Types of Fire Extinguishers

A fire extinguisher is a useful tool to have in any home or workplace. However, it must be used correctly to prevent injuries and minimize property damage. It is recommended that everyone in a household be trained in the proper use of a fire extinguisher. A fire extinguisher should be positioned close to the source of the fire and within easy reach. It should be mounted at the correct height, as determined by NFPA guidelines and ADA compliance. There are many different types of fire extinguishers available to choose from, but they all have the same basic function – to put out the fire by discharging an agent into the fire. The agent is usually either a liquid, foam or powder. Fires are classified into categories according to the type of materials that are burning: class A fires are ordinary combustibles, such as wood and paper; class B fires are flammable liquids; and class C fires are in electrical equipment. Smaller fires can be extinguished with water, while larger ones require the help of a fire department.

There are some special extinguishers designed for class D fires involving combustible metals such as titanium and magnesium. These extinguishers have a unique design with a special low-velocity nozzle or discharge wand to avoid disrupting the finely divided metallic particles that are involved in these fires. Some extinguishers are also designed to dispense the agent in large volumes rather than in a mist to better ensure that the combustible metals are thoroughly saturated with the suppressant.

The other common type of extinguisher is a dry chemical type (classes ABC and BC). These have a powdery substance that covers the fire and provides a smothering blanket. The powder is absorbed by the burning material and reduces its heat conductivity. These are not effective on class A fires, but are good for class B and class C fires.

Another type of fire extinguisher is a clean agent, which is a gas or mist that does not conduct electricity. These are typically designed for class A and class B fires, but are effective on some class C fires as well. A clean agent is nonconductive and leaves no residue, and it also does not harm electronics equipment. The most popular clean agent is bromochlorodifluoromethane, a.k.a. Halon 1211. It is a replacement for carbon dioxide that is more effective than carbon dioxide on a weight-of-agent basis, and it does not leave any residue.

Some fire extinguishers have a combination of clean agents and wet chemicals, such as those that contain potassium bicarbonate or ammonium dihydrogen phosphate. These are typically rated for classes A, B and C, but can be used on some class D fires as well. These have a green-colored label that says “clean agent” or “BC/ABC.” The NFPA and ICC now allow these to be used on class A, B and C fires without the need for the 30-day inspection requirement. This is a welcome change that makes these more accessible to homeowners.