Industrial hygiene
Industrial hygiene questions on the CSMP exam test the classical sequence-anticipate, recognize, evaluate, control-and the quantitative judgment behind exposure decisions. You must know how occupational exposure limits differ and how sampling results are averaged.
Core rules and concepts
- OSHA PELs are legally enforceable; ACGIH TLVs and NIOSH RELs are health-based guidance unless adopted by a state plan or contract.
- Compare full-shift exposures as 8-hour time-weighted averages (TWA); STELs are 15-minute averages, and ceiling limits are never to be exceeded.
- Noise: the OSHA action level is 85 dBA as an 8-hour TWA, triggering hearing conservation; the PEL is 90 dBA. A 5-dB exchange rate doubles permitted exposure time under OSHA.
- Respiratory protection follows 29 CFR 1910.134: fit testing, medical evaluation, training, and assigned protection factors.
- Control at the source with ventilation or substitution before relying on PPE.
Worked example
A worker is sampled for solvent vapor: 4 hours at 80 ppm and 4 hours at 20 ppm. The 8-hour TWA is [(80 × 4) + (20 × 4)] ÷ 8 = (320 + 80) ÷ 8 = 50 ppm. If the substance has an 8-hour PEL of 50 ppm, the exposure is at the limit, not comfortably below it. A single short sample cannot be compared directly with an 8-hour PEL unless it represents the full shift.
Traps that cost marks
Averaging a 15-minute STEL result over 8 hours understates peak risk. Treating a TLV as a legal limit is wrong. Ignoring calibration and sampling uncertainty, or assuming a respirator protects without a fit test, are common losses.