Fire Extinguishers

Remember the acronym “P.A.S.S.”

P – Pull the pin.

A – Aim the extinguisher nozzle at the base of the flames.

S – Squeeze trigger while holding the extinguisher.

S – Sweep the extinguisher from side to side.

How To Extinguish Small Fires:

Class A – Extinguish ordinary combustibles by cooling the material below its ignition temperature and soaking the fibers to prevent re-ignition. Use pressurized water, foam or multi-purpose(ABC-rated) dry chemical extinguishers. DO NOT USE carbon dioxide or ordinary (BC-rated) dry chemical fire extinguishers on Class A fires.

Class B – Extinguish flammable liquids, greases or gases by removing the oxygen, preventing the vapors from reaching the ignition source or inhibiting the chemical chain reaction. Foam, carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical fire extinguishers may be used to fight Class B fires.

Class C – Extinguish energized electrical equipment by using an extinguishing agent that is not capable of conducting electrical currents. Carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical fire extinguishers may be used to fight Class C fires. DO NOT USE water extinguishers on energized electrical equipment.

Class D – Extinguish combustible metals such as magnesium, titanium, potassium and sodium with dry powder extinguishing agents specially designated for the material involved. In most cases, they absorb the heat from the material, cooling it below its ignition temperature.

NOTE: Multipurpose (ABC-rated)chemical extinguishers leave a residue that can harm sensitive equipment, such as computers and other electronic equipment. Because of this, carbon dioxide fire extinguishers are preferred in these instances because they leave very little residue. ABC dry powder residue is mildly corrosive to many metals. For example, residue left over from the use of an ABC dry powder extinguisher in the same room with a piano can seriously corrode piano wires. Carbon dioxide fire extinguishers are provided for most labs and computer areas on campus.


All ratings are shows on the extinguisher faceplate. Some extinguishers are marked with multiple ratings such as AB, BC and ABC. These extinguishers are capable of putting out more than one class of fire.

Class A and B extinguishers carry a numerical rating that indicates how large a fire an experienced person can safely put out with that extinguisher.

Class C extinguishers have only a letter rating to indicate that the extinguishing agent will not conduct electrical current. Class C extinguishers must also carry a Class A or B rating.

Class D extinguishers carry only a letter rating indicating their effectiveness on certain amounts of specific metals.


  • Should your path of escape be threatened.
  • Should the extinguisher run out of agent.
  • Should the extinguisher prove to be ineffective.
  • Should you no longer be able to safely fight the fire.


How To Inspect Your Fire Extinguishers:

  • Know the locations of the fire extinguishers in your area.
  • Make sure the class of the extinguisher is safe to use on fires likely to occur in the immediate area.
  • Check the plastic seal holding the pin in the extinguisher handle. Has the extinguisher been tampered with or used before? Replace any extinguishers with new if the seals are broken.
  • Look at the gauge and feel the weight. Is the extinguisher full? Does it need to be recharged?
  • Water, some foam, and dry chemical extinguishers have gauges indicating the pressure inside the extinguisher. The pressure needle should be in the “green” area (generally 100-175 lbs., depending on the type of agent).
  • CO2 (carbon dioxide) extinguishers are high pressure cylinders with pressures ranging from 1500 lb to 2150 lb. These extinguishers DO NOT have gauges and must be weighed to determine the amount of contents remaining.
  • Make sure the pin, nozzle and nameplate are intact.

The APPEARANCE of different types of extinguishers:

Generally, you can tell with a glance which type an extinguisher is hanging on the wall, or in the cabinet, just by looking at its shape. Check the labels of the extinguishers in your area and note the color and shape/size of the extinguisher. This may help if someone runs in to help you fight a fire with the WRONG extinguisher (i.e. water on an electrical fire) – you can STOP them before they are injured or make matters worse!

ABC-rated multipurpose dry powder extinguishers are the most common. They are almost always RED in color and have either a long narrow hose or no hose (just a short nozzle). These extinguishers are very light (5-25 lbs total weight).

Water extinguishers are generally SILVER (chrome-metal) in color, have a flat bottom, have a long narrow hose, are quite large (2-1/2 gallons). Foam extinguishers look similar and the type without gauges have a handle inset in the flat bottom (you turn the extinquisher upside down to start it and use it)

CO(carbon dioxide) extinguishers are generally red, have a LARGE “tapered” nozzle (horn), are VERY HEAVY (15-85 lbs.) -some CO2 extinguishers for special industrial use are so large as to require roll-around carts to move them. These are all high-pressure cylinders. Care should be used not to drop a CO2cylinder; if it is damaged it can punch a hole through the nearest wall(s).  (The containers are quite sturdy, but don’t abuse them.) CO2 cylinders do not have a pressure gauge – they must be weighed to determine the amount of contents.

“If I just use a little, do I have to refill or replace the extinguisher?”

YES! You should want FULL extinguishers at all your locations.

While CO2 and fire extinguishers will generally hold their pressure after a slight discharge, BC and ABC rated DRY CHEMICAL extinguishers will usually NOT hold a charge after partial use. This is true for all your personal home and vehicle dry chemical extinguishers, too!

While the gauge may hold steady in the green immediately after a slight use, check it the next day and you’ll find the gauge on EMPTY! This is because upon use the dry powder gets inside the seals and allows the nitrogen carrier to escape over a period of time.

After ANY use a BC or ABC extinguisher MUST be serviced and recharged. This is very important for home extinguishers also; YOU MUST HAVE THE EXTINGUISHER REFILLED AFTER ANY USE. You can’t “test” an extinguisher and put it back in the cabinet!