How Does a Fire Extinguisher Work?

Fire extinguishers function fast and efficiently to put out fires. But how do they work? Find out below.

How Do Fire Extinguishers Work?

Fires are chemical combustion reactions ignited in an atmosphere with oxygen and a fuel source. Fires produce extreme heat and can spread easily when near combustible materials such as wood, paper, rubbish, or grease, among others.

Three elements must be present to sustain a fire and include:

  • Oxygen
  • Fuel
  • Heat

The purpose of a fire extinguisher is to break this process by removing or blocking one of these three elements. Once this happens, the fire will either extinguish immediately or burn out. To remove heat, a fire extinguisher can smother the fire. To remove oxygen, the fire extinguisher can smother it as well. Fuel will not be removed by a fire extinguisher and may need to be physically removed or just burn out.

Modern fire extinguishers are made of a metal cylinder attached to a handle with a squeezable trigger mechanism. Most fire extinguishers also have a pressure gauge. When the trigger is squeezed, the contents are released at high pressure and spray out at a safe distance to the user. A good comparison to a fire extinguisher is a aerosol paint can which is a metal container with contents stored under pressure.

The contents of a fire extinguisher are dry powders, liquids such as water, or a gas specially made for fighting fires. The propellant, which forces out the contents, are stored under extreme pressure, which is why the container is made of steel.

How Does a C02 Fire Extinguisher Work?

A C02 fire extinguisher works similar to other types, except for a few differences. Out of the handle is attached a large, cone-shaped horn, usually black in color. This allows the carbon dioxide gas to expel, then expand, and turn into a mixture of gas and a frozen snow-like substance. The cone is shaped in way as not to become blocked by freezing snow material, and also keep the C02 and freezing contents continually mixing as to prevent only a C02 blast from coming out.

A C02 fire extinguisher has the following parts:

  • A pressurized liquid carbon dioxide tank
  • A squeezable trigger mechanism.
  • Valve
  • Discharge cone made of hard plastic
  • A nipple to attach the horn to

A C02 fire extinguisher will not have a pressure gauge becuase C02 is always stored at 830 psi, so a gauge is useless.

How A Fire Extinguisher Works

How Does a Dry Chemical Fire Extinguisher Work?

A dry chemical fire extinguisher contains the following elements:

  • An operating lever or squeezable trigger
  • A metal safety pin
  • A pressure gauge
  • A metal cylinder
  • An internal gas cylinder or compartment
  • A nozzle
  • An internal siphon

A dry chemical fire extinguisher works differently than a C02 fire extinguisher. For one, the pressure inside the container must be checked and maintained at a certain level. If the indicator points to ‘RECHARGE’ or “OVERCHARGE’, then the extinguisher must be serviced by a trained professional.

To use a dry chemical fire extinguisher, first the safety pin must be pulled and then the trigger squeezed. There is an internal gas cylinder release valve that is pierced with an actuading rod that pushes down when the trigger is squeezed. This releases the gas stored in the cylinder. The metal safety pin is there to preven the trigger from being pressed accidentally, such as while moving the extinguisher, or by a small child.

Inside the main container, the compressed gas is released from its compartment and forces the dry powder up through the siphon and out the nozzle at high speed.

How Does a Water Fire Extinguisher Work?

Water fire extinguishers are very common and works similar to a dry powder type. It contains a small gas compartment inside the metal cylinder which forces out the water through the nozzle when it is released. The stored gas is usually carbon dioxide or nitrogen.

Water fire extinguisher contain the following elements:

  • A metal outer container filled with water
  • An internal gas cylinder or compartment
  • A squeezable trigger
  • A nozzle
  • An internal siphon
  • A safety pin

A water fire extinguisher releases a stream of water at high pressure to put out wood, paper, and rubbish fires. It acts similar to a large water toy squirt gun, but with much more water being released.

How Does a Foam Fire Extinguisher Work?

Foam fire extinguishers, also called aqueous film-forming foam or AFFFs, have the added benefit of producing more sprayable contents compared to a similar sized water fire extinguisher. The foam mixture produces more spray quantity than water alone because it expands when mixed, which makes these very effective fire extinguishers. They excel at smothering the fire and cutting off the oxygen supply.

Foam fire extinguishers usually use compressed nitrogen or C02 gas and spray a dry powder or foam mixture.

The foam is sent out of the container while swirling and mixing and this produces a large volume of spray. The foam is a mixture of water and chemicals, and the water provides a cooling effect on the fire.

How Does a Fire Extinguisher Gauge Work?

Fire extinguisher gauges are included on fire extinguishers to show how much pressure is stored within the container. If the pressure drops too low, the extinguisher will not have enough to force the contents out. If the pressure is too high, the fire extinguisher has the risk of spraying with too much force and either injuring the user or making the fire spread further.

Fire extinguisher gauges will have a three section marking on them, This includes a “full”, “empty”, “recharge”, or “overcharged” label. The middle section will be a green color and this is where you want the indicator pointing to.

Fire extinguisher pressure gauges should be checked atleast once per month.

To Close

Fire extinguishers are very effective at what they do and are designed as such. However, they must be kept functioning properly over time so they can be relied upon when you really need them. So, make sure your fire extinguishers are inspected in regular intervals.

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Nick Klamecki, Author
About Nick Klamecki, Author

Nick Klamecki is a certified Fire and Workplace Safety expert with 15 years experience in product research and testing. He has a degree from U.C. Davis, is an active outdoorsman and spent years ensuring the safety of special needs children. Nick researches and tests workplace, industrial and safety products and provides advice on their safe use. Learn more about Nick here or connect with him on LinkedIn | Medium