Carbon dioxide is suitable for class B and C fires, does not damage electrical appliances and it is effective in enclosed spaces. It cools down and suffocates the fuel. While carbon dioxide is inside the fire extinguisher, it is at the liquid state, and it becomes “dry ice” as soon as it is expelled. It sublimates quickly, so it leaves no trace. It should not be used on class A or D fires (so, in general, on fire generated by solid fuel) and, obviously, not on appliances that could be damaged by thermal shocks (carbon dioxide reaches -75°C inside fire extinguishers). If possible, do not direct it on human beings, as the extremely low temperature could cause frostbites and it could lead to death by suffocation, as it removes oxygen.
Foam suffocates and cools down fuels. There are different types of foam used as extinguishing agents.The most common is AFFF (aqueous film forming foam), that is a water solution of foaming agents. It is particularly effective on class A and B fires, thanks to the film it creates that isolates fuel from oxygen and, at the same time, lowers the temperature. It should be mentioned that AFFF is mainly made of water, so, unless the fire extinguisher has passed the dielectric test, it should not be used on electrical appliances. It is not advisable to use it on class C and D fires.
DRY CHEMICAL AND DRY POWDER
Basically, when dry chemical or dry powder come into contact with heat, they release inert gases which create incombustible residues. The composition of dry chemical may extensively vary, every mixture is more or less effective on different fire classes. The most common mixture, and the one with the broader spectrum, is the multi-purpose dry chemical, whose main component is monoammonium phosphate. It is also called ABC dry chemical, because it is possible to extinguish any class of fire with it, with the exception of class D fires. Standard ABC dry chemical contains 40% monoammonium phosphate, while dry chemical used for an enhanced fire suppression may contain up to 90% monoammonium phosphate.