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Published: May 13, 2024 4 min read

Fire extinguishers are the most recognizable tool in fire safety. Designed to be easily accessible and noticeable, we see them in virtually every public building, yet most people have never used one and may not be sure how to operate one properly. Let’s learn how fire extinguishers work and how to use one.

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What is a fire extinguisher?

A fire extinguisher is a handheld fire protection device that is used to control small fires. They are filled with a pressurized agent, usually a chemical, that works as a fire retardant by interfering with the three components needed for the chemical reaction that produces fire: oxygen, heat and fuel.

There are different types of fires, which are classified in the United States by letters in order of how common they are. The classes range from ordinary combustibles such as paper and wood, flammable liquids and electrical equipment to more complicated fires involving metals or oil.

  • Class A: Ordinary combustibles
  • Class B: Flammable liquids and gasses
  • Class C: Electrical equipment
  • Class D: Combustible metals
  • Class K: Cooking oil or fat

The most common type of fire extinguisher contains a multipurpose dry chemical called monoammonium phosphate that can put out Class A, B and C fires. This compound is also commonly used in fertilizers.

Regulations by the National Fire Prevention Association (NFPA) require fire extinguishers to be inspected once a month, assuring that the device is full, its pressure gauge is in the suggested range and it’s easily accessible. The NFPA also recommends that workplaces have one extinguisher per 3,000 square feet.

Types of fire extinguishers

There have been all kinds of devices invented to extinguish fires since the 1700s. Some of them were self activating, releasing a liquid when being exposed to fire. Some chemicals previously used for extinguishing fires, such as carbon tetrachloride, were discontinued after its toxicity was discovered. Fire grenades, which are water and salt mixtures in a glass encasing meant to be thrown at the base of a fire, were a type of rudimentary extinguisher.

The carbon dioxide stored-pressure fire extinguisher was invented in the United States at the request of Bell Telephone to extinguish the difficult-to-control fires of telephone switchboards. It was later replaced by a number of chemical formulas as better extinguishing agents became more easily available.

Guide to how to use a fire extinguisher

A helpful way to learn how to use a fire extinguisher is to remember the PASS acronym: pull, aim, squeeze and sweep.

Pull the safety pin

Pull the ring located between the nozzle and the handle. This will allow the handle to be activated and release the pressurized extinguishing agent at will.

Aim at the base of the fire

Aim the nozzle at the base of the fire to make sure you cover the source of the flame with the neutralizing agent. Make sure you are a safe distance away from the flames when aiming.

Squeeze the handle to discharge

Squeeze the handle to discharge the chemical compound onto the fire. Squeeze slowly at first so you can ascertain how much force is needed for the release of the fire retardant.

Sweep the nozzle from side to side

Sweep the nozzle from side to side, making sure to cover all parts of the fire’s source with the dry chemical. Continue until the fire has been extinguished.

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