work practice control are infeasible and exposures are intermittent and limited in duration, where feasible engineering and work practice controls are not yet sufficient to reduce exposures below the PELs, in regulated areas and in emergencies. These limitations on the required use of respirators are consistent with the requirements of other OSHA health standards (e.g. asbestos, 1910.1001; ethylene oxide 1910.1047; benzene, 1910.1028) and with good industrial hygiene practice. They reflect OSHA's determination, as detailed in the preceding section on methods of compliance, that respirators are inherently less reliable than engineering and work practice controls. OSHA has proposed, therefore, to allow reliance on respirators to control exposures above the PEL only in designated situations.

The proposal requires employers to provide respirators at no cost to the employee and to ensure that employees use the respirators properly. OSHA views this allocation of costs as necessary to effectuate the purposes of the Act. This requirement would make explicit an Agency position which has long been implicit in the promulgation of health standards under section 6(b) of the Act.

The proposal also contains a table (Table 1) listing the types of respiratory protection to be provided based on airborne concentrations of MC in the workplace. The respirator selection table is consistent with OSHA's experience of the performance capabilities of the various types of respirators available. Employers would be allowed to provide respirators with a higher level of protection in lower concentrations of MC.

With the exception of emergency escape situations, OSHA is not allowing the use of air-purifying respirators. NIOSH performed a respirator cartridge breakthrough study with MC (Ex. 7-242) which showed breakthrough times of approximately 40 minutes for cartridges exposed to 15 ppm MC. Because of the short service life of cartridges, NIOSH does not recommend the use of air-purifying respirators for MC. Since the useful service life of cartridges for MC are too short to provide an adequate margin of safety, OSHA is proposing that only supplied air respirators be allowed for use during exposure to MC above the PELs, with the exception of emergency escape, during which gas masks with organic vapor canisters are allowed. These canisters must be replaced after any emergency use.

NIOSH intends to further study the breakthrough characteristics of MC in organic vapor cartridges and canisters in order to better assess the ability of filter respirators to protect MC-exposed employees. NIOSH expects to have this study completed in time to be considered during this rulemaking. OSHA will closely observe NIOSH's progress on this matter and make available any information gathered during the rulemaking process.

Under proposed paragraph (g)(2), employers shall select respirators from those certified as being acceptable for protection against MC exposure by the Mine Safety and Health Administration (MSHA) and by the National Institute for Occupational Safety and Health (NIOSH), under the provisions of 30 CFR Part 11. NIOSH has proposed the revision of the 30 CFR Part 11 respirator certification requirements (52 FR 32401) and their repromulgation as 42 CFR Part 84. OSHA is reviewing the NIOSH proposed respirator certification changes, and will be following the progress of the NIOSH's rulemaking on respirator certification.

Under proposed paragraph (g)(3), whenever respirator use is permitted under the proposal to control exposures to MC, the employer must implement a comprehensive respiratory protection program. The protection program must include the elements set forth in the general respiratory protection standard, 29 CFR 1910.134, which contains basic requirements for proper selection, fit, use, training of employees, cleaning, and maintenance of respirators. For employers to ensure that employees use respirators properly, OSHA has found that the employees need to understand the respirator's limits and the hazard it is protecting against in order to appreciate why specific requirements must be followed when respirators are used.

OSHA is currently revising its general respiratory protection standard, and will be updating and expanding the current 29 CFR 1910.134 provisions to account for advances in respiratory protection, fit testing and selection, and other changes in respiratory protection practices since the current standard was adopted in 1971. Since the respiratory protection revision rulemaking and the MC standard revision are taking place concurrently, OSHA is utilizing the respiratory experience gained during the revision of 29 CFR 1910.134 in preparing the respirator provisions of this MC proposal. OSHA requests comments on all of the respirator provisions in the proposal and their effects on the use of respirators to control exposures to MC.

Under the terms of proposed paragraph (g)(4), employers shall permit employees to leave the regulated area to readjust the respirator facepiece to their faces for proper fit. Employees are also permitted to leave the regulated area to wash their faces to avoid potential skin irritation associated with respirator use.

Proposed paragraph (g)(5) requires initial and annual respirator fit testing when negative pressure respirators are used. A negative pressure is created within the facepiece of a properly fitted respirator when the wearer inhales. A poorly fitted respirator allows contaminated workplace air to enter the facepiece through gaps and leaks in the seal between the face and the facepiece. Employers will be required to perform fit testing in accordance with 29 CFR 1910.134. Qualitative fit testing has been validated by Los Alamos National Laboratory, DuPont, and 3M for protection factors of 10 times the 8-hour TWA, with quantitative fit testing required for higher concentrations. This standard would allow the use of qualitative fit testing for respirators up to an exposure level of 250 ppm of MC (protection factor of 10 x 25 ppm = 250 ppm). In order to use respirators in areas that require higher protection factors, quantitative fit testing must be used.

Proposed paragraph (g)(5)(iii) requires that fit testing follow the protocols in Appendix C. Where quantitative fit testing is used, Appendix C provides that a fit factor of 10 times the assigned protection factor for that class of respirator must be achieved during the fit test. For example, if the assigned protection factor is 10, a fit factor of 100 must be obtained. These fit factor levels are easily obtainable with tight fitting respirators that properly fit the employee. Respirator fit testing is conducted in a laboratory setting, and experience with fit testing has shown that the quantitative fit factors measured in the test booth do not directly translate to those that would be achieved consistently in the workplace. Therefore, the proposal requires that fit factors of 10 times the assigned protection factor be obtained during quantitative fit testing to better assure that the required levels of protection will be achieved under actual use conditions. Obtaining a proper fit for each employee may require the employer to provide two to three different sizes and types of masks so that an employee can select the most comfortable respirator having a facepiece with the least leakage around the face seal. After the fit testing has been completed, the employer shall provide and assure that the employee wears the respirator that provides the appropriate protection according to the fit test results.

Once the proper respirator has been selected, a simple facepiece seal fit check performed at the start of each shift by each employee wearing a tight fitting respirator can meet the objective of demonstrating that a proper facepiece seal is being obtained. This test, which is required by 1910.134 (e)(5)(i), can be either a positive pressure fit check, in which the exhalation valve is closed and the wearer exhales into the facepiece to produce a positive pressure, or a negative pressure fit check, in which the inlet is closed and the wearer inhales so that the facepiece collapses slightly. Employees must receive training to perform this test properly.

Proposed paragraph (g)(6) requires that employers provide and ensure the use of the appropriate protective clothing and equipment. Protective clothing used during exposure to MC, such as gloves or aprons, must be resistant to MC. It is the responsibility of the employer to provide protective clothing and equipment at no cost to the employee and to launder, repair, replace and safely dispose of that clothing and equipment. The proposal is sufficiently performance-oriented to allow the employer enough flexibility to provide only the protective clothing and equipment necessary to protect employees in each particular work operation from the MC exposure encountered.

OSHA is aware that many employees may be splashed with MC in the course of occupational exposure. As noted in the Health Effects section, above, "contact with liquid MC is accompanied by an intense burning sensation after a few minutes." Therefore the Agency is considering whether the proposed rule for MC should include requirements for quick-drench showers and eye-wash facilities to protect employees from the potentially serious acute health effects of MC splashes.

When a worker is splashed with MC, the severity of the reaction is determined by the concentration of MC and the length of time it remains in contact with the skin or eyes. The hazard would be reduced by removing the MC from the employee's skin or eyes and by diluting the MC concentration on the employee's skin or clothing. Quick-drench showers that could drench an affected employee with piped-in water applied with force, and eye-wash facilities that could flush eyes repeatedly with a great amount of water, are already required in the OSHA health standard for formaldehyde (29 CFR 1910.1048(j)). In addition, the health standards for 1,2-dibromo-3-chloropropane (29 CFR 1910.1044(l)), acrylonitrile (29 CFR 1910.1045(m)) and ethylene oxide (29 CFR 1910.1047 (Appendix A)) provide for wash and shower facilities to protect employees' eyes and skin from hazards. OSHA discusses its concerns regarding eye and skin effects, gives notice that hygiene facilities may be needed to protect employees from those effects and requests pertinent information in Issue 38, above.

H. Emergency Situations: Paragraph (h)

Paragraph (h) of OSHA's proposed rule for MC requires that employers develop written plans for emergency situations and that appropriate portions of the plan be implemented in the event of an emergency. The plan must contain a requirement that employees engaged in correcting an emergency situation be provided with appropriate personal protective equipment, such as respiratory protection. Employers must also be prepared to alert employees to evacuate the workplace in the event of an emergency. The performance-oriented language of the proposed paragraph will give employers the flexibility to choose any effective method of alerting employees, including communications systems, voice communication, or a bell or other alarm.

OSHA is proposing specific provisions for emergency situations because of the potential adverse health effects associated with high MC exposures. To clarify that the intent of this provision is to protect employees from unexpected and substantial releases of MC, OSHA has defined "Emergency" as "an occurrence such as, but not limited to, equipment failure, rupture of containers, or failure of control equipment that may result in an unexpected significant release of MC." The types of emergency situations which may be encountered are those which require securing internal or external emergency services such as rescue, fire, or emergency medical services. OSHA recognizes that not all sudden releases constitute emergencies. For example, the accidental breaking of a sampling syringe containing a minute amount of MC would not normally be regarded as an emergency. On the other hand, failure of a valve on a reaction vessel under pressure or failure of a safety relief valve would definitely constitute an emergency.

OSHA believes that compliance with these requirements will ensure that affected employees are substantially protected against exposures which arise in emergency situations.

I. Medical surveillance: Paragraph (i)

Section 6(b)(7) of the OSH Act requires that, where appropriate, occupational health standards shall prescribe the type and frequency of medical exams or other tests to be made available, by the employer or at his cost, to exposed employees in order to determine if the employee's health is adversely affected by exposure to workplace hazards.

The purpose of the medical surveillance program for MC is four-fold:

(1) To determine if an individual can be exposed to the concentration of MC present in his or her workplace without experiencing adverse health effects;

(2) To detect, to the extent possible, early or mild clinical conditions due to MC exposure so that appropriate preventative measures can be taken;

(3) To diagnose any occupational diseases that occur as the result of MC exposure; and

(4) To determine the employee's fitness to use respiratory protective equipment if his or her exposure levels exceed either the PEL or STEL.

The most serious health effect expected from MC exposure is cancer. While the medical surveillance program proposed cannot detect MC-induced cancer at a preneoplastic stage, OSHA anticipates that, as in the past, methods for early detection and treatments leading to increased survival rates will continue to evolve. It is also not presently possible to identify all diseases that may be associated with exposure to MC, so the level of protection afforded the worker by the proposed standard cannot be predicted with any certainty. Thus, an important goal of the medical surveillance program is to provide information on the adequacy of the proposed PELs for MC.

Proposed paragraph (i)(1) specifies the circumstances under which employers must provide medical surveillance for employees exposed to MC. OSHA proposes to require that employers to institute a medical surveillance program for all employees exposed to MC at or above the action level for 30 days or more in a year. Medical surveillance would be made available to employees exposed to MC for at least 10 days a year, if their exposure exceeds either of the permissible exposure limits. Appropriate surveillance would also be required to be made available for employees exposed in an emergency regardless of the airborne concentrations of MC normally present in the workplace. Including such employees within the medical surveillance program ensures that employees, for whom medical surveillance will be of the greatest benefit, will be offered the opportunity to participate.

Inclusion of a cut-off based on duration of exposure recognizes that the most serious diseases associated with MC exposure are chronic diseases, so that employees exposed for only a few days in a year will be at much lower risk of developing MC-related disease. Employers would be able to focus valuable medical surveillance resources on high-risk employees. OSHA believes that the limits placed on medical surveillance by these cutoffs, based both on exposure level and on the number of days an employee is exposed to MC, are reasonable and an administratively convenient way to provide medical surveillance benefits to MC-exposed workers. The proposed cut-offs are also consistent with the approach taken in the promulgated Benzene rule (29 CFR 1910.1028).

In contrast, medical examinations for emergencies are not triggered by airborne concentrations routinely found in a workplace. Where very large amounts of materials are kept in a sealed system, routine exposure may be essentially zero. However, rupture of the container might result in catastrophe. Thus, employers who have identified that they have operations where there is a potential for an emergency involving MC must take necessary actions to assure that, in the event an emergency occurs, facilities will be available and medical assistance by professionals knowledgeable about the toxic effects of MC will be rendered to exposure victims promptly.

The most severe acute effects of MC (narcosis, skin and eye burns at high concentrations) are essentially reversible, even at near fatal exposures. Of course, any acute effects, such as skin burns, narcosis or eye irritation, observed in an employee exposed to MC should be treated.

Employees exposed above the PELs must wear respirators. Should the respirator fail or not be worn as prescribed, the employee may be placed at higher risk. Thus, enhanced surveillance based on level of exposure is a reasonable allocation of scarce medical resources. Employers would also be required to have a physician provide a written opinion establishing the fitness of any employee likely to be required to wear a respirator, regardless of the number of days for which respirator use is anticipated. This determination would be required before respirator use was implemented and annually thereafter.

Under proposed paragraph (i)(2), and consistent with other recently promulgated standards, including Benzene (29 CFR 1910.1028) and Formaldehyde (29 CFR 1910.1048), OSHA is proposing that all medical procedures be performed by or under the supervision of a licensed physician. Clearly, a licensed physician is the appropriate person to supervise and evaluate a medical examination. However, certain parts of the required examination, such as recording the medical history and drawing blood for blood tests, do not necessarily require the physician's expertise and these may be conducted by other suitably qualified health care personnel under the supervision of the physician.

The proposed requirement that examinations are to be offered without cost to the employee and given at a reasonable time and place and without loss of pay is necessary to ensure that employees will participate in the medical surveillance program. This provision is also consistent with other OSHA health standards and with provisions contained in the OSH Act.

Under proposed paragraph (i)(3), medical examinations and consultations would be provided to employees covered by paragraph (i) as follows: before their initial assignment to work in an area where they would be exposed to MC or within 180 days of the effective date of the MC standard, annually thereafter, upon termination of employment or reassignment to an area where they are no longer exposed to MC at airborne concentrations at or exceeding the action level, and at frequencies other than the above when recommended by the examining physician.

OSHA's requirement for a preplacement examination is intended to achieve the objective of determining if an individual will be able to work with the given MC exposure without adverse effects. It also serves the useful function of establishing a general health baseline for future reference.

OSHA is considering adding a provision in the final rule giving credit to employers for medical examinations performed within one year prior to the effective date of the standard to fulfill the requirements for the initial medical examination. Employers would then be required to offer successive yearly exams at least within one year of the credited exam. OSHA is requesting public comment on the usefulness of including a provision of this type in the final rule.

The main goal of periodic medical surveillance for workers is to detect adverse health effects at an early, and potentially still reversible stage. Routine screening, occupational and medical histories, and physical examinations must be offered annually for all employees eligible to participate. The interval proposed is consistent with other OSHA health standards. Based on OSHA's experience with these other standards, the Agency believes that annual surveillance would strike a proper balance between the need to diagnose health effects, such as cancer, at an early stage, increasing the possibility of remission through medical intervention, and the limited number of cases likely to be identified through the surveillance program.

To assure that no employee terminates employment while carrying an active, but undiagnosed, disease, OSHA is proposing to require that the employer offer a medical examination to employees when their employment is terminated or when employees are transferred to an area where they would no longer remain eligible for surveillance. OSHA has some concern that this may not be wholly adequate for identifying cancer in high risk employees. Therefore, the Agency requests public comment on whether continued annual surveillance should be offered to employees who have left employment, retired, or transferred to other areas within the employer's operations.

OSHA is also considering the possibility of expanding the proposed medical surveillance to include retirees and presently employed workers who were formerly exposed to MC in previous jobs. Such an approach would be consistent with the requirement in the Benzene standard (29 CFR 1910.1028) which makes medical surveillance available to employees who were exposed to greater than 10 ppm of benzene (the former standard) for 30 or more days in a year prior to the effective date of the standard, when such exposures occurred while the employee worked for his or her current employer. OSHA is seeking comments from the public on whether an expanded medical surveillance program should be included in the final rule and whether any limitations should be imposed on participation in such a program.

Proposed paragraph (i)(4) sets the content for a medical examination. The medical evaluation would include a detailed work and medical history with special emphasis on neurological symptoms, mental status and cardiac health. This information, collected in the initial exam, would assist the physician in identifying pre-existing conditions that might place the employee at increased risk when exposed to MC. It also establishes a health baseline for future monitoring. In subsequent annual evaluations, changes in neurological symptoms, mental status or cardiac health, in combination with laboratory analyses and information on exposure history, may provide early warnings of MC toxicity.

Laboratory surveillance of employees exposed to MC would include post shift carboxyhemoglobin tests and complete blood count. Because carbon monoxide (CO) is a metabolite of MC, annual post-shift carboxyhemoglobin (COHb) tests would be required for workers exposed to MC. COHb levels greater than 3% can exacerbate angina symptoms, decrease exercise tolerance and increase risks for myocardial infarctions (heart attacks) in susceptible individuals. COHb concentrations can also be used as a rough estimate of worker exposure to MC (taking into consideration smoking behavior and other CO sources) to corroborate personal MC monitoring measurements.

Complete blood count would be used to determine whether an individual is anemic or has an impaired oxygen carrying capacity, and therefore at greater risk for adverse health effects, such as heart attacks, resulting from MC-induced carboxyhemoglobinemia.

Because of the production of CO as a result of MC metabolism and the epidemiological association of solvent exposure and miscarriage, OSHA is proposing to require inclusion of an assessment of the reproductive health of interested employees, especially women. CO has been identified as a risk factor for low birth weight babies and fetal abnormalities (Exs. 7-200, 7-201). Epidemiological evidence has suggested a relationship between occupational exposure to solvents, including MC, and miscarriages (Ex. 7-199). For these reasons, the possibility of adverse reproductive health effects should be assessed by the physician.

The extent and the type of service to be made available to employees who are concerned about their reproductive health would be determined by the examining physician so that affected employees can benefit from new technological developments and the responsible physician can provide services appropriate to the risk to the concerned individual.

In the comments received subsequent to publication of the ANPR for MC (Exs. 10-3, 10-10, 10-28), several industrial sources indicated that urine analysis, liver function tests and chest X-rays are commonly performed as part of the medical surveillance programs of these companies. OSHA has found no medical justification for annual urine analysis or chest X-ray which is specific for detection of MC-related health effects. Liver function tests have also been evaluated for inclusion as a requirement in the medical surveillance provision. Animal studies and human clinical studies show an association between chronic MC exposure and some indications of liver toxicity. However, this association is only apparent after high doses of MC for prolonged periods of time. The changes in liver function test parameters are not consistent in the human clinical studies and not specific or unique to MC exposure. Therefore, OSHA sees no diagnostic value to requiring annual laboratory analysis of the liver function parameters at this time. OSHA specifically seeks comment on the appropriateness of the three tests described above, that have not been included in the medical surveillance provisions of the proposal. The Agency also seeks medical evidence pertinent to determining if those or other tests should be incorporated into the final rule for MC.

Proposed paragraph (i)(5) allows the medical surveillance examination to be expanded to include any additional tests, examinations, consultations or referrals deemed necessary by the examining physician. This requirement is provided to ensure that adequate flexibility is incorporated into the standard, so that any occupational diseases due to MC exposure are adequately diagnosed and treated.

Under proposed paragraph (i)(6), employers would be required to provide the examining physician, and any specialist involved, with the information needed to assure that they will be adequately informed to reach a medical determination. OSHA is proposing that the employer provide the physician or specialist with a copy of the standard and all relevant appendices. The employer would also be required to supply the physician with information from any previous medical examinations, not otherwise available to the examining physician or specialist.

Proposed paragraph (i)(6) also requires employers to supply the results of exposure monitoring and information on any personal protective equipment and respiratory protection used, or to be used, by the employee to the physician responsible for medical surveillance. A well-documented exposure history assists the physician in determining if a disease that is observed may be related to MC exposure, and it helps the physician to determine if any restrictions should be placed on the employee's occupational exposure to MC based on medical findings. For employees exposed during emergencies, the employer would be required to supply the physician with a description of the emergency and exposure levels encountered by the employee during the emergency. This information would assist the physician in determining if an employee is likely to be at risk of harmful effects from acute MC exposure.

Proposed paragraph (i)(7) requires employers to obtain from the examining physician a written opinion containing the results of the medical examination with regard to MC exposure, the physician's opinion as to whether the employee would be placed at increased risk of material health impairment as a result of exposure to MC, and any recommended limitations on the employee's exposure or use of personal protective equipment. In rendering an opinion regarding the employee's suitability for work with MC, the physician must rely on the obtained results of clinical and other tests performed to support his or her conclusions.

The physician must exclude findings or diagnoses which are unrelated to MC exposure in the written opinion provided to the employer. OSHA has included this provision to reassure employees participating in medical surveillance that they will not be penalized or embarrassed by the employer's obtaining information about them not directly pertinent to MC exposure. The employee would be informed directly by the physician of all results of his or her medical examination including diseases of a non-occupational origin.

Also under proposed paragraph (i)(7), employers would be required to provide a copy of the physician's written opinion to the employee within 15 days of receiving the opinion to ensure that the employee has been informed of the results of the medical examination in a timely manner.

J. Communication of Methylene Chloride Hazards to Employees: Paragraph (j)

In this proposed MC standard, OSHA includes a paragraph entitled:

"Communication of methylene chloride hazards to employees." This paragraph addresses the issue of transmitting information to employees about the hazards of MC through the use of: (1) signs and labels, (2) material safety data sheets, and (3) information and training. Previous OSHA health standards generally included separate paragraphs on employee information and training and signs and labels. This standard incorporates both of those areas into this single paragraph, along with material safety data sheet provisions, to be consistent with the Hazard Communication Standard (HCS) (29 CFR 1910.1200) which addresses these areas.

On November 25, 1983, the Occupational Safety and Health Administration published its final rule on Hazard Communication at 48 FR 53280 and 52 FR 31852. The HCS requires all chemical manufacturers and importers to assess the hazards of the chemicals which they produce or import. It also requires all employers to provide information concerning the hazards of such chemicals to their employees. The transmittal of hazard information to employees is to be accomplished by such means as container labeling and other forms of warning, material safety data sheets and employee training.

Since the HCS "is intended to address comprehensively the issue of evaluating the potential hazard of chemicals and communicating information concerning hazards and appropriate protective measures to employees" (52 FR 31877), OSHA proposes this new paragraph entitled "Communication of Methylene Chloride Hazards to Employees" to avoid repetition of those requirements now comprehensively laid out in §1910.1200 while specifying additional particular requirements that are needed to protect employees exposed to MC. While avoiding a duplicative administrative burden on those employers attempting to comply with the requirements of several different applicable OSHA health standards, the proposed requirements nevertheless provide the necessary protection for employees through provisions for signs and labels, material safety data sheets, and employee information and training. It should be noted that the communication of MC hazards paragraph of the MC standard has been designed to be substantively as consistent as possible with the HCS requirements for employers. The HCS also addresses the responsibility of producers of chemicals to provide information to downstream employers.

Proposed paragraph (j)(1) requires that regulated areas be posted with signs stating: "Danger, Methylene Chloride, Potential Cancer Hazard, Authorized Personnel Only, Respirators Required in this Area". OSHA intends that the posting of these signs serve as a warning to employees who may otherwise not know they are entering a regulated area. Such warning signs would be required whenever a regulated area exists, that is, whenever the permissible exposure limit is exceeded. For some work sites, regulated areas exist as a permanent situation, because there is an area where exposures cannot be reduced below the PEL by the use of engineering controls. In those situations, the signs are needed to warn employees not to enter the area unless they are authorized, wearing respirators, and unless there is a need for entering the area.

Regulated areas may also exist on a temporary basis, such as during maintenance and/or emergency situations. The use of warning signs in these types of situations is also important, since a maintenance or emergency situation is by nature a new or unexpected exposure to employees who are regularly scheduled to work at these sites.

These signs are intended to supplement the training which employees are to receive under the other provisions of this paragraph, since even trained employees need to be reminded of the locations of regulated areas and of the precautions necessary to be taken before entering these dangerous areas.

The proposed standard specifies the wording of the warning signs for regulated areas in order to ensure that the proper warning is given to employees. OSHA believes that the use of the word "Danger" is appropriate, based on the evidence of the toxicity and carcinogenicity of MC. "Danger" is used to attract the attention of workers, to alert them to the fact that they are in an area where the permissible exposure limit is exceeded, and to emphasize the importance of the message that follows. The use of the word "Danger" is also consistent with other recent OSHA health standards dealing with carcinogens. The proposed standard also requires that the legend, "Respirators Required in this Area", be included on the warning sign. Regulated areas are defined as areas in which the PEL and STEL are, or are likely to be, exceeded. To ensure that these employees are adequately protected, it is necessary that the sign alert them to the need to wear respirators.

Proposed paragraph (j)(2) requires that warning labels be affixed to all shipping and storage containers containing MC. The labels must state: "Danger, Contains Methylene Chloride, Potential Cancer Hazard". It is proposed that required labels would remain affixed to containers leaving the workplace. The purpose of this requirement is to ensure that all affected employees, not only those of a particular employer, are apprised to the hazardous nature of MC exposure where exposure could exceed the action level.

In addition to being consistent with the requirements of the HCS, these requirements are consistent with the mandate of section 6(b)(7) of the Act, which requires OSHA health standards to prescribe the use of labels or other appropriate forms of warning to apprise employees of the hazards to which they are exposed.

Proposed paragraph (j)(3) requires the employer to obtain or develop and to distribute and provide access to a material safety data sheet for MC in accordance with the requirements of 29 CFR 1910.1200 (g). OSHA feels that a properly completed material safety data sheet (MSDS), if readily available to employees, can serve as an excellent, concise source of information regarding the hazards associated with MC. OSHA's primary intent in this section of the proposed standard, as stated in its recently promulgated HCS, is to ensure that employees will receive as much information as is needed concerning the hazards posed by chemicals in their workplaces. The material safety data sheet ensures that this information will be available to them in a usable, readily accessible and concise form. The material safety data sheet also serves as the central source of information to employees and downstream employers who must be provided with an MSDS if MC or a product containing MC is produced and shipped out of the plant. In addition, the MSDS serves as the basic source of information on the hazards of MC essential to the training provisions of this and other applicable health standards.

Producers and importers have the primary responsibility, under the HCS to develop or prepare the material safety data sheet. The manufacturer or importer is most likely to have the best access to information about the product, and is therefore responsible for disseminating this information to downstream users of the material. For employers whose employees' exposure to MC is from products received from outside sources, the information necessary for a complete MSDS or the MSDS itself is to be obtained from the manufacturer and made available to affected employees. The requirements for the information that is to be contained on the material safety data sheet are explained in detail at 29 CFR 1910.1200(g).

Paragraph (j)(4) of this proposed MC standard requires employers to provide all employees who are exposed to MC with information and training on MC at the time of initial assignment and at least annually thereafter. A record shall be maintained of the contents of such programs. The training program is to be in accordance with the requirements of the HCS paragraphs (h)(1) and (2), including specific information required to be provided by that section and those items stipulated in the proposed paragraph (j)(4)(iii) of this standard. In addition, employees are to be provided with an explanation of the contents of Appendix A (Substance Safety Data Sheet and Technical Guidelines for MC) of the MC standard. Employees are to be informed where a copy of the final MC standard is accessible to them, and receive a description of the medical surveillance program required under proposed paragraph (i). Employees are also to receive an explanation of the purpose of paragraph (i), medical surveillance program, for MC.

OSHA has determined during other rulemakings that an information and training program, as incorporated in this proposed standard in an overall "Communication of Methylene Chloride Hazards to Employees" paragraph, is essential to inform employees of the hazards to which they are exposed and to provide employees with the necessary understanding of the degree to which they themselves can minimize the health hazard potential. As part of an overall communication program for employees, training serves to explain and reinforce the information presented to employees on labels and material safety data sheets. These written forms of information and warning will be successful and relevant only when employees understand the information presented and are aware of the actions to be taken to avoid or minimize exposures thereby reducing the possibility of experiencing adverse health effects. Training is essential to an effective overall hazard communication program. Active employee participation in training sessions can result in the effective communication of hazard information to employees which can further result in workers taking conscientious protective actions at their job duties, thereby decreasing the possibility of occupationally-related illnesses and injuries.

OSHA proposes the training provisions of this standard to be in performance-oriented, rather than specified and detailed language. The proposed standard, in requiring training to be in accordance with the requirements of 29 CFR 1910.1200, lists the categories of information to be transmitted to employees and not the specific ways that this is to be accomplished. The use of such performance-oriented requirements will encourage employers to tailor their training needs to their specific workplaces, thereby resulting in the most effective training program suitable for each specific workplace.

OSHA believes that the employer is in the best position to determine how the training he or she is providing is being received and absorbed by the employees. OSHA has, therefore, described the objectives to be met and the intent of its training to ensure they can help to protect themselves. The specifics of how this is to be accomplished are left up to the employer.

K. Recordkeeping: Paragraph (k)

Section 8(c)(3) of the Act provides for the promulgation of "regulations requiring employers to maintain accurate records of employee exposures to potentially toxic materials or harmful physical agents which are required to be monitored or measured under section 6." Proposed paragraph (k)(1) requires that employers who rely on objective data in order to gain exemption from the proposed monitoring requirements maintain records that show the basis and reasoning used in reaching the conclusion that the employer should be exempted. In this respect, the objective data substitute for the initial monitoring results. Also, compliance with the requirement to maintain a record of objective data protects the employer at later dates from the contention that initial monitoring was improperly omitted. The employer would be required to maintain the record for the duration of the employer's reliance upon objective data.

Proposed paragraph (k)(2) requires that employers establish and keep an accurate record of all measurements taken to monitor employee exposure to MC. In particular, the proposal requires that employers keep records of the name, social security number, job classification and exposure of each employee represented by monitoring, indicating which employees were actually monitored. In addition, proposed paragraph (k)(3) requires that the employer keep accurate medical records for each employee subject to medical surveillance. Section 8(c) of the Act authorizes the promulgation of regulations requiring an employer to keep necessary and appropriate records regarding activities to permit the enforcement of the Act or to develop information regarding the causes and prevention of occupational illnesses. OSHA has determined that, in this context, requiring employers to maintain both medical and exposure records (including pulmonary function test results related to respirator use and initial determinations or justifications of exemption from monitoring) is necessary and appropriate. In addition, medical records are necessary for the proper evaluation of the employee's health. Since no purpose is served by long term retention of respirator fit test results (required in mandatory Appendix C), OSHA has proposed to require keeping these test results only until the next fit testing.

The proposed standard would require that all required records be made available upon written request to the Assistant Secretary and Director of NIOSH for examination and copying. Access to these records would be necessary for OSHA to monitor compliance. These records also contain information which either of the agencies may need to carry out other statutory responsibilities.

The proposed rule would provide that employees, former employees, and their designated representatives would have access to exposure determinations and records upon request. Section 8(c) (3) of the Act explicitly provides for the promulgation of regulations to "provide employees or their representatives with an opportunity to observe such monitoring or measuring and to have access to the records thereof." Several other provisions of the Act contemplate that employees and their representatives are entitled to have an active role in the enforcement of the Act. Employees and their representatives need the pertinent information concerning exposures to toxic substances and the consequences for the health and safety of the employees if they are to benefit properly from these statutorily created rights.

In addition, proposed paragraph (k) specifies that access to exposure and medical records by employees' designated representatives, NIOSH and OSHA shall be provided in accordance with 29 CFR 1910.20. OSHA promulgated 29 CFR 1910.20 as the generic rule for access to employee exposure and medical records on May 23, 1980 (45 FR 35212). It applies to records created pursuant to specific standards and to records which are voluntarily created by employers. OSHA retains unrestricted access to medical and exposure records but its access to personally identifiable records is subject to the Agency's rules of practice and procedure concerning OSHA access to employee medical records, which have been published at 29 CFR 1913.10. An extensive discussion of the provisions and the rationale for §1910.20 may be found at 45 FR 35312. The discussion of §1913.10 may be found at 45 FR 35384. It is noted that revisions to the access to records standard are being developed in an ongoing rulemaking proceeding. Proposed paragraph (k) may be affected by any changes which result from that rulemaking effort.

It is necessary to keep records for extended periods of time because of the long latency periods commonly observed for the induction of cancer caused by exposures to carcinogens. Cancer generally cannot be detected until 20 or more years after onset of exposure. The extended record retention period is therefore needed for two purposes. First, possession of past and present exposure data and medical records furthers the diagnosis of workers' ailments. In addition, retaining records for extended periods makes possible a review at some future date of the effectiveness and adequacy of the proposed standard.

The time periods required for retention of exposure records and medical records would be thirty years and the period of employment plus thirty years, respectively. These retention requirements would be consistent with those in the OSHA records access standard and with pertinent sections of the Toxic Substances Control Act.

Proposed paragraph (k)(5) requires employers to comply with the requirements of 29 CFR 1910.20(h). That provision requires the employer to notify the Director of NIOSH in writing at least 90 days prior to the disposal of records and to transfer those records to NIOSH unless told not to do so by NIOSH. The employer would be required to comply with any other applicable requirements set forth in the records retention standard.

L. Observation of Monitoring: Paragraph (l)

Section 8(c)(3) of the Act requires that employers provide employees and their representatives with the opportunity to observe monitoring of employee exposures to toxic substances or harmful physical agents. In accordance with this section, the proposal contains provisions for such observation of monitoring of MC exposures.

The observer, whether an employee or a designated representative, must be provided with, and is required to use, any personal protective clothing or equipment required to be worn by employees working in the area that is being monitored, and must comply with all other applicable safety and health procedures.

M. Date: Paragraph (m)

As proposed, the final rule would become effective sixty (60) days following publication in the Federal Register. OSHA proposes that the requirements for paragraphs (c) through (l) be completed within one-hundred eighty (180) days after the effective date of the final rule, except for provisions for initial monitoring, paragraph (d)(2), and implementation of engineering controls, paragraph (f)(1). Consequently, employers will have 8 months from publication of the standard to accomplish those requirements, which OSHA believes is sufficient time. Initial monitoring (paragraph (d)(2)) shall be completed within one-hundred twenty (120) days from the effective date of the standard. This provision should allow employers sufficient time to complete initial monitoring or prepare objective data exempting them from initial monitoring. Implementation of engineering and work practice controls would be required to be completed no later than one year after the effective date of the standard. This is to allow affected employers sufficient time to design (where necessary), obtain, and install the necessary control equipment. The Agency is soliciting comment on the adequacy of these proposed start-up dates.

N. Appendices: Paragraph (n)

Four appendices have been included in this proposed standard. Appendices A, B, and D have been included primarily for purposes of information. None of the statements contained therein should be construed as establishing a mandatory requirement not otherwise imposed by the standards, or as detracting from an obligation which the standard does impose. Appendix C, however, is a mandatory appendix, which contains protocols on respiratory fit testing.

The information contained in Appendix A is designed to aid the employer in complying with requirements of the standard. The information in Appendix B primarily provides information needed by the physician to evaluate the results of the medical examination. It should be noted that paragraph (j) specifically requires that the information contained in Appendix A be provided to employees as part of their information and training program. Appendix C contains the "Qualitative and Quantitative Fit Testing Procedures." Proposed paragraph (g)(5)(iii) requires that fit testing be conducted in accordance with Appendix C. Appendix D gives details of the OSHA sampling method for use in monitoring employee exposures to MC.

XIII. Public Participation

Interested persons are invited to submit written data, views, and arguments with respect to this proposed standard. These comments must be postmarked on or before April 6, 1992, and submitted in quadruplicate to the Docket Officer, Docket No. H-71, Room N-2625, U.S. Department of Labor, 200 Constitution Avenue, N.W., Washington, D.C. 20210. Comments limited to 10 pages or less also may be transmitted by facsimile to 202-523-5046 or FTS 8-523-5046, provided the original and three copies are sent to the Docket Office thereafter. Written submissions must clearly identify the provisions of the proposal which are addressed and the position taken with respect to each issue.

The data, views, and arguments that are submitted will be available for public inspection and copying at the above address. All timely written submissions will be made a part of the record of the proceeding.

Additionally, under section 6(b)(3) of the OSH Act (29 U.S.C. 655), section 107 of the Construction Safety Act (41 U.S.C. 333), and 29 CFR 1911.11, interested persons may file objections to the proposal and request an informal hearing. The objections and hearing requests should be submitted in quadruplicate to the Docket Officer at the address above and must comply with the following conditions:

1. The objections must include the name and address of the objector;

2. The objections must be postmarked by April 6, 1992;

3. The objections must specify with particularity the provisions of the proposed rule to which each objection is taken and must state the grounds therefor;

4. Each objection must be separately stated and numbered; and

5. The objections must be accompanied by a detailed summary of the evidence proposed to be adduced at the requested hearing.

XIV. State Plan Applicability

The 25 states with their own OSHA-approved occupational safety and health plans must adopt a comparable standard within six months of the publication date of a final standard. These States include: Alaska, Arizona, California, Connecticut (for state and local government employees only), Hawaii, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Nevada, New Mexico, New York (for State and local government employees only), North Carolina, Oregon, Puerto Rico, South Carolina, Tennessee, Utah, Vermont, Virginia, Virgin Islands, Washington, Wyoming. Until such time as a State standard is promulgated, Federal OSHA will provide interim enforcement assistance, as appropriate.

XV. Authority and Signature

This document was prepared under the direction of Gerard F. Scannell, Assistant Secretary of Labor for Occupational Safety and Health, U.S., Department of Labor, 200 Constitution Avenue, N.W., Washington, D.C. 20210.

Pursuant to sections 4, 6(b), 8(c) and 8(g) of the Occupational Safety and Health Act (29 U.S.C. 653, 655, 657), section 107 of the Contract Work Hours and Safety Standards Act (the Construction Safety Act) (40 U.S.C. 333); the Longshore and Harbor Workers' Compensation Act (33 U.S.C. 941); the Secretary of Labor's Order No. 1-90 (55 FR 9033); and 29 CFR part 1911; it is hereby proposed to 1) amend part 1910 of 29 CFR by adding new §1910.1052 as set forth below and delete the reference to MC from Table Z-2 of §1910.1000, 2) amend part 1915 of 29 CFR by adding new §1915.1102, and 3) amend part 1926 of 29 CFR by adding new §1926.61. In addition, pursuant to section 4(b)(2) of the Act, OSHA has determined that this new standard would be more effective than the corresponding standards now in subpart B of part 1910, and in part 1918 of Title 29, Code of Federal Regulations. Therefore, any such corresponding standards would be superseded by this new §1910.1052. This determination, and the application of the new standard to the longshoring industry, would be implemented by adding a new paragraph (m) to §1910.19.

List of Subjects in 29 CFR Part 1910

Methylene Chloride, Occupational safety and health, Chemicals, Cancer, Health risk--assessment.

Signed at Washington, D.C., this 22nd day of October 1991.

Gerard F. Scannell Assistant Secretary of Labor.

XVI. Proposed Standard and Appendices:

General Industry

Part 1910 of Title 29 of the Code of Federal Regulations is proposed to be amended as follows:

Part 1910-(AMENDED)

Subpart B-(Amended)

1. The authority citation for subpart B of part 1910 is revised to read as follows:

Authority: Secs. 4, 6 and 8 of the Occupational Safety and Health Act, 29 U.S.C. 653, 655, 657; Walsh-Healy Act, 29 U.S.C. 35 et seq; Service Contract Act of 1965, 41 U.S.C. 351 et seq; Contract Work Hours and Safety Standards Act (Construction Safety Act) 40 U.S.C. 333; Longshore and Harbor Worker's Compensation Act, 33 U.S.C. 941; National Foundation on Arts and Humanities, 20 U.S.C. 951 et seq; Secretary of Labor's Order 1-90 (55 FR 9033); and 29 CFR part 1911.

2. By adding a new paragraph (m) to §1910.19 to read as follows:

1910.19 Special provisions for air contaminants.

*           *           *           *

(m) Methylene Chloride (MC): Section 1910.1052 shall apply to the exposure of every employee to MC in every employment and place of employment covered by § 1910.16, in lieu of any different standard on exposure to MC which would otherwise be applicable by virtue of that section.

Subpart Z-(Amended)

3. The authority citation for Subpart Z of 29 CFR Part 1910 is revised to read as follows:

Authority: Secs 6 and 8, Occupational Safety and Health Act, (29 U.S.C. 655, 657), Secretary of Labor's Order No. 1-90 (55 FR 9033); and 29 CFR part 1911.

1910.1000 [Amended]

4. By deleting the entry for "Methylene Chloride from Table Z-2 of 1910.1000.

5. By adding a new §1910.1052 to read as follows:

1910.1052 Methylene Chloride

(a) Scope and application. (1) This section applies to all occupational exposures to methylene chloride (MC), Chemical Abstracts Service Registry No 75-092-2 except as provided in paragraph (a)(2) of this section.

(2) This section does not apply to the processing, use, or handling of products containing MC where objective data are reasonably relied upon that demonstrate that the product or process is not capable of releasing MC in airborne concentrations at or above the action level or in excess of the short-term exposure limit (STEL) under the reasonably foreseeable conditions of processing, use, or handling that will cause the greatest possible release.

(3) Where products containing MC are exempted under paragraph (a)(2) of this section, the employer shall maintain records of the objective data supporting that exemption and the basis for the employer's reliance on the data, as provided in paragraph (k) (1) of this section.

(b) Definitions: For the purpose of this section, the following definitions shall apply:

"Action level" means a concentration of airborne MC of 12.5 ppm calculated as an eight-hour time-weighted average.

"Assistant Secretary" means the Assistant Secretary of Labor for Occupational Safety and Health, U.S. Department of Labor, or designee.

"Authorized person" means any person specifically authorized by the employer whose duties require the person to enter a regulated area, or any person entering such an area as a designated representative of employees for the purpose of exercising the right to observe monitoring and measuring procedures under paragraph (l) of this section, or any other person authorized by the Act or regulations issued under the Act.

"Day" means any part of a calendar day.

"Director" means the Director of the National Institute for Occupational Safety and Health, U.S. Department of Health and Human Services, or designee.

"Emergency" means any occurrence, such as, but not limited to, equipment failure, rupture of containers, or failure of control equipment, which may or does result in an unexpected significant release of MC (e.g., purging lines or cleaning sludge from tanks).

"Employee exposure" means exposure to airborne MC which would occur if the employee were not using respiratory protection.

"Methylene chloride" (MC) or dichloromethane means an organic compound with chemical formula, CH(2)C1(2). Its Chemical Abstracts Registry Number is 75-09-2. Its molecular weight is 84.9 g/mole.

"Regulated area" means any area, demarcated by the employer, where airborne concentrations of MC exceed or can reasonably be expected to exceed a permissible exposure limit, expressed either as an 8-hour time-weighted average exposure or the short-term exposure limit.

(c) Permissible exposure limits (PELs). (1) Eight-hour time-weighted average (TWA) limit: The employer shall ensure that no employee is exposed to an airborne concentration of MC in excess of twenty-five parts MC per million parts of air (25 ppm) as an eight-hour time-weighted average (8-hour TWA).

(2) Short-term exposure limit (STEL). The employer shall ensure that no employee is exposed to an airborne concentration of MC in excess of one hundred and twenty-five parts of MC per million parts of air (125 ppm) as determined over a sampling period of fifteen minutes.

(d) Exposure monitoring. (1) General. (i) Determinations of employee exposure shall be made from breathing zone air samples that are representative of the 8-hour TWA and 15-minute short-term exposures of each employee.

(ii) Representative 8-hour TWA employee exposure shall be determined on the basis of one or more samples representing full-shift exposure for each shift for each job classification in each work area.

(iii) Representative 15-minute short-term employee exposures shall be determined on the basis of one or more samples representing 15-minute exposures associated with operations that are most likely to produce exposures above the STEL for each shift for each job classification in each work area.

(iv) Except for initial monitoring as required under paragraph (d)(2) of this section, where the employer can document that exposure levels are equivalent for similar operations in different work shifts, the employer need only determine representative employee exposure for that operation during the one shift where the highest exposure is expected.

(2) Initial monitoring. (i) Each employer who has a workplace or work operation covered by this standard, except as provided for in paragraph (a)(2) of this section, shall perform initial monitoring to determine accurately the airborne concentrations of MC to which employees may be exposed.

(ii) Where the employer has monitored within one year prior to the effective date of this standard and the monitoring satisfies all other requirements of this section, the employer may rely on such earlier monitoring results to satisfy the requirements of paragraph (d)(2)(i) of this section, provided that the conditions under which the monitoring was conducted remain unchanged.

(3) Periodic Monitoring. (i) If the monitoring required by paragraph (d)(2) of this section reveals employee exposure at or above the action level but at or below both the 8-hour TWA and the 15-minute STEL, the employer shall repeat such monitoring for each such employee at least every six months.

(ii) If the monitoring required by paragraph (d)(2)(i) of this section reveals employee exposure above the 8-hour TWA, the employer shall repeat such monitoring for each such employee at least every three months.

(iii) If the monitoring required by paragraph (d)(2) of this section reveals employee exposure above the 15-minute STEL, the employer shall repeat such monitoring for each such individual at least every three months and more often as necessary to evaluate exposures to employees subject to short-term exposures.

(iv) The employer may alter the monitoring schedule from quarterly to semi-annually for any employee for whom two consecutive measurements taken at least 7 days apart indicate that the employee's exposure has decreased to or below the 8-hour TWA and STEL, but is at or above the action level.

(4) Termination of monitoring. (i) If the initial monitoring required by paragraph (d)(2) of this section reveals employee exposure to be below the action level and at or below the 15-minute STEL, the employer may discontinue the monitoring for those employees who are represented by the initial monitoring except as otherwise required by paragraph (d)(5) of this section.

(ii) If the periodic monitoring required by paragraph (d)(3) of this section reveals that employee exposures, as indicated by at least two consecutive measurements taken at least 7 days apart, are below the action level and at or below that STEL, the employer may discontinue the monitoring for those employees who are represented by such monitoring except as otherwise required by paragraph (d)(5) of this section.

(5) Additional monitoring. (i) The employer shall institute the exposure monitoring required under paragraphs (d)(2) and (d)(3) of this section whenever there has been a change in the production, process, control equipment, personnel or work practices that may result in new or additional exposures to MC or when the employer has a reasonable suspicion that a change at the workplace may result in new or additional exposures.

(ii) Whenever spills, leaks, ruptures or other breakdowns occur that may lead to employee exposure above the action level or above the STEL, the employer shall repeat the monitoring which is required by paragraph (d)(2)(i) of this section after the clean up of the spill or repair of the leak, rupture or other breakdown.

(6) Accuracy of monitoring. Monitoring shall be accurate, to a confidence level of 95 percent, to within plus or minus 25 percent for airborne concentrations of MC at or above the 25 ppm 8-hour TWA limit and to within plus or minus 35 percent for airborne concentrations of MC above the action level of 12.5 ppm and below the 25 ppm 8-hour TWA limit.

(7) Employee notification of monitoring results. (i) The employer shall, within 15 working days after the receipt of the results of any monitoring performed under this standard, notify the affected employee of these results in writing, either individually or by posting of results in an appropriate location that is accessible to affected employees.

(ii) The written notification required by paragraph (d)(7)(i) of this section shall contain the corrective action being taken by the employer to reduce employee exposure to or below the PEL or STEL, wherever monitoring results indicated that the 8-hour TWA or 15-minute STEL has been exceeded.

(e) Regulated areas. (1) The employer shall establish a regulated area wherever occupational exposures to airborne concentrations of MC may exceed the permissible exposure limits, either the 8-hour TWA of 25 ppm or 15-minute STEL of 125 ppm.

(2) Access to regulated areas shall be limited to authorized persons.

(3) Each person entering a regulated area shall be supplied with and required to use a respirator, selected in accordance with paragraph (g)(2) of this section.

(4) Regulated areas shall be demarcated from the rest of the workplace in any manner that adequately establishes and alerts employees of the boundaries of the area and minimizes the number of employees exposed to MC within the regulated area.

(5) An employer at a multi-employer worksite who establishes a regulated area shall communicate the access restrictions and locations of these areas to other employers with work operations at that worksite.

(f) Methods of compliance. (1) Engineering controls and work practices. (i) The employer shall institute engineering controls and work practices to reduce and maintain employee exposure to or below the permissible limits, except to the extent that the employer can establish that these controls are not feasible or where paragraph (g)(1) of this section applies.

(ii) Wherever the feasible engineering controls and work practices which can be instituted are not sufficient to reduce employee exposure to or below the PEL or STEL, the employer shall use them to reduce employee exposure to the lowest levels achievable by these controls and shall supplement them by the use of respiratory protection that complies with the requirements of paragraph (g) of this section.

(iii) To the extent feasible, employers shall institute a program to detect leaks and spills. In work areas where spillage may occur, the employer shall make provisions to contain the spill and safely dispose of the waste. The employer shall insure that all leaks are repaired and spills are cleaned promptly by employees wearing appropriate protective equipment and trained in proper methods of cleanup. Compliance with procedures, such as those described in Appendix A of this standard, would be considered to satisfy this requirement.

(iv) The employer shall not implement a schedule of employee rotation as a means of compliance with the PELs.

(2) Compliance program. (i) Where the PELs are exceeded, the employer shall establish and implement a written program to reduce employee exposure to or below the PELs by means of engineering and work practice controls, as required by paragraph (f)(1)(i) of this section. To the extent that engineering and work practice controls cannot reduce exposures to or below the PELs, the compliance program shall provide for the use of respiratory protection.

(ii) The written compliance program shall include a schedule for development and implementation of the engineering controls and work practice controls, including periodic leak detection surveys, and a written plan for emergency situations, as specified in paragraph (h)(1)(i) of this section.

(iii) The written compliance program shall be furnished upon request for examination and copying to the Assistant Secretary, the Director, affected employees and designated employee representatives. Such plans shall be reviewed at least every 12 months, and shall be updated as necessary to reflect significant changes in the status of the employer's compliance program.

(g) Respiratory protection and other personal protective equipment. (1) General. The employer shall provide respirators, and ensure that they are used, where required by this section. Respirators shall be used in the following circumstances.

(i) During the time interval necessary to install or implement feasible engineering and work practice controls;

(ii) In work operations, such as maintenance and repair activities, vessel cleaning, or other activities for which engineering and work practice controls are demonstrated to be infeasible, and exposures are intermittent in nature and limited in duration;

(iii) In work situations where feasible engineering and work practice controls are not yet sufficient to reduce exposure to or below the PELs; and

(iv) In emergencies.

(2) Respirator selection. (i) Where respirators are required or allowed under this section, the employer shall select and provide, at no cost to the employee, the appropriate respirator as specified in Table 1, and shall ensure that the employee uses the respirator provided.

(ii) The employer shall select respirators from among those atmosphere supplying respirators approved and certified jointly by the Mine Safety and Health Administration (MSHA) and the National Institute for Occupational Safety and Health (NIOSH) under the provisions of 30 CFR Part 11. When employers elect to provide gas masks with organic vapor canisters for use in emergency escapes, the organic vapor canisters shall bear the approval of MSHA/NIOSH.

TABLE 1. - MINIMUM REQUIREMENTS FOR RESPIRATORY PROTECTION FOR AIRBORNE
          METHYLENE CHLORIDE
_______________________________________________________________________
Concentration of |  
airborne methylene | Minimum Respirator Required(1)
chloride or condition |  
of Use |  
__________________________ | ____________________________________________
  |  
Up to 625 ppm............. | (1) Continuous flow supplied air respirator,
  | hood or helmet.
Up to 1250 ppm............ | (1) Full facepiece supplied air respirator
  | operated in negative pressure (demand)
  | mode.
  | (2) Full facepiece self-contained breathing
  | apparatus (SCBA) operated in negative
  | pressure (demand) mode.
Up to 5000 ppm............ | (1) Continuous flow supplied air respirator,
  | full facepiece.
  | (2) Pressure demand supplied air respirator,
  | full facepiece.
  | (3) Positive pressure full facepiece SCBA.
Unknown concentration, | (1) Positive pressure full facepiece
or above 5000 ppm | SCBA.
  | (2) Full facepiece pressure demand supplied
  | air respirator with an auxiliary
  | self-contained air supply.
Fire fighting............. | Positive pressure full facepiece SCBA.
Emergency escape.......... | (1) Any continuous flow or pressure demand
  | SCBA.
  | (2) Gas mask with organic vapor canister.
_________________________ | _____________________________________________
FOOTNOTE (1): Respirators assigned for higher environmental
concentrations may be used at the lower concentrations.
________________________________________________________________________

(iii) Any employee who cannot wear a negative pressure air-supplied respirator shall be given the option of wearing a respirator with less breathing resistance such as positive pressure SCBA.

(iv) During emergency escape, any employee who cannot wear a negative pressure (organic vapor canister) respirator shall be given the option of wearing a respirator with less breathing resistance, such as a powered air-purifying respirator (PAPR) or SCBA.

(3) Respirator program. Where respiratory protection is required by this section, the employer shall institute a respirator program in accordance with 29 CFR 1910.134(b), (d), (e), and (f).

(4) Respirator use. (i) The employer shall permit employees who wear respirators to leave the regulated area to readjust the facepieces to their faces for a proper fit, and to wash their faces and respirator facepieces as necessary in order to prevent skin irritation associated with respirator use.

(ii) Employers who provide gas masks with organic vapor canisters for the purpose of emergency escape shall replace those canisters after any emergency use before they are returned to service.

(5) Respirator fit testing. (i) The employer shall assure that each respirator issued to the employee exhibits the least possible facepiece leakage and that the respirator is fitted properly.

(ii) Depending on the MC exposure concentration, the employer shall perform either quantitative or qualitative fit tests at the time of initial fitting and at least annually thereafter for each employee wearing a negative pressure respirator. The test shall be used to select a respirator facepiece which exhibits minimum leakage and provides the required protection as prescribed in Table 1.

(iii) Fit testing shall be conducted in accordance with Appendix C of this standard.

(6) Protective Work Clothing and Equipment. (i) Personal protective clothing and equipment shall be worn where appropriate to prevent eye contact and limit dermal exposure to liquid MC and solutions containing MC. Protective clothing and equipment which is resistant to MC shall be provided by the employer at no cost to the employee and the employer shall assure its use where appropriate. Eye and face protection shall meet the requirements of 29 CFR 1910.133.

(ii) The employer shall provide clean and protective clothing and equipment at least weekly to each affected employee.

(iii) The employer shall clean, launder, repair and replace all protective clothing and equipment required by this paragraph to maintain their effectiveness.

(iv) The employer shall be responsible for the safe disposal of such clothing and equipment. Compliance with such procedures as described in Appendix A of this standard would be considered to satisfy this requirement.

(h) Emergency situations. (1) Written plan. (i) A written plan for emergency situations shall be developed for each workplace where there is a possibility of an emergency. Appropriate portions of the plan shall be implemented in the event of an emergency.

(ii) The plan shall specifically provide that employees engaged in correcting emergency conditions shall be equipped with appropriate personal protective equipment, such as respirators.

(2) Alerting employees. Where there is the possibility of employee exposure to MC due to an emergency, the employer shall alert each potentially affected employee. If an emergency arises, the employer shall ensure that employees not essential to correcting the situation are immediately evacuated and restricted from the area, and that normal operations are halted until the emergency is abated.

(i) Medical surveillance. (1) Employees covered. (i) The employer shall institute a medical surveillance program for all employees who are or may be exposed to MC concentrations at or above the action level (AL) for at least 30 days a year and for employees who are or may be exposed to MC at or above the 8-hour TWA or above the STEL for at least 10 days a year.

(ii) For any employee required to work in an atmosphere with MC concentrations above the 8-hour TWA or STEL, and therefore required to use a respirator, the employer shall direct the examining physician to ascertain the employee's ability to wear a respirator and, for employees who are able to wear respirators, provide a written opinion to the employer stating that fact.

(iii) The employer shall make medical surveillance available for all employees exposed to MC during an emergency.

(2) Examination by a physician. (i) All medical procedures shall be performed by or under the supervision of a licensed physician and all laboratory tests are to be conducted by an accredited laboratory. All examinations and diagnostic procedures shall be provided without cost to the employee, without loss of pay, and at a reasonable time and place.

(3) Frequency of examinations. The employer shall make available medical examinations and consultations to each employee covered under paragraph (i)(1) of this section on the following schedules:

(i) Within 180 days of the effective date of this standard, or before the time of initial assignment of the employee, whichever is last.

(ii) Annually

(iii) At termination of employment or reassignment to an area where exposure to MC is consistently below the action level, if three months or more have elapsed since last medical examination.

(iv) At frequencies other than the above when recommended in the physician's written opinion.

(4) Content of Medical Examination. Medical examinations made available pursuant to paragraphs (i) (3) of this section shall include, at a minimum:

(i) A comprehensive or interim (from time of last exam) medical and work history with special emphasis on neurological symptoms, mental status, and cardiac health.

(ii) Physical examination giving particular attention to the lungs, liver, nervous system, and breast.

(iii) Laboratory surveillance including carboxyhemoglobin levels and a complete blood count.

(iv) Determination of any reproductive difficulties, such as miscarriages and inability to conceive.

(v) Any additional information determined by the examining physician to be necessary to provide an appropriate assessment.

(5) Additional examinations and referrals (i) Where the examining physician determines it is necessary, the scope of the medical examination shall be expanded and the appropriate referrals, consultation or additional medical surveillance services shall be provided.

(6) Information provided to the physician. The employer shall provide the following information to the examining physician and to any specialist involved in the diagnosis:

(i) A copy of this standard including its appendices;

(ii) A description of the affected employee's past, current and anticipated future duties as they relate to the employee's MC exposure;

(iii) The employee's former or current exposure levels or, for employees not yet occupationally exposed to MC, the employee's anticipated exposure levels and the frequency and exposure levels of abnormal events (i.e., emergencies);

(iv) A description of any personal protective equipment, such as respirators, used or to be used; and

(v) Information from previous employment-related medical examinations of the affected employee which is not otherwise available to the examining physician or the specialist.

(7) Physician's written opinion. (i) For each examination required by this standard, the employer shall obtain and provide the employee with a copy of the examining physician's written opinion within 15 days of the examination. The written opinion shall be limited to the following information:

(A) The results of any tests or related evaluation concerning MC exposure carried out as part of the medical evaluation;

(B) The physician's opinion concerning whether the employee has any detected medical condition(s) which would place the employee's health at increased risk of material impairment from exposure to MC. Clinical and other test results shall be used by the physician to support any findings and recommendations.

(C) Any recommended limitations upon the employee's exposure to MC or upon the employee's use of protective clothing or equipment and respirators;

(D) A statement that the employee has been informed by the physician of the results of the medical examination and any medical conditions resulting from MC exposure which require further explanation or treatment.

(ii) The employer shall instruct the physician not to reveal to the employer, orally or in the written opinion, any specific records, findings, and diagnoses that have no bearing on occupational exposures to MC.

(j) Communication of methylene chloride hazards to employees.

(1) Warning Signs. (i) Warning signs shall be provided and displayed in regulated areas. In addition, warning signs shall be posted at all approaches to regulated areas so that an employee may read the signs and take necessary protective steps before entering the area.

(ii) The warning signs required by paragraph (j)(1)(i) of this standard shall comply with the requirements of the Hazard Communication Standard, 29 CFR 1910.1200(f) (general industry), 29 CFR 1915.99(f) (shipyard employment) and 29 CFR 1926.59(f) (construction industry) and shall bear the following information.

DANGER

METHYLENE CHLORIDE

POTENTIAL CANCER HAZARD

AUTHORIZED PERSONNEL ONLY

RESPIRATORS REQUIRED IN THIS AREA

(2) Warning Labels. (i) Shipping and storage containers containing MC, shall bear appropriate warning labels, as specified in paragraph (j)(2)(ii) of this section.

(ii) The labels shall comply with the requirements of the Hazard Communication Standard 29 CFR 1910.1200(f) (general industry), 29 CFR 1915.99(f) (shipyard employment) and 29 CFR 1926.59(f) (construction industry), and shall include the following information:

DANGER

CONTAINS METHYLENE CHLORIDE

POTENTIAL CANCER HAZARD

(3) Material safety data sheets. Employers who are manufacturers or importers of MC shall comply with the requirements regarding development and distribution of material safety data sheets as specified in 29 CFR 1910.1200(g) of OSHA's Hazard Communication Standard. All employers with employees potentially exposed to MC shall maintain material safety data sheets and provide their employees with access to them, in accordance with the requirements of 29 CFR 1910.1200(g) and 29 CFR 1926.59(g).

(4) Employee information and training. Employers shall provide each employee with information and training in accordance with the requirements of the Hazard Communication Standard, 29 CFR 1910.1200(h) (general industry), and 29 CFR 1926.59(h) (construction industry). In addition:

(i) The employer shall institute a training program for all employees who are potentially exposed to MC at or above the action level or the STEL, assure employee participation in the program and maintain a record of the contents of such program.

(ii) Training shall be provided prior to or at the time of initial assignment to a job potentially involving exposure to MC and at least annually thereafter.

(iii) The training program shall be conducted in a manner that the employee is able to understand. The employer shall assure that each employee is informed of the following:

(A) The health hazards associated with MC exposure, with special attention to the information incorporated in Appendix A;

(B) The quantity, location, manner of use, release, and storage of MC and the specific nature of operations that could result in exposure to MC, especially exposures above the 8-hour TWA or STEL;

(C) The engineering controls and work practices associated with the employee's job assignment;

(D) The measures employees can take to protect themselves from exposure to MC, including modification of their habits, such as smoking and personal hygiene;

(E) Specific procedures the employer has implemented to protect employees from exposure to MC, such as appropriate work practices, emergency procedures, and personal protective equipment;

(F) The details of the hazard communication program developed by the employer, including an explanation of the signs, labeling system and material safety data sheets, and how employees can obtain and use the appropriate hazard information;

(G) The purpose, proper selection, fitting, proper use, and limitations of respirators and protective clothing;

(H) The purpose and a description of the medical surveillance program required by paragraph (i) of this standard;

(I) The contents of this standard and its appendices, and

(J) The right of any employee exposed to MC at or above the action level or above the STEL to obtain:

(1) Medical examinations as required by paragraph (i) at no cost to the employee;

(2) The employee's medical records required to be maintained by paragraph (k)(3) of this section;

(3) All air monitoring results representing the employee's exposure to MC and required to be kept by paragraph (k)(2) of this section.

(iv) The employer shall make a copy of this standard and its appendices readily available without cost to all affected employees and shall provide a copy if requested.

(v) The employer shall provide to the Assistant Secretary or the Director, upon request, all materials relating to the employee information and training program.

(k) Recordkeeping. (1) Objective data for exempted operations. (i) Where an employer seeks to demonstrate through reasonable reliance on objective data that any materials in the workplace containing MC will not release MC at levels meeting or exceeding the action level or the STEL under foreseeable conditions of exposure, the employer shall establish and maintain an accurate record of the objective data reasonably relied upon in support of the exemption.

(ii) This record shall include at least the following information:

(A) The product qualifying for exemption;

(B) The source of the objective data;

(C) The testing protocol, results of testing, and/or analysis of the material for the release of MC;

(D) A description of the operation exempted and how the data support the exemption; and

(E) Other data relevant to the operations, materials, processing, or employee exposures covered by the exemption.

(iii) The employer shall maintain this record for the duration of the employer's reliance upon such objective data.

(2) Exposure measurements. (i) The employer shall establish and keep an accurate record of all measurements taken to monitor employee exposure to MC as prescribed in paragraph (d) of this section.

(ii) This record shall include at least the following information:

(A) The date of measurement for each sample taken;

(B) The operation involving exposure to MC which is being monitored;

(C) Sampling and analytical methods used and evidence of their accuracy;

(D) Number, duration, and results of samples taken;

(E) Type of personal protective equipment, such as respiratory protective devices, worn, if any; and

(F) Name, social security number, job classification and exposure of all of the employees represented by monitoring, indicating which employees were actually monitored.

(iii) The employer shall maintain this record for at least thirty (30) years, in accordance with 29 CFR 1910.20.

(3) Medical surveillance. (i) The employer shall establish and maintain an accurate record for each employee subject to medical surveillance under paragraph (i)(1)(i) of this section.

(ii) The record shall include at least the following information:

(A) The name, social security number and description of the duties of the employee;

(B) Physicians' written opinions;

(C) Any employee medical complaints related to exposure to MC; and

(D) A copy of the information provided to the physician as required by paragraph (i)(6) of this section.

(iii) The employer shall ensure that this record is maintained for the duration of employment plus thirty (30) years, in accordance with 29 CFR 1910.20.

(4) Respirator fit testing. (i) The employer shall establish and maintain accurate records for each employee subject to negative pressure fit testing required by this standard.

(ii) This record shall include:

(A) A copy of the protocol selected for respirator fit testing. (B) A copy of the results of any quantitative fit testing performed. (C) The size and manufacturer of the types of respirators available for selection.

(D) The date of the most recent fit testing, the name and social security number of the tested employee, and the respirator type and facepiece selected.

(iii) Respirator fit testing records shall be kept until replaced by a more recent record.

(5) Availability. (i) The employer, upon written request, shall make all records required to be maintained by this section available to the Assistant Secretary and the Director for examination and copying in accordance with 29 CFR 1910.20.

(ii) The employer, upon request, shall make any records required by paragraphs (k)(1) and (k)(2) of this section available for examination and copying by affected employees, former employees, designated representatives.

(iii) The employer, upon request, shall make employee medical records required to be kept by paragraph (k)(3) of this section available for examination and copying by the subject employee and by anyone having the specific written consent of the subject employee.

(6) Transfer of records. The employer shall comply with the requirements concerning transfer of records set forth in 29 CFR 1910.20(h).

(l) Observation of monitoring. (1) Employee observation. The employer shall provide affected employees or their designated representatives an opportunity to observe any monitoring of employee exposure to MC conducted in accordance with paragraph (d) of this section.

(2) Observation procedures. When observation of the monitoring of employee exposure to MC requires entry into an area where the use of protective clothing or equipment is required, the employer shall provide the observer with and the observer shall be required to use such clothing and equipment and shall comply with all other applicable safety and health procedures.

(m) Dates (1) Effective date. This section shall become effective sixty (60) days after the date of publishing the final standard in the Federal Register.

(2) Start-up dates. (i) The requirements of paragraphs (c) through (l) of this section, including feasible work practice controls but not including initial monitoring as required by paragraph (d)(2) and engineering controls specified in paragraph (f)(1), shall be complied with within one-hundred and eighty (180) days after the effective date of this section.

(ii) Initial monitoring required by paragraph (d)(2) shall be completed within 120 days after the effective date of this section or the introduction of MC into the workplace.

(iii) Engineering controls specified by paragraph (f)(1) of this section shall be implemented within one (1) year after the effective date of this section.

(n) Appendices. The information contained in the appendices is not intended, by itself, to create any additional obligations not otherwise imposed or to detract from any existing obligation. The protocols on respiratory fit testing in Appendix C are mandatory. Appendix C will be codified in the final rule.

Appendix A to 1910.1052--Substance Safety Data Sheet and Technical Guidelines for Methylene Chloride

I. Substance Identification

A. Substance: Methylene chloride (CH(2)Cl(2)).

B. Synonyms: Dichloromethane (DCM); Methylene dichloride;

Methylene bichloride; Methane dichloride; CAS-75-09-2; NCI-C50102.

C. Physical data:

1. Molecular weight: 84.9

2. Boiling point (760 mm Hg,): 39.8 degrees C (104 degrees F).

3. Specific gravity (water=1): 1.3

4. Vapor density (air = 1 at boiling points): 2.9

5. Vapor pressure at 20 degrees C (68 degrees F): 350 mm Hg

6. Solubility in water, g/100 g water at 20 degrees C (68 degrees F) = 1.32.

7. Appearance and odor: colorless liquid with a chloroform-like odor.

D. Uses: MC is used as a solvent, especially where high volatility is required. It is a good solvent for oils, fats, waxes, resins, bitumen, rubber and cellulose acetate and is a useful paint stripper and degreaser. It is used in paint removers, in propellant mixtures for aerosol containers, as a solvent for plastics, as a degreasing agent, as an extracting agent in pharmaceutical industry and as a blowing agent in polyurethane foams. Its solvent property is sometimes increased by mixing with methanol, petroleum naphtha or tetrachloroethylene.

E. Appearance and odor: MC is a clear colorless liquid with a chloroform-like odor. It is slightly soluble in water and completely miscible with most organic solvents.

F. Permissible exposure: Exposure may not exceed 25 parts MC per million parts of air (25 ppm) as an eight-hour time-weighted average (8-hour TWA), short-term exposure limit (STEL) may not exceed 125 parts of MC per million parts of air (125 ppm) averaged over a 15-minute period.

II. Health Hazard Data

A. MC can affect the body if it is inhaled or if the liquid comes in contact with the eyes or skin. It can also affect the body if it is swallowed. Employers shall advise employees of all areas and operations where exposure to MC occurs.

B. Effect of overexposure:

1. Short-term Exposure: MC is an anesthetic. Inhaling the vapor may cause mental confusion, light-headedness, nausea, vomiting, and headache. Continued exposure may cause increased light-headedness, staggering, unconsciousness, and even death. High vapor concentrations may also cause irritation of the eyes and respiratory tract. Exposure to MC may make the symptoms of angina worse. Skin exposure to the liquid MC may cause irritation. If the liquid MC is held in contact with the skin, it may cause skin burns. Splashes of the liquid into the eyes may cause irritation.

2. Long-term (chronic) exposure: The evidence for the carcinogenic potential of MC is primarily based upon chronic studies in which MC was administered to three species of laboratory rodents (rats, mice and hamsters). MC exposure produced lung and liver tumors in mice and mammary tumors in rats. No carcinogenic effects of MC were found in hamsters.

C. Reporting signs and symptoms: You should inform your employer if you develop any signs or symptoms and suspect that they are caused by exposure to MC.

D. Warning Properties:

1. Odor Threshold: Different authors have reported varying odor thresholds for MC. Kirk-Othmer and Sax both reported 25 to 50 ppm; Summer and May both reported 150 ppm; Spector reports 320 ppm. Patty, however, states that since one can become adapted to the odor, it cannot be considered that MC has an adequate warning property.

2. Eye Irritation Level: Grant reports that MC "presents no particular hazard to the eyes." Kirk-Othmer, however, reports that "MC vapor is seriously damaging to the eyes." Sax agrees with Kirk-Othmer's statement. The Documentation of TLVs states that irritation of the eyes has been observed in workers who had been exposed to concentrations up to 5000 ppm.

3. Evaluation of Warning Properties: Since there is a wide range of MC odor threshold (25-320 ppm), and human adaption to the odor, MC is considered as a material with poor warning properties.

III. Emergency First Aid Procedures

In the event of emergency, institute first aid procedures and send for first aid or medical assistance.

A. Eye and Skin Exposures: If there is a potential that liquid MC can come in contact with eye or skin, face shields and skin protective equipment must be provided and used. If liquid MC comes in contact with the eye, get medical attention. Contact lenses should not be worn when working with this chemical.

B. Breathing: If a person breathes in large amounts of MC, move the exposed person to fresh air at once. If breathing has stopped, perform artificial respiration. Keep the affected person warm and at rest. Get medical attention as soon as possible.

C. Rescue: Move the affected person from the hazardous exposure immediately. If the exposed person has been overcome, notify someone else and put into effect the established emergency rescue procedures. Understand the facility's emergency rescue procedures and know the locations of rescue equipment before the need arises. Do not become a casualty.

IV. Respirators, Protective Clothing, and Eye Protection

A. Respirators: Good industrial hygiene practices recommend that engineering controls be used to reduce environmental concentrations to the permissible exposure level. However, there are some exceptions where respirators may be used to control exposure. Respirators may be used when engineering and work practice controls are not feasible, when such controls are in the process of being installed, or when these controls fail and need to be supplemented. Respirators may also be used for operations which require entry into tanks or closed vessels, and in emergency situations. If the use of respirators is necessary, the only respirators permitted are those that have been approved by the Mine Safety and Health Administration (MSHA) or the National Institute for Occupational Safety and Health (NIOSH). Supplied-air respirators are required because air-purifying respirators do not provide adequate respiratory protection against MC. In addition to respirator selections, a complete written respiratory protection program should be instituted which includes regular training, maintenance, inspection, cleaning, and evaluation. If you can smell MC while wearing a respirator, proceed immediately to fresh air. If you experience difficulty in breathing while wearing a respirator, tell your employer.

B. Protective Clothing: Employees should be provided with and required to use impervious clothing, gloves, face shields (eight-inch minimum), and other appropriate protective clothing necessary to prevent repeated or prolonged skin contact with liquid MC or contact with vessels containing liquid MC. Any clothing which becomes wet with liquid MC should be removed immediately and not reworn until the employer has ensured that the protective clothing is fit for reuse.

C. Eye Protection: Employees should be provided with and required to use splash-proof safety goggles where liquid MC may contact the eyes.

V. Housekeeping and Hygiene Facilities

For purposes of complying with 29 CFR 1910.141, the following items should be emphasized:

A. The workplace should be kept clean, orderly, and in a sanitary condition. The employer is required to institute a leak and spill detection program for operations involving liquid MC in order to detect sources of fugitive MC emissions.

B. Emergency drench showers and eyewash facilities are recommended. These should be maintained in a sanitary condition. Suitable cleansing agents should also be provided to assure the effective removal of MC from the skin.

C. Because of the hazardous nature of MC, contaminated protective clothing should be placed in a regulated area designated by the employer for removal of MC before the clothing is laundered or disposed of.

VI. Precautions for Safe Use, Handling, and Storage

A. Fire and Explosion Hazards: MC has no flash point in conventional closed tester, but it forms flammable vapor-air mixtures at approximately 100oC (212oF), or higher. It has a lower explosion limit of 12%, and an upper explosion limit of 19% in air. It has an autoignition temperature of 556.1oC (1033oF), and a boiling point of 39.8oC (104oF). It is heavier than water with a specific gravity of 1.3. It is slightly soluble in water.

B. Reactivity Hazards: Conditions contributing to instability of MC are heat and moisture. Contact with strong oxidizers, caustics, and chemically active metals such as aluminum or magnesium powder, sodium and potassium may cause fires and explosions. Special precautions: Liquid MC will attack some forms of plastics, rubber, and coatings.

C. Life Hazard: Liquid MC is painful and irritating if splashed in the eyes or if confined on the skin by gloves, clothing, or shoes. Vapor in high concentrations may cause narcosis and death.

D. Storage: Protect against physical damage. Because of its corrosive properties, and its high vapor pressure, MC should be stored in plain, galvanized or lead lined, mild steel containers in a cool, dry, well ventilated area away from direct sunlight, heat source and acute fire hazards.

E. Piping Material: All piping and valves at the loading or unloading station should be of material that is resistant to MC and should be carefully inspected prior to connection to the transport vehicle and periodically during the operation.

F. Usual Shipping Containers: Glass bottles, 5- and 55-gallon steel drums, tank cars, and tank trucks.

G. Electrical Equipment: Electrical installations in Class I hazardous locations as defined in Article 500 of the National Electrical Code, should be installed according to Article 501 of the code; and electrical equipment should be suitable for use in atmospheres containing MC vapors. See Flammable and Combustible Liquids Code (NFPA No. 325M), Chemical Safety Data Sheet SD-86 (Manufacturing Chemists' Association, Inc.).

H. Fire Fighting: When involved in fire, MC emits high toxic and irritating fumes such as phosgene, hydrogen chloride and carbon monoxide. Wear breathing apparatus and use water spray to keep fire-exposed containers cool. Water spray may be used to flush spills away from exposures. Extinguishing media are dry chemical, carbon dioxide, foam. For purposes of compliance with 29 CFR 1910.307, locations classified as hazardous due to the presence of MC shall be Class I.

I. Spills and Leaks: Persons not wearing protective equipment and clothing should be restricted from areas of spills or leaks until cleanup has been completed. If MC has spilled or leaked, the following steps should be taken:

1. Remove all ignition sources.

2. Ventilate area of spill or leak.

3. Collect for reclamation or absorb in vermiculite, dry sand, earth, or a similar material.

J. Methods of Waste Disposal: Small spills should be absorbed onto sand and taken to a safe area for atmospheric evaporation. Incineration is the preferred method for disposal of large quantities by mixing with a combustible solvent and spraying into an incinerator equipped with acid scrubbers to remove hydrogen chloride gases formed. Complete combustion will convert carbon monoxide to carbon dioxide. Care should be taken for the presence of phosgene.

K. You must not keep food, beverage, or smoking materials, nor are you permitted to eat or smoke in regulated areas where MC concentrations are above the permissible exposure limits.

L. Portable heating units should not be used in confined areas where MC is used.

M. Ask your supervisor where MC is used in your work area and for any additional plant safety and health rules.

VII. Medical Requirements

Your employer is required to offer you the opportunity to participate in a medical surveillance program if you are exposed to MC at concentrations exceeding the action level (12.5 ppm 8-hour TWA) for more than 30 days a year or at concentrations exceeding the PELs (25 ppm 8-hour TWA or 125 ppm 15-minute STEL) for more than 10 days a year. If you are exposed to MC at concentrations over either of the PELs, the medical surveillance will also include tests to ensure that you are able to wear the respirator that you are assigned. Your employer must provide all medical examinations relating to your MC exposure at a reasonable time and place and at no cost to you.

VIII. Monitoring and Measurement Procedures

A. Exposure above the Permissible Exposure Limit:

1. Eight-hour exposure evaluation: Measurements taken for the purpose of determining employee exposure under this section are best taken with consecutive samples covering the full shift. Air samples must be taken in the employee's breathing zone.

2. Monitoring techniques: The sampling and analysis under this section may be performed by collection of the MC vapor on two charcoal adsorption tubes in series or other composition adsorption tubes, with subsequent chemical analysis. Sampling and analysis may also be performed by instruments such as real-time continuous monitoring systems, portable direct reading instruments, or passive dosimeters as long as measurements taken using these methods accurately evaluate the concentration of MC in employees breathing zones.

Appendix D describes the validated method of sampling and analysis which has been tested by OSHA for use with MC. The employer has the obligation of selecting a monitoring method which meets the accuracy and precision requirements of the standard under his unique field conditions. The standard requires that the method of monitoring must be accurate, to a 95 percent confidence level, to plus or minus 25 percent for concentrations of MC at or above 25 ppm, and to plus or minus 35 percent for concentrations at or below 25 ppm. In addition to the method described in Appendix D, there are numerous other methods available for monitoring for MC in the workplace.

B. Since many of the duties relating to employee exposure are dependent on the results of measurement procedures, employers must assure that the evaluation of employee exposure is performed by a technically qualified person.

IX. Observation of Monitoring

Your employer is required to perform measurements that are representative of your exposure to MC and you or your designated representative are entitled to observe the monitoring procedure. You are entitled to observe the steps taken in the measurement procedure, and to record the results obtained. When the monitoring procedure is taking place in an area where respirators or personal protective clothing and equipment are required to be worn, you or your representative must also be provided with, and must wear protective clothing and equipment.

X. Access To Information

A. Each year, your employer is required to inform you of the information contained in this Appendix. In addition, your employer must instruct you in the proper work practices for using MC, emergency procedures, and the correct use of protective equipment.

B. Your employer is required to determine whether you are being exposed to MC. You or your representative has the right to observe employee measurements and to record the results obtained. Your employer is required to inform you of your exposure. If your employer determines that you are being over exposed, he or she is required to inform you of the actions which are being taken to reduce your exposure to within permissible exposure limits.

C. Your employer is required to keep records of your exposures and medical examinations. These records must be kept by the employer for at least thirty years (30).

D. Your employer is required to release your exposure and medical records to you or your representative upon your request.

XI. Common Operations and Controls

The following list includes some common operations in which exposure to MC may occur and control methods which may be effective in each case:

___________________________________________________________________
          Operations | Controls
____________________________________ | ______________________________
  |  
Use as solvent in paint | General dilution
   and varnish removers; | ventilation; local
   manufacture of aerosols; | exhaust ventilation;
   cold cleaning and | personal protective
   ultrasonic cleaning; and as an | equipment.
   extraction solvent for |  
   foods and furniture |  
   processing. |  
Use as solvent in vapor | Process enclosure; local
   degreasing. | exhaust ventilation;
  | chilling coils.
Use as a secondary | General dilution
   refrigerant in air | ventilation; local
   conditioning and | exhaust ventilation;
   scientific testing. | personal protective
  | equipment.
____________________________________ | __________________________

Appendix B to 1910.1052--Medical Surveillance for Methylene Chloride

I. Primary Route of Entry

Inhalation

II. Toxicology

Methylene Chloride (MC) is primarily an inhalation hazard. The principle acute hazardous effects are the depressant action on the central nervous system and possible liver toxicity. The range of CNS effects are from a decreased eye/hand coordination and decreased performance in vigilance tasks to narcosis and even death of the individuals exposed at very high doses. Elevated liver enzymes and irritation to the respiratory passages and eyes have also been reported for both humans and experimental animals resulting from exposure to MC vapors. MC is metabolized to carbon monoxide and carbon dioxide via two separate pathways. Through the first pathway, MC is metabolized to carbon monoxide as an end-product via the P-450 mixed function oxidase pathway located in the microsomal fraction of the cell. This biotransformation of MC to carbon monoxide occurs through the process of microsomal oxidative dechlorination which takes place primarily in the liver. The amount of conversion to carbon monoxide is significant as measured by the concentration of carboxyhemoglobin; up to 12% measured in the blood following occupational exposure of up to 610 ppm. Through the second pathway, MC is metabolized to carbon dioxide as an end product (with formaldehyde and formic acid as metabolic intermediates) via the glutathione dependent enzyme found in the cytosolic fraction of the liver cell. MC has been tested for carcinogenicity in several laboratory rodents. These rodent studies indicate that there is clear evidence that MC is carcinogenic to male and female mice and female rats. Based on three epidemiologic studies, OSHA preliminarily concludes that there is suggestive evidence of increased cancer risk in MC-related worker populations. The epidemiological evidence is consistent with the finding of excess cancer in the experimental animal studies. NIOSH regarded MC as a potential occupational carcinogen and the International Agency for Research Cancer (IARC) classified MC as an animal carcinogen. OSHA considered MC as a suspected human carcinogen.

III. Medical Signs and Symptoms of Acute Exposure

Skin exposure to liquid MC may cause irritation. If liquid MC comes in contact with the skin or eyes, it may cause skin irritations and burns. At very high concentrations in air, MC is an anesthetic and may cause breathing problems, leading to bronchitis and pulmonary edema, nausea, vomiting, light-headedness, numbness of the extremities, blood changes, unconsciousness and even death.

At lower concentrations in air, MC may cause irritation to the skin, eye, and respiratory tract and occasionally headache and nausea. Perhaps the greatest problem from exposure to low concentrations of MC is the CNS effects on coordination and alertness that may cause unsafe operations of machinery and equipment, leading to self-injury or accidents. Low levels and short duration exposures do not seem to produce permanent disability, but chronic exposures to MC have been demonstrated to produce liver toxicity in animals, and therefore, the evidence is suggestive for liver toxicity in humans after chronic exposure.

IV. Surveillance and Preventative Considerations

As discussed above, MC is classified as a suspect or potential human carcinogen. It is a central nervous system (CNS) depressant and a skin, eye and respiratory tract irritant. At extremely high concentrations, MC has caused liver damage in animals.

The principal toxic effect of MC is on the CNS, acting as a narcotic. The observation of the symptoms characteristic of CNS depression along with a physical examination would provide the best detection of early neurological disorders. Since exposure to MC also increases the carboxyhemoglobin level in the blood, ambient carbon monoxide levels would have an additive effect on that carboxyhemoglobin level. Based on such information, the medical surveillance should include a periodic carboxyhemoglobin test as an index of the presence of carbon monoxide in the blood.

Based on the animal evidence and three epidemiologic studies previously mentioned, OSHA preliminarily concludes that MC is a suspect human carcinogen. The proposed medical surveillance program is designed to observe exposed workers on a regular basis. While the proposed medical surveillance program cannot detect MC-induced cancer at a preneoplastic stage, OSHA anticipates that, as in the past, early detection and treatments of cancers leading to enhanced survival rates will continue to evolve.

A. Medical and Occupational History

The medical and occupational work history plays an important role in the initial evaluation of workers exposed to MC. It is therefore extremely important for the examining physician to evaluate the MC-exposed worker carefully and completely and to focus the examination on MC's potentially associated health hazards.

The medical evaluation should include a detailed work and medical history with special emphasis on neurological symptoms and mental status. A complete physical examination with special attention focusing on the lungs, liver, nervous system and breast with an evaluation of pre-existing skin disorders and history of cardiac disease should also be included.

The most important goal of the proposed medical history would be to elicit information from the worker regarding potential signs or symptoms associated with increased levels of carboxyhemoglobin due to the presence of carbon monoxide in the blood. Physicians should ensure that the smoking history of all MC exposed employees is known. Exposure to MC may cause a significant increase in carboxyhemoglobin level in all exposed persons. However, smokers as well as workers with anemia or heart disease and those concurrently exposed to carbon monoxide are at especially high risk of toxic effects because of an already reduced oxygen carrying capacity.

It is important for the physician to become familiar with the operating conditions in which exposure to MC is likely to occur. The physician also must become familiar with the signs and symptoms that may indicate that a worker is receiving otherwise unrecognized and exceptionally high exposure levels of MC.

B. Physical Examination

The complete physical examination, when coupled with the medical and occupational history, will assist the physician in detecting pre-existing conditions that might place the employee at increased risk, and will establish a baseline for future health monitoring. These examinations shall include, but shall not be limited to the following:

1. a comprehensive or interim medical and work history to include, but not limited to, occurrence of headache, dizziness, fatigue, pain in the limbs, and irritation of the skin and eyes.

2. a complete blood test that covers the following: white blood corpuscles, red blood corpuscles, hemoglobin, and hematocrit. In addition, clinical impressions of the nervous system and pulmonary function should be made, with additional tests conducted where indicated or determined by the examining physician to be necessary.

3. An evaluation of the advisability of the workers using respirators, because the use of respirators places an additional burden on the cardiopulmonary system. It is necessary for the attending physician to evaluate the cardiopulmonary function of these workers, in order to inform the employer in a written medical opinion of the worker's ability or fitness to work in an area requiring the use of respiratory protective equipment. The presence of facial hair or scars that might interfere with the workers ability to wear certain types of respirators should also be noted during the examination and in the physician's medical opinion.

Because of the importance of lung function to workers required to wear respirators to protect themselves from MC exposure, these workers must receive an assessment of pulmonary function before they begin to wear a respirator and at least annually thereafter. The recommended pulmonary function tests include measurement of the employee's forced vital capacity (FVC), forced expiratory volume at one second (FEV1), as well as calculation of the ratios of FEV1 to FVC, and the ratios of measured FVC and measured FEV1 to expected respective values corrected for variation due to age, sex, race, and height. Pulmonary function evaluation must be conducted by a licensed physician experienced in pulmonary function tests.

4. It is also recommended that end of shift carboxyhemoglobin levels be determined periodically, and any level above 5% for non-smokers and above 8-10% for smokers should prompt an investigation of the worker and his workplace. This test is recommended because MC is metabolized to CO, which combines strongly with hemoglobin, resulting in a reduced capacity to transport oxygen in the body. This is of particular concern for cigarette smokers because they already have a diminished hemoglobin capacity due to the presence of CO in cigarette smoke.

C. Additional Examinations and Referrals

1. Examination by a Specialist

When a worker examination reveals unexplained symptoms or signs (i.e. in the physical examination or in the laboratory tests), follow-up medical examinations would be necessary to assure that MC exposure is not adversely affecting the worker's health. When the examining physician finds it necessary, additional tests should be included to determine the nature of the medical problem and the underlying cause. Where relevant, the worker should be sent to a specialist for further testing and treatment as deemed necessary.

The proposal provides a mechanism whereby these additional investigations would be covered under the standard for occupational exposure to MC, and it also permits physicians to add appropriate or necessary tests to improve the diagnosis of disease should such tests become available in the future.

2. Emergencies

The examination of workers exposed to MC in an emergency would be directed at the organ systems most likely to be affected. If the worker has received a severe acute exposure, hospitalization may be required to assure proper medical intervention. It is not possible to precisely define "severe", but the physician's judgement should not merely rest on hospitalization. If the worker has suffered significant conjunctival, oral, or nasal irritation, respiratory distress, or discomfort, the physician should instigate appropriate follow-up procedures. These include attention to the eyes, lungs and the neurological system. The frequency of follow-up examinations should be determined by the attending physician. This testing would permit the early identification essential to proper medical management of such workers.

D. Employer Obligations

The employer would be required to provide the responsible physician and any specialists involved in a diagnosis with the following information: a copy of the MC standard including relevant appendices, a description of the affected employee's duties as they relate to his or her exposure to MC; an estimate of the employee's exposure including duration (e.g. 15hr/wk, three 8-hour shifts/wk, full time); a description of any personal protective equipment used by the employee, including respirators; and the results of any previous medical determinations for the affected employee related to MC exposure to the extent that this information is within the employer's control.

E. Physician's Obligations

The standard would require the employer to obtain a written statement from the physician. This statement would have to contain the physician's opinion, based on a written evaluation of test results and the physical examination, as to whether the employee has any medical condition placing him or her at increased risk of impaired health from exposure to MC or use of respirators, as appropriate. The physician would also have to state his or her opinion regarding any restrictions that should be placed on the employee's exposure to MC or upon the use of protective clothing or equipment such as respirators. If the employee wears a respirator as a result of his or her exposure to MC, the physician's opinion would have to also contain a statement regarding the suitability of the employee to wear the type of respirator assigned. Finally, the physician would have to inform the employer that the employee has been told the results of the medical examination and of any medical conditions which require further explanation or treatment. This written opinion is not to contain any information on specific findings or diagnosis unrelated to employee's occupational exposures.

The purpose in requiring the examining physician to supply the employer with a written opinion is to provide the employer with a medical basis to assist the employer in placing employees initially, in assuring that their health is not being impaired by exposure to MC, and to assess the employee's ability to use any required protective equipment.

Appendix C to 1910.1052--Qualitative and Quantitative Fit Testing Procedures.

A. Fit Test Protocols

The employer shall include the following provisions in the fit test procedures. These provisions apply to both qualitative fit testing (QLFT) and quantitative fit testing (QNFT).

1. The test subject shall be allowed to pick the most comfortable respirator from a selection including respirators of various sizes from different manufacturers. The selection shall include at least three sizes of elastomeric facepieces of the type of respirator that is to be tested, i.e., three sizes of half mask; or three sizes of full facepiece; or three sizes of quarter facepiece respirator, and units from at least two manufacturers.

2. Prior to the selection process, the test subject shall be shown how to put on a respirator, how it should be positioned on the face, how to set strap tension and how to determine a comfortable fit. A mirror shall be available to assist the subject in evaluating the fit and positioning the respirator. This instruction may not constitute the subject's formal training on respirator use, as it is only a review.

3. The test subject shall be informed that he/she is being asked to select the respirator which provides the most comfortable fit. Each respirator represents a different size and shape, and if fitted and used properly, will provide adequate protection.

4. The test subject shall be instructed to hold each facepiece up to the face and eliminate those which obviously do not give a comfortable fit.

5. The more comfortable facepieces are noted; the most comfortable mask is donned and worn at least five minutes to assess comfort. Assistance in assessing comfort can be given by discussing the points in item 6 below. If the test subject is not familiar with using a particular respirator, the test subject shall be directed to don the mask several times and to adjust the straps each time to become adept at setting proper tension on the straps.

6. Assessment of comfort shall include reviewing the following points with the test subject and allowing the test subject adequate time to determine the comfort of the respirator:

(i) position of mask on the nose;

(ii) room for eye protection;

(iii) room to talk (iv) position of mask on face cheeks

7. The following criteria shall be used to help determine the adequacy of the respirator fit:

(i) chin properly placed;

(ii) adequate strap tension, not overly tightened;

(iii) fit across nose bridge;

(iv) respirator of proper size to span distance from nose to chin;

(v) tendency of respirator to slip;

(vi) self-observation in mirror to evaluate fit; and respirator position.

8. The test subject shall conduct the negative and positive pressure fit checks as described below or ANSI Z88.2-1980. Before conducting the negative or positive pressure test, the subject shall be told to seat the mask on the face by moving the head from side-to-side and up and down slowly while taking in a few slow deep breaths. Another facepiece shall be selected and retested if the test subjects fails to fit check tests.

9. The test shall not be conducted if there is any hair growth between the skin and the facepiece sealing surface, such as stubble beard growth, beard, or long sideburns which cross the respirator sealing surface. Any type of apparel which interferes with a satisfactory fit shall be altered or removed.

10. If a test subject exhibits difficulty in breathing during the tests, she or he shall be referred to a physician trained in respiratory disease or pulmonary medicine to determine whether the test subject can wear a respirator while performing her or his duties.

11. The test subject shall be given the opportunity to wear the successfully fitted respirator for a period of two weeks. If at any time during this period the respirator becomes uncomfortable, the test subject shall be given the opportunity to select a different facepiece and to be retested.

12. The employer shall maintain a record of the fit test administered to an employee. The record shall contain at least the following information:

(i) name of employee;

(ii) type of respirator;

(iii) brand, size of respirator;

(iv) date of test;

(v) where QNFT is used: the fit factor, strip chart recording or other recording of the results of the test.

The record shall be maintained until the next fit test is administered.

13. Exercise regimen. Prior to the commencement of the fit test, the test subject shall be given a description of the fit test and the test subject's responsibilities during the test procedure. The description of the process shall include a description of the test exercises that the subject will be performing. The respirator to be tested shall be worn for at least 5 minutes before the start of the fit test.

14. Test Exercises. The test subject shall perform exercises, in the test environment, in the manner described below:

(i) Normal breathing. In a normal standing position, without talking, the subject shall breathe normally.

(ii) Deep breathing. In a normal standing position, the subject shall breathe slowly and deeply, taking caution so as to not hyperventilate.

(iii) Turning head side to side. Standing in place, the subject shall slowly turn his/her head from side to side between the extreme positions on each side. The head shall be held at each extreme momentarily so the subject can inhale at each side.

(iv) Moving head up and down. Standing in place, the subject shall slowly move his/her head up and down. The subject shall be instructed to inhale in the up position (i.e., when looking toward the ceiling).

(v) Talking. The subject shall talk out loud slowly and loud enough so as to be heard clearly by the test conductor. The subject can read from a prepared text such as the Rainbow Passage, count backward from 100, or recite a memorized poem or song.

(vi) Grimace. The test subject shall grimace by smiling or frowning.

(vii) Bending over. The test subject shall bend at the waist as if he/she were to touch his/her toes. Jogging in place shall be substituted for this exercise in those test environments such as shroud type QNFT units which prohibit bending at the waist.

(viii) Normal breathing. Same as exercise 1. Each test exercise shall be performed for one minute except for the grimace exercise which shall be performed for 15 seconds.

The test subject shall be questioned by the test conductor regarding the comfort of the respirator upon completion of the protocol. If it has become uncomfortable, another model of respirator shall be tried.

B. Qualitative Fit Test (QLFT) Protocols

1. General

(i) The employer shall ensure that qualitative fit testing shall only be used for respirators to be worn in atmospheric concentrations of MC of 10 times the 8 hour TWA or less (10 X 25 ppm = 250 ppm).

(ii) The employer shall assign specific individuals who shall assume full responsibility for implementing the respirator qualitative fit test program.

(iii) The employer shall ensure that persons administering QLFT are able to prepare test solutions, calibrate equipment and perform tests properly, recognize invalid tests, and assure that test equipment is in proper working order.

(iv) The employer shall assure that QLFT equipment is kept clean and well maintained so as to operate at the parameters for which it was designed.

2. Isoamyl Acetate Protocol

(i) Odor threshold screening

The odor threshold screening test, performed without wearing a respirator, is intended to determine if the individual tested can detect the odor of isoamyl acetate.

(a) Three 1 liter glass jars with metal lids are required.

(b) Odor free water (e.g. distilled or spring water) at approximately 25 degrees C shall be used for the solutions.

(c) The isoamyl acetate (IAA) (also known at isopentyl acetate) stock solution is prepared by adding 1 cc of pure IAA to 800 cc of odor free water in a 1 liter jar and shaking for 30 seconds. A new solution shall be prepared at least weekly.

(d) The screening test shall be conducted in a room separate from the room used for actual fit testing. The two rooms shall be well ventilated but shall not be connected to the same recirculating ventilation system.

(e) The odor test solution is prepared in a second jar by placing 0.4 cc of the stock solution into 500 cc of odor free water using a clean dropper or pipette. The solution shall be shaken for 30 seconds and allowed to stand for two to three minutes so that the IAA concentration above the liquid may reach equilibrium. This solution shall be used for only one day.

(f) A test blank shall be prepared in a third jar by adding 500 cc of odor free water.

(g) The odor test and test blank jars shall be labeled 1 and 2 for jar identification. Labels shall be placed on the lids so they can be periodically peeled, dried off and switched to maintain the integrity of the test.

(h) The following instruction shall be typed on a card and placed on the table in front of the two test jars (i.e., 1 and 2): "The purpose of this test is to determine if you can smell banana oil at a low concentration. The two bottles in front of you contain water. One of these bottles also contains a small amount of banana oil. Be sure the covers are on tight, then shake each bottle for two seconds. Unscrew the lid of each bottle, one at a time, and sniff at the mouth of the bottle. Indicate to the test conductor which bottle contains banana oil."

(i) The mixtures used in the IAA odor detection test shall be prepared in an area separate from where the test is performed, in order to prevent olfactory fatigue in the subject.

(j) If the test subject is unable to correctly identify the jar containing the odor test solution, the IAA qualitative fit test shall not be performed.

(k) If the test subject correctly identifies the jar containing the odor test solution, the test subject may proceed to respirator selection and fit testing.

(ii) Isoamyl acetate fit test

(a) The fit test chamber shall be similar to a clear 55-gallon drum liner suspended inverted over a 2-foot diameter frame so that the top of the chamber is about 6 inches above the test subject's head. The inside top center of the chamber shall have a small hook attached.

(b) Each respirator used for the fitting and fit testing shall be equipped with organic vapor cartridges or offer protection against organic vapors. The cartridges or masks shall be changed at least weekly.

(c) After selecting, donning, and properly adjusting a respirator, the test subject shall wear it to the fit testing room. This room shall be separate from the room used for odor threshold screening and respirator selection,and shall be well ventilated, as by an exhaust fan or lab hood, to prevent general room contamination.

(d) A copy of the test exercises and any prepared text from which the subject is to read shall be taped to the inside of the test chamber.

(e) Upon entering the test chamber, the test subject shall be given a 6-inch by 5-inch piece of paper towel, or other porous, absorbent, single-ply material, folded in half and wetted with 0.75 cc of pure IAA. The test subject shall hang the wet towel on the hook at the top of the chamber.

(f) Allow two minutes for the IAA test concentration to stabilize before starting the fit test exercises. This would be an appropriate time to talk with the test subject; to explain the fit test, the importance of his/her cooperation, and the purpose for the head exercises; or to demonstrate some of the exercises.

(g) If at any time during the test, the subject detects the banana like odor of IAA, the test has failed. The subject shall quickly exit from the test chamber and leave the test area to avoid olfactory fatigue.

(h) If the test has failed, the subject shall return to the selection room and remove the respirator, repeat the odor sensitivity test, select and put on another respirator, return to the test chamber and again begin the procedure described in (1) through (7) above. The process continues until a respirator that fits well has been found. Should the odor sensitivity test be failed, the subject shall wait about 5 minutes before retesting. Odor sensitivity will usually have returned by this time.

(i) When a respirator is found that passes the test, its efficiency shall be demonstrated for the subject by having the subject break the face seal and take a breath before exiting the chamber.

(j) When the test subject leaves the chamber, the subject shall remove the saturated towel and return it to the person conducting the test. To keep the test area from becoming contaminated, the used towels shall be kept in a self sealing bag so there is no significant IAA concentration build-up in the test chamber during subsequent tests.

3. Saccharin Solution Aerosol Protocol

The saccharin solution aerosol QLFT protocol is the only currently available, validated test protocol for use with particulate disposable dust respirators not equipped with high-efficiency filters. The entire screening and testing procedure shall be explained to the test subject prior to the conduct of the screening test.

(i) Taste threshold screening.

The saccharin taste threshold screening, performed without wearing a respirator, is intended to determine whether the individual being tested can detect the taste of saccharin.

(a) Threshold screening as well as fit testing subjects shall wear an enclosure about the head and shoulders that is approximately 12 inches in diameter by 14 inches tall with at least the front portion clear and that allows free movements of the head when a respirator is worn. An enclosure substantially similar to the 3M hood assembly, parts # FT 14 and # FT 15 combined, is adequate.

(b) The test enclosure shall have a 3/4-inch hole in front of the test subject's nose and mouth area to accommodate the nebulizer nozzle.

(c) The test subje