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This guideline summarizes pertinent information about acetic anhydride for workers and employers as well as for physicians, industrial hygienists, and other occupational safety and health professionals who may need such information to conduct effective occupational safety and health programs. Recommendations may be superseded by new developments; readers are therefore advised to regard these recommendations as general guidelines and to determine periodically whether new information is available.
For Structure, see paper copy)
Acetic acid anhydride, acetic oxide, acetyl oxide, ethanoic anhydride, acetyl ether.
Acetic anhydride is a colorless liquid with a strong, pungent odor.
CHEMICAL AND PHYSICAL PROPERTIES
* Physical data
The National Fire Protection Association has assigned a flammability rating of 2 (moderate fire hazard) to acetic anhydride.
Containers of acetic anhydride may explode in the heat of the fire and should be moved from the fire area if it is possible to do so safely. If this is not possible, cool containers from the sides with water until well after the fire is out. Avoid directing water into containers of acetic anhydride. Stay away from the ends of containers. Personnel should withdraw immediately if a rising sound from a venting safety device is heard or if there is discoloration of a container due to fire. Dikes should be used to contain fire-control water for later disposal. If a tank car or truck is involved in a fire, personnel should isolate an area of a half a mile in all directions. Firefighters should wear a full set of protective clothing, including a self-contained breathing apparatus, when fighting fires involving acetic anhydride. Chemical protective clothing that is specifically recommended for acetic anhydride may not provide thermal protection unless so stated by the clothing manufacturer. Firefighters' protective clothing is not effective against fires involving acetic anhydride.
* Warning properties
No quantitative data are available on the odor threshold for acetic anhydride. For the purpose of respirator selection, this substance is therefore considered to have inadequate odor warning properties.
* Eye irritation properties
No quantitative data are available on the eye irritation threshold for acetic anhydride; however, a vapor concentration of 5 parts per million (ppm) parts of air is known to cause immediate irritation of the eyes in humans.
The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for acetic anhydride is 5 ppm (20 milligrams per cubic meter (mg/m(3)) as a ceiling limit [29 CFR Table Z-1-A]. The National Institute for Occupational Safety and Health (NIOSH) has not issued a recommended exposure limit (REL) for acetic anhydride; however, NIOSH concurs with the PEL established for this substance by OSHA [NIOSH 1988]. The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned acetic anhydride a ceiling limit value of 5 ppm (21 mg/m(3)), which should not be exceeded during any part of the working exposure [ACGIH 1989, p. 11]. The OSHA and ACGIH limits are based on the risk of irritant effects associated with exposure to acetic anhydride.
HEALTH HAZARD INFORMATION
* Routes of exposure
Exposure to acetic anhydride can occur via inhalation, ingestion, and eye or skin contact. Acetic anhydride also penetrates the skin very quickly.
* Summary of toxicology
In the event of an emergency, remove the victim from further exposure, send for medical assistance, and initiate the following emergency procedures:
The following operations may involve acetic anhydride and lead to worker exposures to this substance:
Workers who may be exposed to chemical hazards should be monitored in a systematic program of medical surveillance that is intended to prevent occupational injury and disease. The program should include education of employers and workers about work-related hazards, placement of workers in jobs that do not jeopardize their safety or health, early detection of adverse health effects, and referral of workers for diagnosis and treatment. The occurrence of disease or other work-related adverse health effects should prompt immediate evaluation of primary preventive measures (e.g., industrial hygiene monitoring, engineering controls, and personal protective equipment). A medical monitoring program is intended to supplement, not replace, such measures. To place workers effectively and to detect and control work-related health effects, medical evaluations must be performed (1) before job placement, (2) periodically during the period of employment, and (3) at the time of job transfer or termination.
* Pre-placement medical evaluation
Before a worker is placed in a job with a potential for exposure to acetic anhydride, the examining physician should evaluate and document the worker's baseline health status with thorough medical, environmental, and occupational histories, a physical examination, and physiologic and laboratory tests appropriate for the anticipated occupational risks. These should concentrate on the function and integrity of the eyes, skin, and respiratory system. Medical monitoring for respiratory disease should be conducted using the principles and methods recommended by NIOSH and the American Thoracic Society.
A pre-placement medical evaluation is recommended to assess an individual's suitability for employment at a specific job and to detect and assess medical conditions that may be aggravated or may result in increased risk when a worker is exposed to acetic anhydride at or below the prescribed exposure limit. The examining physician should consider the probable frequency, intensity, and duration of exposure as well as the nature and degree of any applicable medical condition. Such conditions (which should not be regarded as absolute contraindications to job placement) include a history and other findings consistent with diseases of the eyes, skin, or respiratory system.
* Periodic medical examinations and biological monitoring
Occupational health interviews and physical examinations should be performed at regular intervals during the employment period, as mandated by any applicable Federal, State, or local standard. Where no standard exists and the hazard is minimal, evaluations should be conducted every 3 to 5 years or as frequently as recommended by an experienced occupational health physician. Additional examinations may be necessary if a worker develops symptoms attributable to acetic anhydride exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of acetic anhydride on the eyes, skin or respiratory system. Current health status should be compared with the baseline health status of the individual worker or with expected values for a suitable reference population.
Biological monitoring involves sampling and analyzing body tissues or fluids to provide an index of exposure to a toxic substance or metabolite. No biological monitoring test acceptable for routine use has yet been developed for acetic anhydride.
* Medical examinations recommended at the time of job transfer or termination
The medical, environmental, and occupational history interviews, the physical examination, and selected physiologic or laboratory tests that were conducted at the time of placement should be repeated at the time of job transfer or termination to determine the worker's medical status at the end of his or her employment. Any changes in the worker's health status should be compared with those expected for a suitable reference population.
WORKPLACE MONITORING AND MEASUREMENT PROCEDURES
Determination of a worker's exposure to airborne acetic anhydride is made using a standard midget bubbler containing 10 milliliters of alkaline hydroxylamine hydrochloride solution. The absorbing solution is made up of equal volumes of hydroxylamine hydrochloride (200 g in 1 liter distilled water) and sodium hydroxide (200 g in 1 liter distilled water). The solution is mixed just prior to use and is stable only for two hours. Samples are collected at a recommended flow rate of 0.2 to 1 liter per minute until a recommended air volume of 25 to 100 liters is collected. Analysis is performed calorimetrically using visible absorption spectrophotometry. A purple-colored complex is formed by adding ferric chloride solution to the sample. The limit of detection for this procedure is 0.05 mg/sample. This method is described in NIOSH Method of the NIOSH Manual of Analytical Methods, Volume 1 [NIOSH 1984].
PERSONAL HYGIENE PROCEDURES
If acetic anhydride contacts the skin, workers should flush the affected areas immediately with plenty of water for 15 minutes, followed by washing with soap and water. Get medical help immediately.
Clothing and shoes contaminated with acetic anhydride should be removed immediately; if gross exposure occurs, remove contaminated clothing under a safety shower. Speed in removing the contaminated material from theskin is extremely important. Provisions should be made for the safe removal of the chemical from the clothing. Persons laundering the clothes should be informed of the hazardous properties of acetic anhydride, particularly its potential to be corrosive to the skin.
A worker who handles acetic anhydride should thoroughly wash hands, forearms, and face with soap and water before eating, using tobacco products, or using toilet facilities.
Workers should not eat, drink, or use tobacco products in areas where acetic anhydride or a solution containing acetic anhydride is handled, processed, or stored.
Acetic anhydride should be stored in a cool, dry, well-ventilated area intightly sealed containers that are labeled in accordance with OSHA's Hazard Communication Standard [29 CFR 1910.1200]. Outside or detached storage is preferred. Inside storage must be in a standard flammable liquids storage room or cabinet. Steel, galvanized tin, tinned iron,copper, or copper alloys should not be used for piping or valves that will be in contact with acetic anhydride. Containers of acetic anhydride should be protected from physical damage and should be separated from water, alcohols, strong oxidizers, chromic acid, amines, strong caustics, heat, sparks, and open flame. Because containers that formerly contained acetic anhydride may still hold product residues, they should be handled appropriately.
SPILLS AND LEAKS
In the event of a spill or leak involving acetic anhydride, persons not wearing protective equipment and clothing should be restricted from contaminated areas until cleanup has been completed. The following steps should be undertaken following a spill or leak:
The Environmental Protection Agency's (EPA's) regulatory requirements for emergency planning, community right-to-know, and hazardous waste management may vary over time. Users are therefore advised to determine periodically whether new information is available.
* Emergency planning requirements
Acetic anhydride is not subject to EPA emergency planning requirements under the Superfund Amendments and Reauthorization Act (Title III).
* Reportable quantity requirements (releases of hazardous substances)
A hazardous substance release is defined by EPA as any spilling, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment including the abandonment or discarding of containers) of hazardous substances. In the event of a release that is above the reportable quantity for that chemical, employers are required by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) to notify the proper Federal authorities.
The reportable quantity for acetic anhydride is 5000 pounds. If an amount equal to or greater than this quantity is released within an hour period, CERCLA [40 CFR Part 302.6] requires employers to notify the National Response Center IMMEDIATELY at (800) 424-8802 (in Washington, D.C. at (202) 426-2675).
* Community right-to-know requirements
Employers are not required by Section 313 of the Superfund Amendments and Reauthorization Act (SARA) to submit a Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of acetic anhydride emitted or released from their facility annually.
* Hazardous waste management requirements
EPA considers a waste to be hazardous if it exhibits any of the following characteristics: ignitability, corrosivity, reactivity, or toxicity, as defined in 40 CFR 261.21-261.24. Under the Resource Conservation and Recovery Act (RCRA), EPA has specifically listed many chemical wastes as hazardous. Although acetic anhydride is not specifically listed as a hazardous waste under RCRA, EPA requires employers to treat any waste as hazardous if it exhibits any of the characteristics discussed above.
Providing more information about the removal and disposal of specific chemicals is beyond the scope of this guideline. EPA, U.S. Department of Transportation, and State and local regulations should be followed to ensure that removal, transport, and disposal of this substance are conducted in accordance with existing regulations. To be certain that chemical waste disposal meets EPA regulatory requirements, employers should address any questions to the RCRA hotline at (202) 382-3000 (in Washington, D.C.) or toll-free at (800) 424-9346 (outside Washington, D.C.). In addition, relevant State and local authorities should be contacted for information on any requirements they may have for the waste removal and disposal of this substance.
* Conditions for respirator use
Good industrial hygiene practice requires that engineering controls be used where feasible to reduce workplace concentrations of hazardous materials to the prescribed exposure limit. However, some situations may require the use of respirators to control exposure. Respirators must be worn if the ambient concentration of acetic anhydride exceeds prescribed exposure limits. Respirators may be used (1) before engineering controls have been installed, (2) during work operations such as maintenance or repair activities that involve unknown exposures, (3) during operations that require entry into tanks or closed vessels, and (4) during emergency situations. If the use of respirators is necessary, the only respirators permitted are those that have been approved by NIOSH and the Mine Safety and Health Administration (MSHA).
* Respiratory protection program
Employers should institute a complete respiratory protection program that, at a minimum, complies with the requirements of OSHA's Respiratory Protection Standard [29 CFR 1910.134]. Such a program must include respirator selection (see Table 1), an evaluation of the worker's ability to perform the work while wearing a respirator, the regular training of personnel, fit testing, periodic workplace monitoring, and regular respirator maintenance, inspection, and cleaning. The implementation of an adequate respiratory protection program (including selection of the correct respirator) requires that a knowledgeable person be in charge of the program and that the program be evaluated regularly. For additional information on the selection and use of respirators and on the medical screening of respirator users, consult the NIOSH Respirator Decision Logic and the NIOSH
Guide to Industrial Respiratory Protection
Table 1 lists the respiratory protection that NIOSH recommends for workers exposed to acetic anhydride. The recommended protection may vary over time because of changes in the exposure limit for acetic anhydride or in respirator certification requirements. Users are therefore advised to determine periodically whether new information is available.
PERSONAL PROTECTIVE EQUIPMENT
Protective clothing should be worn to prevent any possibility of skin contact with acetic anhydride. Chemical protective clothing should be selected on the basis of available performance data, manufacturers' recommendations, and evaluation of the clothing under actual conditions of use. The following materials have been recommended for use against permeation by acetic anhydride and may provide protection for more than 4 but fewer than 8 hours: butyl rubber and Teflon. Polyvinyl chloride, nitrile rubber, Viton, and natural rubber have all demonstrated poor resistance to permeation by acetic anhydride.
If acetic anhydride is dissolved in water or an organic solvent, the permeation properties of both the solvent and the mixture must be considered when selecting personal protective equipment and clothing.
Safety glasses, goggles, or face shields should be worn during operations in which acetic anhydride might contact the eyes (e.g., through vapors or splashes of solution). Eyewash fountains and emergency showers should be available within the immediate work area whenever the potential exists for eye or skin contact with acetic anhydride. Contact lenses should not be worn if the potential exists for acetic anhydride exposure.
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Table 1. NIOSH recommended respiratory protection for workers exposed to acetic anhydride*
Condition Minimum respiratory protection**
Airborne concentration of acetic anhydride: