Occupational Health, Hygiene, and Ergonomics
Core Concepts
Occupational hygiene follows a recognition, evaluation, control sequence. Recognize agents (chemical, physical, biological, ergonomic, psychosocial), evaluate exposure through sampling and comparison with occupational exposure limits, then control.
Understand exposure limits: time-weighted averages (TWA) over a shift or week, short-term exposure limits (STEL) for brief peaks, and ceiling limits that must never be exceeded. Questions test whether a measured concentration is compared to the right limit for the right duration. Also know that skin absorption can make airborne limits insufficient protection.
Sampling concepts: personal versus area sampling, representative sampling, detection limits, and the difference between a single sample and a full-shift assessment. Controls follow the hierarchy; local exhaust ventilation is an engineering control and must be designed, not improvised.
Ergonomics addresses musculoskeletal risk: force, repetition, posture, vibration, and recovery time. Assess tasks using recognized methods and prioritize redesign over training. Health surveillance - audiometry for noise, spirometry for respiratory hazards - detects early effects; it is not a substitute for control.
Traps
- Comparing a 15-minute peak sample to an 8-hour TWA.
- Assuming a substance with a ceiling limit is safe below the TWA.
- Treating health surveillance as a control measure.
- Ignoring combined exposures (noise plus ototoxic chemicals).
- Relying on PPE when ventilation could remove the contaminant at source.
Worked Example
A solvent measured at 40 ppm over 20 minutes, with an 8-hour TWA limit of 50 ppm and a STEL of 25 ppm. The correct conclusion: the STEL is exceeded, so the exposure is unacceptable despite the TWA appearing acceptable.