CO2 Fire Extinguisher

How Does a CO2 Extinguisher Work?

Carbon dioxide is stored as a liquid under pressure inside the extinguisher cylinder. When the operating lever is depressed, CO2 is released through a discharge horn, where it immediately expands and converts to gas. This rapid expansion also creates a significant cooling effect (the horn becomes extremely cold — never hold the horn directly).

The CO2 gas displaces oxygen around the fire, breaking the combustion triangle. Because it leaves no residue — unlike powder or foam extinguishers — it is ideal for protecting electronic equipment, server rooms, commercial kitchens (for electrical fires only), and any environment where contamination would cause secondary damage.

Which Fires Can CO2 Extinguishers Be Used On?

• Class B fires — flammable liquids such as petrol, oils (excluding cooking oils), paint, and solvents
• Electrical fires — CO2 is non-conductive and safe for live electrical equipment (up to 1,000 V according to BS EN 3)

CO2 extinguishers are not suitable for Class A fires (ordinary combustibles like wood and paper — CO2 does not cool the material sufficiently to prevent re-ignition), Class F fires (cooking oils — risk of hot oil splatter), or use in confined spaces (risk of oxygen depletion for the user).

Where Are CO2 Extinguishers Used?

CO2 extinguishers are the standard choice for:

• Server rooms and data centres
• Electrical switchgear rooms and transformer areas
• Office environments where computer equipment is present
• Workshops and laboratories where flammable solvents are used
• Locations where a dry powder extinguisher would cause unacceptable damage to equipment

Under BS 5306-8, CO2 extinguishers should generally be provided alongside a water or foam extinguisher in offices and commercial premises, since CO2 alone is not effective on Class A materials which make up the majority of office combustibles.

Colour Coding and Identification

Under BS EN 3 and the UK's colour coding scheme (BS 7863:1996), CO2 extinguishers are identified by a black label panel on a red body. This replaced the older all-black body that was used before 1997. Never use a fire extinguisher unless you have confirmed it is the correct type for the fire — check the label and colour coding.

Maintenance and Servicing Requirements

Under BS 5306-3:2017, CO2 extinguishers require:

• Annual basic service — visual inspection, weight check, label check, and seal inspection
• Extended service at 5 years — full internal inspection of the valve and body
• Hydraulic pressure test (discharge test) at 10 years — the cylinder is tested to 1.5× working pressure
• Replacement or retest as required after any use or significant damage

Servicing must be carried out by a competent person as defined in BS 5306-3. The BFC EAL Level 3 Fire Extinguisher qualification is the recognised standard for competence in extinguisher maintenance across all extinguisher types, including CO2.