Occupational Health and Industrial Hygiene
Industrial hygiene questions follow a fixed sequence: anticipate, recognize, evaluate, control. The exam tests whether you can name the agent and route of entry, choose a defensible exposure limit, design sampling that represents real exposure, and select controls that hold exposure below the limit.
Exposure limits you must distinguish
- OSHA PELs are legally enforceable, mostly 8-hour time-weighted averages, with some ceiling and peak limits.
- NIOSH RELs are health-based recommendations, often stricter.
- ACGIH TLVs are consensus values updated annually; they are not law but are strong evidence of a recognized hazard.
- Forms: 8-hour TWA, 15-minute STEL, and ceiling values that must never be exceeded.
Sampling strategy
Personal breathing-zone samples represent what the worker inhales; area samples only characterize a source. Group similar jobs into homogeneous exposure groups, sample the worst case and a representative share of the group, cover the full shift, and use accredited labs with field blanks and chain of custody. Compare results to the limit after accounting for sampling and analytical error and for shifts longer than eight hours.
Worked example: noise dose
A worker is exposed to 95 dBA for four hours; the rest of the shift is quiet. Under the OSHA 5-dB exchange rate, allowable time T = 8 / 2^((95-90)/5) = 8 / 2 = 4 hours. Dose = (4 / 4) x 100 = 100 percent, exactly at the PEL. The action level of 85 dBA TWA is already exceeded, so a hearing conservation program with audiometric testing is required. At 100 dBA, allowable time halves again to two hours.
Agent categories to recognize
Inhalation, skin absorption, ingestion, and injection. Common exam agents include respirable crystalline silica, lead, solvents, hydrogen sulfide, asbestos, isocyanates, plus physical and ergonomic stressors and heat stress measured by WBGT.
Traps that cost marks
- Citing an ACGIH TLV as though it were an OSHA requirement.
- Applying the 3-dB exchange rate inside OSHA's 5-dB noise formula.
- Defending personal exposure with an area sample.
- Treating odor as a reliable warning property for hydrogen sulfide.
- Forgetting skin absorption and ingestion routes when the agent has a skin notation.