FPFF-L1.1

The chemistry of fire and classes of fire

Fighting fire well starts with understanding it, because the way to put a fire out follows directly from what fire needs to burn. This lesson covers the chemistry of fire and the classes of fire.

Entry & progression

Certificate: STCW Fire Prevention and Fire Fighting (A-VI/1-2) — one of the four STCW basic safety elements. It teaches every seafarer to prevent fire and to fight it in its early stages as part of a team. Entry: none. Progresses to Advanced Fire Fighting (A-VI/3) for those who will control operations. Revalidation: refresher training required, typically every 5 years.

The fire triangle and tetrahedron

The fire triangle

Fire needs three things — heat, fuel and oxygen, the fire triangle — plus a self-sustaining chemical chain reaction, which makes the fire tetrahedron. Remove any one and the fire goes out: cooling removes heat (as water does), starving removes fuel, smothering removes oxygen (as a fire blanket or CO2 does), and some agents interrupt the chain reaction chemically. Understanding this tells you why a given extinguisher works and why the wrong one can be useless or dangerous.

Class Fuel Suitable media
A Solids: wood, paper, textiles Water, foam
B Flammable liquids: fuel, oil Foam, CO2, dry powder
C Gases Dry powder, isolate the supply
D Metals Special dry powder only
F (K) Cooking oils and fats Wet chemical
The classes of fire and the media that suit them.

WARNING — The wrong medium can be deadly Never use water on a burning liquid or on live electrical equipment: water spreads a liquid fire and conducts electricity back to the firefighter. Match the medium to the class of fire — this is the single most important firefighting judgement.

NOTE — Electrical fires: cut the power first Fire in electrical equipment is fought by first isolating the power, then using a non-conductive medium such as CO2 or dry powder. Once the power is off, it becomes a fire of whatever is burning.

Practice questions

5 questions
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The fire triangle consists of heat, fuel and: (a) Water (b) Oxygen (c) Smoke (d) Foam

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Water should never be used on: (a) Class A fires (b) A burning liquid or live electrical equipment (c) Wood fires (d) Paper fires

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A Class F (kitchen) fire of cooking oil is best tackled with: (a) Water (b) Wet chemical extinguisher (c) A fan (d) More oil

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Smothering a fire removes the: (a) Heat (b) Fuel (c) Oxygen (d) Chain reaction only

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An electrical fire is fought by first: (a) Adding water (b) Isolating the power, then using a non-conductive medium (c) Fanning it (d) Ignoring it

AI-drafted training content pending subject-matter-expert review. Figures indicative; verify against current provider materials.

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