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Elements of Fire

The combustion process is observed as occurring in two modes: The flaming type (including explosions) and the flameless surface type (including glow and deep seated glowing embers).

  • FUEL

In order to select the proper type of fire extinguisher, it is necessary to know how fires may be extinguished.

  1. REMOVAL OF FUEL --eg. turning off the fuel supply.
  2. EXCLUSION OF OXYGEN --eg. extinguishing a grease fire in a frying pan by putting on the lid (smothering);
  3. REDUCTION OF TEMPERATURE --eg. putting water on a paper fire (cooling);
  4. INHIBITION OF CHAIN REACTION --eg. certain chemical substances (halon, dry chemical powder) have the ability to break up the reaction.

Classification of Fires and Extinguishing Methods

  • Class A: Fires involving ordinary combustible materials (such as wood, cloth, paper, rubber and plastics). Requires the heat-absorbing (cooling) effects of water.
  • Class B: Fires involving flammable or combustible liquids, gasoline, grease, paint. Smothering is most effective.
  • Class C: Fires involving electrical equipment, appliances, wiring. Can be controlled with
    non-conductive agents.
  • Class D: Fires involving certain combustible metals, such as magnesium, titanium, sodium, potassium, etc. Requires special extinguishing agents.

Markings / Codes

Just as fires are classified into classes, so are fire extinguishers. Using the correct extinguishers on a particular type of fire will ensure its effectiveness. Some extinguishers can be used on two or three classes of fire, but none are suitable for all four classes. Using the wrong extinguisher can cause personal injury and may spread the fire.

Most extinguishers are marked with "A", "B", "C", and "D" symbols to coincide with the four classes of fire. They also have distinctive markings.

  • CLASS "A" (in a green triangle), containing white letter "A".
  • CLASS "B" (in a red square), containing white letter "B".
  • CLASS "C" ( in a blue circle), containing white letter "C"
  • CLASS "D" (in a yellow star), containing white letter "D"


  1. Correct Position: Most extinguishers must be held in an upright position to achieve maximum effectiveness. Most extinguishers deliver their quantity of extinguishing agent in a matter of seconds.
  2. How to Remove Restraining and/or Locking Devices: Generally, the restraining and/or locking device found on extinguishers is referred to as the "PIN". Simply twist the pin as you pull it out. Do not squeeze the lever or trigger as you attempt to do this or the pin will not come free.
  3. How to Activate Agent Discharge: The extinguisher is activated by simply squeezing the lever or trigger handle.
  4. How to Direct the Extinguishing Agent at the Fire: The nozzle or hose of the extinguisher should be directed first at the base of the flames. Next, sweep the flames off the burning surface. This is accomplished by directing the discharge to the near edge of the fire, gradually progressing forward, moving the discharge from side to side. The application should be continued even after the flames appear to be extinguished to allow added time for cooling or smothering and to prevent a flash from adjacent hot surfaces or open flames.
  5. Operators Distance from Fire: When using a Type "A" (water type) extinguisher, normal operation is anywhere up to 30 feet from the fire. When using dry chemicals, "BC" or "ABC" extinguisher, stand approximately 8 to 10 feet away. When using a CO2 extinguisher, stand approximately 3 to 5 feet away.

Prior to beginning the extinguishment process, the operator should locate an escape route. Should the extinguishment effort fail and the fire begins to spread rapidly, the operator should know in advance where he/she intends to retreat to. Whenever possible, face your back to an exit before attempting to extinguish the fire.

One person should never attempt to extinguish a fire by himself/herself. Use the buddy system. If problems occur, there will be someone there to summon help.

A basic word to remember when attempting to use an extinguisher is "PASS".

  • P = #1. Pull the pin
  • A= #2. Aim the nozzle
  • S= #3. Squeeze the trigger handle.
  • S= #4. Sweep from side to side

REMEMBER: Never place a used extinguisher back in its cabinet. Whenever an extinguisher is used, it must be recharged to ensure its future effectiveness.

Extinguisher Types

Air pressure water tank Pressurized dry chemical Pressurized dry chemical
Hand pump water tank Carbon dioxide Carbon dioxide
Fire hose lines Halon Halon
Multi-purpose (ABC) dry chemi-cal extinguishers are suitable for Class "A", "B" and "C" type fires. However, all Class "A" fires must be followed up with water to ensure extinguishment of all deep-seated smoldering fire.