Hazard and Risk Assessment
What the candidate must know
Risk assessment combines hazard (the inherent danger) with exposure potential (time, distance, shielding) to produce a risk decision. Candidates must understand the routes of exposure (inhalation, absorption, ingestion, injection), toxicology basics (IDLH, TLV/TWA, STEL, PEL), physical hazards (flammability range, flash point, vapor density, vapor pressure, reactivity, BLEVE potential), and the behavior of releases (liquids pooling, vapors traveling, gases settling or rising). Know the difference between isolation and protective action distance, and how to read ERG guide tables and the green pages for initial isolation and protective action zones.
Traps in questions
- Confusing flash point with ignition temperature; a low flash point means ignitable at low ambient temperatures.
- Assuming all vapors rise; vapors heavier than air accumulate in low areas and travel.
- Treating IDLH as a permissible exposure limit; it is an escape-only threshold.
- Forgetting that risk assessment is continuous and changes as the incident evolves.
Rule of thumb
Establish initial isolation and protective action distances from the ERG first, then refine with monitoring and product-specific data. If the product is unknown, use the most conservative guide and distances.
Worked example
A tanker leaking a flammable liquid with a flash point below ambient temperature: the vapor may be within its flammable range near the pool. Set up exclusion zones upwind and uphill, eliminate ignition sources, and use monitoring to confirm the extent of the flammable atmosphere before allowing entry.