What is a Fire Extinguisher?

A fire extinguisher is a portable container filled with an agent that can be used to put out small flames and stop them from spreading. There are several different types of fire extinguishers, designed for specific classes of fires. Fire extinguishers are an important safety tool for everyone, but they are only useful if you know how to use them correctly. The key is understanding the basic principles of how they work, and regular maintenance is important to keep them in working order.

When you look at a fire extinguisher, it looks a little like a giant aerosol can, but with two distinct substances inside: a solid, liquid, or gas substance for fighting the fire, and a pressurized chemical called a propellant that makes that fire-fighting agent come out when you push on the handle. The cans themselves are made from strong steel to resist the pressure of the propellant and to prevent them from exploding.

There are two main categories of hand-held fire extinguishers: handheld models and cart-mounted (also known as wheeled) models. Handheld models weigh from 0.5 to 14 kilograms (1.1 to 30.9 lb) and are easily transported by one person. Cart-mounted fire extinguishers are larger and often mounted on a trolley, making them easy to maneuver and more appropriate for use in large areas, such as airport runways, heliports, and docks.

Water-based extinguishers contain either a liquid water or foaming solution, both of which soak up the burning material and cool it down by reducing the oxygen supply to the fire. They are generally recommended for class A fires that burn combustible materials such as paper, cardboard, and textiles. They are not typically suitable for electrical fires, as they may cause electrocution.

Dry chemical fire extinguishers are typically used on class B and C fires. They release a powder or granular substance that smothers the fire by driving oxygen away from it, and they are not suitable for electrical fires, as they may generate toxic gases such as carbon monoxide.

A wet chemical fire extinguisher contains a liquid agent such as sodium bicarbonate that, when activated, releases a cloud of carbon dioxide which smothers the fire by driving off oxygen and stopping its chemical reaction. These are not usually suitable for electrical fires, as they may produce a combination of gases including hydrogen cyanide, acrolein, and ammonia in addition to carbon monoxide.

Fires that involve organic or vegetable oil or cooking fats require a different type of fire extinguisher, which can be identified by the colour coding on the fire rating label. Foam extinguishers, sometimes called AFFFs (aqueous film-forming foam), are effective in class A and class B fires by occupying the space where the fire is and cutting off its air supply.

If a fire is too big, or if you don’t feel comfortable using an extinguisher, the best course of action is to evacuate the area and call the fire department. If you do decide to tackle the fire, position yourself with an exit at your back and remember to stay away from the flames and the smoke. It is also a good idea to wear a face mask in case the fire produces toxic fumes such as carbon monoxide.