Occupational Health, Hygiene and Industrial Toxicology
Domain 6 tests exposure assessment and the health logic behind controls: which agents cause which occupational diseases, and how exposure limits are applied.
Exposure and dose
- Route matters: inhalation, skin absorption, ingestion, injection. Skin absorption defeats respiratory protection.
- Compare measured exposure with the occupational exposure limit (OEL), usually an 8-hour time-weighted average (TWA), plus short-term (STEL) and ceiling values for irritants and fast-acting agents.
- Dose-response means harm depends on concentration and duration, so a TWA is calculated from partial-period samples: TWA = sum of (C x T) divided by 8.
- The sampling strategy must cover the highest-risk task, the most exposed worker and a representative number of samples. One convenient sample is not an exposure assessment.
Health effects you must recognise
Silica and coal dust cause silicosis and coal workers' pneumoconiosis; asbestos causes asbestosis and mesothelioma; noise causes noise-induced hearing loss; hand-arm vibration causes HAVS; lead and mercury affect neurological and renal function; organic solvents damage the CNS and peripheral nerves; isocyanates cause asthma. Health surveillance (pre-placement, periodic, exit) links exposure to early detection, and biological monitoring measures internal dose.
Worked example
A worker is exposed to respirable crystalline silica at 0.10 mg/m3 for 4 hours and 0.03 mg/m3 for 4 hours. TWA = (0.10 x 4 + 0.03 x 4) / 8 = 0.065 mg/m3. Compare with the applicable OEL and its averaging period. If exceeded, apply local exhaust ventilation and wet methods before relying on respirators, and enrol the worker in periodic health surveillance.
Traps
Comparing a peak reading with a TWA limit; assuming smell or absence of symptoms means safe exposure; treating PPE as the primary control; ignoring skin absorption; single samples; forgetting non-routine tasks.