CO2 Fire Extinguishers: Everything You Need to Know
Knowing your fire extinguishers is important when it comes to applying proper fire safety. Different types of fire extinguishers are suitable for extinguishing separate classes of fires and identifying which one to use and have on your premises could be the difference between life and death.
There are five types of fire extinguisher: CO2 (carbon dioxide), dry powder, foam, water and wet chemical. A carbon dioxide fire extinguisher, sometimes called a CO2 cylinder or simply ‘fire extinguisher CO2’, works differently to the others and choosing the right size and location for one is just as important as knowing how to use it.
In this blog post, we’ll cover everything you need to know about carbon dioxide fire extiguishers including what a CO2 cylinder is user for, how to size one for your property, how it compares with other extinguisher types and how to maintain a carbon dioxide fire extinguisher properly.
What Are CO2 Fire Extinguishers Used For?
Carbon dioxide fire extinguishers are primarily used to extinguish electrical fires. Foam extinguishers have some effect on electrical fires, but nothing works as well for dousing fires on electrical equipment as carbon dioxide extinguishers.
Carbon dioxide forms a barrier between the source of electrical fires and the surrounding oxygen. This helps to suffocate the blaze and douse the fire.
CO2 fire extinguishers are also effective in extinguishing certain flammable liquid fires, known as Class B fires. There’s a fine line in this regard, though, and knowing your specifics about the different fire classes is essential. Why? Several types of flammable liquids don’t respond well to the addition of CO2 – a Class B fire from oil, for example, could get worse!
For electrical fires, though, there’s nothing better to use than CO2 fire extinguishers. Electrical fires generally start because of a type of electrical appliance overheating or breaking down. A short in some electrical wires, or a defective plug socket could also start an electrical blaze.
When you attempt to put out electrical fires or flammable liquid fires using a CO2 fire extinguisher, focus on the combustible electric equipment or burning liquid itself. CO2 fire extinguishers are not effective against fires in flammable solids.
If the fire has spread to a solid material like paper or wood, the fire risks have increased and you’ll need a Class A extinguisher to douse it.
It’s never advisable to use CO2 fire extinguishers, or any others, in confined spaces. The primary function of carbon dioxide extinguishers is to reduce the spread of oxygen to a fire. Within a confined space, low oxygen can be extremely hazardous. It could end up leading to asphyxiation.
CO2 fire extinguishers aren’t very useful outdoors. Weather elements like strong breezes or wind can disperse the CO2 before it finds its intended target.
CO2 fire extinguishers are usually found in two and five-kilogram containers. These should be positioned in locations where flammable liquid or live electrical equipment are common.
These areas include hospitals, schools, shops, offices, server rooms and data centres. Where flammable liquid is found, foam fire extinguishers will likely accompany CO2 fire extinguishers, in accordance with fire safety provisions.
How CO2 Fire Extinguishers Work
CO2 fire extinguishers hold liquid carbon dioxide in a highly pressurised environment. When the lever on a carbon dioxide fire extinguisher is used, the pressure inside the container is reduced. This results in the carbon dioxide inside converting to gas form. The resulting discharge is immensely cold due to the quick transformation of the fire extinguisher’s contents.
The resulting carbon dioxide gas emitted is virtually dry ice. It brings down the temperature of the fire’s flames by attacking the ‘heat’ corner of the combustion triangle. You should note that, although the cooling effect of a CO2 fire extinguisher is effective, water and foam extinguishers actually cool flames more.
As carbon dioxide has a greater mass than oxygen, the rapid rate at which it leaves the fire extinguisher container displaces any oxygen feeding the flames of electrical fires or burning liquid. The CO2 forms a barrier between the fire and the surrounding air, cutting off the ‘oxygen’ corner of the combustion triangle to douse the flames.
What Colour is a CO2 Fire Extinguisher?
Under BS EN3, all UK fire extinguishers have a predominantly red body, with a coloured band or panel identifying the extinguishing agent inside. CO2 extinguishers are identified by a black label or panel and their distinctive hard horn nozzle, no other extinguisher type uses this shape of nozzle, which makes CO2 units easy to identify at a glance even before reading the label.
| Extinguisher type | Label/panel colour |
|---|---|
| Water | Red (no additional panel) |
| Foam | Cream |
| Dry powder | Blue |
| CO2 | Black |
| Wet chemical | Canary yellow |
A CO2 fire extinguisher has a clear black label on.
Which Fires Can a CO2 Fire Extinguisher Be Used On?
UK fire classifications (BS EN2) group fires by fuel type. CO2 extinguishers are effective on some classes and unsuitable, even dangerous, on others:
| Fire class | Fuel type | Suitable for CO2? |
|---|---|---|
| Class A | Solid combustibles: wood, paper, textiles | No: won’t penetrate or cool sufficiently, risk of reignition |
| Class B | Flammable liquids: petrol, solvents, paint | Partially: effective on some, not all; check the specific liquid |
| Class C | Flammable gases | No: not rated for gas fires |
| Class D | Flammable metals | No: requires specialist dry powder |
| Class F | Cooking oils and fats | No: risk of splashing hot oil and spreading the fire |
| Live electrical equipment | Fires involving energised electrical equipment | Yes: CO2 is the preferred choice as it’s non-conductive and residue-free |
CO2 vs Foam vs Powder vs Water: Which Extinguisher for Which Fire?
| Extinguisher Type | Fire Classes Covered | Best For | Key Limitation vs CO2 |
|---|---|---|---|
| Water | Class A | Wood, paper, textiles | Conducts electricity — never use near live equipment |
| Foam | Class A, B | Solid and liquid fires | Leaves residue; less safe than CO2 on live electrical equipment |
| Powder (ABC) | Class A, B, C, electrical | Mixed-risk environments | Reduces visibility/breathing indoors; doesn’t cool, risk of reignition |
| CO2 (carbon dioxide) | Class B (partial), electrical | Live electrical equipment, server rooms, offices | Not effective on Class A solids; risk of asphyxiation in confined spaces |
| Wet Chemical | Class A, F | Commercial kitchens, cooking oil fires | Not designed for electrical or general Class B fires |
The main advantage of a CO2 fire extinguisher over foam, powder or water is that it’s non-conductive and leaves zero residue. The only extinguisher type safe to use directly on live electrical equipment without additional risk to the equipment or the person using it. Powder is also non-conductive but reduces visibility and causes breathing problems indoors, and doesn’t cool the fire, so reignition is more likely. CO2’s main trade-off is that it’s not effective on Class A solids like wood or paper and shouldn’t be used in confined, poorly ventilated spaces.
Advantages of CO2 Fire Extinguishers
- Best for electrical fires: CO2 doesn’t conduct electricity. For this reason, CO2 fire extinguishers are more effective for extinguishing electrical fires in live electrical equipment than any other type of fire extinguisher.
- Cause no damage: CO2 is a non-corrosive gas. As such, there is no solid material included making it a pure extinguishing agent. CO2 fire extinguishers leave no residue behind on surfaces after use.
- Long-lasting and reliable: CO2 extinguishers last longer than any other extinguishers. An extended service is only required after 10 years.
- Can be used on some Class B fires: CO2 fire extinguishers are also good at dousing Class B fires involving certain types of flammable liquids.
Disadvantages of CO2 Fire Extinguishers
- More dangerous to use: Users can experience freeze burn if touching CO2 fire extinguishers on the pipe leading to the horn during use.
- Can’t be used in small spaces: CO2 fire extinguishers emit CO2 which replaces oxygen in the air. As such, their use in confined spaces could lead to asphyxiation.
- Don’t work on all types of fires: Carbon dioxide fire extinguishers are of no use in extinguishing fires in flammable solids.
- Not effective outdoors: CO2 fire extinguishers are limited outdoors, as the CO2 gas can be dispersed by wind.
- Worse for the environment: CO2 fire extinguishers are less friendly to the environment than other types of fire extinguishers.
- Risk of reignition: After CO2 dissipates, any remaining hot embers could reignite a fire.
Maintenance and Inspection
You have to service your CO2 extinguishers once every 12 months. This is the same fire safety stipulation as for the vast majority of other extinguisher types. Unlike most others, though, you can save costs as you needn’t refill them every five years. A CO2 fire extinguisher only requires refilling once a decade.
Upon servicing, a CO2 extinguisher is weighed to establish whether it is still full. A CO2 fire extinguisher doesn’t have a pressure gauge. For this reason, the service technician must use finely-calibrated scales when weighing.
Alongside the annual professional service, a few simple checks keep a CO2 extinguisher safe between visits:
- Visual inspection: check monthly that the safety pin and tamper seal are intact and undamaged
- Check for damage: look for dents, corrosion or damage to the horn and hose. A damaged CO2 extinguisher should be taken out of service immediately
- Storage conditions: confirm it’s still within its -30 degree to 60 degree storage range and out of direct sunlight
- Weight check: because CO2 extinguishers have no pressure gauge only a calibrated-scale weight check by a qualified technician can confirm it’s still full. This is why annual servicing by an accredited engineer is a legal requirement, not just best practice
After 10 years, carbon dioxide extinguishers require compulsory refurbishment, which includes replacing the safety pin. As such, it is often easier and more cost-effective to simply replace a CO2 fire extinguisher instead.
Regulations and Standards
According to UK government fire regulations and standards, any commercial building that holds live electrical equipment must have at least a two-kilogram CO2 fire extinguisher on the premises. If there is heavier-rated equipment of an electrical nature on site (415 volts +) the CO2 extinguisher needs to be at least five kilograms.
How Do I Choose the Right Size of CO2 Fire Extinguisher for My Property?
The right size depends on the fire risk in the specific area you’re protecting, not a single figure for the whole building.
- Live electrical equipment under 415 volts: a 2kg CO2 extinguisher is the minimum required to be sited nearby
- Live electrical equipment rate 415 volts or higher (server rooms, plant rooms, heavy machinery): step up to a 5kg CO2 extinguisher
- General cover under BS 5306-8: as a baseline, most premises need at least one Class A extinguisher per floor (minimum 26A rating for floor areas up to 400 m2), with CO2 units added specifically near electrical equipment rather than used as the sole extinguisher on a floor
- Larger of higher-risk sites: server rooms, data centres and multi-site estates often need more than the legal minimum. A free site survey is the only reliable way to confirm exact numbers and positions
Because sizing depends on floor area, voltage and the mix of other extinguisher types already on site, Chilman scopes the exact number and size of CO2 extinguishers you need against your floorplan during a free site survey.
Use
CO2 fire extinguishers are not difficult to operate but still need to be used carefully. Without the correct level of care, you could do yourself serious injury. The safest way to use a CO2 extinguisher is to note the following instructions:
Firstly, remove the safety pin to break the anti-tamper seal and make the extinguisher ready for use. Avoid the extinguisher horn, and the pipe leading to it, when holding. These parts get extremely cold when releasing the CO2, and touching them could result in cold burns. Of course, if your extinguisher has a frost-free horn, you don’t have to worry.
From a reasonable distance away (one metre is safe), pull the lever and use the CO2 spray to put out the fire. The type of fire you’re extinguishing defines the position you should aim the extinguisher towards.
For electrical fires, aim the spray onto the fire directly. If you’re dousing a fire caused by flammable liquids, start by spraying at the fire’s base and raise the nozzle slowly higher into the flames.
Storage
You must ensure that your CO2 extinguishers are stored in temperatures between -30 degrees and 60 degrees centigrade. The extinguishers should also be stored out of the sun, so make use of covers or blinds if need be. Alternatively, keep your extinguishers away from entrances or windows that let in the sunlight.
Training
As part of the UK Regulatory Reform (Fire Safety) Order 2005, businesses need to provide reasonable training in fire safety to workplace staff. It’s also necessary to appoint fire marshals and wardens.
Fire safety training is crucial for making sure your staff is safe from fires, and it’s the law. Contravention could result in fines or worse. At Chilman, offer a Fire Awareness Training Course to improve fire safety in your workplace.
At Chilman, we have the knowledge and experience to assist you with your fire protection needs and questions. Contact us for your fire risk assessment and workforce’s mandatory fire training.
Frequently Asked Questions About CO2 Fire Extinguishers
Are CO2 fire extinguishers suitable for electric fires?
Yes. CO2 fire extinguishers are the safest and most effective choice for fires involving live electrical equipment, because CO2 gas is non-conductive and leaves no residue that could damage sensitive electronics. This is why CO2 units are the standard choice near computers, servers, control panels and other electrical equipment.
What is a CO2 fire extinguisher used for?
A CO2 fire extinguisher is used mainly on electrical fires and some flammable-liquid (Class B) fires. It’s the safest extinguisher type to use around live electrical equipment because it’s non-conductive and leaves no residue.
What is a CO2 fire cylinder?
CO2 fire cylinder and CO2 fire extinguisher refer to the same thing: a pressurised cylinder containing liquid carbon dioxide that converts to gas on discharge to starve a fire of oxygen. The cylinder itself is red with a black label and a distinctive hard horn nozzle.
What are CO2 fire extinguishers used for in an office?
In offices, CO2 extinguishers are positioned near computers, servers and other electrical equipment, where a residue-free, non-conductive extinguishing agent is essential to avoid damaging sensitive electronics.
How does a CO2 fire extinguisher work?
It releases pressurised liquid CO2, which rapidly converts to gas on discharge. The gas displaces oxygen around the fire and cools the flame, extinguishing it by cutting off its air supply.
What colour is a CO2 fire extinguisher?
CO2 extinguishers have a red body with a black label or panel, and a distinctive hard horn nozzle not used on any other extinguisher type.
Can a CO2 extinguisher be used on all types of fire?
No. CO2 extinguishers are effective on electrical fires and some Class B liquid fires, but are not suitable for Class A (solids), Class C (gases), Class D (metals) or Class F (cooking oil) fires.
How often does a CO2 extinguisher need to be serviced?
Every 12 months, the same as most extinguisher types. Because CO2 units have no pressure gauge, servicing involves weighing the extinguisher to check it’s still full.
Why shouldn’t you use a CO2 extinguisher in a confined space?
Because it works by displacing oxygen, using a CO2 extinguisher in an unventilated confined space can lower oxygen levels enough to cause asphyxiation.
What can a carbon dioxide fire extinguisher be used on?
Primarily live electrical equipment and certain flammable liquids. It should not be used on solid combustibles, flammable gases, flammable metals, or cooking oil fires.
What are the main advantages of CO2 fire extinguishers over other types?
CO2 is the only extinguisher type that’s both non-conductive and residue-free, making it the safest option for live electrical equipment. Unlike powder, it doesn’t reduce visibility or leave a mess to clean up and unlike water or foam, it won’t damage electronics. Its main limitations are that it doesn’t work on Class A solid fires and shouldn’t be used in unventilated confined spaces.