TL;DR
CO2 extinguishers are the go-to choice for electrical hazards and server rooms, leaving no residue behind, while foam extinguishers are better suited to Class A and B fires involving solid materials and flammable liquids. The right choice depends on your building’s specific fire risk profile, the types of hazards present, and your compliance obligations under UK fire safety legislation. A competent fire safety professional can advise which type, or combination, is appropriate for your premises.
Key Takeaways
- CO2 extinguishers work by displacing oxygen and are rated for Class B fires and electrical hazards, while foam extinguishers are effective on Class A and Class B fires but must never be used on live electrical equipment.
- Foam extinguishers leave a residue that can aid in preventing re-ignition of flammable liquids, whereas CO2 extinguishers discharge cleanly with no damaging mess, making them ideal for sensitive equipment.
- Both types must be supplied, installed, and maintained in accordance with BS 5306-3, the British Standard covering the commissioning and maintenance of portable fire extinguishers.
- CO2 extinguishers typically require less frequent internal inspection but must be checked and weighed regularly to confirm charge integrity, while foam extinguishers require annual servicing and an extended service every five years.
- Under the Regulatory Reform (Fire Safety) Order 2005, responsible persons must ensure the correct type, number, and placement of extinguishers is identified through a suitable fire risk assessment.
Contents
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What is a CO2 Extinguisher?
A CO2 (carbon dioxide) extinguisher works by smothering a fire, displacing the oxygen that flames need to sustain combustion. Stored as a liquid under high pressure, the CO2 converts to a gas upon discharge, rapidly cooling and suffocating the fire at its source. Because it leaves absolutely no residue, it is particularly well suited to environments where damage to equipment or contamination of a workspace would be a serious concern, including server rooms, electrical switchgear areas, and office environments with sensitive electronics.
CO2 extinguishers are rated for Class B fires (flammable liquids such as petrol and oils) and for use on live electrical equipment, though it is worth noting they offer no cooling effect on Class A materials such as wood or paper. They are identified by a black label in line with BS EN 3 colour-coding requirements. If your premises also present risks from solid combustibles, you may need to consider a mixed provision alongside your CO2 units. For a broader view of how CO2 compares to other agent types, the guide on CO2 Extinguisher vs Water Mist Extinguisher, Which is Right for You? offers useful additional context.
What is a Foam Extinguisher?
Foam extinguishers, typically identified by a cream-coloured label under BS EN 3, work through a dual mechanism. The foam forms a blanket over the surface of a burning liquid, sealing off oxygen and preventing re-ignition, while the water content of the solution also provides a cooling effect on the fire. This makes them effective against both Class A fires (wood, paper, textiles) and Class B fires (flammable liquids), giving them broader coverage than a CO2 unit in many general commercial settings.
Foam extinguishers are commonly found in warehouses, retail environments, offices, and hospitality venues where both solid material and liquid fire risks are present. However, they must not be used on live electrical equipment or cooking oil fires. For premises where cooking presents a fire risk, a different agent is required, and the comparison of Wet Chemical Extinguisher vs Foam Extinguisher, Which is Right for You? may help clarify the distinction. Modern AFFF (aqueous film-forming foam) and fluorine-free alternatives are now widely available, with the latter increasingly preferred for environmental compliance reasons.
Head-to-Head Comparison
| Feature | CO2 Extinguisher | Foam Extinguisher |
|---|---|---|
| Mechanism | Displaces oxygen, smothers the fire | Forms a foam blanket, cools and seals the fuel surface |
| Best suited for | Class B fires, live electrical equipment, server rooms | Class A and Class B fires, general commercial and retail settings |
| Cost range | Typically mid to higher range due to high-pressure cylinder construction | Typically lower to mid range; widely available |
| Installation complexity | Low; wall-mounted bracket installation | Low; wall-mounted bracket installation |
| Maintenance | Annual check and weight verification; extended service typically every 5 years | Annual service required; extended internal inspection every 5 years |
| Compliance standards | BS 5306-3, BS EN 3; RRO 2005 | BS 5306-3, BS EN 3; RRO 2005 |
| Typical lifespan | Typically 10 years before replacement is recommended | Typically 5 years for the agent; cylinder up to 25 years with correct servicing |
Costs and specifications vary. Contact London City Fire for a site-specific assessment.
Which is Right for You?
If your premises contain a significant amount of electrical equipment, data infrastructure, or server hardware, a CO2 extinguisher is likely to be an essential part of your fire safety provision. Its clean discharge means that in the event of a fire, the equipment itself stands a much better chance of survival compared to the residue left by foam or powder alternatives. Office environments, data centres, and commercial kitchens with adjacent electrical panels in London frequently rely on CO2 units for exactly this reason.
For general commercial settings where the fire risk includes both combustible materials and flammable liquids, foam extinguishers often provide a more versatile first line of defence. Retail units, warehouses, and mixed-use properties in particular tend to benefit from foam coverage across their floor area. That said, it is worth noting that foam extinguishers are not a universal solution. If you are comparing foam against other agent types such as water, the guide on Water Extinguisher vs Foam Extinguisher, Which is Right for You? can help you evaluate the options in more detail.
In practice, many London properties require a combination of extinguisher types to fully address all identified risks. The appropriate selection, placement, and quantity must be determined through a proper fire risk assessment carried out by a competent person, as required under the Regulatory Reform (Fire Safety) Order 2005. Rather than making this decision based on cost alone, it is advisable to seek professional guidance tailored to your specific building, occupancy type, and hazard profile.
Why Choose London City Fire?
London City Fire has been providing professional fire safety services across the capital for over 20 years. Our team includes IFSM-registered assessors (Institute of Fire Safety Managers) who carry out fire risk assessments in full compliance with the Regulatory Reform (Fire Safety) Order 2005 and the Fire Safety Act 2021. When it comes to fire extinguisher supply and servicing, we ensure that every unit we install or maintain meets the requirements of BS 5306-3, giving responsible persons confidence that their provision is both appropriate and audit-ready. Whether you need a single site visit or ongoing maintenance across a portfolio of London properties, our approach is always tailored to the specific fire risk profile of each building.
We work with a wide range of clients including commercial landlords, property developers, housing associations, retail operators, and hospitality venues. Our local knowledge of London’s diverse building stock, from Victorian conversions to modern mixed-use developments, means we understand the practical challenges that come with achieving compliance in real-world settings. If you are ready to get the right extinguisher provision in place, you can request a Fire Extinguisher Quote or speak directly with our team by calling 0204 572 0661 or emailing info@londoncityfire.co.uk.
Frequently Asked Questions
Q: “Which is cheaper, a CO2 extinguisher or a foam extinguisher?”
A: Foam extinguishers are typically the more affordable option upfront, as CO2 units require high-pressure cylinders that add to the manufacturing cost. However, the right choice should not be driven by purchase price alone. Annual servicing costs, the frequency of replacements, and the cost of fire damage if the wrong agent is deployed should all factor into the decision. Contact London City Fire for a quote based on your specific requirements.
Q: “Can I use a foam extinguisher on electrical equipment?”
A: No. Foam extinguishers must not be used on live electrical equipment due to the risk of electric shock from the conductive liquid content. If your premises contain electrical hazards, CO2 extinguishers are the appropriate choice for those specific risks. A competent fire safety professional can advise on correct placement and signage to ensure occupants use the right extinguisher in an emergency.
Q: “Which extinguisher type meets UK fire safety regulations?”
A: Both CO2 and foam extinguishers, when correctly specified and maintained, meet UK fire safety requirements under the Regulatory Reform (Fire Safety) Order 2005 and BS 5306-3. The key regulatory obligation is not simply owning an extinguisher but ensuring the correct type is present for the identified fire risks, is properly maintained, and is accessible to building occupants. A fire risk assessment is the proper mechanism for establishing this.
Q: “Which is better for a large commercial property in London?”
A: In most cases, larger commercial properties in London require a combination of extinguisher types rather than a single agent throughout the building. Electrical plant rooms and server areas will typically require CO2 units, while open office floors, storage areas, and reception spaces may be better served by foam extinguishers. The precise mix should be determined by a fire risk assessment that accounts for the building’s occupancy, layout, and hazard profile.
Q: “Do I need a professional to decide between CO2 and foam extinguishers?”
A: Yes, in most cases professional advice is strongly recommended. The Regulatory Reform (Fire Safety) Order 2005 places a duty on the responsible person to ensure fire fighting equipment is suitable for the risks present, and this determination should be made by a competent person. Getting this wrong can leave your building non-compliant and, more importantly, occupants at greater risk. London City Fire offers professional fire risk assessments and extinguisher surveys to help you make the right decision with confidence.
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Disclaimer: The comparisons on this page are for general informational purposes only. The suitability of any fire safety equipment or system depends on the specific risks, layout, and occupancy of your property. Always consult a qualified fire safety engineer before selecting or replacing equipment. London City Fire recommends a site-specific fire risk assessment as the starting point for any fire safety decision.