Page 22 - OHS, October 2022

INDUSTRIAL HYGIENE
The Impact of Revising the Benzene Threshold Exposure Limit
It is estimated that nearly 1.37 million workers are exposed to benzene at work.
TBY BERNARD FONTAINE
he American Conference of Governmental Industrial Hygienists (ACGIH) proposes to reduce the eight-hour time-weighted average exposure threshold limit value (TLV) for benzene to 0.02 ppm and reduce the 15-minute
short-term exposure limit (STEL) to 0.1 ppm. So, what is known about workers who were exposed to benzene, and how does this change the paradigm of what is already known? The U.S. National Occupational Exposure Survey (1981–1983) estimated that about 272,300 workers were potentially exposed to benzene in the U.S. alone. Due to economic growth, technological and innovations in industry over the past 40 years, the current exposed population may be closer to 1.37 million workers nationwide.
Sampling data collected by the OSHA Integrated Management Information System (IMIS) shows limited evidence of data across the spectrum of industrial markets. The data collected shows that most workers (94.5 percent) would be exposed to benzene above the proposed ACGIH TLV. Only 2.9 percent of workers were exposed above the current ACGIH TLV of 0.5 ppm and 1.6 percent of workers were exposed above the OSHA Permissible Exposure Limit (PEL) of 1 ppm as an eight-hour TWA. So why has only limited evidence been collected to evaluate the workforce? Benzene is considered a confirmed human carcinogen by ACGIH, International Agency for Research on Cancer (IARC), National Toxicology Program (NTP) and the EPA. Global burden of cancer is high and continues to increase based on epidemiological data. The evidence is clear that all workplaces should be reassessed for benzene vapor to determine occupational exposure if the ACGIH TLV and STEL are reduced.
Introduction to Benzene
Benzene or benzol is a clear, colorless, highly flammable liquid with a sweet odor. The chemical is abundant as a component in gas emissions in motor vehicle exhaust, volcanic or forest fires and it is found in gasoline, crude oil and cigarette smoke.
Benzene is a component of many industrial products derived from coal and petroleum and it is found in gasoline and other fossil fuels. Trace amounts of benzene can be found in chemicals like toluene, ethylbenzene and xylene, and it is used to make chemicals like cumene and cyclohexane. Benzene is used in the manufacture of plastics, detergents, pesticides, synthetic fibers, rubber, lubricants, dyes, resins, drugs and so many other industrial chemicals. Additionally, ink and variety of painting products, such as spray paints, base and top coat paints, also contain some portions of benzene. Benzene ranks in the top 20 chemicals for production by volume. Most people can begin to smell benzene in air at approximately 60 parts per million parts of air (ppm) and recognize it as benzene at 100 ppm. According to the National Institute for Occupational Safety and Health (NIOSH), the odor threshold level is 4.68 ppm in air.
Historical Perspectives of Benzene
Industry has known that benzene is dangerous to workers for
18 Occupational Health & Safety | OCTOBER 2022
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a long time. In 1928, medical experts recognized a connection between benzene exposure and leukemia. In 1938, a study of benzene-exposed workers in the printing industry showed high levels of blood disease. A 1948 study published by the American Petroleum Institute (API) showed that benzene can cause leukemia. The API study concluded that the only “safe” level of benzene exposure is no exposure at all. By about the end of World War II, the ACGIH recommended limits on industrial exposure to the chemical, recognizing health risks associated with exposure.
Historically, benzene was used as a degreaser of metals and a solvent for organic materials. Benzene occurs naturally in petroleum products (e.g. crude oil and gasoline), and is also added to unleaded gasoline for its octane-enhancing and anti- knock properties. Typically, the concentration of benzene in these fuels is 1 to 2 percent by volume.2 Gasoline can be enriched with benzene by adding ethyl benzene-toluene-xylene, which is generated during coke making. Where necessary, side stream petroleum is added to adjust the octane rating; for example, reformate includes 5 to 12 percent benzene.3
The primary use of benzene today is in the manufacture of organic chemicals like styrene, phenol, cyclohexane, aniline, maleic anhydride, alkylbenzenes and chlorobenzenes. It is an intermediate in the production of anthraquinone, hydroquinone, benzene hexachloride and benzene sulfonic acid. The second- largest use of benzene in the U.S. (accounting for 22 percent of demand) is in the manufacture of cumene (isopropyl benzene), nearly all of which is consumed in phenol production. Also, benzene is used to make chemical intermediates: cyclohexane, nylon monomers (15 percent); nitrobenzene, intermediate for aniline and other products (7 percent); alkylbenzene, detergents (2 percent); chlorobenzenes, engineered polymers (1 percent); and miscellaneous uses (1 percent).4
Occupational Health Effects from Exposure
Individuals employed in industries that make or use benzene may be exposed to benzene. These industries include benzene
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