Page 26 - OHS, October 2022

INDUSTRIAL HYGIENE
production (petrochemicals, petroleum refifining, and coke and coal chemical manufacturing), rubber tire manufacturing, storage or transport of benzene and petroleum products containing benzene. Other workers exposed to benzene include coke oven workers in the steel industry, printers, rubber workers, shoe makers, laboratory technicians, firefighters and gas station employees.
The major effect of benzene from long-term exposure is on the hematopoietic system. Long-term exposure means exposure of a year or more. Benzene can cause harmful effects on the bone marrow by decreasing the production of red blood cells, leading to various forms of leukemia. It can cause excessive bleeding and affect the immune system, increasing the chance for infection.
Benzene can penetrate through intact skin. The amount of benzene absorbed through the skin (e.g., hands) depends on the solvent. Even at current contamination levels, which are less than 0.1 percent in most products, the amount of benzene absorbed over a long period can be significant, depending on exposure time and skin surface area.5
With occupational exposures less than five years to more than 30 years, individuals over time died from cancer including leukemia and multiple myeloma.6 Long-term exposure to this substance causes neurological symptoms and affects the bone marrow causing aplastic anemia, excessive bleeding and damage to the immune system. Benzene is linked to an increased risk of developing lymphatic and hematopoietic cancers, acute myelogenous leukemia, as well as chronic lymphocytic leukemia.
The early experiences of high occupational exposures led to the identification of hematopoietic effects of benzene and the need for improved control and regulation. As with most occupational standards, a reduction in exposure limits requires air monitoring, engineering and administrative controls along with respirators and personal protective equipment, training and education, medical surveillance and biological monitoring. In 1946, the U.S. occupational exposure limit for benzene, promulgated by the ACGIH, was 325 mg/m3 [100 ppm], but now most European and North American countries have harmonized at 1.63-3.25mg/m3 [0.5-1 ppm].
The IARC classifies benzene as “carcinogenic to humans,” based on sufficient evidence that benzene causes acute myeloid leukemia. IARC notes that benzene exposure has been linked with acute lymphocytic leukemia, chronic lymphocytic leukemia, multiple myeloma and non-Hodgkin lymphoma.
The NTP is a tripart of several different U.S. government agencies, including the National Institutes of Health, Centers for Disease Control and Prevention and Food and Drug Administration. NTP has classified benzene as “known to be a human carcinogen.” The EPA maintains the Integrated Risk Information System, which is another electronic database with information on human health effects and exposure to various substances in the environment. The EPA classifies benzene as a known human carcinogen.
Global Occupational Exposure Limits
The original OSHA PEL of 10 ppm was based on the association of benzene exposure with aplastic anemia and the risk of cancers. The eight-hour time-weighted average (TWA) OSHA PEL and 15-minute STEL for general industry are 1 ppm [3.19 mg/m3]
and 5 ppm [15.95 mg/m3], respectively (29 CFR 1910.1028). ThThese OELs also apply to the construction and maritime industry. Reported deaths at low levels of benzene exposure were associated with multiple myeloma and a long latency period, insteadofleukemia,whichjustififiedfurtherloweringofthe exposure limit. At that time, the risk assessment model was found to be non-significant for response at very low levels of exposure. A re-evaluation of the exposure data indicates that past evaluations may have underestimated the risk and the need to further reduce
the OELs.
The European Union and most European countries have an
OEL of 1 ppm, as does the Scientific Committee on Occupational Exposure Limits, but a few countries have opted for lower exposure values. In Germany, the MAK-Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area proposed an acceptable risk corresponding to an eight-hour TWA of 1.9 mg/m3 [0.59 ppm] and 0.02 mg/m3 [0.01 ppm].7
ACGIH TLV Chemical Substances Committee recommended that benzene be considered an A1 carcinogen and lowered the TLV during an eight-hour TWA to 0.5 ppm [1.6 mg/m3] and a STEL of 2.5 ppm [~8 mg/m3]. NIOSH recommended exposure level for the 8-hour TWA is 0.1 ppm [0.32 mg/m3] and the STEL is 1 ppm [3.19 mg/m3].
In 2022, ACGIH published a Notice of Intended Change to modify the TLV to 0.02 ppm for an eight-hour TWA and 0.1 ppm for a 15-minute STEL. Significantly lowering the OELs based on updated epidemiological and toxicological data may trigger the need for further exposure risk assessments where previous information suggested healthy workers were considered protected.
OSHAIntegratedManagementInformationSystem
OSHA compliance safety and health officers (CSHOs) often take personal or area air samples when monitoring worker exposures to chemical hazards. Samples are submitted to the Salt Lake Technical Center for analysis using a vetted analytical standard. IMIS is a resource to compile the OSHA sampling data.
Between 1984 and 2020, OSHA compliance sampling information on benzene in the IMIS database was reviewed.8 Workers across a spectrum of industries were evaluated for their benzene exposure by OSHA CSHOs. The frequency and duration of each exposure varied by industry, operation and process.
Personal sampling results represent workers who wore a sampling device. Area samples are taken in a fixed location and results represented the potential risk from airborne contaminants to workers in that area. Bulk samples help verify if benzene was present in the product. Bulk samples are used individually or in conjunction with personal or area samples to help interpret the level of worker risk. Figure 1 shows the average concentration of 73 bulk samples at 0.29 percent, ranging from 0.04 to 1.84 percent, which is above the 0.1 percent OSHA reporting requirement for chemical carcinogens used in products under the OSHA Hazard Communication Standard (29 CFR 1910.1200). Such information should be published in the Safety Data Sheets.
It is estimated that nearly 1.37 million workers are exposed to benzene at work. The OSHA IMIS database showed 304 personal and area samples were collected and analyzed. The air sample
22 Occupational Health & Safety | OCTOBER 2022
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