Carbon dioxide extinguishes fire mainly by displacing oxygen in the flame zone with an inert atmosphere. There are also degrees of physical and chemical action. It is therefore a little more efficient than the inert gases, requiring lower concentrations for a given application.
Since it is in a liquid state until it reaches the nozzle, it has a reasonable 'throw' and thus can be readily used to smother fires on the surface of flammable liquids in local application mode.
Carbon dioxide is about 1.5 times as heavy as air, but readily mixes in an enclosure to form a uniform concentration. It is a colourless, odourless, electrically non-conductive gas. On discharge it leaves no residue. It is almost completely inert, not breaking down in a fire to form corrosive by-products.
However, although it is non-toxic at low concentration levels, it becomes hazardous at concentration levels below those necessary to extinguish fires, and therefore it can only be discharged safely once areas are unoccupied.
A very wide range of hazards can be protected, such as:
- switch rooms, control cabinets, floor voids, electrical and electronic equipment rooms, engine test bays, ships engine and cargo holds
- drying ovens, large electrical and electronic cabinets
- paint spray booths, dip varnishing units, vapour exhaust systems
- transformers, generators, turbines
- flammable liquids and chemical products, foam materials