Hazardous Materials and Special Fire Risks
What the exam tests
Hazardous Materials and Special Fire Risks tests recognition, isolation, PPE, decontamination and agent selection for chemicals, gases, flammable liquids and special risks such as BLEVE, dust explosions and confined spaces.
Core rules
- Identify using placards, UN numbers, labels, safety data sheets and the Emergency Response Guidebook. Approach from upwind, uphill and upstream.
- Establish hot, warm and cold zones; only trained, PPE-equipped crews enter the hot zone; decontamination is at the warm-zone boundary.
- Vapour density: gases heavier than air (for example propane and chlorine) collect in low areas; lighter gases (methane and hydrogen) rise and accumulate at roofs.
- Water-reactive materials such as sodium and calcium carbide must not receive water; use dry powder or dry sand.
- BLEVE: a pressurised liquid vessel heated by fire; watch for rising pressure, bulging, torching flame and increasing noise. Cool from protected positions or withdraw.
- Dust explosions need fuel, oxygen, dispersion and ignition; secondary explosions are often more destructive.
Worked example
A leaking chlorine cylinder (vapour density about 2.5) is in a basement. Chlorine is heavier than air, so it will collect at low level. Establish exclusion zones at low level, keep out of basements, use positive-pressure BA and do not use water spray to "push" the gas unless trained and authorised. Reasoning: vapour density predicts where the gas goes, and that dictates your position and PPE.
Traps
Approaching from downwind; using water on water-reactive chemicals; entering without BA; treating a BLEVE vessel as stable; forgetting decontamination.