What are the different classes of fires?

Fires are grouped into classes which depend on the material or substance that is present.

Class A - Fires involving ordinary combustibles such as paper, wood, cloth, rubber, or plastics.
Class B - Fires involving flammable or combustible liquids, gases, oil, paints, or lacquer.
Class C - Fires involving energized (live) electrical equipment such as motors, appliances, or power tools.
Class D - Fires involving combustible metals such as magnesium, titanium, sodium, and potassium.
Class K - Fires involving combustible cooking oils, or fats in cooking appliances.

What are the different types of portable fire extinguishers?

To fight the different classes of fires, there are different types of fire extinguishers. Each has its own characteristics, capabilities, and limitations.

Three main types of portable fire extinguishers include:

Water extinguishers: Water extinguishers are filled about two-thirds with water and then pressurized with air. When used for Class A fires, these extinguishers remove the heat from the burning materials.

Do not use water to extinguish an electrical fire. Water is a good conductor and can increase the possibility of electrocution.
Do not use water to extinguish flammable liquid or cooking oil fires. Water is ineffective as it helps to spread the liquid and the fire.

Carbon Dioxide (CO2) extinguishers: The extinguishing media is pressurized CO2. When used for Class B and C fires, the CO2 covers the fuel by blanketing it, and stops the reaction at the surface by displacing oxygen. Be thorough when using a CO2 extinguisher. It has a moderate spray range and last only 10 to 30 seconds. A hard horn attached to the end of the spray tube helps to contain and aim the spray at the target area.

Do not use CO2 extinguishers in confined spaces as CO2 can displace the oxygen in the air, making breathing difficult. Only use in a confined space if workers have appropriate respiratory protection.
Do not use CO2 extinguishers for Class A fires because the fire may continue to smolder and re-ignite after the CO2 disperses.

Dry Chemical extinguishers: Dry chemical extinguishers are the most common and available in few types. These extinguishers will be marked for the classes they are designed to extinguish (e.g., ABC type extinguisher will put out Class A, B and C fires). The extinguishers discharge a blanket of fine powder which creates a break between the fuel and the oxygen in the air. The powder also works to break the chemical reaction. Be accurate when using as they have a short to moderate spray range and last only 10 to 25 seconds.

Be cautious of the residue after using dry chemical extinguishers. The residue can damage motors, computers and other electrical equipment.

Below is a summary of these and other common extinguishers.

Extinguisher Comparison Table
Extinguisher	Class	Range	Empties	Other
Water	A	Long	60 sec	Fights re-ignition
CO2	B and C	Short	10-20 sec	May make breathing difficult in enclosed areas
Dry Chemical	B and C Some A	Moderate	10-25 sec	Leaves residue
Liquid Gas	B and C Some A	Short	10 sec	May make breathing difficult in enclosed areas
Chemical Foam	A and B	Moderate	10-30 sec	Leaves residue
Bucket of Sand / Dry Powder	D			Check with your supervisor regarding equipment for Class D fire fighting
Wet Chemical	K			Prevents re-ignition

How will portable fire extinguisher be marked?

Portable fire extinguisher may use the following markings to indicate which class of fire they are designed to fight. These symbols are recommended by the National Fire Protection Association (NFPA) in the USA. The symbols may be shown using colours.