Extinguishing media are the substances used for suppressing fires. They include liquids, powders, gases, and foam concentrates.
Extinguishing media are also known as firefighting media.
A fire will continue burning as long as heat, fuel, and oxygen are present. Suppressing a fire, therefore, requires the elimination of one of those factors. This is the role extinguishing media plays.
Which extinguishing media should be used to combat a fire will depend on a few considerations, including the type of fire, the surroundings, and which firefighting methods are available.
The right type of extinguishing media will depend on the type of fire that needs to be suppressed. The National Fire Protection Association (NFPA) categorizes fires into five classes:
- Class A: ordinary combustibles (wood, paper, cloth, plastic)
- Class B: burning liquids and gases (gasoline, oil)
- Class C: live electrical equipment (fuses, electrical wires, electrical appliances)
- Class D: combustible metals (magnesium, lithium, titanium, zirconium, sodium, potassium)
- Class K: kitchen fires (oils, grease, fats)
Types of Extinguishing Media
The most common types of extinguishers are:
- Water - Primarily used for Class A fires. May include additives like antifreeze or wetting agents.
- Carbon dioxide (CO2) - Used for Class B and Class C fires. CO2 does not leave a residue, making it a preferred extinguishing medium where delicate electronic equipment is used or food is prepared. Due to its short range, it is not recommended for outdoor use.
- Foam - Aqueous film-forming foam (AFFF) and film-forming fluoro protein (FFFP) are rated for use in Class A and Class B fires. When used on flammable liquid fires, these foams float to the surface to prevent re-ignition.
- Dry chemical powders - Ordinary dry chemical powder deploys small particulates and is mainly used in Class B fires. Multipurpose dry chemical powder has the additional benefit of softening and sticking to hot surfaces, smothering the fire. These are especially effective for Class A fires.
- Dry powder - Used for Class D fires and specific metals. Special techniques and manufacturer’s recommendations have to be followed during use.
- Wet chemical - Used for Class A and Class K fires. The media may comprise solutions of water and potassium acetate, potassium citrate, potassium carbonate, or a combination of these. The agent works as a coolant on Class A fires. For Class K fires, it forms a foam blanket that prevents re-ignition.