A fire hydrant, waterplug, or firecock (archaic) is a connection point by which firefighters can tap into a water supply. It is a component of active fire protection. Underground fire hydrants have been used in Europe and Asia since at least the 18th century. Above-ground pillar-type hydrants are a 19th-century invention.
Before piped mains supplies, water for firefighting had to be kept in buckets and cauldrons ready for use by ‘bucket-brigades‘ or brought with a horse-drawn fire-pump. From the 16th century, as wooden mains water systems were installed, firefighters would dig down to the pipes and drill a hole for water to fill a “wet well” for the buckets or pumps. This had to be filled and plugged afterwards, hence the common US term for a hydrant, ‘fireplug’. A marker would be left to indicate where a ‘plug’ had already been drilled to enable firefighters to find ready-drilled holes. Later wooden systems had pre-drilled holes and plugs. When cast-iron pipes replaced the wood, permanent underground access points were included for the fire fighters. Some countries provide access covers to these points, while others attach fixed above-ground hydrants – the first cast iron ones were patented in 1801 by Frederick Graff, then chief-engineer of the Philadelphia Water Works. Invention since then has targeted problems such as tampering, freezing, connection, reliability etc.
The user attaches a hose to the fire hydrant, then opens a valve on the hydrant to provide a powerful flow of water, on the order of 350 kilopascals (51 psi); this pressure varies according to region and depends on various factors (including the size and location of the attached water main). This user can attach this hose to a fire engine, which can use a powerful pump to boost the water pressure and possibly split it into multiple streams. One may connect the hose with a threaded connection, instantaneous “quick connector” or a Storz connector. A user should take care not to open or close a fire hydrant too quickly, as this can cause a water hammer, which can damage nearby pipes and equipment. The water inside a charged hose line causes it to be very heavy and high water pressure causes it to be 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. The valving arrangement of most dry-barrel hydrants is for the drain valve to be open at anything other than full operation. Usage at partial-opening can consequently result in considerable flow directly into the soil surrounding the hydrant, which, over time, can cause severe scouring. Gate or butterfly valves can be installed directly onto the hydrant orifices to control individual outputs and allow for changing equipment connections without turning off the flow to other orifices. These valves can be up to 12 inches (30 cm) in diameter to accommodate the large central “steamer” orifices on many US hydrants. It is good practice to install valves on all orifices before using a hydrant as the protective caps are unreliable and can cause major injury if they fail.
New firefighters are often trained extensively on fire hydrants in the fire academy to be quick and safe while connecting the fire engine to the fire hydrant (usually within 1 minute). Time is often critical as other firefighters will be waiting for the water supply. When operating a hydrant, a firefighter typically wears appropriate personal protective equipment, such as gloves and a helmet with face shield worn. High-pressure water coursing through a potentially aging and corroding hydrant could cause a failure, injuring the firefighter operating the hydrant or bystanders.
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 3 to 5 metres (10 to 16 ft), often indicated by yellow or red paint on the curb. The rationale behind these laws is that hydrants need to be visible and accessible in an emer
In 1896, during a terrible heatwave in New York City, the Commissioner of Public Works ordered the opening of the fire hydrants to provide relief to the population. Today 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. 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.
To prevent casual use or misuse, the hydrant requires special tools to be opened, usually a large wrench with a pentagonal 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. Most fire hydrants in Australia are protected by a silver-coloured cover with a red top, secured to the ground with bolts to protect the hydrant from vandalism and unauthorized use. The cover must be removed before use.
In most areas of the United States, 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 sewerage 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.
Since fire hydrants are one of the most accessible parts of a water distribution system, they are often used for attaching pressure gauges or loggers or monitor system water pressure. Automatic flushing devices are often attached to hydrants to maintain chlorination levels in areas of low usage. Hydrants are also used as an easy above-ground access point by leak detection devices to locate leaks from the sound they make.