Black band fire extinguisher: CO2 for electrical and liquid fires

A black band marks a carbon dioxide (CO2) extinguisher. It is the clean choice for live electrical equipment and flammable liquids because it leaves no residue, but it has its own hazards, from a frozen horn to gas in confined spaces.

What a black band means

Black is the colour for CO2 on the red extinguisher body. CO2 units also have a distinctive flared discharge horn, which is the part that gets dangerously cold in use.

How CO2 works

CO2 smothers a fire by displacing the oxygen around it. The gas leaves nothing behind, so it does not damage computers or machinery the way water, foam or powder can, which is why it is the usual choice for electrical risks. The trade-off is that it barely cools the fuel, so a fire can re-ignite once the gas disperses.

What it is for

Fire services list CO2 for flammable liquid fires (Class B) and for live electrical equipment, including where the supply cannot be isolated. Hereford & Worcester Fire and Rescue also lists it for flammable gas fires. If you can safely switch off the power, do that first: it removes the cause as well as the risk.

The hazards nobody mentions

• Do not hold the horn. It becomes very cold during discharge and can cause cold burns.
• It is loud. The discharge makes a loud noise when it starts. Expect it, and do not drop it.
• Confined spaces. The gas displaces breathable air. In a small room or cupboard it can be harmful, so ventilate once the fire is under control.

Never use it on

• Chip and fat pan fires. Fire services say not to use CO2 on these. A wet chemical extinguisher is the right tool in a commercial kitchen.
• Smouldering solids such as upholstery or bedding. With little cooling effect, the fire can start again.

Only fight a fire if it is small, you are trained, the alarm is raised and you have a clear exit behind you. Otherwise get out, stay out and call 999.

How to use it

• Raise the alarm and keep your escape route clear.
• Hold the extinguisher by the body and handle, not the horn.
• Aim at the base of the flames from the distance shown on the label and sweep across.
• When the fire is out, stay and watch for re-ignition, and ventilate the space.

Where you will find one

CO2 units sit beside electrical risks: server and comms rooms, switch rooms, plant and offices with a lot of equipment. A typical office pairs one with a water or foam unit for general risks.

Frequently asked questions

Why should you not hold the horn on a CO2 extinguisher?

The gas expands as it leaves, and the horn gets extremely cold. Holding it can cause cold burns, so hold the body and handle.

Can CO2 be used on a kitchen fire?

Not on chip or fat pan fires. In commercial kitchens, wet chemical is the right choice for cooking oil and fat fires.

Does CO2 damage electrical equipment?

It leaves no residue, which is why it is preferred around electronics. Isolating the power first, if it is safe to do so, is still the best step.

Related guides

• Fire extinguisher colours and chart: what each band means
• Which fire extinguisher for which fire?
• Yellow band fire extinguisher: wet chemical for cooking oil fires
• Cream band fire extinguisher: foam and where it fits
• Red band fire extinguisher: what water is for, and what it isn't
• Blue band fire extinguisher: dry powder, and the catch indoors

Sources

• Fire extinguishers (Hereford & Worcester Fire and Rescue Service)
• Fire extinguishers (Avon Fire & Rescue Service)
• BS 5306-10:2019, colour coding of portable fire extinguishers (BSI)

This guide is for learning and applies to England & Wales. Always work from the current standards, the label on your own extinguisher and your fire risk assessment; Scotland and Northern Ireland have equivalent regimes.