A Wet Riser is the foremost vertical pipe intended to dispense water to multiple levels of a building as an element of a fire suppression system. Wet risers are permanently charged with water. This is as opposed to dry risers which do not contain water when they are not being used but are charged with water by fire service pumping appliances when necessary.
Wet risers are used to supply water inside buildings for fire-fighting purposes. The facility of a built-in water delivery system means that fire fighters do not need to use their own distribution system in order to fight a fire and it avoids the opening of fire compartments by running hose lines between them.
Part B of the building regulations (Fire Safety) requires that fire mains are provided in all buildings that are more than 18 m tall. In buildings less than 50 m tall, either a wet riser or dry riser fire main can be provided. However, where a building extends to more than 50 m above the rescue service vehicle access level, wet risers are necessary as the pumping pressure required to charge the riser is higher than can be provided by a fire service appliance, and to ensure an immediate supply of water is available at high level. .
Wet risers are charged with water from a pressurised supply, often pumped from a storage tank, with landing valves at specified locations on each floor. Generally, a wet riser supply system would be capable of maintaining a minimum running pressure at top outlet at roof level of 4 bar at a flow rate of 22.7l/s. the maximum running pressure permitted with only one outlet in operation is 5 bar. Wet riser outlets, or 'landing valves' may be within in protected lobbies, stairs or enclosures where these are available.
Wet risers are inspected and tested regularly to make sure that the equipment is operating correctly and ready for use.
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