Fire extinguisher

A fire extingusher is a device used to put out a fire, often in an emergency situation. They consist of a pressurised container of chemicals that when discharged can put out a fire. It is important to familiarise yourself with the use of fire extinguishers in your vicinity, as improper or untimely use may be counterproductive.

Table of contents

1 Classification
2 Chemistries
3 Related Articles

Classification

There are five classes of fire exinguishers, A, B, C, D, and K.

Class A extinguishers are used for putting out fires of general combustibles such as wood or paper. These usually contain a foam-like mixture of water and carbon dioxide. The symbol is a triangle around the letter A.
Class B extinguishers are intended for use on liquids or grease and are distinguished by a square around the letter B.
Class C extinguishers are used on electrical fires. Their mixture is non-conducting to prevent zapping the user.
Class D extinguishers are used on fires of exotic metals. They are designated with a star around the letter D. These are rarely encountered and much more expensive than class A, B, or C extinguishers.
Class K extinguishers are used in Kitchens and environments with the high probability of grease fires. These are rare.

Fire extinguishers generally are designed for one or more classes. Commonly available are A (water), BC (carbon dioxide), ABC (dry powder), and ABCD (halon).

Chemistries

A fire extinguisher may emit a solid, liquid, or gaseous chemical.

Water is the most common chemical for class A fires and is quite effective as one would imagine. Water works to extinguish a fire by simply cooling it below the ignition point. However, it will merely exasperate other fire classes. For instance, water sprayed over burning liquid petroleum merely spreads the flames around.

For classes B and C, a dry powder is used. This provides a blanket which blocks the fuel from oxidising.

Carbon dioxide also works on classes B and C and works by displacing the less dense oxygen. This can be problematic in enclosed occupied spaces as we need oxygen too!

Halon is the universal extinguisher. It will extinguish any type of fire and is highly effective. It works by breaking the chemical reaction of the fire. Halon is a chlorofluorocarbon and is being phased out for more environmentally-friendly alternatives. Halon fire extinguishers may cost upwards of 800 USD due to production and import restrictions.

fire-suppression system - Halon - fire alarm - fire hydrant - fire engine - arson