Portable Fire Extinguishers: Classes of Fire, Types, Correct Use and Maintenance

Fire Doesn't Come in One Flavour, and Neither Do Extinguishers

Using the wrong extinguisher on the wrong class of fire doesn't just fail to put it out — on an electrical or cooking-oil fire, it can actively make things worse. Knowing the classes and matching the right agent to each isn't a certification-only skill; it's the difference between a fire that goes out in seconds and one that spreads because the wrong agent bought it more fuel or a conductive path.

Classes of Fire

• Class A — ordinary solid combustibles: wood, paper, textiles, most general shipboard rubbish. Leaves glowing embers.
• Class B — flammable liquids: oils, paints, solvents, fuels.
• Class C — flammable gases: propane, acetylene, and similar. Extremely dangerous to fight directly — the priority is isolating the gas supply, not just extinguishing the flame, since gas can continue escaping and re-ignite or explode.
• Class D — burning metals: magnesium, titanium, and similar. Rare aboard most vessels but relevant in machinery spaces with certain alloys. Requires specialist Class D powder — nothing else is safe to use.
• Class F (UK/EU classification; Class K in the US) — cooking oils and fats. Common in galleys. Needs wet chemical agent specifically — water or a standard extinguisher on a hot fat fire causes a violent, boiling explosion of burning oil.
• Electrical fires — not a separate lettered class under the UK/EU system, but a critical practical category. Water and foam conduct electricity and must never be used on a live electrical fire. Isolate the power supply first if it's safe to do so.

Matching Extinguisher to Fire

• Water — Class A only. Never on B, C, D, F, or electrical fires.
• Foam — Class A and B. Not for C, D, F, or electrical (foam is water-based and conductive).
• CO2 (Carbon Dioxide) — Class B and electrical fires specifically, because it leaves no residue and doesn't conduct electricity. Not effective on Class A deep-seated fires (no cooling effect) and not for Class D.
• Dry Powder — the most versatile for A, B, and C, and specialist Class D powder exists separately for metal fires. Not recommended in enclosed accommodation spaces (breathing hazard, and it doesn't cool the fire effectively for a deep-seated Class A re-ignition risk).
• Wet Chemical — Class F specifically. Designed to cool the oil below its ignition point and form a soapy barrier film across the surface (saponification), preventing re-ignition.