Imagine a fire breaks out in a small server room or equipment cupboard. Your immediate instinct might be to reach for the nearest fire extinguisher.
We all know a carbon dioxide extinguisher is best for an electrical fire because the gas is clean, leaves no messy residue, and is non-conductive. It ensures all of your precious equipment remains undamaged.
However, there are serious dangers to using a CO2 extinguisher in a confined space – including creating a potentially lethal environment for yourself and others.
What is the risk CO2 extinguishers pose?
The very thing that makes carbon dioxide effective at putting out a fire is what makes it dangerous to humans – oxygen displacement.
A fire needs oxygen to burn. CO2 extinguishers work by starving the flames of that oxygen. In a large, open-plan office, this isn’t usually an issue. However, in a confined space, CO2 will rapidly replace the air you need to breathe.
The risk of asphyxiation
You cannot smell or see CO2 gas. When you use a CO2 extinguisher in a confined space, the concentration of CO2 can jump to dangerous levels in seconds. This can result in symptoms like:
- Dizziness
- Rapid breathing
- Loss of consciousness
- Asphyxiation
Bear in mind a CO2 concentration of only 4% or higher is considered life threatening. And because CO2 is heavier than air, it also sinks. So if you are crouched down fighting a fire at floor level in a small room, you are instantly in the danger zone.
Other extinguishers you should NOT use in confined spaces
Apart from CO2 extinguishers, you should avoid using dry powder extinguishers in a confined space.
While not toxic in the same way, powder extinguishers discharge a cloud of fine dust. In a small room, the dust can cause severe respiratory distress if inhaled in high concentrations, and can also make it difficult to see your exit route.
HSE guidelines
The Health and Safety Executive (HSE) in the UK defines a confined space as ‘one which is both enclosed or largely enclosed and has a reasonably foreseeable specified risk to workers of fire [and] asphyxiation’.
While there isn’t a specific prohibition for CO2 extinguishers in all confined spaces, the HSE strongly emphasises risk assessment.
If a room is so small that the discharge of a CO2 extinguisher would reduce the oxygen levels below safe limits (typically cited as rooms under 30 cubic metres for a 5kg unit), then alternative measures or specific safety protocols like evacuation plans and ventilation must be put in place.
So, what extinguishers are safe to use in confined spaces?
If your risk assessment shows that a CO2 extinguisher is too risky for your server room or office space, what should you use instead?
- Water mist extinguishers: A type of water extinguisher, they release a ‘mist’ of ultra-fine, microscopic water particles at high pressure to cool a fire and starve it of oxygen. They carry no asphyxiation risk, and leave no residue. What’s more, they are safe for use on live electrical equipment up to 1000V at a distance of 1 metre.
- Clean agent extinguishers: Also known as clean gas fire extinguishers, they often use gases like Fluoroketone or Novec 1230 that are designed specifically for high-value tech areas. They interrupt the chemical reaction of the fire rather than just smothering the oxygen, making them much safer for occupied, confined spaces.
- Automatic ceiling extinguishers: In spaces that are too small to be regularly occupied, for example a server cupboard where the door stays closed, the most practical solution is often a ceiling-mounted automatic fire extinguisher. These detect and suppress a fire without anyone needing to enter the space at all, removing the asphyxiation risk entirely.
The Bottom Line
It’s worth keeping this risk in perspective. The asphyxiation danger from a CO2 extinguisher only becomes a realistic concern in a very small, enclosed space. And in a space that small, the scenario of someone standing inside, with the door closed, CO2 extinguisher in hand, is genuinely unlikely.
That said, it’s still good practice to think carefully about what you install where. In compact, unoccupied spaces like server cupboards, an automatic extinguisher is usually the smarter choice anyway – it does the job without anyone needing to be present.
For occupied rooms, even small ones, water mist extinguishers and clean agent extinguishers give you peace of mind without the risks that CO2 can pose in tighter environments.
