Fire hydrant

Construction

Depending on the country or location, hydrants can be above or below ground. In countries including Japan, the UK, Ukraine, Russia or Spain hydrants are accessible under a heavy metal cover. In other countries, such as the US, and many parts of China, an accessible part of the hydrant is above ground. It can also be mounted in an exterior wall of a building.

In areas subject to freezing temperatures, at most only a portion of the hydrant is above ground. The valve is located below the frost line and connected by a riser to the above-ground portion. A valve rod extends from the valve 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, above-ground hydrants may be used with one or more valves in the above-ground portion. Unlike with 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.

Both wet- and dry-barrel hydrants typically have multiple outlets. Wet barrel hydrant outlets are typically individually controlled, while a single stem operates all the outlets of a dry barrel hydrant simultaneously. Thus, wet barrel hydrants allow single outlets to be opened, requiring somewhat more effort, but simultaneously allowing more flexibility.

A typical US dry-barrel hydrant has two smaller outlets and one larger outlet. The larger outlet is often a Storz connection if the local fire department has standardized on hose using Storz fittings for large diameter supply line. The larger outlet is known as a "steamer" connection, because they were once used to supply steam powered water pumps, and a hydrant with such an outlet may be called a "steamer hydrant", although this usage is becoming archaic. Likewise, an older hydrant without a steamer connection may be called a "village hydrant."

Appearance

Above-ground hydrants are coloured for visibility, to signal their characteristics, or for aesthetics. In the United States, the AWWA and NFPA recommend hydrants be colored chrome yellow for rapid identification apart from the bonnet and nozzle caps which should be coded according to their available flow. Class AA hydrants (>1500 gpm) should have their nozzle caps and bonnet colored light blue, Class A hydrants (1000–1499 gpm) green, Class B hydrants (500–999 gpm) orange, Class C hydrants (0–499 gpm) red, and inoperable or end-of-system (risking water hammer) black. These aids arriving firefighters in determining how much water is available and whether to call for additional resources or find another hydrant.

Other codings can be and frequently are used, some of greater complexity, incorporating pressure information, others more simplistic. In Ottawa, Ontario, 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. Where artistic and/or aesthetic considerations are paramount, hydrants can be extremely varied, or more subdued. In both instances this is usually at the cost of reduced practicality.

In Germany, the Netherlands, Spain, the UK, and many other countries, most hydrants are located below ground and are reached by a riser, which provides the connections for the hoses. The covers can also be artistically designed.

In East Asia (China, Japan and South Korea) and former Socialist countries of Eastern Europe, there are two types of fire hydrants, of which one is on the public ground and the other inside a building. The ones inside a building are installed on a wall. They are big, rectangular boxes that also provide alarms (sirens), a fire extinguisher and, at certain times, emergency kits.

Signage

In the United Kingdom and Ireland, 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 diameter of the water main (top number) and the distance from the sign (lower number). Modern signs show these measurements in millimetres and metres, whereas older signs use inches and feet. Because the orders of magnitude are so different (6 inches versus 150 mm) there is no ambiguity whichever measuring system is used.

In areas of the United States 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 found 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 found during heavy snowfall periods. The tops of the fire hydrants indicate available flow in gallons per minute; the color helps make a more accurate choice of what hydrants will be utilized to supply water to the fire scene.

• Blue: 1,500 US gallons per minute (1,249 imp gal/min; 95 L/s) or more; very good flow
• Green: 1,000–1,499 US gallons per minute (833–1,248 imp gal/min; 63–95 L/s); good for residential areas
• Orange: 500–999 US gallons per minute (416–832 imp gal/min; 32–63 L/s); marginally adequate
• Red: below 500 US gallons per minute (416 imp gal/min; 32 L/s); inadequate

The hydrant bodies are also color-coded.

• Chrome Yellow: Municipal System
• Red: Private System
• Violet: Non-potable supply

These markings and colours are prescribed in NFPA 291: Recommended Practice for Water Flow Testing and Marking of Hydrants. but most municipal water authorities do not actually follow these guidelines.

In Australia, hydrant signage varies, with several types displayed across the country. Most Australian hydrants are underground, being of a ballcock system (spring hydrant type), and a separate standpipe with a central plunger is used to open the valve. Consequently, hydrant signage is essential, because of their concealed nature.

In the Fire Rescue Victoria fire district, L-type hydrants are above-ground hydrants with a non-reflective Signal Red cover top for identification. Fire Rescue Victoria advises that L-type covers should not be used to identify below-ground hydrants because they cause unnecessary delays in obtaining water.

• Painted markers – Usually a white or yellow (sometimes reflective paint) triangle or arrow painted on the road, pointing towards the side of the road the hydrant will be found on. These are most common in old areas, or on new roads where more advanced signs have not been installed. These are almost always coupled with a secondary form of signage.
• Hydrant Marker Plates – Found on power poles, fences, or street-signs, these are a comprehensive and effective system of identification. The plate consists of several codes; H (Potable water Hydrant), RH (Recycled/Non-Potable), P (Pathway, where the hydrant cover can be found), R (Roadway). The plate is vertically oriented, around 8 cm wide, and 15 cm high. It usually faces in the direction of the hydrant. Found on this plate, from top to bottom, are the following features:
  • The codes listed above, Potable/Non-potable at the top, Path/Roadway on the bottom of the plate.
  • Below this, a number giving the distance to the hydrant (in meters), then a second number below that giving the size (in millimeters) of the water main.
  • A black line across the center of the plate indicates the hydrant is found on the opposite side of the road to which the plate is affixed.
  • Plates for recycled water have a purple background, as well as the RH code, normal potable hydrants are white, with the H code.
• Road markers or Cat's eyes – Almost exclusively blue, these are placed on one side or the other of the centre line of the road, to indicate on which side of the road the hydrant lies. They are visible for several hundred meters at night in heavy rain, further in clear conditions.

In Germany the hydrant marker plates follow the style of other marker plates pointing to underground installations. Fire hydrant marker plates have a red border. Other water hydrants may have a blue border. A gas hydrant would have a yellow background instead of a white one for fire hydrants. All of them have large central T with the installation identification on top of it – an "H" or older "UH" is located in the ground, a "OH" is above ground, followed by the pipe inner diameter in millimeters (with a small 80 mm in residential areas). The numbers around the T allow to locate the installation in reference to the plate's location – the number left of the T is in meter left of the sign, the number right of the T is in meter right of the sign, and number below the T tells the distance in meter in front of the sign, where a negative number would point to a place behind the sign. The distance numbers are always given with a comma decimeter precision. If it is not a common fire hydrant type then another identification may be used, for example "300 m³" would point to a cistern usable to pump water from.

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- or even 10-year warranties, although the longer warranty does not remove the need for periodic inspections or maintenance. These inspections are generally performed by the local municipalities or fire departments, 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. Such hydrants have met the requirements of insurance underwriters and are often referred to as UL/FM hydrants. Usually, companies are contracted out to inspect private fire hydrants, unless the municipality has undertaken that task.

Some 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, while others have incorporated proprietary features to provide long-term lubrication of the hydrant's operating mechanism. In any case, periodic inspection of lubricants is recommended. Lubrication is generally done with a food-grade non-petroleum lubricant to avoid contamination of the distribution system.

Occasionally a stone or foreign object will mar the seat gasket. In this case, most hydrants have a special seat wrench that allows removal of the seat to replace the gasket or other broken parts without removing the hydrant from the ground. Hydrant extensions are also available for raising a hydrant if the grade around the hydrant changes. Without extending the height, the wrenches to remove caps would not clear and the break flanges for traffic models would not be located correctly in case they were hit. Hydrant repair kits are also available to repair sacrificial parts designed to break when hit by a vehicle.

Many fire departments use the hydrants for flushing out water line sediments. When doing so, they often use a hydrant diffuser, a device that diffuses the water so that it does not damage property and is less dangerous to bystanders than a solid stream. Some diffusers also dechlorinate the water to avoid ground contamination. Hydrants are also sometimes used as entry or exit points for pipe cleaning pigs.

In 2011, Code for America developed an "Adopt a Hydrant" website, which enables volunteers to sign up to shovel out fire hydrants after snowstorms. As of 2014, the system has been implemented in Boston; Providence, Rhode Island; Anchorage, Alaska; and Chicago.

Non-pressurized (dry) Hydrants

In rural areas where municipal water systems are not available, dry hydrants are used to supply water for fighting fires. A dry hydrant is analogous to a standpipe. A dry hydrant is usually an 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 or wildlife, such as fish, from entering the pipe. The other end is above ground and has a hard sleeve connector.

When needed, a pumper fire engine will pump from the lake or pond by drafting water. This is done by vacuuming the air out of the dry hydrant, hard sleeve, and the fire engine pump with a primer. Because lower pressure now exists at the pump intake, atmospheric pressure on the water and the weight of the water forces water into the above-water portion of the dry hydrant, into the hard sleeve, and finally into the pump. This water can then be pumped by the engine's centrifugal pump.

Other types

• Water wells are also sometimes classified as fire hydrants if they can supply enough water volume and pressure.
• Standpipes are connections for firehoses within a building and serve the same purpose inside larger structures as fire hydrants do outdoors. Standpipes may be "dry" or "wet" (permanently filled with water); a dry standpipe requires an external source of water such as firefighting equipment.

History

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.