How does water put out fire?

There are various methods of putting out a fire that address what a fire needs to exist: Fuel, heat and oxygen. So if you want to stop the flames, you have to turn off at least one of these elements.

Withdraw fuel

A fire needs a constant supply of flammable substances. If it is possible to remove all fuel from its vicinity, it must soon be extinguished. This applies both on a small scale and on a large scale. As a preventive measure against forest fires, but also for active fire fighting, firebreaks are created. These clearing strips in a forest should be so wide that a fire cannot "jump over" them.

Fire brigade when extinguishing - Paul-Georg Meister /

Decrease heat

A fire itself generates heat, which in a chain reaction enables further combustion. On the other hand, if the temperature falls below the fire point or flash point, the fire goes out. People take advantage of this effect in the most common fire fighting method: the Extinguishing with water.

Contrary to popular belief, it is not moisture that fights the fire, but moisture cooling from the water. The fire heats the water until it turns into water vapor and loses energy in the process. Theoretically, fire can also be cooled in other ways, but water usually has the advantage of being available in large quantities.

Attempting to extinguish the fire with snow would hardly bring any advantages compared to water, since a house fire, for example, can reach temperatures of over 1000 degrees, whereas the temperature difference between liquid and frozen water is marginal.

Cut off the supply of oxygen

Fire is usually based on an oxidation process with oxygen. If you want to start a fire - like a grill or a fireplace - you have to improve the oxygen supply. In order to extinguish a fire, the opposite is necessary: ​​The extinguishing agent used in this case should create a separating layer between the fire and the outside air. The separating layer prevents the oxidation from continuing. The fire is, as they say, "suffocated".

As a separating material come among other things Sand, foam, fire blankets or extinguishing powder in question. Some fire extinguishers are filled with foam or so-called ABC powder. The extinguishing powder consists mainly of the flame-retardant substances ammonium dihydrogen phosphate and ammonium sulfate.

In addition to the primary cooling effect, extinguishing water also helps to reduce the supply of oxygen. The water heats up to form water vapor, which can cover the seat of the fire like a shielding cloud.

Fire classes

Not every fire can be fought with the same methods and extinguishing agents. For example are allowed to Never extinguish fat fires with water become. The water droplets are enveloped in the hot fat, expand quickly, become gaseous and create a dangerous explosion in the process.

The European Union has defined five "fire classes" for a successful and safe extinguishing process. All flammable substances can be classified in this standard:

  • Fire class A: Solid fires, e.g. of wood or coal, which can be extinguished with water, among other things
  • Fire class B: Liquid fires, e.g. from gasoline or alcohol, which can be smothered with foam, powder or carbon dioxide
  • Fire class C: Gas fires, e.g. of natural gas, hydrogen or methane, which are mainly fought with extinguishing powder after the gas supply has been stopped
  • Fire class D: Metal fires, a comparatively rare type that can best be smothered with so-called D-extinguishing powder - as a makeshift with completely dry sand or cement powder
  • Fire class F: Fat and oil fires which, like metal fires, should never be treated with water; In addition to professional extinguishing agents from the fire brigade, the best chance is to smother a grease fire in a pan with a lid.