Occupational Health, Industrial Hygiene and Exposure Control
Occupational Health, Industrial Hygiene, and Exposure Control
This domain tests the classic industrial hygiene sequence: anticipate, recognize, evaluate, and control. Numerical exposure questions are common.
Core rules
- Occupational exposure limits include OSHA PELs (legally enforceable), NIOSH RELs (health-based recommendations), and ACGIH TLVs (consensus guidance). The most protective applicable limit should drive design, even when only the PEL is enforceable.
- Evaluation requires representative sampling of the worker's exposure, not a single grab sample. An 8-hour time-weighted average is calculated as the sum of concentration times time, divided by 8.
- Controls follow the hierarchy: eliminate or substitute the agent, engineer ventilation or enclosure, then administrative controls, then PPE such as respirators under 1910.134.
- Noise: the OSHA action level is 85 dBA as an 8-hour TWA; the PEL is 90 dBA. Hearing conservation includes monitoring, audiometric testing, training, and hearing protection. OSHA uses a 5 dB exchange rate; NIOSH uses 3 dB.
- Medical surveillance and biological monitoring may be required for specific agents such as lead, silica, and asbestos.
Worked example
A worker is exposed to 30 ppm of a solvent for 6 hours and 90 ppm for 2 hours. TWA = [(30 x 6) + (90 x 2)] / 8 = (180 + 180) / 8 = 45 ppm. The 8-hour PEL of 50 ppm is not exceeded. However, if the substance has a 15-minute STEL of 75 ppm, the 90 ppm period may still be a violation. The reasoning: compliance is evaluated against both the 8-hour TWA and any short-term limit, not the average alone.
Traps
- Averaging concentrations without weighting by time.
- Treating a PEL as a safe level rather than a legal minimum.
- Selecting a respirator before evaluating engineering controls.
- Ignoring dermal exposure and ingestion routes.