Reducing the oxygen content from the normal 21% down to 14% will extinguish most surface fires thus requiring a 34% CO2 concentration level. Depending upon the application a significant amount of cooling is also provided. Rapid expansion of the snow to gas reduces the ambient temperature in the hazardous area which accelerates the extinguishing process and retards reignition. CO2 is stored as a liquid under pressure, usually 57 bars at 20°C, in high pressure steel containers.

The CO2 system is actuated by different modes:

• Electric solenoid.
• Pneumatic.
• Local manual release (at control head).
• Remote manual release

When the system is actuated, the closed valve opens, allowing the container vapour pressure to propel the liquid CO2 via the distribution pipe work to discharge through specially designed nozzles where it readily vapourises resembling a cloud of steam. This clouding is due to moisture in the air becoming frozen as a result of the extremely low temperature of the expanding CO2.