Fire Triangle vs Fire Tetrahedron
The classic fire triangle (fuel, heat, oxygen) explains ignition. The tetrahedron adds the chain reaction as a fourth side — relevant because some extinguishing agents (Halon, dry powder, clean agents) work by interrupting the chain reaction, not simply by cooling or smothering. An examiner may probe which agent acts on which side.
Classes of Fire
| Class | Type | Primary agent |
|---|---|---|
| A | Solid combustibles (wood, fabric) | Water, foam |
| B | Flammable liquids | Foam, CO₂, dry powder |
| C | Flammable gases | Dry powder; isolate supply |
| D | Combustible metals | Specialist dry powder |
| F | Cooking oils/fats | Wet chemical |
Electrical fires have no letter class — they are a Class A, B or C fire that involves live equipment. The correct response is to de-energise first, then treat the underlying class. Water and foam must not be used on live electrical equipment.
Fixed vs Portable Appliances
Fixed systems protect defined spaces automatically or by remote release: CO₂ or clean-agent systems for engine rooms and paint lockers; wet or dry sprinkler systems for accommodation. They are designed to flood a volume — personnel must be clear before activation.
Portable extinguishers are for incipient (early-stage) fires where a crew member can attack safely. Selecting the wrong extinguisher (e.g. water on a Class B fire) can spread burning liquid and worsen the situation.
Hose reels and hydrants are the backbone of a firefighting attack on a developed fire and are fed from the fire main, which must be pressurised as early as possible in any structural fire response.
Fire and Safety Plans
Under SOLAS, vessels must carry permanently exhibited fire control plans showing:
- Fire sections and fire/smoke-tight boundaries
- Locations of all firefighting appliances, detectors and alarms
- Means of control for ventilation, fuel and electrical systems
- Escape routes
A duplicate set must be stored in a weathertight container outside the deckhouse for use by shore-based fire brigades. Plans must be kept up to date whenever structural or equipment changes are made.
Fire Prevention Focus Areas
- Engine room bilges free of oil accumulation
- Hot-work permits and fire watch procedures
- Correct storage of flammable materials (paint stores ventilated, away from ignition sources)
- Galley exhaust trunking regularly degreased
- Electrical systems — no overloaded circuits, no unapproved modifications
Prevention is always the primary control; detection and suppression are secondary lines of defence.