Benzene Exposure Assessment at a Petroleum Terminal

Sum the 12 samples: 0.6+0.9+1.2+0.8+1.5+0.4+0.7+1.1+0.9+0.5+1.3+0.6 = 10.5 ppm. The arithmetic mean is 10.5/12 = 0.875 ppm. Sorted values are 0.4, 0.5, 0.6, 0.6, 0.7, 0.8, 0.9, 0.9, 1.1, 1.2, 1.3, 1.5; the median is (0.8+0.9)/2 = 0.85 ppm. Three of 12 samples exceed the OSHA PEL of 1 ppm (1.2, 1.3, 1.5), so the mean is below the PEL but individual exposures are not compliant. All 12 exceed the NIOSH REL of 0.1 ppm, and 11 of 12 exceed the ACGIH TLV of 0.5 ppm. The 20-minute tank-cleaning sample of 8 ppm exceeds the OSHA STEL of 5 ppm and the ACGIH STEL of 2.5 ppm. Compliance and risk are different questions: the OSHA PEL is a legal minimum, while the TLV and REL reflect lower health-based targets. Benzene is a known human leukemogen, and no threshold has been established, so a mean below 1 ppm does not mean the group is safe. The action level of 0.5 ppm is also exceeded, which triggers exposure monitoring and medical surveillance obligations.

Air sampling alone underestimates total dose because benzene is volatile and can penetrate skin, especially with liquid contact during tank cleaning, spills, or glove failure. Nitrile gloves have finite breakthrough times, and cotton coveralls are not chemical-protective; the lack of a dermal assessment is a gap. Mixed exposure to other petroleum hydrocarbons can add CNS effects and confound symptoms such as headache and dizziness. For medical surveillance under the OSHA benzene standard, the action level of 0.5 ppm as an 8-hour TWA triggers offering surveillance to employees exposed above that level for more than 30 days per year; exposure above the PEL also triggers it. Surveillance includes a history, physical examination, and CBC with platelet count. The worker with platelets of 110,000/µL is below the normal range and needs prompt hematology evaluation and removal from further benzene exposure pending assessment; the 145,000/µL value is borderline and should be repeated. A single low platelet count is not diagnostic of benzene-induced toxicity, but it is a sentinel finding. Record the sampling method, detection limit, and whether samples were representative; spot samples may miss peak tasks.

First, stop the uncontrolled tank-cleaning exposure and require supplied-air respiratory protection, not air-purifying respirators, until engineering controls are in place. Substitute or enclose the benzene-containing process where possible; use local exhaust ventilation, closed-transfer systems, and vapor recovery. Implement a written respiratory protection program, skin protection with appropriate chemical-resistant gloves and suits, and decontamination. Repeat personal breathing-zone sampling with task-based sampling to characterize peaks, and add dermal and biological monitoring as appropriate. Because the OSHA PEL is exceeded, the employer must implement a regulated area, exposure monitoring, medical surveillance, and training under the benzene standard. The worker with platelets of 110,000/µL should be removed from benzene exposure and referred for evaluation; the decision should not wait for a repeat air sample. The worker with 145,000/µL should be rechecked and monitored. Do not rely on symptoms alone, because headache and dizziness are nonspecific. The goal is not merely to get the mean below 1 ppm but to reduce exposure as low as reasonably achievable, given the carcinogenicity and the lower TLV and REL.