Fires are grouped into classes which depend on the material or substance that is present.
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.
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.
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|
|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
|Moderate||10-25 sec||Leaves residue|
|Liquid Gas||B and C
|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|
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.