Wet and Dry Rising Mains
A rising main is a system of pipe work and valves, often found in high-rise buildings, which allows fire fighting water to be easily delivered to all floors. It consists of a vertical pipe with an inlet at ground level on an outside face of the building and outlets (known as landing valves) fitted in cabinets at each floor level, allowing fire and rescue service personnel to pressurise the main from their appliances.
Rising mains in buildings can be either filled with water (Wet Riser) or left dry (Dry Riser). Where mains are supplied from rooftop tanks1 and pumps in very tall buildings, the mains are referred to as ‘Falling Mains’ or sometimes ‘Downcomers’.
The installation of risers removes the need for fire fighters to have to drag charged fire hoses all the way up through tall buildings which could delay fire-fighting operations or create a hazard during evacuation.
Wet and Dry Risers should be designed and installed in accordance with BS9990: Code of practice for nonautomatic fire-fighting systems in buildings.:2006
Dry Rising Mains
The pipes in dry risers are empty and are only filled with water by fire fighters when they arrive. Fire fighters will connect the pump outlet in one of their appliances to the dry riser inlet. Water is then drawn from the nearest public fire hydrant (fed by the water supplier’s service main2) and this is pressurised by the fire pump to provide water at the correct flow and pressure for fire fighting operations at the relevant floor level.
Wer Rising Mains
The pipes in wet risers are full of water at all times and have pumps that deliver the water to the outlets, these pumps drawing water from storage tanks. The pumps operate when the pressure in the rising mains drops when a landing valve is opened. They do not depend on the fire brigade appliance or water from the local mains.