Fire Safety
Fire safety questions are practical: the fire triangle, extinguisher classes and selection, PASS technique, detection and alarm, and evacuation. Marks are lost by mixing up which extinguisher suits which fire.
The science
Fire needs fuel, heat and oxygen; removing any one breaks the triangle. The fourth element in the chain reaction is chemical, which is why clean agents work.
Classes and extinguishers
- Class A - solids such as wood, paper, cloth: water or ABC dry powder.
- Class B - flammable liquids such as petrol, paint, oil: foam, dry powder, CO2.
- Class C - flammable gases: isolate the supply and use dry powder.
- Class D - combustible metals such as magnesium: special dry powder only; never water.
- Electrical fires - CO2 or dry powder; isolate the power first. Never water.
- Class K / cooking oil - wet chemical extinguisher; water causes violent spitting.
PASS technique
Pull the pin, Aim at the base of the fire, Squeeze the handle, Sweep side to side. Keep a safe distance, stay on the windward side, and back away if the fire grows rather than deepens.
Detection, alarm and evacuation
Smoke and heat detectors feed an alarm panel; call points (MCPs) allow manual raising of the alarm. On alarm: raise the alarm, inform the fire brigade (101) and internal fire officer, switch off power if safe, use the nearest safe exit, never use lifts, and assemble at the designated assembly point for roll call.
Worked example. An electrical panel smoulders and sparks. Reasoning: the fuel is live electrical equipment, so water would conduct and endanger the user. Correct action: isolate the supply at the nearest breaker if safe, then use CO2 or dry powder on the base, raise the alarm and evacuate if it spreads.
Traps
- Water on electrical or oil fires.
- Storing the extinguisher behind the door it protects.
- Forgetting that extinguishers need periodic inspection and refill, so a gauge in the red means out of service.