Fire Extinguishers

In order to effectively use a fire extinguisher, you must first understand some fire basics.

Anatomy of a Fire

Fire is a chemical reaction that takes place when a material oxidizes (reacts with oxygen) rapidly. In order for this process to occur, the three elements of the fire triangle must be present:

Fire Triangle image
Fuel Image – can be any combustible or flammable material, and may be a solid, a liquid, or a gas
Oxygen Image – makes up about 21% of the air that we breathe. To sustain a fire, a ratio of 16% oxygen (or greater) is needed
Heat Image – is needed both to initially ignite the fire, and also to sustain it (many fires will generate their own heat once burning, feeding the process)

In order to extinguish a fire, one of the sides of the triangle must be eliminated.  In the majority of cases, removal of the fuel is impossible, but an extinguishing agent may be used which reduces either the availability of oxygen, the level of heat, or both.

Fire Classes

Fires are grouped into classes, according to the fuel that is involved. Based on assessment of the class of fire, a suitable extinguisher type can be determined.

Class of Fire Fuel
CLSA Image Combustible solids such as wood, paper, textiles, and many plastics. You can remember Class ‘A’ fires by the characteristic Ash they leave.
CLSB Image Burning liquids. A fire involving flammable or combustible liquids (or gases) is classified as a Class ‘B’ fire. Think of B for Boil.
CLSC Energized electrical equipment. Kitchen appliances, switchgear, or faulty wiring could become involved in a Class ‘C’ fire. Remember C for Circuit. If you remove power from a Class ‘C’ fire, it usually becomes a Class ‘A’ fire.
CLSD Image Combustible metal fires. Sodium, potassium, magnesium, and aluminum are examples of metals that will burn at high temperatures, and which could be involved in a Class ‘D’ fire.


Fire Extinguishers You’ll Find on Campus

Dry ChemicalDry-Chemical Extinguisher

Generally located in: Labs where significant quantities of flammables are used or stored, kitchens, some fire hose cabinets, utility rooms.

Characteristics: Various colours, has a gauge, may or may not have a flexible nozzle (hose).
Suitable for: The majority of these extinguishers are rated for use on Class A, B, and C fires. Some, however, are rated for B and C only. Check the extinguishers in your area to see what classes of fire they can be used upon.

Carbon Dioxide ImageCarbon Dioxide Extinguisher

Generally located in: Electrical rooms, high-voltage transformer vaults, some additional utility areas.

Characteristics: Red in colour, no gauge, has a “horn” through which the carbon dioxide is discharged.
Suitable for: Class B and C fires.

H2O Extinguisher ImagePressurized Water Extinguisher

Generally located in: Fire hose cabinets in most buildings, some are optionally wall-mounted.

Characteristics: Silver, has a gauge, has a flexible nozzle (hose).
Suitable for: Class A fires.

Fighting Fires with Extinguishers

If you are confronted with a fire in your environment, your first action should always be send for help. Activate the building fire alarm, or send someone else to do it. Only after the fire alarm is sounding should you consider using a fire extinguisher. You should NOT try to fight a fire if:

  • it is generating a substantial amount of smoke
  • it is in close proximity to other flammable or combustible materials
  • it’s too large to handle with one extinguisher
  • it could cut off your exit
  • you’re unsure about the use of an extinguisher

If none of these factors come into play, you must act quickly in order to be successful in extinguishing the fire, while minimizing your own risk. Here’s what to do:

  1. Determine the Class of the fire: A, B, C, or D…
  2. Verify that the extinguisher you will be using is rated for this Class of fire. It can save valuable time if you have already familiarized yourself with the extinguishers (and their class ratings) in your area…
  3. Use the extinguisher to put out the fire. This brings us to our next topic…

How to Use an Extinguisher

Make sure you are standing at least six feet from the fire, and keep your EXIT at your back. Now, think of the word PASS, which will prompt you for each of the four following steps:

P Pull the pin of the extinguisher. This pin normally prevents accidental discharge, and its removal unlocks the trigger mechanism. Don’t squeeze the lever as you remove the pin, but hold the extinguisher by the lower handle only.
A Aim the nozzle of the extinguisher at the BASE of the fire. This is where the fuel is actually burning.
S Squeeze the handle lever. This allows the pressurized extinguishing agent to be discharged onto the target area.
S Sweep from side to side. Work the extinguishing agent over the entire surface of the fire, starting at the closest point and forcing the fire BACK and out. Watch for possible re-ignition. It’s better to use too much extinguisher than too little.

If you run out of extinguishing agent before the fire is put out, or if the fire spreads or grows, GET OUT. Don’t endanger yourself further if your first attempt is unsuccessful.

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