Fire hydrant

A fire hydrant (also known colloquially as a fire plug in the USA or as a johnny pump in New York City), is an active fire protection measure, and a source of water provided in most urban, suburban and rural areas with municipal water service to enable firefighters to tap into the municipal water supply to assist in extinguishing a fire.

The concept of fire plugs dates to at least the 1600s. This was a time when firefighters responding to a call would dig down to the water mains and hastily bore a hole to secure water to fight fires via bucket brigades or, later, via hand pumped fire engines. The holes were then plugged with stoppers, which over time came to be known as fire plugs. This is the source of the colloquial term fire plug still used for fire hydrants today. After the Great Fire of London in 1666, the city installed water mains with holes drilled at intervals, equipped with risers, placing the fire plugs at street level.

It has been claimed that Birdsill Holly invented the fire hydrant, but his 1869 design was preceded by many other patents for fire hydrants, and a number of these earlier designs were produced and successfully marketed. Numerous wooden cased fire hydrant designs existed prior to the development of the familiar cast iron hydrant. Although the development of the first above ground hydrant in the USA traces back to Philadelphia in 1803, underground fire hydrants — common in parts of Europe and Asia — have existed since the 1700s.

Operation

A hose is attached to the fire hydrant, then the valve is opened to provide a powerful source of water, 50 lbf/in² (350 kPa) in some areas (possibly 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 use a powerful pump to boost the water pressure and possibly split it into multiple streams. The hose may be connected with a threaded connection or a Storz connector. Care should be taken not to open or close a fire hydrant too quickly, as this can create a water hammer which can damage nearby pipes and equipment. The high water pressure inside the hose causes it to be very heavy, stiff, and unable to make a tight turn while pressurized. When a fire hydrant is unobstructed, this is not a problem, as there is enough room to adequately position the hose.

Most fire hydrant valves are not designed to throttle the water flow; they are designed to be operated full-on or full-off. Attempting to throttle the flow with the hydrant valve can cause damage to some hydrant designs. A hose with a closed nozzle valve, or fire truck connection, or closed gate valve is always attached to the hydrant prior to opening the hydrant's main valve.

In most jurisdictions it is illegal to park a car within a certain distance of a fire hydrant. In North America the distances are commonly 10 to 15 ft, or 3 to 5 m, often indicated by yellow or red paint on the curb. In the UK, yellow lines are used to keep cars from parking over underground hydrants. Parking restrictions are sometimes ignored (especially in cities where available street parking is scarce), however these laws are usually enforced. The rationale is that hydrants need to be visible and accessible in an emergency.

Other uses

To prevent casual use or misuse, the hydrant requires special tools to be opened, usually a large wrench with a pentagon-shaped socket. Vandals sometimes cause monetary loss by wasting water when they open hydrants. Such vandalism can also reduce municipal water pressure and impair firefighters' efforts to extinguish fires. Sometimes those simply seeking to play in the water remove the caps and open the valve, providing residents a place to play and cool off in summer. However, this is usually discouraged as residents have been struck by passing automobiles while playing in the street in the water spray. In spite of this, some US communities provide low flow sprinkler heads to enable residents to use the hydrants to cool off during hot weather, while gaining some control on water usage.

In most US areas, contractors who need temporary water may purchase permits to use hydrants. The permit will generally require a Hydrant Meter, a gate valve and sometimes a clapper valve (if not designed into the hydrant already) to prevent back-flow 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.

Municipal services, such as street sweepers and tank trucks, may also be allowed to use hydrants to fill their water tanks. Often sewer maintenance trucks need water to flush out sewer lines, and fill their tanks on site from a hydrant. If necessary, the municipal workers will record the amount of water they used, or use a meter.

Construction

In areas subject to freezing temperatures, only a portion of the hydrant is above ground. The valve is located below the frost line and connected via a riser to the above-ground portion. A valve rod extends from the valve itself up through a seal at the top of the hydrant, where it can be operated with the proper wrench. This design is known as a "dry barrel" hydrant, in that the barrel, or vertical body of the hydrant, is normally dry. A drain valve underground opens when the water valve is completely closed; this allows all water to drain from the hydrant body to prevent the hydrant from freezing.

In warm areas, hydrants are used with one or more valves in the above-ground portion. Unlike cold-weather hydrants, it is possible to turn the water supply on and off to each port. This style is known as a "wet barrel" hydrant.

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. In many localities, hydrants are color-coded to indicate the amount of water, in 500 US gal/min (32 L/s) increments, that the hydrant is capable of providing. This aids arriving firefighters in determining how much water is available and whether to call for additional resources, or locate another hydrant. In other places, such as in Ottawa, hydrant colors communicate different messages to firefighters; for example, if the inside of the hydrant is corroded so much that the interior diameter is too narrow for good pressure, it will be painted in a specific scheme to indicate to firefighters to move on to the next one. In many localities, a white or purple top indicates that the hydrant provides non-potable water.

Signage

In the UK, hydrants are located in the ground. Yellow "H" hydrant signs indicate the location of the hydrants, and are similar to the blue signs in Finland. Mounted on a small post or nearby wall etc, the two numbers indicate the size of the water main in millimetres (top number) and the distance in metres from the sign (lower number). Older signs may use Imperial units.

In areas of the U.S. without winter snow cover, blue reflectors embedded in the street are used to allow rapid identification of hydrants at night. In areas with snow cover, tall signs or flags are used so that hydrants can be located even if covered with snow. In rural areas tall narrow posts painted with visible colours such as red are attached to the hydrants to allow them to be located during heavy snowfall periods.

Inspection and maintenance

In most areas fire hydrants require annual inspections and maintenance - they normally only have a one year warranty, but some have 5 year warranties. These inspections are generally performed by the local municipalities but they often do not inspect hydrants that are identified as private. Private hydrants are usually located on larger properties to adequately protect large buildings in case of a fire and in order to comply with the fire code. Some companies are contracted out to inspect private fire hydrants unless the municipality has undertaken that task.

Fire Hydrant manufacturers recommend lubricating the head mechanism and restoring the head gaskets and o-rings annually in order that the fire hydrant perform the service expected of them.

Historical inventions and innovations

Around the world, fire hydrants take on many designs and guises. Many of these designs carry with them a history. The inventor of the injected fire hydrant was James Henry Greathead. Greathead was an innovator and inventor and the injected fire hydrant was only one of his minor inventions. Another one of his inventions was the Greathead tunnelling shield.

Non-pressurized hydrants

In rural areas where municpal water systems are not available, dry hydrants are used to supply water for fighting fires. A dry hydrant is similar to a standpipe. A dry hydrant is usually a unpressurized permanently installed pipe that has one end below the water level of a lake or pond. This end usually has a strainer to prevent debris from entering the pipe. The other end is above ground and has a standard fire hose connector. When needed, a pumper fire engine will pump water from the lake or pond using suction. For more information and photos see www.dryhydrants.com [1]

Other types

Water wells are also sometimes classified as fire hydrants if they can supply enough water volume and pressure.

References

U.S. patent 909 -- Issued to John Jorden on September 8, 1838 for "...a new and useful improvement in Fire-Plugs and Hydrants...". This is an early wooden bodied hydrant, the earliest hydrant patent extant; the patent office itself burned to the ground in 1836, taking with it all prior hydrant patents.
U.S. patent 37,466 -- Issued to Richard Stileman on January 20, 1863. An early iron hydrant, believed the first patented hydrant with the larger size steamer port to supply steam fire engines. Manufactured and marketed as the Stileman hydrant. See also Stileman page at FireHydrant.org.
U.S. patent 80,143 -- Issued to Zebulon Erastus Coffin on July 21, 1868. This is a cast iron hydrant very similar to modern fire hydrants, it was produced by Boston Machine Co. See also Boston Machine page at FireHydrant.org.
U.S. patent 94,749 -- Issued to Birdsill Holly on September 14, 1869. Birdsill Holly himself makes no claim in his patent text that he invented the fire hydrant. What is more, his improvements are relatively minor, and today, obsolete. See also Holly page at FireHydrant.org.
Wohleber, Curt. "The Fire Hydrant". In The American Heritage of Invention & Technology. Winter 2002. Retrieved December 25, 2005. Provides a history with dates of fire hydrant development.

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