Dry and wet rising mains are pipework systems specifically for delivering large volumes of water to the storeys of a building for fire protection purposes. Whilst fires within buildings up to 18m in height can be adequately dealt with by the Fire and Rescue Service, all new buildings intended to be greater in height than this require either dry or wet rising fire mains integrated into their design to accommodate the Fire and Rescue Service in gaining access to a supply of water.
• Dry Risers
A dry riser is a system of empty pipework installed within buildings. It comprises a two way breeching inlet at ground level and a series of water outlets at appropriate locations throughout a building. The two way breeching inlet enables connection to a fire appliance via a hose for the supply of water.
The system of empty pipework feeds landing valves located throughout the storeys of a building as required. At the highest level of the dry riser an automatic air release valve allows trapped air to escape when water is being pumped into the inlet breeching connection and seals itself when the water reaches the top. At this point firefighting water is available at the landing valves enabling fire fighters to attach their hoses and tackle any fire with the confidence that the water supply is plentiful.
Dry risers must be serviced every six months to ensure they comply with regulations. They must undergo an initial wet test, as well as having a visual inspection every six months. This applies to all buildings above 18 metres and below 60 metres (buildings over 60 metres require wet risers).
• Wet Risers
A wet riser system is a system of pipework which is fully and permanently charged with its own dedicated water supply. This water supply would typically be situated in the basement of a building and would comprise water storage tanks normally feeding two wet riser pumps. These pumps can generate a high pressure supply of water and as such wet riser pipework can extend to a much greater height than that of a dry riser system.
As with dry riser systems, wet riser systems enable fire fighters to access a plentiful supply of water and tackle a fire effectively.