Carbon dioxide (CO₂) fire extinguishers are among the most common types found in UK workplaces, particularly offices, server rooms, laboratories, workshops, and any environment with electrical equipment. Selecting the correct fire extinguisher is critical not only for compliance but also for ensuring a safe and effective response in the event of a fire. This guide provides a comprehensive, practical overview to help business owners, facilities managers, and staff understand when CO₂ extinguishers should be used, how they work, and the key safety considerations that accompany them.

1. Introduction

Not all fire extinguishers are designed for every type of fire. Using the wrong extinguisher can worsen a fire, create additional hazards, or put staff at unnecessary risk. CO₂ fire extinguishers play a crucial role in workplace fire safety, particularly where electrical systems and flammable liquids are present.

This guide covers everything your business needs to know: from the basic science behind CO₂ extinguishers to step-by-step usage, safety warnings, siting requirements, and regulatory responsibilities. It is written to support effective workplace fire safety planning and compliance with UK standards.

2. What Is a CO₂ Fire Extinguisher?

A CO₂ fire extinguisher contains pressurised carbon dioxide gas, stored at extremely high pressure in a reinforced steel cylinder. When discharged, the gas expands rapidly, forming a cold, white vapour cloud.

Key characteristics include:

• Residue-free extinguishing – ideal for sensitive electrical equipment.
• Cooling effect – the CO₂ rapidly cools the fire surface as it expands.
• Oxygen displacement – CO₂ replaces the oxygen around the flame, suffocating the fire.

How to identify a CO₂ extinguisher:

• Black label stating “CO₂”.
• A distinctive horn-type nozzle rather than a hose.
• High-pressure discharge that is loud and forceful.

3. How CO₂ Fire Extinguishers Work

CO₂ extinguishers rely on two mechanisms:

Oxygen Displacement

Fires need oxygen to burn. When CO₂ is discharged, it displaces the oxygen around the flames, effectively smothering the combustion process.

Rapid Cooling

As the liquid CO₂ turns into gas, it expands and cools dramatically. This cooling effect helps reduce the temperature of the surface and the immediate fire area. These combined actions make CO₂ suitable for specific fire types but not appropriate for all fire classes, especially where deep-seated burning may continue after the CO₂ cloud disperses.

4. When to Use a CO₂ Fire Extinguisher

CO₂ extinguishers are primarily recommended for:

Electrical Fires

This includes:

• Computers, servers, and IT equipment
• Electrical control panels
• Distribution boards
• Manufacturing machinery

Because CO₂ leaves no residue, it is ideal for protecting high-value electronics.

Class B Fires (Flammable Liquids)

Suitable for small, contained fires involving:

• Petrol
• Solvents
• Oils
• Paints

Clean Extinguishing Needs

Workplaces such as laboratories, healthcare environments, and technology settings often require extinguishing agents that leave no contamination. CO₂ meets this requirement.

5. When NOT to Use a CO₂ Fire Extinguisher

CO₂ extinguishers are not universal. Misuse can lead to ineffective extinguishment or heightened danger.

Avoid using CO₂ extinguishers in the following situations:

Class A Fires (Deep-Seated Material Fires)

Fires involving wood, paper, cardboard, and textiles may re-ignite because CO₂ does not provide lasting cooling. Water or foam extinguishers are generally more suitable.

Confined or Poorly Ventilated Spaces

CO₂ displaces oxygen. In small rooms or enclosed spaces, this poses a risk of asphyxiation.

Cooking Oil or Grease Fires (Class F)

CO₂ is not effective and may cause hot oil to splatter. A wet chemical extinguisher is required.

Large or Rapidly Growing Fires

If a fire is beyond the incipient stage, the priority should be evacuation, not extinguishment.

6. How to Use a CO₂ Fire Extinguisher: Step-by-Step

Correct technique is essential. The PASS method provides a simple, structured approach.

P – Pull the pin

Break the tamper seal and pull the pin to unlock the handle.

A – Aim the horn at the base of the fire

Always aim at the source of the flames, not the flames themselves.

S – Squeeze the handle

This releases the CO₂ under high pressure.

S – Sweep from side to side

Use controlled side-to-side motions until the fire appears extinguished.

Safety notes when using a CO₂ extinguisher:

• Do not hold the horn unless it has an insulated handle. Uninsulated horns can cause frostbite.
• Maintain a safe distance, typically 1–2 metres.
• Expect loud noise and a strong, cold discharge cloud.
• CO₂ dissipates quickly; monitor for re-ignition once the vapour clears.
• Always ensure there is a clear escape route behind you.

7. Safety Considerations and Common Hazards

While CO₂ extinguishers are extremely useful, they must be used with care.

Risk of Asphyxiation

Discharging CO₂ in small, unventilated areas can reduce oxygen levels to dangerous levels. Only use in well-ventilated spaces.

Frostbite Hazard

Direct skin contact with the horn or nozzle can cause cold-burn injuries.

Re-Ignition Risks

Because CO₂ does not fully cool Class A materials, fires involving wood, paper, or fabric may restart after the gas disperses.

Evacuation Judgement

Staff must be trained to recognise when to attempt extinguishment and when to evacuate immediately. Personal safety takes precedence over property protection.

8. Business Owner Responsibilities

Employers have legal and practical duties to ensure fire extinguishers are correctly supplied, maintained, and understood by staff.

Siting Requirements

CO₂ extinguishers should be:

• Positioned near electrical equipment and fire risks.
• Mounted visibly and at an accessible height.
• Paired with a foam or water extinguisher for Class A coverage.

Staff Training

Employees must receive fire safety instruction, including:

• How and when to use CO₂ extinguishers
• Understanding fire classes
• Evacuation protocols

Routine Checks

Monthly visual inspections should verify:

• Correct weight
• Intact horn and safety pin
• No obstructions
• Clear signage

Annual Servicing

Servicing must follow BS 5306 requirements, carried out by a competent technician.

Fire Risk Assessment Integration

The presence, number, and placement of CO₂ extinguishers should form part of the site’s formal risk assessment.