Disclaimer: The information contained in these guidelines is intended for reference purposes only. It provides a summary of information about chemicals that workers may be exposed to in their workplaces. The information may be superseded by new developments in the field of industrial hygiene. Readers are therefore advised to regard these recomendations as general guidelines and to determine whether new information is available.

OCCUPATIONAL SAFETY AND HEALTH GUIDELINE FOR TRIMETHYL BENZENE

INTRODUCTION

This guideline summarizes pertinent information about trimethyl benzene 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 Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new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(9)H(12)

* Structure

(For Structure, see paper copy)

* Synonyms

1,2,3-Trimethyl benzene or hemimellitene; 1,2,4-trimethyl benzene or pseudocumene; 1,3,5-trimethyl benzene or mesitylene

* Identifiers

1. CAS No.: 25551-13-7 (commercially available product is a mixture of isomers); 526-73-8 (1,2,3-trimethyl benzene); 108-67-8 (1,3,5-trimethyl benzene); 95-63-6 (1,2,4-trimethyl benzene)

2. RTECS No.: DC3300000 (1,2,3-trimethyl benzene); OX6825000 (1,3,5-trimethyl benzene); DC3325000 (1,2,4-trimethyl benzene)

3. DOT UN: 2325 26 (1,3,5-trimethyl benzene)

4. DOT label: Flammable Liquid (1,3,5-trimethyl benzene)

* Appearance and odor

Trimethyl benzene is a clear, colorless liquid with a pleasant aromatic odor. An odor threshold of 0.55 part per million (ppm) parts of air has been reported.

CHEMICAL AND PHYSICAL PROPERTIES

* Physical data

1. Molecular weight: 120.19

2. Boiling point (at 760 mm Hg): 176 degrees C (348.8 degrees F) (1,2,3-trimethyl benzene); 164.6 degrees C (328.3 degrees F) (1,3,5-trimethyl benzene); 168.9 degrees C (336.0 degrees F) (1,2,4-trimethyl benzene)

3. Specific gravity: 0.8944 (1,2,3-trimethyl benzene); 0.8652 (1,3,5-trimethyl benzene); 0.8758 (1,2,4-trimethyl benzene) at 20 degrees C (68 degrees F)

4. Vapor density: 4.1

5. Melting point: -25.4 degrees C (-13.72 degrees F) (1,2,3-trimethyl benzene); -44.7 degrees C (-48.46 degrees F) (1,3,5-trimethyl benzene); -43.8 degrees C (-46.84 degrees F) (1,2,4-trimethyl benzene)

6. Vapor pressure: Data not available.

7. Solubility: Miscible with ethyl alcohol, benzene, and ethyl ether; insoluble in water.

8. Evaporation rate: Data not available.

* Reactivity

1. Conditions contributing to instability: Exposure to heat, sparks and open flame.

2. Incompatibilities: Contact between trimethyl benzene and oxidizers such as perchlorates, peroxides, permanganates, chlorates, nitrates, chlorine, bromine and fluorine should be avoided.

3. Hazardous decomposition products: None reported.

4. Special precautions: None reported.

* Flammability

The National Fire Protection Association has assigned a flammability rating of 2 (moderate fire hazard) to trimethyl benzene.

1. Flash point: 1,2,3-trimethyl benzene - Data not available; 1,3, 5-trimethyl benzene - 50 degrees C (122 degrees F) (closed cup); 1,2, 4-trimethyl benzene - 44 degrees C (112 degrees F) (closed cup)

2. Autoignition temperature: Data not available.

3. Flammable limits in air: Data not available.

4. Extinguishant: For small fires use dry chemical, carbon dioxide, water spray, or alcohol-resistant foam. Use water spray, fog, or alcohol-resistant foam to fight large fires involving trimethyl benzene.

Fires involving trimethyl benzene should be fought upwind from the maximum distance possible. Keep unnecessary people away; isolate the hazard area and deny entry. Isolate the area for 1/2 mile in all directions if a tank, rail car, or tank truck is involved in the fire. For a massive fire in a cargo area, use unmanned hose holders or monitor nozzles; if this is impossible, withdraw from the area and let the fire burn. Emergency personnel should stay out of low areas. Vapors may travel to a source of ignition and flash back. Vapors are an explosion and poison hazard indoors, outdoors, or in sewers. Containers of trimethyl benzene 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. 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. Firefighters should wear a full set of protective clothing and self-contained breathing apparatus when fighting fires involving trimethyl benzene.

EXPOSURE LIMITS

* OSHA PEL

The Occupational Safety and Health Administration (OSHA) does not currently regulate trimethyl benzene.

* NIOSH REL

The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for trimethyl benzene of 25 ppm (125 mg/m(3)) as a TWA for up to a 10-hour workday and a 40-hour workweek [NIOSH 1992].

* ACGIH TLV

The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned trimethyl benzene a threshold limit value (TLV) of 25 ppm (123 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1994, p. 35].

* Rationale for Limits

The NIOSH limit is based on the risk of skin irritation, central nervous system depression, and respiratory failure [NIOSH 1992].

The ACGIH limit is based on the risk of irritation and central nervous system effects [ACGIH 1991, p. 1649].

HEALTH HAZARD INFORMATION

* Routes of Exposure

Exposure to trimethyl benzene can occur through inhalation, ingestion, and eye or skin contact.

* Summary of toxicology

1. Effects on Animals: Trimethyl benzene is a skin irritant and also affects the lungs and central nervous system in experimental animals [ACGIH 1991]. The oral LD(50) in rats is 8,970 mg/kg [NIOSH 1991]. Instillation of trimethyl benzene into the lungs caused chemical pneumonitis at the site of contact [ACGIH 1991]. High concentrations of trimethyl benzene vapors cause central nervous system depression [ACGIH 1991]. During a 24-hour exposure to 2,400 ppm of the 1,3, 5-trimethyl benzene isomer, 4 of 16 rats died of respiratory arrest [ACGIH 1991]. Rats exposed to 1,700 ppm for four months had reduced body weight gain, central nervous system depression, and increasing lymphopenia and neutrophilia. The hematological effects were attributed to benzene contamination of the trimethyl benzene [ACGIH 1991].

2. Effects on Humans: Workers exposed to a solvent containing 80 percent trimethyl benzenes complained of nervousness, tension, anxiety, and asthmatic bronchitis; in addition, the peripheral blood showed a tendency to hypochromic anemia and prolonged coagubility of blood; the peripheral blood effects were attributed to benzene contamination of the solvent [ACGIH 1991].

* Signs and symptoms of exposure

1. Acute exposure: No signs or symptoms of acute exposure to trimethyl benzene have been reported in humans.

2. Chronic exposure: Chronic exposure to trimethyl benzene has caused nervousness, tension, anxiety, asthmatic bronchitis and blood changes in humans.

EMERGENCY MEDICAL PROCEDURES

* Emergency medical procedures: [NIOSH to supply]

5. 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 trimethyl benzene and lead to worker exposures to this substance:

• The manufacture and transportation of trimethyl benzene
• Use as a raw material for chemical synthesis
• Use as a solvent and paint thinner
• Use as ultraviolet stabilizers in plastics

Methods that are effective in controlling worker exposures to trimethyl benzene, depending on the feasibility of implementation, are as follows:

• Process enclosure
• Local exhaust ventilation
• General dilution ventilation
• Personal protective equipment

Workers responding to a release or potential release of a hazardous substance must be protected as required by paragraph (q) of OSHA's Hazardous Waste Operations and Emergency Response Standard [29 CFR 1910.120].

Good sources of information about control methods are as follows:

1. ACGIH [1992]. Industrial ventilation--a manual of recommended practice. 21st ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

2. Burton DJ [1986]. Industrial ventilation--a self study companion. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

3. Alden JL, Kane JM [1982]. Design of industrial ventilation systems. New York, NY: Industrial Press, Inc.

4. Wadden RA, Scheff PA [1987]. Engineering design for control of workplace hazards. New York, NY: McGraw-Hill.

5. Plog BA [1988]. Fundamentals of industrial hygiene. Chicago, IL: National Safety Council.

MEDICAL SURVEILLANCE

OSHA is currently developing requirements for medical surveillance. When these requirements are promulgated, readers should refer to them for additional information and to determine whether employers whose employees are exposed to trimethyl benzene are required to implement medical surveillance procedures.

* Medical Screening

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, 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 surveillance program is intended to supplement, not replace, such measures. To detect and control work-related health effects, medical evaluations should be performed (1) before job placement, (2) periodically during the term of employment, and (3) at the time of job transfer or termination.

* Preplacement medical evaluation

Before a worker is placed in a job with a potential for exposure to trimethyl benzene, a licensed health care professional 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 central nervous system.

A preplacement medical evaluation is recommended to assess medical conditions that may be aggravated or may result in increased risk when a worker is exposed to trimethyl benzene at or below the prescribed exposure limit. The health care professional 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 central nervous system.

* Periodic medical evaluations

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 trimethyl benzene exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of trimethyl benzene on the central nervous 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.

* Termination medical evaluations

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.

* Biological monitoring

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 trimethyl benzene.

WORKPLACE MONITORING AND MEASUREMENT

Determination of a worker's exposure to airborne trimethyl benzene is made using a charcoal tube (100/50 mg sections, 20/40 mesh). Samples are collected at a maximum flow rate of 0.1 liter/minute until a maximum collection volume of 10 liters is reached. The sample is then treated with carbon disulfide. Analysis is conducted by gas chromatography using a flame ionization detector (GC/FID). This method is described in the OSHA Computerized Information System [OSHA 1994] and is partially validated.

PERSONAL HYGIENE PROCEDURES

If trimethyl benzene contacts the skin, workers should flush the affected areas immediately with plenty of water, followed by washing with soap and water.

Clothing contaminated with trimethyl benzene 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 trimethyl benzene, particularly its potential for causing central nervous system effects.

A worker who handles trimethyl benzene 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 trimethyl benzene or a solution containing trimethyl benzene is handled, processed, or stored.

STORAGE

Trimethyl benzene 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 trimethyl benzene should be protected from physical damage and sources of ignition, and should be stored separately from oxidizers such as perchlorates, peroxides, permanganates, chlorates, nitrates, chlorine, bromine and fluorine.

SPILLS AND LEAKS

In the event of a spill or leak involving trimethyl benzene, 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:

1. Do not touch the spilled material; stop the leak if it is possible to do so without risk.

2. Notify safety personnel.

3. Remove all sources of heat and ignition.

4. Ventilate the area of the spill or leak.

5. Water spray may be used to reduce vapors, but the spray may not prevent ignition in closed spaces.

6. For small spills, take up with sand or other noncombustible absorbent material and place into closed containers for later disposal.

7. For large liquid spills, build dikes far ahead of the spill to contain the trimethyl benzene for later reclamation or disposal.

SPECIAL REQUIREMENTS

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

Trimethyl benzene 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 trimethyl benzene; 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 trimethyl benzene 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 trimethyl benzene 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 trimethyl benzene 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 trimethyl benzene. 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 trimethyl benzene. The resistance of one type of PPE material to permeation by the 1,2,4-trimethyl benzene isomer is shown below:

Material	Breakthrough time (hr)
Responder	>8

To evaluate the use of this or other PPE materials with trimethyl benzene, 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 trimethyl benzene.

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.

REFERENCES

ACGIH [1991]. Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

ACGIH [1994]. 1994-1995 Threshold limit values for chemical substances and physical agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

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NIOSH [1991]. Registry of toxic effects of chemical substances: Trimethyl benzene. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Standards Development and Technology Transfer, Technical Information Branch.

NIOSH [1992]. Recommendations for occupational safety and health: Compendium of policy documents and statements. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 92-100.

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