Winter 2025

The American Conference of Governmental Industrial Hygienists Reduces Its Threshold Limit Value for Benzene

By David Dodge, M.S., DABT, CIH

Benzene is a volatile aromatic hydrocarbon that is ubiquitous in air due to natural and human-made sources.  With sufficient exposure, it can cause toxicity primarily to the blood and bone marrow, including a blood cancer called acute myeloid leukemia (AML).  In December 2023, the American Conference of Governmental Industrial Hygienists (ACGIH) lowered its occupational exposure limit (OEL) for benzene (ACGIH, 2023).  This article provides some context for this decision, as well as potential implications for workplaces where occupational exposures to airborne benzene occur.

Although definitions vary slightly, OELs are intended generally to protect all, or the vast majority of, workers against adverse health effects during their working lifetime and beyond.”

Benzene occurs naturally in crude oil and can be formed during biomass combustion (e.g., forest fires, cigarette smoking).  It is made purposely, mostly from petroleum, to produce other chemicals, such as styrene, cumene, and cyclohexane, and for use in the manufacture of certain products, such as rubber, lubricants, dyes, detergents, drugs, and pesticides (ATSDR, 2007).  As a component of crude oil, benzene can be found in crude oil-refining operations and in refined products, such as petroleum solvents and gasoline (ATSDR, 2007; ACGIH, 2023).  Workers in industries that use or make benzene or benzene-containing products are most likely to have occupational exposures to benzene.  These include, but are not limited to, workers in petrochemical plants, petroleum refineries, coke and coal chemical plants, tire manufacturing plants, bulk terminals and plants, tank truck transportation, and gasoline stations (ATSDR, 2007).

OELs serve a critical role in risk assessment and risk management of occupational hazards, and their use is established in the field of industrial hygiene.  In general, an OEL reflects an airborne concentration of a chemical that serves as a recommended or regulatory exposure limit to protect worker health, and OELs are derived by various organizations in the US and around the world.  Information about exposure concentrations experienced by workers in a specific work scenario can be compared to an OEL to make decisions about worker health risks and whether additional controls are needed to adequately protect worker health.  Although definitions vary slightly, OELs are intended generally to protect all, or the vast majority of, workers against adverse health effects during their working lifetime and beyond.  In the US, ACGIH, a private, nonprofit corporation, is one of the primary OEL-setting organizations that publishes OELs known as threshold limit values (TLVs).  TLVs serve as recommendations rather than standards but are nonetheless influential in the field of industrial hygiene.  The Occupational Safety and Health Administration (OSHA) is another primary OEL-setting organization in the US.  It develops OELs called permissible exposure limits (PELs), which are legally enforceable standards for those workplaces in which the standards apply.

[W]orkplaces that currently meet the OSHA PEL or the prior ACGIH TLV [for benzene] may not meet the newly reduced ACGIH TLV.”

The new ACGIH TLV for benzene, as an 8-hour, time-weighted average (TWA) value, is 0.02 parts per million (ppm), a 25-fold reduction from its prior value of 0.5 ppm adopted in 1997 (ACGIH, 2023).  The new TLV is intended to minimize the potential for bone marrow toxicity, as well as other adverse effects such as AML and chromosomal damage.  The lowering of the ACGIH TLV was prompted by newer human studies suggesting bone marrow toxicity at benzene exposures lower than previously considered relevant.  In contrast, the legally enforceable OSHA PEL for benzene is 1 ppm (OSHA, 1987), which is 50-fold higher than the new ACGIH TLV.  The recent lowering of the ACGIH TLV follows a trend in reductions in benzene OELs over time (see Table).

Occupational Exposure Limits for Benzene Over Time

In recent decades, increased awareness of the hazards of exposure to benzene and more stringent benzene-related regulatory requirements have led to reductions in the uses of benzene and worker exposures to benzene.  Nonetheless, workplaces that currently meet the OSHA PEL or the prior ACGIH TLV may not meet the newly reduced ACGIH TLV.  Since the ACGIH is an influential organization and its new TLV for benzene reflects the most recent scientific literature on the health effects of benzene, it may be prudent for workplaces where occupational exposures to benzene occur to take action to monitor worker exposures and, if necessary, employ additional exposure control measures.