Element 10: Fire

10.1 Fire principles

Fire needs three things: a source of ignition (heat), fuel and oxygen. This is the fire triangle. In a workplace, ignition sources include electrical equipment, hot work, smoking and friction; fuel includes paper, wood, flammable liquids and gases; oxygen is in the air, and oxidising materials can supply extra oxygen.

Classification of fires depends on the fuel (different local classifications are accepted).

A widely used system of fire classes:

• Class A: ordinary solids such as wood and paper.
• Class B: flammable liquids.
• Class C: gases.
• Class D: metals.
• A class for cooking oils and fats (Class F in some countries, K in others).

Local systems differ: for example, in some countries Class C means electrical fires, so always use the system taught in your own country. Fires involving electrical equipment are treated by cutting the supply, then the fire is handled according to the material burning.

Heat is transmitted by:

• Convection (hot gases rising).
• Conduction (through solids).
• Radiation (heat waves).
• Direct burning (flames touching material).

Common causes of fire: electrical faults, arson, careless smoking, hot work, poor housekeeping, and heating equipment. Consequences include death and injury, damage to property, loss of business and environmental harm.

Key terms

• Fire triangle: Ignition, fuel and oxygen: the three things a fire needs.

Study tip: Controls work by removing one side of the triangle.

Practice questions for 10.1

10.2 Preventing fire and fire spread

To reduce the chance of a fire starting:

• Eliminate or reduce the quantities of flammable and combustible materials used or stored
• Control ignition sources (including using suitable electrical equipment in flammable atmospheres)
• Use safe systems of work (for example permits for hot work)
• Keep a good standard of housekeeping

Flammable liquids should be stored in the smallest practical quantities, in closed containers, in a designated safe location or fire-resisting cabinet away from ignition sources, and only small amounts in workrooms.

Structural measures slow the spread of fire and smoke: building materials with fire resistance (including fire doors), compartmentation (dividing a building into fire-resisting sections), and protecting openings and voids such as ducts and shafts.

Study tip: Compartmentation buys time for people to escape.

Practice questions for 10.2

10.3 Fire alarms and fire-fighting

Detection and alarm systems: manual call points, smoke detectors, heat detectors and sounders (and in some places voice systems and links to emergency services). Systems must be maintained and tested regularly.

Portable fire-fighting equipment must be suitable for the fire risk, sited where people can find it (for example near exits), maintained, and used by trained people.

Extinguishing media:

• Water: cools; for class A fires; not for electrical or liquid fires.
• Foam: liquids and solids.
• Dry powder: liquids, gases and some metals.
• Carbon dioxide: electrical and liquid fires, leaves no residue but gives little cooling.
• Wet chemical: cooking oil and fat fires.

Each has advantages and limitations, so the choice depends on the type of fire.

Access for fire and rescue services and vehicles must be planned and kept clear.

Study tip: Never choose water for a flammable liquid or live electrical fire.

Practice questions for 10.3

10.4 Fire evacuation

Means of escape: sufficient exits, with limits on the travel distance to a safe place; suitable stairs, passageways and doors; emergency lighting; clear exit and directional signs; and assembly points outside the building.

An emergency evacuation procedure sets out the alarm, who does what, how people reach the assembly point and how everyone is accounted for. Fire marshals (or wardens) are appointed and trained to check areas, help people to leave and report to the person in charge.

Drills test the procedure, and a roll call checks that everyone is accounted for.

Provisions for people with disabilities, for example personal emergency evacuation plans, refuges and evacuation aids. Escape routes should be recorded in building plans.

Study tip: Escape routes must be kept clear, unlocked and well lit at all times.

Practice questions for 10.4