Fire extinguishers are fairly simple devices. Most use compressed air or nitrogen to expel their particular fire suppression agent. There are a few exceptions, Carbon Dioxide (CO2) and halon extinguishers use compressed gasses as their fire suppression agent so don't need another gas to propel the agent. Some dry chemical extinguishers known as stored pressure extinguishers use a cartridge to pressurize the extinguishers at the time of use instead of being under constant pressure. An older type of extinguisher is the Soda, acid extinguisher, these used a chemical mixture to create pressure forcing out the water carried in the body of the extinguisher. These extinguishers are identified by their brass bodies and are turned on their top to mix the chemicals when they are used. Most fire apparatus carry one or more extinguishers for small fires or in case the vehicle itself has a fire.
There are four classes of fire extinguisher
A) Normal combustibles (paper, wood etc). The most common class A extinguisher is the pressurized water can but there are many multi-purpose dry chemical extinguishers which work on these fires too. Some fire departments use a hand pumped water can for small fires.
B) Flammable liquids. Dry chemical extinguishers are the most common type of extinguisher for these fires (they use a material similar to baking soda), but CO2, Halon and Pressurized water cans with a foam additive may also be used.
C) Energized electrical. Extinguishers for electrical fires use non conductive medium (they don't conduct electricity) for suppression agents. Dry chemical, halon and CO2 extinguishers are used for these fires.
D) Flammable metal. There are some metals that will burn intensely under the right conditions. Extinguishers for these fires resemble dry chemical extinguishers but use a different chemical which is often specific to the type of metal. These extinguishers are known as Dry Powder to distinguish them from the more common dry chemical extinguishers and the extinguishers are often not red to help identify them.
|Fire extinguishers||2 1/2 gallon pressurized water extinguisher||5 lb Dry chemical extinguisher||10 lb Dry chemical extinguisher||20 lb Dry chemical extinguisher|
|40 lb Dry chemical extinguisher||Stored pressure dry chemical extinguisher||Carbon dioxide extinguisher||Carbon dioxide extinguisher||Halon extinguisher|
|Dry powder extinguisher||Pump can||Soda Acid Extinguisher||Soda Acid Extinguisher||Handle, gauge and pin assembly|
|Handle, gauge and pin assembly||Extinguisher mount||Extinguisher mount||Extinguisher mount||Extinguisher mount|
|Extinguisher mount||Extinguisher mount||Extinguisher mount|