Fire Extinguisher Calculator

BS 5306-8:2023 sizes Class A provision per storey: the required aggregate Class A rating of a storey = 0.065 × its floor area in m², rounded up, subject to a minimum aggregate of 26A. A 400 m² storey therefore needs 26A (400 × 0.065). Provide enough extinguishers of the chosen type for their combined rating to meet that figure — a 13A water or foam unit covers about 200 m² (13 ÷ 0.065), a 21A unit about 323 m². Each storey over 50 m² needs at least two extinguishers; a single high-rated unit is allowed on a storey of 50 m² or less. Add CO2 near electrical equipment and wet chemical for kitchens. A fire risk assessment determines the final provision.

Offices typically need water or foam AFFF extinguishers as the primary Class A provision (for paper, wood and general combustibles), plus CO2 extinguishers near electrical equipment such as server rooms, switch rooms and areas with significant IT equipment. Foam AFFF is often preferred as a versatile choice — it covers Class A and B and is safe near (but not on) electrical equipment. Water mist extinguishers are another option that is safe on electrical equipment.

Commercial kitchens require wet chemical fire extinguishers (yellow label) for Class F fires involving cooking oils and fats. A wet chemical extinguisher is designed to cool and emulsify burning cooking oil, preventing re-ignition. Water, foam and CO2 extinguishers must NOT be used on deep fat fryer fires. A 6-litre wet chemical extinguisher should be positioned within 2m of the cooking appliance. A fire blanket to BS EN 1869 is also recommended.

BS 5306-3 requires annual servicing by a competent engineer (typically a BAFE registered company). Monthly visual checks should be carried out by the building responsible person — confirming extinguishers are in position, not obstructed, seals intact and pressure gauge in green zone. Extended service intervals apply: CO2 every 10 years, water/foam every 5 years (refurbishment or replacement). Out-of-date extinguishers must be replaced or refurbished.

BS 5306-8 specifies a maximum travel distance of 30 metres to the nearest Class A (water/foam) extinguisher. For special risks the limit is shorter: 10 metres to a Class B extinguisher and 10 metres to an extinguisher suitable for electrical equipment risk. This means a person should not have to walk more than 30 m to reach a general Class A extinguisher, or more than 10 m to reach cover for a flammable-liquid or electrical risk. Extinguishers should be positioned on escape routes, near exits and at fire points.