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Fire hydrant

City Fire Hydrant

A fire hydrant (or colloqually, fire plug) is a source of water provided by most metropolitan communities to enable firefighters to tap into the water supply to assist in extinguishing a fire. It enables them to draw water from the municipal water supply. To prevent casual use or misuse, the hydrant requires special tools to be opened.

A hose is attached to the hydrant, then the valve is opened to provide a powerful source of water, 50 psi in some areas, more in others, depending on various factors including the size and location of the attached water main. This hose can be further attached to a fire engine, which can then boost the pressure and possibly split it into multiple streams. Care should be taken not to open or close a fire hydrant too quickly, as this can create water hammer which can damage pipes and equipment.

Some communities provide sprinkler heads to enable residents to use the hydrants to cool off during hot weather. Due to the presence of standing water inside the hydrant for weeks and months at a time, it is necessary to drain them on occasion to prevent bacteria from seeping back into the drinking water system serving the hydrant.

A siamese clappered inlet
In most areas, contractors who need temporary water may be permitted to use hydrants subject to attaching a meter and a clapper valve to prevent backflow into the hydrant. Additionally, residents who wish to use the hydrant to fill their in-ground swimming pool are commonly permitted to do so provided they pay for the water and agree to allow firefighters to draft from their pool in the case of an emergency.

Due to their constant presence and utilitarian nature, some cities and towns allow fire hydrants to be painted in various colors and/or as whimsical characters. The most common colors are red and yellow.

It is illegal, in most jurisdictions, to park a car in front of or within a certain distance of a fire hydrant. The distances are commonly 10-15 feet, or 3-5 meters. Especially in cities, this is commonly ignorned, and causes a headache to firefighters who need to connect to the hydrant. In the movie Backdraft, a firefighter faced with this problem smashes the windows in the car and passes the firehose through the car to the fire hydrant. Whether this scene was inspired by a true incident or the movie inspired some firefighters to use this technique, it has happened in actual situations.

See also: fire extinguisher, sprinkler, arson.