25/07/2026
A CO₂ fire extinguisher contains liquid carbon dioxide (CO₂) stored under very high pressure (about 55–60 bar at room temperature).
Here's what happens inside and how it works:
Inside the cylinder: Carbon dioxide is stored mostly as a liquid, with a small space above it filled with COâ‚‚ gas. The high pressure keeps the COâ‚‚ in liquid form.
When you squeeze the handle: The valve opens, allowing the pressurized liquid COâ‚‚ to rush up the siphon tube and out through the horn.
As it leaves the extinguisher: The pressure drops suddenly, causing the liquid CO₂ to expand rapidly into gas. Some of it also turns into tiny particles of dry ice (solid CO₂), making the discharge extremely cold (around −78.5°C).
How it puts out the fire:
Displaces oxygen: COâ‚‚ forms a cloud around the fire, reducing the oxygen level below what is needed to sustain combustion.
Cooling effect: The very cold COâ‚‚ helps cool the burning material, though its main extinguishing action is oxygen displacement.
Best used on:
Electrical fires (live electrical equipment)
Flammable liquid fires (Class B)
Not recommended for:
Deep-seated Class A fires (wood, paper, cloth), because the fire can reignite once the COâ‚‚ dissipates.
As someone involved in fire safety training, a simple way to explain it is:
A COâ‚‚ extinguisher works by releasing high-pressure carbon dioxide, which expands into a very cold gas that blankets the fire, pushes away oxygen, and stops combustion without leaving any residue.
