OCCUPATIONAL SAFETY AND HEALTH GUIDELINE FOR 

BENZENE 

POTENTIAL HUMAN CARCINOGEN 

INTRODUCTION 

This guideline summarizes pertinent information about benzene for workers, employers, and 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 Recommendations may be superseded by new developments in these 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; therefore, readers are advised to regard these recommendations as general guidelines. 

SUBSTANCE IDENTIFICATION 

• Formula: C6H6 

• Structure: 0 • Synonyms: Benzol, benzole, benzolene, bicarburet of hydrogen, carbon oil, coal naphtha 

• Identifiers: CAS 71-43-2; RTECS C¥1400000; DOT 1114, 

label required: "Flammable Liquid" 

• Appearance and odor: Colorless liquid with an aromatic 

odor 

CHEMICAL AND PHYSICAL PROPERTIES 

• Physical data 

I. Molecular weight: 78.12 

2. Boiling point (at 760 mmHg): 80.1 °C (176°F) 

3. Specific gravity (water = 1): 0.88 

4. Vapor density (air = I at boiling point of benzene): 2.7 

5. Melting point: 5.5°C (42 °F) 

6. Vapor pressure at 20°C (68°F): 75 mmHg 

7. Solubility in water, g/100 g water at 20°C (68°F): 0.06 

8. Evaporation rate (butyl acetate = 1): 5.1 

9. Saturation concentration in air (approximate) at 25 oc 

(7rF): 12.5% (125,000 ppm) 

10. Ionization potential: 9.25 eV 

• Reactivity 

Incompatibilities: Benzene reacts with strong oxidizers including chlorine, oxygen, and bromine with iron. 

2. Hazardous decomposition products: Toxic vapors and gases 

(e.g., carbon monoxide) may be released in a fire involving 

benzene. 

3. Caution: Benzene will attack some forms of plastics, coatings, and rubber. 

• Flammability 

I. Flash point: -II.I°C (12°F) (closed cup) 

2. Autoignition temperature: 498 oc (928 °F) 

3. Flammable limits in air, % by volume: Lower, 1.4; upper, 7.1 

4. Extinguishant: Alcohol foam, carbon dioxide, and dry 

chemical extinguishants are effective. Water may be an ineffective extinguishant but may be used to cool fire-exposed containers. 

5. Class IB Flammable Liquid (29 CFR 1910.106), Flammability Rating 3 (NFPA) 

6. Unusual fire and explosion hazards: Benzene liquid is flammable, and its vapors can easily form explosive mixtures. 

Flashbacks may occur along a vapor trail. 

• Warning properties 

I. Odor threshold: 12 ppm 

2. Eye irritation levels: 3,000 ppm for 0.5-1 hour 

3. Other information: 3,000 ppm may irritate nose and respiratory tract. 

4. Evaluation of warning properties for respirator selection: 

Warning properties are not considered in recommending respirators for use with carcinogens. 

EXPOSURE LIMITS 

The current Occupational Safety and Health Administration 

(OSHA) permissible exposure limit (PEL) for benzene is I part 

of benzene per million parts of air (PPM) as a time-weighted 

average (TWA) concentration over an 8-hour workshift; the 

short-term exposure limit is 5 ppm in any 15-minute sampling 

period. The National Institute for Occupational Safety and 

Health (NIOSH) recommends that benzene be controlled and 

handled as a potential human carcinogen in the workplace and 

that exposure be reduced to the lowest feasible limit. The 

NIOSH recommended exposure limit (REL) is 0.1 ppm [0.32 

milligrams of benzene per cubic meter of air (mg/m3)] as an 

8-hour TWA and I ppm (3.2 mg/m3) as a ceiling in any 

15-minute sampling period. The NIOSH REL is the lowest conU.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 

1988 Benzene 1 
centration detectable by current NIOSH-validated sampling 

and analytical methods. The American Conference of Governmental Industrial Hygienists (ACGIH) has designated benzene 

as an A2 substance (suspected human carcinogen) having an 

assigned threshold limit value (TLV"') of 10 ppm (30 mg/m3) 

as a TWA for a normal 8-hour workday and a 40-hour 

workweek. 

Table 1.-0ccupational exposure limits 

for benzene 

OSHA PEL TWA 

Short-term exposure 

limit (15 min) 

NIOSH REL (Ca)* TWA 

Ceiling (15 min) 

ACGIH TLV"' TWA (A2)t 

Exposure limits 

ppm mglm' 

5 

0.1 

I 

10 

0.32 

3.2 

30 

* (Ca): NIOSH recommends treating as a potential human carcinogen. 

t(A2): Suspected human carcinogen. 

HEALTH HAZARD INFORMATION 

• Routes of exposure 

Benzene may cause adverse health effects following exposure 

via inhalation, ingestion, or dermal or eye contact. 

• Summary of toxicology 

I. Effects on animals: Acute inhalation of benzene by rats, mice, 

or rabbits caused narcosis, spontaneous heart contractions 

(ventricular fibrillation), and death due to respiratory paralysis. Subchronic inhalation of benzene by rats produced 

decreased white blood cell counts, decreased bone marrow cell 

activity, increased red blood cell activity, and cataracts. In rats, 

chronic inhalation or oral administration of benzene produced 

cancers of the liver, mouth, and Zymbal gland. Inhalation of 

benzene by pregnant rats caused retardation of fetal development and increased fetal mortality. 

2. Effects on humans: Acute inhalation exposure of benzene 

has caused nerve inflammation (polyneuritis), central nervous 

system depression, and cardiac sensitization. Chronic exposure 

to benzene has produced anorexia and irreversible injury to the 

blood-forming organs; effects include aplastic anemia and 

leukemia. 

• Signs and symptoms of exposure 

1. Short-term (acute): Exposure to benzene can cause dizziness, euphoria, giddiness, headache, nausea, staggering gait, 

weakness, drowsiness, respiratory irritation, pulmonary edema and pneumonia, gastrointestinal irritation, convulsions, and 

paralysis. Benzene can also cause irritation to the skin, eyes, 

and mucous membranes. 

2. wng-term (chronic): Exposure to benzene can cause futigue, 

nervousness, irritability, blurred vision, and labored breath2 Benzene 

ing. Repeated skin contact can cause redness, blistering, and 

dry, scaly dermatitis. 

RECOMMENDED MEDICAL PRACTICES 

• Medical surveillance program 

Workers with potential exposures to chemical hazards should 

be monitored in a systematic program of medical surveillance 

intended to prevent or control 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 and health, earliest possible detection of adverse health effects, and referral of workers 

for diagnostic confirmation and treatment. The occurrence of 

disease (a "sentinel health event," SHE) 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. 

A medical surveillance program should include systematic collection and epidemiologic analysis of relevant environmental 

and biologic monitoring, medical screening, morbidity, and 

mortality data. This analysis may provide information about 

the relatedness of adverse health effects and occupational exposure that cannot be discerned from results in individual 

workers. Sensitivity, specificity, and predictive values of biologic monitoring and medical screening tests should be evaluated on an industry-wide basis prior to application in any given 

worker group. Intrinsic to a surveillance program is the dissemination of summary data to those who need to know, including employers, occupational health professionals, 

potentially exposed workers, and regulatory and public health 

agencies. 

• Preplacement medical evaluation 

Prior to placing a worker in a job with a potential for exposure 

to benzene, the 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, liver, and respiratory, 

nervous, and hematopoietic (blood-cell-forming) systems. The 

physician should obtain baseline values for the complete blood 

count and a stained differential count of all blood cell types. 

Medical surveillance for respiratory disease should be conducted by using the principles and methods recommended by 

NIOSH and the American Thoracic Society (ATS). 

A preplacement medical evaluation is recommended in order 

to detect and assess preexisting or concurrent conditions which 

may be aggravated or result in increased risk when a worker 

is exposed to benzene at or below the NIOSH REL. The examining physician should consider the probable frequency, intensity, and duration of exposure, as well as the nature and 

degree of the condition, in placing such a worker. Such conditions, which should not be regarded as absolute contraindi1988 
cations to job placement, include a history of chronic skin 

disease, concurrent dermatitis, or mild non-hemolytic anemia 

(e.g., mild iron-deficiency anemia). 

• Periodic medical screening and/or biologic monitoring 

Occupational health interviews and physical examinations 

should be performed at regular intervals. Additional examinations may be necessary should a worker report symptoms that 

may be attributed to exposure to benzene. The interviews, examinations, and appropriate medical screening and/or biologic 

monitoring tests should be directed at identifying an excessive 

decrease or adverse trend in the integrity and physiologic function of the skin, liver, and respiratory, nervous, and hematopoietic (blood-cell-forming) systems as compared to the 

baseline status of the individual worker or to expected values 

for a suitable reference population. The following tests should 

be used and interpreted according to standardized procedures 

and evaluation criteria recommended by NIOSH and the ATS: 

standardized questionnaires and tests of lung function. 

• Medical practices recommended at the time of job transfer or termination. 

The medical, environmental, and occupational history interviews, the physical examination, and selected physiologic and 

laboratory tests which were conducted at the time of placement 

should be repeated at the time of job transfer or termination. 

Any changes in the worker's health status should be compared 

to those expected for a suitable reference population. Because 

occupational exposure to benzene may cause diseases of 

prolonged induction-latency, the need for medical surveillance 

may extend well beyond termination of employment. 

• Sentinel health events 

1. Acute SHE's include: Acute myeloid leukemia and contact 

and/or allergic dermatitis. 

2. Delayed-onset SHE's include: Decrease in the number (neutropenia) or absence (agranulocytosis) of certain white blood 

cells in the peripheral circulation and/or in the bone marrow 

(aplastic anemia) and cancer of the red blood cells (erythroleukemia). 

MONITORING AND MEASUREMENT 

PROCEDURES 

• TWA exposure evaluation 

Measurements to determine worker exposure to benzene 

should be taken so that the TWA exposure is based on a single 

entire workshift sample or an appropriate number of consecutive samples collected during the entire workshift. Under certain conditions, it may be appropriate to collect several 

short-term interval samples (up to 30 minutes each) to determine the average exposure level. Air samples should be taken 

in the worker's breathing zone (air that most nearly represents 

that inhaled by the worker). 

• Ceiling concentration evaluation 

Measurements to determine worker exposure should be taken 

during periods of maximum expected airborne concentrations 

of benzene. Each measurement to determine the NIOSH REL 

(ceiling exposure) in the worker's breathing zone (air that most 

nearly represents that inhaled by the worker) should consist 

of a 15-minute sample. A minimum of three measurements 

1988 

should be taken during one workshift, and the highest of all 

measurements taken is an estimate of the worker's exposure. 

If the periods of maximum exposure are not clearly defined, 

a statistical procedure which can be used as a peak exposure 

detection strategy is given in the Occupational Exposure Sampling Strategy Manual. 

• Method 

Sampling and analysis may be performed by collecting benzene vapors with charcoal tubes followed by desorption with 

carbon disulfide and analysis by gas chromatography. Directreading devices calibrated to measure benzene may also be used 

if available. A detailed sampling and analytical method for benzene may be found in the N/OSH Manual of Analytical Methods 

(method number 1500). 

PERSONAL PROTECTIVE EQUIPMENT 

Chemical protective clothing (CPC) should be selected after 

utilizing available performance data, consulting with the 

manufucturer, and then evaluating the clothing under actual use 

conditions. 

Workers should be provided with and required to use CPC, 

gloves, and other appropriate protective clothing necessary to 

prevent skin contact with benzene. 

SANITATION 

Clothing which is contaminated with benzene should be removed immediately and placed in sealed containers for storage 

until it can be discarded or until provision is made for the 

removal of benzene from the clothing. If the clothing is to be 

laundered or cleaned, the person performing the operation 

should be informed of benzene's hazardous properties. Reusable clothing and equipment should be checked for residual 

contamination before reuse or storage. 

A change room with showers, washing facilities, and lockers 

that permit separation of street and work clothes should be 

provided. 

Workers should be required to shower following a workshift 

and prior to putting on street clothes. Clean work clothes should 

be provided daily. 

Skin that becomes contaminated with benzene should be 

promptly washed with soap and water. 

Workers who handle benzene should wash their fuces, hands, 

and forearms thoroughly with soap and water before eating, 

smoking, or using toilet facilities. 

The storage, preparation, dispensing, or consumption of food 

or beverages, the storage or application of cosmetics, the 

storage or use of smoking materials, or the storage or use of 

products for chewing should be prohibited in work areas. 

COMMON OPERATIONS AND CONTROLS 

Common operations in which exposure to benzene may occur 

and control methods which may be effective in each case are 

listed in Table 2. 

Benzene 3 
Table 2.-0perations and methods of 

control for benzene 

Operations 

During the manufacture and 

processing of benzene; during use as a raw material in 

the production of aromatic 

compounds and derivatives 

During the use of chemicals 

in which benzene may be an 

impurity (e.g., naphthas, 

toluene, xylene) 

During the manufacture and 

use of motor fuel blends in 

which benzene is used as an 

ingredient; during use as an 

extracting solvent 

During the preparation and 

use of paint and varnish 

removers, rubber cements, 

and lacquers 

Controls 

Process enclosure, local exhaust ventilation, personal 

protective equipment 

Process enclosure, local exhaust ventilation, personal 

protective equipment 

Process enclosure (when 

possible), local exhaust ventilation, personal protective 

equipment, material substitution 

Process enclosure (when 

possible), local exhaust ventilation, personal protective 

equipment, material substitution 

EMERGENCY FIRST AID PROCEDURES 

In the event of an emergency, remove the victim from further 

exposure, send for medical assistance, and initiate emergency procedures. 

• Eye exposure 

Where there is any possibility of a worker's eyes being exposed 

to benzene, an eye-wash fountain should be provided within 

the immediate work area for emergency use. 

If benzene gets into the eyes, flush them immediately with large 

amounts of water for 15 minutes, lifting the lower and upper 

lids occasionally. Get medical attention as soon as possible. 

Contact lenses should not be worn when working with this 

chemical. 

• Skin exposure 

Where there is any possibility of a worker's body being exposed 

to benzene, fucilities for quick drenching of the body should 

be provided within the immediate work area for emergency use. 

If benzene gets on the skin, wash it immediately with soap and 

water. If benzene penetrates the clothing, remove the clothing 

immediately and wash the skin with soap and water. Get medical attention promptly. 

• Rescue 

If a worker has been incapacitated, move the affected worker 

from the hazardous exposure. Put into effect the established 

emergency rescue procedures. Do not become a casualty. Understand the fucility's emergency rescue procedures and know 

the locations of rescue equipment before the need arises. 

4 Benezene 

SPILLS AND LEAKS 

Workers not wearing protective equipment and clothing should 

be restricted from areas of spills or leaks until cleanup has been 

completed. 

If benzene is spilled or leaked, the following steps should he 

taken: 

1. Remove all ignition sources. 

2. Ventilate area of spill or leak. 

3. For small quantities of liquids containing benzene, absorb 

on paper towels and place in an appropriate container. 

4. Large quantities of liquids containing benzene may he absorbed in vermiculite, dry sand, earth, or a similar material 

and placed in an appropriate container. 

5. Liquids containing benzene may he collected by vacuuming with an appropriate system. If a vacuum system is used, 

there should be no sources of ignition in the vicinity of the spill, 

and flashback prevention devices should be provided. 

WASTE REMOVAL AND DISPOSAL 

U.S. Environmental Protection Agency, Department of Transportation, and/or state and local regulations shall be followed 

to assure that removal, transport, and disposal are in accordance with existing regulations. 

RESPIRATORY PROTECTION 

It must be stressed that the use of respirators is the least 

preferred method of controlling worker exposure and should 

not normally be used as the only means of preventing or 

minimizing exposure during routine operations. However, 

there are some exceptions for which respirators may be used 

to control exposure: when engineering and work practice controls are not technically feasible, when engineering controls 

are in the process of being installed, or during emergencies and 

certain maintenance operations including those requiring 

confined-space entry (Table 3). 

In addition to respirator selection, a complete respiratory protection program should be instituted which as a minimum complies with the requirements found in the OSHA Safety and 

Health Standards, 29 CFR 1910.134. A respiratory protection 

program should include as a minimum an evaluation of the 

worker's ability to perform the work while wearing a respirator, the regular training of personnel, fit testing, periodic environmental monitoring, maintenance, inspection, and 

cleaning. The implementation of an adequate respiratory protection program, including selection of the correct respirators, 

requires that a knowledgeable person be in charge of the program and that the program he evaluated regularly. 

Only respirators that have been approved by the Mine Safety 

and Health Administration (MSHA, formerly Mining Enforcement and Safety Administration) and by NIOSH should he 

used. Remember! Air-purifying respirators will not protect from oxygen-deficient atmospheres. 

1988 
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Benzene 5 
Thble 3.-Respiratory protection for benzene 

Condition Minimum respiratory protection• 

Any detectable concentration Any self-contained breathing apparatus with a full facepiece and operated in a pressure-demand 

or other positive pressure mode 

Planned or emergency entry 

into environments containing 

unknown or any detectable 

concentration 

Firefighting 

Escape only 

Any supplied-air respirator with a full facepiece and operated in a pressure-demand or other 

positive pressure mode in combination with an auxiliary self-contained breathing apparatus operated in a pressure-demand or other positive pressure mode 

Any self-contained breathing apparatus with a full facepiece and operated in a pressure-demand 

or other positive pressure mode 

Any supplied-air respirator with a full facepiece and operated in a pressure-demand or other 

positive pressure mode in combination with an auxiliary self-contained breathing apparatus operated in a pressure-demand or other positive pressure mode 

Any self-contained breathing apparatus with a full facepiece and operated in a pressure-demand 

or other positive pressure mode 

Any air-purifying full facepiece respirator (gas mask) with a chin-style or front- or back-mounted 

organic canister 

Any appropriate escape-type self-contained breathing apparatus 

* Only NIOSH/MSHA-approved equipment should be used. 

6 Benzene 1988