A halon extinguisher is a type of extinguisher that is extremely effective on many different types of fires. It is particularly effective on fires that involve electronics. It uses a colorless, odorless halon gas to put out fires, and it does not cause further damage to the fire area. In recent years, halon has been found to be a significant cause of ozone damage so for many applications its use is being discontinued.
There are three main types, or classes, of fires: class A involves ordinary flammable materials such as paper or wood, class B involves flammable liquids, and class C involves electricity and electrical equipment. Water or carbon dioxide extinguishers are only effective on some classes of fire, and while dry chemicals can work on classes A, B, and C, it's usually very messy and can cause damage to property.
The reasons a halon extinguisher is so effective has a lot to do with unique properties of the gas itself. Halon gas is colorless, odorless, and non-toxic. It's also attracted to heat and actually seeks out the fire when it is released from the extinguisher. It works to put out the fire by cooling and smothering it, and it also interferes chemically with the burning process. Another feature of the halon extinguisher is that it does not require clean up after use since it is non-corrosive and leaves no stains.
Halon extinguishers are especially useful on fires involving electrical equipment because the halon gas doesn't conduct electricity. The cleanliness and non-corrosiveness also won't damage electrical components the way other extinguishers can. These factors also make it a popular choice for use in places like that housed many valuables like museums.
The combination of non-conductivity, lack of residue and general cleanliness make the halon extinguisher the best choice for fires in airplane cockpits as well. Although there are other extinguishers that could put out a cockpit fire, they leave a great deal of powdery residue that would be virtually impossible to clean off sensitive aviation equipment.
In spite of its usefulness, the halon extinguisher is in the process of gradual replacement with other fire fighting measures. Halon gas has been found to be very damaging to the ozone layer, and according to the Vienna Convention for the Protection of the Ozone Layer, and the Montreal Protocol on Substances that Deplete the Ozone Layer the production and use of halon gas needs to be reduced and eventually eliminated. Countries around the world are in various stages of complying with this directive, with the exception of a few vital uses such as aviation and military applications.