Understanding Fire Extinguishers, their Classifications and Operation

Whether at home, in the car, boat, work or school, you’ll find fire extinguishers everywhere; and with good reason. NFPA 10 indicates that the maximum travel distance to an extinguisher is 75 feet in a commercial building. Knowing how to select the appropriate extinguisher is critical. The principles of selecting an appropriate fire extinguisher include determining the type of potential fire hazard, severity of potential fire hazard, environmental conditions of potential fire hazard, effectiveness of extinguisher on potential fire hazard, training and physical capabilities of available personnel to operate extinguisher, and the upkeep and maintenance requirements of extinguisher.

Extinguisher Classifications

Fire extinguishers are classified by types of fires that can be extinguished by fuel sources. These classifications include Class A, B, C, D and K. Below are the classifications as defined by NFPA based on the fuel type:

Class A: Ordinary combustible materials, such as wood, cloth, paper, rubber and many plastics. They burn with an ember and leave an ash. Extinguish by cooling the fuel to a temperature that is below the ignition temp. Water and other extinguishing agents are effective.

Class B: Flammable liquids (burn at room temperature) and combustible liquids (require heat to ignite). Petroleum greases, tars, oils, oil-based paints, solvents, lacquers, alcohols, and flammable gases. High fire hazard; water may not extinguish. Extinguish by creating a barrier between the fuel and the oxygen, such as layer of foam.

Class C: Fuels that would be A or B except that they involve energized electrical equipment. Special techniques and agents required to extinguish, most commonly carbon dioxide or dry chemical agents. Use of water is very dangerous because water conducts electricity.

Class D: Combustible metals, such as magnesium, titanium, zirconium, sodium, lithium and potassium. Most cars contain numerous such metals. Because of extremely high flame temperatures, water can break down into hydrogen and oxygen, enhancing burning or exploding. Extinguish with special powders based on sodium chloride or other salts; also clean dry sand.

Class K: Fires in cooking appliances that involve combustible cooking media (vegetable or animal oils and fats).

Source: NFPA Reporter’s Guide: All about fire

Operation of Fire Extinguishers

PASS is a common acronym used by fire fighters and professionals to educate others on how to operate portable fire extinguisher cabinets. The illustration below shows the 4 phases:

P – Pull the Pin; A – Aim at the Base of Fire; S – Squeeze the Handle and S – Sweep the base of the fire


Nystrom understands the codes and complexities with fire extinguishers and fire safety products. To find out how Nystrom can assist on your next project, please visit www.Nystrom.com.