Fire water
Fire water used to fire departments in combating of fires as extinguishing agents . A fire goes out when the burning material is cooled below its ignition temperature .
The extinguishing water is carried on vehicles to the scene of the incident or it is pumped on site by means of water extraction .
When extinguishing fires, the extinguishing water can create a conductive connection between live parts (cables, electrical devices) or a so-called short circuit , or the person doing the fire can become part of an electrical circuit via the water and receive an electric shock . This is another reason why water is sprayed as much as possible during extinguishing work in order to avoid a compact and therefore electrically conductive water jet.
advantages
Water as an extinguishing agent is inexpensive and readily available. Liquid water does not get hotter than 100 ° C, so its maximum temperature is lower than the ignition temperature of many flammable substances. It is also safe for humans and animals and not harmful to the environment. Due to the high heat of evaporation, water can absorb large amounts of heat. The water vapor produced during extinguishing also displaces the oxygen required for combustion .
Application limits of extinguishing water
- Alkali metals and burning alkaline earth metals react immediately and violently with water, producing extremely flammable hydrogen .
- Chimney fires : One liter of water produces approx. 1700 l of water vapor , the sudden evaporation and the associated increase in volume can blow up a chimney.
- Hot fires in confined spaces: If the extinguishing tactics are incorrect, there is a risk of scalding due to the large amounts of water vapor generated.
- Hot fats , oils and waxes with temperatures above 100 ° C: After sinking into the liquid, the water evaporates suddenly (delayed boiling) and splatters the oil, the oil mist can burn explosively .
- Liquids that are specifically lighter than water, e.g. B. Heating oil, diesel, gasoline: The lighter burning liquid floats on the water and is thus distributed. The water itself does not have an extinguishing effect because it is located under the burning medium.
- Fires in electrical systems: The electrical conductivity of water harbors the risk of coming into contact with high voltage and suffering an electric shock or triggering further fires through a short circuit . Therefore, it can only be used if certain minimum distances are observed. In addition, the use of water makes the entire electrical system unusable, including the parts that were spared from the fire.
- (Light) metals and alloys with these as the main constituent (such as those found in modern car engines, for example) burn at very high temperatures at which water dissociates into oxygen and hydrogen . Both substances react with each other again immediately, fan the fire further and, as an oxyhydrogen reaction, can also cause explosions.
- Substances that can absorb the extinguishing water and thereby swell, such as sawdust or wood pellets . The increase in volume caused by the water can lead to the storage vessel bursting. In the case of a hayloft fire (room above a stable in which hay is stored) this effect can also lead to the soaked hay becoming too heavy and the ceiling structure collapsing.
additions
At the point of use, extinguishing water can be produced from extinguishing water by adding foaming agents and net water by adding wetting agents .
history
Before the establishment of fire brigades in the localities, in the event of a fire, all able-bodied residents had to rush to the scene of the fire with buckets filled with extinguishing water and line up in double rows to the extinguishing water pond : "The bucket flew through the hands of a long chain."
See also
- Extinguishing water supply
- Extinguishing water pumping over long distances
- Fire fighting water retention guideline
Web links
Individual evidence
- ^ Franz-Josef Sehr : The fire extinguishing system in Obertiefenbach from earlier times . In: Yearbook for the Limburg-Weilburg district 1994 . The district committee of the Limburg-Weilburg district, Limburg-Weilburg 1993, p. 151-153 .