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This guideline summarizes pertinent information about thioglycolic acid 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 Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new information is available.
SUBSTANCE IDENTIFICATION * Formula C(2)H(4)O(2)S * Structure (For Structure, see paper copy) * Synonyms Mercaptoacetate, mercaptoacetic acid, thiovanic acid, alpha-mercaptoacetic acid, 2-mercaptoacetic acid, 2-thioglycolic acid * Identifiers
Thioglycolic acid is a colorless liquid with a strong, unpleasant odor characteristic of the sulfhydryl group (mercaptans). CHEMICAL AND PHYSICAL PROPERTIES * Physical data
The National Fire Protection Association has not assigned a flammability rating to thioglycolic acid.
Fires involving thioglycolic acid should be fought upwind from the maximum distance possible. Keep unnecessary people away; isolate the hazard area and deny entry. Emergency personnel should stay out of low areas. Vapors are an explosion and poison hazard indoors, outdoors, or in sewers. Containers of thioglycolic acid 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 fire exposed containers from the sides with water until well after the fire is out. Stay away from the ends of containers. Firefighters should wear a full set of protective clothing and self-contained breathing apparatus when fighting fires involving thioglycolic acid. EXPOSURE LIMITS * OSHA PEL The Occupational Safety and Health Administration (OSHA) does not currently regulate thioglycolic acid. * NIOSH REL The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for thioglycolic acid of 1 part per million (ppm) parts of air (4 milligrams per cubic meter (mg/m(3))) as a TWA for up to a 10-hour workday and a 40-hour workweek. NIOSH also assigns a "Skin" notation, which indicates that the cutaneous route of exposure, including mucous membranes and eyes, contributes to overall exposure [NIOSH 1992]. * ACGIH TLV The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned thioglycolic acid a threshold limit value (TLV) of 1 ppm (3.8 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek. The ACGIH also assigns a "Skin" notation to thioglycolic acid [ACGIH 1994, p. 34]. * Rationale for Limits The NIOSH limit is based on the risk of eye or skin irritation, and systemic effects [NIOSH 1992]. The ACGIH limit is based on the risk of dermal effects and eye irritation [ACGIH 1991, p. 1541].
HEALTH HAZARD INFORMATION * Routes of Exposure Exposure to thioglycolic acid can occur through inhalation, ingestion, eye or skin contact, and absorption through the skin. * Summary of toxicology
* Emergency medical procedures: [NIOSH to supply] Rescue: Remove an incapacitated worker from further exposure and implement appropriate emergency procedures (e.g., those listed on the Material Safety Data Sheet required by OSHA's Hazard Communication Standard [29 CFR 1910.1200]). All workers should be familiar with emergency procedures, the location and proper use of emergency equipment, and methods of protecting themselves during rescue operations. EXPOSURE SOURCES AND CONTROL METHODS The following operations may involve thioglycolic acid and lead to worker exposures to this substance:
Good sources of information about control methods are as follows:
Determination of a worker's exposure to airborne thioglycolic acid is made using a midget impinger containing 15 milliliters of deionized water. Samples are collected at a recommended flow rate of 1 liter/minute until a recommended collection volume of 120 liters is reached. Analysis is conducted by high performance liquid chromatography using an ultraviolet detector (HPLC/UV). This method is described in the OSHA Computerized Information System [OSHA 1994] and is not yet validated.
PERSONAL HYGIENE PROCEDURES If thioglycolic acid contacts the skin, workers should flush the affected areas immediately with plenty of water, followed by washing with soap and water. Do not wait to remove contaminated clothing; do it under the stream of water. Clothing contaminated with thioglycolic acid should be removed immediately, and 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 thioglycolic acid, particularly its potential for causing tissue corrosion. A worker who handles thioglycolic acid should thoroughly wash hands, forearms, and face with soap and water before eating, using tobacco products, using toilet facilities, applying cosmetics, or taking medication. Workers should not eat, drink, use tobacco products, apply cosmetics, or take medication in areas where thioglycolic acid or a solution containing thioglycolic acid is handled, processed, or stored. STORAGE Thioglycolic acid should be stored in a cool, dry, well-ventilated area in tightly sealed containers that are labeled in accordance with OSHA's Hazard Communication Standard [29 CFR 1910.1200]. Containers of thioglycolic acid should be protected from physical damage and should be stored separately from strong oxidizing agents, bases, mineral acids, and active metals (such as sodium, potassium, magnesium, calcium). SPILLS AND LEAKS In the event of a spill or leak involving thioglycolic acid, 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:
U.S. Environmental Protection Agency (EPA) requirements for emergency planning, reportable quantities of hazardous releases, community right-to-know, and hazardous waste management may change over time. Users are therefore advised to determine periodically whether new information is available. * Emergency planning requirements Thioglycolic acid is not subject to EPA emergency planning requirements under the Superfund Amendments and Reauthorization Act (SARA) (Title III) in 42 USC 11022. * Reportable quantity requirements for hazardous releases A hazardous substance release is defined by EPA as any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment (including the abandonment or discarding of contaminated containers) of hazardous substances. In the event of a release that is above the reportable quantity for that chemical, employers are required to notify the proper Federal, State, and local authorities [40 CFR 355.40]. Employers are not required by the emergency release notification provisions in 40 CFR Part 355.40 to notify the National Response Center of an accidental release of thioglycolic acid; there is no reportable quantity for this substance. * Community right-to-know requirements Employers are not required by EPA in 40 CFR Part 372.30 to submit a Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of thioglycolic acid 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) [40 USC 6901 et seq.], EPA has specifically listed many chemical wastes as hazardous. Although thioglycolic acid is not specifically listed as a hazardous waste under RCRA, EPA requires employers to treat waste as hazardous if it exhibits any of the characteristics discussed above. Providing detailed information about the removal and disposal of specific chemicals is beyond the scope of this guideline. The U.S. Department of Transportation, EPA, 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 (703) 412-9810 (in the Washington, D.C. area) 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. RESPIRATORY PROTECTION * 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 thioglycolic acid 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 emergencies. Workers should only use respirators 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, an evaluation of the worker's ability to perform the work while wearing a respirator, the regular training of personnel, respirator 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 latest edition of the NIOSH Respirator Decision Logic [NIOSH 1987b] and the NIOSH Guide to Industrial Respiratory Protection [NIOSH 1987a]. PERSONAL PROTECTIVE EQUIPMENT Workers should use appropriate personal protective clothing and equipment that must be carefully selected, used, and maintained to be effective in preventing skin contact with thioglycolic acid. The selection of the appropriate personal protective equipment (PPE) (e.g., gloves, sleeves, encapsulating suits) should be based on the extent of the worker's potential exposure to thioglycolic acid. The resistance of various materials to permeation by thioglycolic acid is shown below: Material Breakthrough time (hr) butyl rubber >8 neoprene >8 viton >8 natural rubber <1(*) nitrile rubber <1(*) polyvinyl alcohol <1(*) polyvinyl chloride <1(*) (*) Not recommended, degradation may occur To evaluate the use of these materials with thioglycolic acid, users should consult the best available performance data and manufacturers' recommendations. Significant differences have been demonstrated in the chemical resistance of generically similar PPE materials (e.g., butyl) produced by different manufacturers. In addition, the chemical resistance of a mixture may be significantly different from that of any of its neat components. Any chemical-resistant clothing that is used should be periodically evaluated to determine its effectiveness in preventing dermal contact. Safety showers and eye wash stations should be located close to operations that involve thioglycolic acid. Splash-proof chemical safety goggles or face shields (20 to 30 cm long, minimum) should be worn during any operation in which a solvent, caustic, or other toxic substance may be splashed into the eyes. In addition to the possible need for wearing protective outer apparel (e.g., aprons, encapsulating suits), workers should wear work uniforms, coveralls, or similar full-body coverings that are laundered each day. Employers should provide lockers or other closed areas to store work and street clothing separately. Employers should collect work clothing at the end of each work shift and provide for its laundering. Laundry personnel should be informed about the potential hazards of handling contaminated clothing and instructed about measures to minimize their health risk. Protective clothing should be kept free of oil and grease and should be inspected and maintained regularly to preserve its effectiveness. Protective clothing may interfere with the body's heat dissipation, especially during hot weather or during work in hot or poorly ventilated work environments.
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