Occupational Health and Ergonomics
Content
This domain blends industrial hygiene, occupational medicine, and ergonomics. Expect exposure assessment, noise, heat, vibration, and musculoskeletal risk.
Noise. OSHA's permissible exposure limit is 90 dBA as an 8-hour TWA with a 5 dB exchange rate; a hearing conservation program is required at the 85 dBA action level. ACGIH uses 85 dBA with a 3 dB exchange rate, so ACGIH is more protective at high levels. A dose of 100 percent equals the PEL.
Heat and vibration. Use WBGT for heat stress, adjusting for acclimatization, metabolic rate, and clothing. Hand-arm vibration is time-weighted; tools are rated in m/s2 and compared to an 8-hour A(8) exposure.
Ergonomics. The NIOSH lifting equation computes a recommended weight limit from a load constant plus horizontal, vertical, distance, asymmetry, frequency, and coupling multipliers; the lifting index is load divided by RWL, and values above 1.0 signal increasing risk. Know anthropometry, work-rest cycles, and the MSD risk factors: force, repetition, posture, vibration, and contact stress. Participatory ergonomics improves both fit and buy-in.
Traps. Applying the 90 dBA PEL when the question asks about the action level; forgetting that a 3 dB exchange rate halves allowable time every 3 dB; confusing a TLV with a PEL; and treating one air sample as a full-shift exposure.
Worked example
A worker spends 4 hours at 95 dBA. Allowable time at 95 dBA under OSHA = 8 / 2^((95-90)/5) = 4 hours. Dose = 4/4 x 100 = 100 percent - exactly at the PEL, with no margin.