Hazard and Risk Assessment
Hazard and Risk Assessment
Hazard assessment identifies what can hurt you; risk assessment judges how likely and how severe that harm is under the actual conditions. The exam tests systematic reasoning, not just chemical recognition.
Core rules
- Separate hazard from risk. A large chlorine inventory is a hazard; the risk depends on release size, wind, population, confinement, and exposure time.
- Assess likelihood and severity together. Consider concentration, duration, dose, exposure routes, PPE performance, terrain, weather, and vulnerable populations.
- Use ERG protective action distances as an initial planning tool, then adjust with monitoring, plume modeling, and site-specific data.
- Consider environmental risk: drains, waterways, soil, air, and sensitive receptors.
- Document assumptions and action levels. Reassess when conditions change.
- Risk-benefit decisions must be justified; do not accept unnecessary risk for a low-value objective.
Worked example
Two incidents involve acetone. One is a small spill in a ventilated laboratory; the other is a railcar leak near a school. Acetone is flammable, so both have ignition and vapor hazards. In the lab, the volume, ventilation, and ignition control may keep risk low enough for a small, trained response. At the railcar, the larger inventory, public exposure, vapor travel, and ignition range raise severity and uncertainty. The second incident demands wider isolation, monitoring, foam or vapor suppression as appropriate, and a higher level of PPE until the product and conditions are confirmed.
Traps
- Calling every chemical incident 'high risk' without exposure analysis.
- Using worst-case assumptions only, or best-case only.
- Ignoring weather, terrain, and drains.
- Treating ERG distances as exact site-specific answers.
- Forgetting that risk changes as the incident evolves.