Health, Safety and Environmental Protection
Scope
This domain tests the hierarchy of control, exposure assessment, effluent and emission control, and environmental impact thinking. It asks whether you can protect people and the environment by design, not by slogans.
Core rules
- Hierarchy of control: eliminate, substitute, engineer controls such as enclosure, local exhaust, and guarding, then administrative controls, then PPE. PPE is the last line and is least reliable.
- Exposure assessment compares measured or predicted concentration with the relevant occupational exposure limit, averaged over the correct reference period: 8-hour time-weighted average versus short-term exposure limit.
- Convert ppm and mg/m3 using molecular weight and molar volume. At 25 C and 1 atm, 1 mol occupies about 24.5 L; check the reference conditions used by the limit.
- Dilution ventilation by mass balance: for a steady release G and target concentration C, airflow Q = G/C under perfect mixing. Real mixing needs a safety factor and local exhaust at source.
- Effluent control: segregate, treat at source, equalise, neutralise, and monitor. Do not dilute to comply.
- Waste hierarchy: prevent, reduce, reuse, recycle, recover, dispose. Environmental impact assessment considers air, water, noise, ecology, and cumulative effects.
Worked example
A solvent evaporates at G = 0.02 kg/s in a room. The target concentration is 50 mg/m3 = 5 x 10^-5 kg/m3. Perfect-mixing dilution gives Q = 0.02 / (5 x 10^-5) = 400 m3/s, an absurd building airflow. This shows why dilution ventilation alone cannot control solvent release. A local exhaust hood capturing 90% reduces the released G to 0.002 kg/s and still needs 40 m3/s if fully mixed. Capture at source and substitution are the real controls. The calculation is a screening tool, not a design.
Traps
- Using an 8-hour TWA for a short-term peak exposure.
- Treating a local exhaust hood as effective without capture velocity and face velocity checks.
- Ignoring fugitive emissions from flanges, seals, and sampling points.
- Assuming dilution is environmental control. It often just moves the problem.
Noise, vibration, and thermal stress are also health hazards. A HSE review that covers only chemicals is incomplete.