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• Publication Date: 06/30/1993
• Publication Type: Final Rules
• Fed Register #: 58:35338-35351
• Standard Number: 1910.1000
• Title: Air Contaminants

DEPARTMENT OF LABOR

Occupational Safety and Health Administration

29 CFR Part 1910

RIN 1218-AB26

Air Contaminants

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

ACTION: Final rule.

SUMMARY: This document announces the revocation of the exposure limits specified in the "Final rule limits" columns of Table Z-1-A of 29 CFR 1910.1000. This implements the Court of Appeals decision in AFL-CIO v. OSHA, 965 F.2d 962 (11th Cir., 1992), vacating those limits. Enforcement of those limits was suspended starting March 23, 1993. The permissible exposure limits specified in the "Transitional limits" columns of Table Z- 1-A and in Tables Z-2 and Z-3 of 29 CFR 1910.1000 have remained in effect and are being enforced. In order to effectuate this action, Table Z-1-A is being removed from 29 CFR 1910.1000 and a Table Z-1 is being added which includes the exposure limits which were included in Table Z-1 before 1989 and which were published in the Transitional limits columns of Table Z-1-A.

EFFECTIVE DATE: June 30, 1993. FOR FURTHER INFORMATION CONTACT: Mr. James F. Foster, OSHA, U.S. Department of Labor, Office of Public Affairs, Room N-3647, 200 Constitution Avenue, N.W., Washington, D.C. 20210. Telephone (202) 219-8151.

SUPPLEMENTARY INFORMATION: OSHA published its final rule on Air Contaminants on January 19, 1989 at 54 FR 2332-2983. That rule amended 29 CFR 1910.1000 by lowering 212 of OSHA's existing permissible exposure limits (PELs) for toxic substances and setting PELs for 164 toxic substances which had been previously unregulated. The final rule left unchanged the PELs for 51 of the 428 substances considered for change, and raised one exposure limit.

That rulemaking did not consider, and consequently left unchanged, 168 other substances which were listed in the tables of 29 CFR 1910.1000. It also did not consider and left unchanged the 24 substances which had their own comprehensive single substance standards codified in 29 CFR 1910.1001-1048.

On July 7, 1992, the Eleventh Circuit Court of Appeals issued a decision stating that the revised air contaminants standard was vacated. American Federation of Labor and Congress of Industrial Organizations, et al. v Occupational Safety and Health Administration Department of Labor (AFL- CI0 v. OSHA), 965 F.2d 962 (11th Cir. 1992). At OSHA's request, the Eleventh Circuit did not issue its mandate or order enforcing its decision while the possibility of appeal was pursued. Consequently the new limits remained in effect and enforced past July 7, 1992.

On October 23, 1992 the Eleventh Circuit denied OSHA's request for rehearing. After consideration, the Government determined not to petition the Supreme Court for review. March 22, 1993 was the last date to file a petition for review in the Supreme Court. As none was filed, there was no longer a basis for OSHA to request the Eleventh Circuit to further stay the issuance of its mandate.

Accordingly, OSHA directed its compliance officers to cease enforcing the new exposure limits (376 more protective, 1 less protective) starting March 23, 1993.

In consequence, as of March 23, 1993, OSHA resumed enforcing, and employers were required to comply with, the air contaminant exposure limits that were in effect prior to the issuance of the new limits on January 19, 1989. These are the exposure limits (both airborne limits and skin designations) which are located in the "Transitional limits" columns of 29 CFR 1910.1000, Table Z-1-A and the limits located in Tables Z-2 and Z-3.

Section 1910.1000 (f)(3)(iii) specifically provides that if the new limits in the Final Rule limits columns of Table Z-1-A are vacated, then the Transitional limits columns of Table Z-1-A and Tables Z-2 and Z-3 remain in effect. This includes the textual language of 1910.1000 (a)-(f) relevant to the Transitional limits of Table Z-1-A and relevant to Tables Z-2 and Z-3. That text is in substance what was in effect prior to the issuance of the new limits.

The Court of Appeals decision does not directly affect the 25 States operating their own OSHA-approved occupational safety and health State plans as their standards were adopted under authority of applicable State law. The 25 State plan States are: Alaska, Arizona, California, Connecticut, Hawaii, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, New Mexico, New York, Nevada, North Carolina, Oregon, Puerto Rico, South Carolina, Tennessee, Utah, Vermont, Virgin Islands, Virginia, Washington and Wyoming. (Connecticut and New York are public sector only plans.) Some States are continuing to enforce the 1989 Air Contaminants standard or an "at least as effective" equivalent. However, in other States the authorizing legislation or other circumstances will require the State to parallel Federal standards-setting actions. Since section 18 of the OSH Act permits, but does not require, the State plan States to maintain standards which are more stringent than those of OSHA, each State must make its own determination based on its legal authority and other circumstances. Accordingly, the changes to the OSHA Air Contaminants standards set forth in today's Federal Register notice do not necessarily apply in the State plan States listed above.

CHANGES TO CFR

In order to implement the Court's decision in a way that is clear and convenient to the public, OSHA is making a number of changes to the Code of Federal Regulations. In 1989, OSHA replaced Table Z-1 with Table Z-1-A. Table Z-1-A included the substantive changes of incorporating 164 substances which had not been regulated before and adding "Final rule limits" columns which included the limits for those 164 plus 212 new limits for substances which had pre-existing limits.

In addition, Table Z-1-A had non-substantive format changes for the convenience of employers and employees. OSHA included in alphabetical order in Table Z-1-A every substance it regulated in 29 CFR Part 1910, Subpart Z. This had not been done in the earlier Table Z-1. Consequently, it listed substances covered by Table Z-1-A, Tables Z-2 and Z-3, and the substances regulated by the substance specific standards in 29 CFR 1910.1001-1048. The "Transitional limits" columns also included the old exposure limits which had existed in Table Z-1.

As a result of these style changes, the public could locate in one place a list of all the substances regulated by Subpart Z, along with the exposure limit or a cross reference to where the exposure limit and other regulatory provisions concerning the substance could be found. Table Z-1-A also presented the Chemical Abstract Service (CAS) numbers for all substances regulated by Subpart Z as a further convenience for the public.

In order to carry out the Court's decision, OSHA is removing Table Z-1-A from the CFR, which of course includes removing its Final rule limits columns which contained the 376 new or more protective limits and one new but higher limit. It is replaced by a new Table Z-1 which does not contain the limits which were in the Final rule limits columns. The new Table Z-1 contains the limits which were in effect prior to 1989 in Table Z-1, and which are also the limits which were in the Transitional limits columns of Table Z-1-A.

In this manner, OSHA is implementing the Eleventh Circuit's decision and removing from the CFR the vacated limits. It is retaining in the CFR the limits in effect prior to the issuance of the 1989 Air Contaminants standard which are the limits that are currently enforceable.

However, OSHA is retaining the non-substantive format advantages of Table Z-1-A for the convenience of the public. The new Table Z-1 lists all the substances regulated by Subpart Z with their CAS numbers. If a regulated substance's exposure limit is not included in the new Table Z-1, then a cross reference to the location of that substance's limit is included. In this manner, employers and employees will be in a better position to find the toxic substance exposure limits which would cover them.

OSHA is also deleting the footnotes to Table Z-1-A which were only relevant to the Final rule limits. It is retaining and relettering those footnotes which are relevant to Table Z-1 and is making a few style changes for format consistency.

Tables Z-2 and Z-3 were not substantively changed when the new Air Contaminants standard was issued in 1989, and they are not being substantively changed now. However, as a number of errors have existed in these tables, OSHA is using this Federal Register Notice as an opportunity to correct those errors.

Specifically, the entries and footnotes for benzene, cadmium and formaldehyde in Table Z-2 are corrected to reflect their current legal status and the status of their single substance standards. Errors in alphabetization are corrected and the footnotes relettered. In Table Z-3, the formulas for the coal dust entries are presented more clearly, the tremolite cross- reference is corrected, certain spelling errors are corrected, the format is made clearer and the footnotes are relettered. OSHA is reprinting the entire tables Z-1, Z-2 and Z-3 in the Federal Register with the corrections made, for the convenience of the public.

In addition, to implement the court's decision, it is necessary to make some changes to the regulatory text. Specifically, it is necessary to delete from the beginning of 29 CFR 1910.1000, the language which is applicable to the exposure limits in the Final rule limits columns of Table Z-1-A. Accordingly, OSHA is removing from 29 CFR 1910.1000, paragraph (a)(3) on the obligation to comply with the Final rule limits, paragraph (a)(5) on definitions applicable to the Final rule 7limits, and most of paragraph (f) on the starting dates and transitional provisions relevant to the Final rule limits.

Retained are the provisions necessary to effectuate the exposure limits in Tables Z-1, Z-2 and Z-3. These provisions are substantively the same as the equivalent provisions which were in effect prior to the issuance of the 1989 Air Contaminants Final Rule and retain the same lettering. A few minor, non-substantive style changes have been made. Thus, paragraphs (a)(1) and (a)(2) which define the compliance requirements of the exposure limits in Table Z-1 (the Transitional limits of Table Z-1-A), paragraph (b) which defines the compliance requirements of the exposure limits in Table Z-2, and paragraph (c) which defines the compliance requirements of the exposure limits in Table Z-3 are all retained.

OSHA followed and enforced the following practice, which it set out explicitly in the CFR and the Federal Register during the PELs rulemaking. In circumstances where there was no available instrumentation to measure a substance instantaneously, OSHA inspectors and employers were permitted to measure the ceiling as a time weighted average over 15 minutes. OSHA is retaining that explicit provision, which was located in paragraph (a)(5)(iii) (which is being removed) and inserting it into paragraph (a)(1).

OSHA is removing paragraph (a)(6) which had explicitly stated that the terms "substance," "air contaminant" and "material" are equivalent. It remains the case that they are equivalent for purposes of 1910.1000. But as this is now generally known and clear from the context, it is unnecessary to retain this definition.

Paragraph (d) concerning the computation formulae, and paragraph (e) concerning the preference for engineering controls are retained unchanged. These provisions were in effect prior to 1989, remained in effect after the 1989 Final rule and continue in effect. These provisions were not opened for comment in the rulemaking which led to the 1989 Final rule.

A new paragraph (f) has been inserted to replace the removed paragraph (f). The new paragraph is informational only. It informs the public that the exposure limits contained in Tables Z-1, Z-2 and Z-3 have been in effect since May 29, 1971.

Various changes are also being made to the authority citation for Subpart Z to reflect the removal of the Final rule limits.

OTHER ISSUES

1. Carbon dioxide was the one substance where OSHA raised the TWA from 5000 to 10,000 ppm but incorporated a 30,000 ppm STEL. As the Court vacated that STEL and the new TWA, it is necessary to return to the 5000 ppm 8 hour TWA. This change is made in Table Z-1.

2. The AFL-CIO and National Grain and Feed Association (NGFA), which had reached a settlement with OSHA on the new grain dust limit, moved the Eleventh Circuit to rule that its decision did not disturb the settlement. The Court, on February 1, 1993, granted the motion and stated, "The settlement agreement remains in full force and effect insofar as this Court is concerned with the appeal filed in this matter." Accordingly, OSHA will continue to enforce the grain dust limit pursuant to the settlement agreement. Therefore, Table Z-1 contains the grain dust limit of 10 mg/m(3) which was issued as a new limit in 1989.

3. Table Z-3 has always contained an entry for "Inert or Nuisance dust." The American Conference of Governmental Industrial Hygienists (ACGIH), the source of that limit, had always intended it to cover both organic and inorganic particulates not otherwise regulated. This is clear from the Appendix D to the 1968 and subsequent editions of the "Threshold Limit Values" by ACGIH, which lists as nuisance particulates such organic substances as cellulose, vegetable oil mists, starch and sucrose. OSHA had also intended that entry to cover organic dusts and issued many citations reflecting that view.

However, the Nuisance Dust entry appeared in a Table which was titled "Mineral Dusts." The Occupational Safety and Health Review Commission, in the case of Bunge Corp. 12 OSHC 1785 (1986), held that because of the location of the nuisance dust entry in Table Z-3, inadequate notice was given to employers that the limit applied to organic dusts.

OSHA made it clear when it issued the Final Air Contaminants rule, that it intended this limit, which was left unchanged, to apply to both organic and inorganic particulates or dusts. See 54 FR 2597 (January 19, 1989). OSHA also gave notice to employers by renaming the Inert or Nuisance Dust limit as the Particulates Not Otherwise Regulated (PNOR) limit and placing it in Table Z-1-A. To provide additional notice, it left the same entry in Table Z-3 under its old name, and added a footnote indicating it applied to organic as well as inorganic dusts.

These were format changes to reflect OSHA's and ACGIH's intentions for over 20 years, and to give full notice to employers that organic dusts and particulates are covered by the standard; they were not substantive changes. Accordingly, in both Table Z-1 and Z-3, OSHA is retaining the equivalent PNOR and Nuisance Dust entries with footnotes to make clear that organic and inorganic particulates or dusts are covered.

OSHA continues to believe that many of the old limits which it will now be enforcing are out of date (they predate 1968) and not sufficiently protective of employee health based on current scientific information and expert recommendations. In addition, many of the substances for which OSHA has no PELs present serious health hazards to employees.

OSHA finds that notice and comment are unnecessary for these changes because they implement the final decision of the Eleventh Circuit Court of Appeals. For the same reason, good cause is found for these changes to take immediate effect.

This document was prepared under the direction of David C. Zeigler, Acting Assistant Secretary of Labor, 200 Constitution Avenue, N.W., Washington, DC 20210.

It is issued under sections 4,6 and 8 of the Occupational Safety and Health Act of 1970 (29 U.S.C. 653, 655 657), 5 U.S.C. 553, Secretary Labor's Order 1-90 (55 FR 9033) and 29 CFR Part 1911.

Signed at Washington, DC, this 30 day of June, 1993.

David C. Zeigler,
Acting Assistant Secretary of Labor.

Part 1910-[AMENDED]

Part 1910 of title 29 of the Code of Federal Regulation is hereby amended as follows:

Subpart Z - Toxic and Hazardous Substances

1. The authority citation for Subpart Z of part 1910 is revised to read in relevant part as follows:

Authority: Secs. 6, 8 Occupational Safety and Health Act, 29 U.S.C. 655, 657: Secretary of Labor's Order 12-71 (36 FR 8754), 9-76 (41 FR 25059), 9-83 (48 FR 35736) or 1-90 (55 FR 9033), as applicable; and 29 CFR Part 1911.

All of Subpart Z issued under section 6(b) of the Occupational Safety and Health Act, except those substances which have exposure limits listed in Tables Z-1, Z-2 and Z-3 of 29 CFR 1910.1000. The latter were issued under section 6(a) (29 U.S.C. 655(a)).

Section 1910.1000, Tables Z-1, Z-2 and Z-3 also issued under 5 U.S.C. 553. Section 1910.1000, Tables Z-1, Z-2 and Z-3 not issued under 29 CFR Part 1911 except for the arsenic (organic compounds), benzene, and cotton dust listings.

* * * * *

1910.1000 [AMENDED]

2. Section 1910.1000, is revised by removing the entire regulatory text and Tables Z-1-A, Z-2 and Z-3, and adding a new regulatory text consisting of an introductory text, paragraphs (a) through (f) and Tables Z-1, Z-2 and Z-3 as follows:

1910.1000 Air contaminants.

An employee's exposure to any substance listed in Tables Z-1, Z-2, or Z-3 of this section shall be limited in accordance with the requirements of the following paragraphs of this section.

(a) Table Z-1. (1) Substances with limits preceded by "C" -Ceiling Values. An employee's exposure to any substance in Table Z-1, the exposure limit of which is preceded by a "C", shall at no time exceed the exposure limit given for that substance. If instantaneous monitoring is not feasible, then the ceiling shall be assessed as a 15-minute time weighted average exposure which shall not be exceeded at any time during the working day.

(2) Other substances - 8-hour Time Weighted Averages. An employee's exposure to any substance in Table Z-1, the exposure limit of which is not preceded by a "C", shall not exceed the 8-hour Time Weighted Average given for that substance in any 8-hour work shift of a 40-hour work week.

(b) Table Z-2. An employee's exposure to any substance listed in Table Z-2 shall not exceed the exposure limits specified as follows:

(1) 8-hour time weighted averages. An employee's exposure to any substance listed in Table Z-2, in any 8-hour work shift of a 40-hour work week, shall not exceed the 8-hour time weighted average limit given for that substance in Table Z-2.

(2) Acceptable ceiling concentrations. An employee's exposure to a substance listed in Table Z-2 shall not exceed at any time during an 8-hour shift the acceptable ceiling concentration limit given for the substance in the table, except for a time period, and up to a concentration not exceeding the maximum duration and concentration allowed in the column under "acceptable maximum peak above the acceptable ceiling concentration for an 8-hour shift."

(3) Example. During an 8-hour work shift, an employee may be exposed to a concentration of Substance A (with a 10 ppm TWA, 25 ppm ceiling and 50 ppm peak) above 25 ppm (but never above 50 ppm) only for a maximum period of 10 minutes. Such exposure must be compensated by exposures to concentrations less than 10 ppm so that the cumulative exposure for the entire 8-hour work shift does not exceed a weighted average of 10 ppm.

(c) Table Z-3. An employee's exposure to any substance listed in Table Z-3, in any 8-hour work shift of a 40-hour work week, shall not exceed the 8-hour time weighted average limit given for that substance in the table.

(d) Computation formulae. The computation formula which shall apply to employee exposure to more than one substance for which 8-hour time weighted averages are listed in subpart Z of 29 CFR Part 1910 in order to determine whether an employee is exposed over the regulatory limit is as follows:

(1)(i) The cumulative exposure for an 8-hour work shift shall be computed as follows:

E =(C(a)T(a) + C(b)T(b) + . . . C(n)T(n)) ö 8

Where:

E is the equivalent exposure for the working shift.

C is the concentration during any period of time T where the concentration remains constant.

T is the duration in hours of the exposure at the concentration C.

The value of E shall not exceed the 8-hour time weighted average specified in Subpart Z of 29 CFR Part 1910 for the substance involved.

(ii) To illustrate the formula prescribed in paragraph (d)(1)(i) of this section, assume that Substance A has an 8-hour time weighted average limit of 100 ppm noted in Table Z-1. Assume that an employee is subject to the following exposure:

Two hours exposure at 150 ppm Two hours exposure at 75 ppm Four hours exposure at 50 ppm Substituting this information in the formula, we have

(2 X 150 + 2 X 75 + 4 X 50) ö 8 = 81.25 ppm

Since 81.25 ppm is less than 100 ppm, the 8-hour time weighted average limit, the exposure is acceptable.

(2)(i) in case of a mixture of air contaminants an employer shall compute the equivalent exposure as follows:

E(m) = (C(1) ö L(1) + C(2) ö L(2)) + . . . (C(n) ö L(n))

Where:

E(m) is the equivalent exposure for the mixture.

C is the concentration of a particular contaminant.

L is the exposure limit for that substance specified in Subpart Z of 29 CFR Part 1910.

The value of E(m) shall not exceed unity (1).

(ii) To illustrate the formula prescribed in paragraph (d)(2)(i) of this section, consider the following exposures:

 
Substance Actual concentration of 8-hour exposure (ppm) 8 hour TWA PEL (ppm)
 
B 500 1,000
C 45 200
D 40 200
 
 
  Substituting in the formula, we have:
  E(m)=500 ö 1,000 + 45 ö 200 + 40 ö 200
  E(m)=0.500 + 0.225 + 0.200
  E(m)=0.925

Since E(m) is less than unity (1), the exposure combination is within acceptable limits.

(e) To achieve compliance with paragraphs (a) through (d) of this section, administrative or engineering controls must first be determined and implemented whenever feasible. When such controls are not feasible to achieve full compliance, protective equipment or any other protective measures shall be used to keep the exposure of employees to air contaminants within the limits prescribed in this section. Any equipment and/or technical measures used for this purpose must be approved for each particular use by a competent industrial hygienist or other technically qualified person. Whenever respirators are used, their use shall comply with 1910.134.

(f) Effective dates. The exposure limits specified have been in effect with the method of compliance specified in paragraph (e) of this section since May 29, 1971.
TABLE Z-1 - LIMITS FOR AIR CONTAMINANTS
FOR TABLE Z-1 SEE PRINTED COPY OF FEDERAL REGISTER ISSUE
TABLE Z-2
Substance 8-hourTime Weighted Average Acceptable ceiling concentration Acceptable maximum peak above the acceptable ceiling concentration for an 8-hr shift
      Concentration Maximum duration
Benzene(a)
(Z37.40-1969) 10 ppm 25 ppm 50 ppm 10 minutes
 
Beryllium and beryllium compounds
(Z37.29-1970) 2 ug/m(3) 5 ug/m(3) 25 ug/m(3) 30 minutes
 
Cadmium fume(b)
(Z37.5-1970) 0.1 mg/m(3) 0.3 mg/m(3)    
 
Cadmium dust(b)
(Z37.5-1970) 0.2 mg/m(3) 0.6 mg/m(3)    
 
Carbon disulfide
(Z37.3-1968) 20 ppm 30 ppm 100 ppm 30 minutes
 
Carbon tetrachloride
(Z37.17-1967) 10 ppm 25 ppm 200 ppm 5 min. in any 4 hrs.
 
Chromic acid and chromates
(Z37.7-1971) 1 mg/10m(3)      
 
Ethylene dibromide
(Z37.31-1970) 20 ppm 30 ppm 50 ppm 5 minutes
 
Ethylene dichloride
(Z37.21-1969) 50 ppm 100 ppm 200 ppm 5 min. in any 3 hrs.
 
Fluoride as dust
(Z37.28-1969)   2.5 mg/m(3)    
 
Formaldehyde; see 1910.1048
 
Hydrogen fluoride
(Z37.28-1969)   3 ppm    
 
Hydrogen sulfide
(Z37.2-1966)   20 ppm 50 ppm 10 mins. once, only if no other meas. exp. occurs
 
Mercury
(Z37.8-1971)   1 mg/10m(3)    
 
Methyl chloride
(Z37.18-1969) 100 ppm 200 ppm 300 ppm 5 mins. in any 3 hrs.
 
Methylene chloride
(Z37.23-1969) 500 ppm 1,000 ppm 2,000 ppm 5 mins. in any 2 hrs.
 
Organo (alkyl) mercury
(Z37.30-1969) 0.01 mg/m(3) 0.04 mg/m(3)    
 
Styrene
(Z37.15-1969)
100 ppm 200 ppm 600 ppm 5 mins. in any 3 hrs.
 
Tetrachloroethylene
(Z37.22-1967) 100 ppm 200 ppm 300 ppm 5 mins. in any 3 hrs.
 
Toluene
(Z37.12-1967) 200 ppm 300 ppm 500 ppm 10 minutes
 
Trichloroethylene
(Z37.19-1967) 100 ppm 200 ppm 300 ppm 5 mins. in any 2 hrs.

(a) This standard applies to the industry segments exempt from the 1 ppm 8-hour TWA and 5 ppm STEL of the benzene standard at 1910.1028.

(b) This standard applies to any operations or sectors for which the Cadmium standard, 1910.1027, is stayed or otherwise not in effect.

TABLE Z-3 Mineral Dusts
Substance mppcf(a) mg/m(3)
     
SILICA:    
CRYSTALLINE    
QUARTZ (RESPIRABLE) 250(b) 10mg/m(3) (e)
  %SiO(2)+5 %SiO(2) + 2
     
QUARTZ (TOTAL DUST) - 30 mg/m(3)
    %SiO(2)+2
     
CRISTOBALITE: Use < the value calculated - -
from the count or mass formulae for quartz    
TRIDYMITE: Use < the value calculated from - -
the formulae for quartz    
     
AMORPHOUS, including natural diatomaceous earth 20 80 mg/m(3)
    %SiO(2)
     
SILICATES (less than 1% crystalline silica):    
Mica 20 -
Soapstone 20 -
Talc (not containing asbestos) 20(c) -
Talc (containing asbestos) Use asbestos limit - -
Tremolite, asbestiform (see 29 CFR 1910.1001) - -
Portland cement 50 -
GRAPHITE (NATURAL) 15 -
     
COAL DUST:    
Respirable fraction less than 5% SiO(2) - 2.4 mg/m(3) (e)
    %SiO(2)+2
     
Respirable fraction greater than 5% SiO(2) - 10 mg/m(3) (e)
    %SiO(2)+2
     
INERT OR NUISANCE DUST(d):    
Respirable fraction 15 5 mg/m(3)
Total dust 50 15 mg/m(3)

Note - Conversion factors - mppcf X 35.3 = million particles per cubic meter = particles per c.c.

(a) Millions of particles per cubic foot of air, based on impinger samples counted by light-field techniques.

(b) The percentage of crystalline silica in the formula is the amount determined from airborne samples, except in those instances in which other methods have been shown to be applicable.

(c) Containing less than 1% quartz; if 1% quartz or more, use quartz limit.

(d) All inert or nuisance dusts, whether mineral, inorganic, or organic, not listed specifically by substance name are covered by this limit, which is the same as the Particulates Not Otherwise Regulated (PNOR) limit in Table Z-1.

(e) Both concentration and percent quartz for the application of this limit are to be determined from the fraction passing a size-selector with the following characteristics:

Aerodynamic diameter Percent passing selector
(unit density sphere)  
2 90
2.5 75
3.5 50
5.0 25
10 0

The measurements under this note refer to the use of an AEC (now NRC) instrument. The respirable fraction of coal dust is determined with an MRE; the figure corresponding to that of 2.4 mg/m(3) in the table for coal dust is 4.5 mg/m(3).

[FR Doc. 93-15292 Filed 6-29-93; 8:45 am]


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