What is Dry Riser System?
Dry risers are required fire-fighting devices that certain types of buildings or indoor areas should be equipped to respond to fires, such as occupied buildings over 18 meters tall, multi-level basements, or hospital corridors.
Such a system has a network of pipes delivering water to the fire scene on the upper floors of a building. First responders from the fire department can use the inlet at the ground level to pump water upward to the outlets installed on the landings of each floor of the building that is on fire. In this way, firefighters can easily hook their hoses to the outlets and
extinguishing the fire with pressurized water.
The fixed distribution system of a riser system largely reduces fire department’s heavy workload because it saves the firefighters carrying their resources or equipment.
The system’s embedded design can also maintain the building’s compartmentation structure.The riser system is mainly composed of three part: the external inlet, the pipework, and the internal outlets.
The external inlet, connected to fire department’s water supplies, is normally located in an external cupboard or enclosure indicating “DRY RISER INLET,” within which a collecting head has at least two BS Instantaneous male couplings can be found.
The pipework is made of galvanized steel and kept dry or free of water, usually in fire resistant shafts/enclosures.
The pipe’s internal diameter is officially set at 100mm in the UK for buildings over 18 meters, and up to 150mm for taller buildings.
An air valve can be found on the top of the pipework to vent out the air in the riser as water comes in the system.
The internal outlets (aka landing valves), consisting of a single/double BS instantaneous female outlet, serve as a connector of the system. They help the firefighters attach the hose lines and extend them to the fire scene in the building.
The outlets are normally located in a protected area or cupboard near the lobby, enclosures, fire escape staircases, or even at the roof level of the building for urgent connection or testing.
All internal outlets are required to meet the standards of BS 5041, BS 5306, BS 9990 and Building Approval Regulations.
What is Wet Riser System?
Similar in design to the dry riser system as described previously, the wet riser system is typically installed in buildings over 50 meters tall. It is, however, constantly charged with pressurized water pumped from a storage tank to provide water supplies for upper reaches of fire scenes on higher floors.
Wet riser systems are a must in high-rise buildings (over 50 meters tall) where higher pumping pressure is needed to charge the riser than that can be provided by fire service’s equipment, with minimum running pressure at 4 bar and a flow rate of 22.7l/s for the roof top outlet. The maximum running pressure (one outlet in operation) is 5 bar.
It is possible but rare for the fire department to provide the wet risers with water supply as the storage tank is running low. Wet riser systems, as are dry risers mentioned previously, are required to be installed in the fire-fighting shafts located closed to fire escape stairs while the outlets should be located around protected lobbies, stairs, or enclosures, whatever is available.
Regular maintenance and inspections are more important for wet risers to ensure normal operation and avoid unexpected malfunction in case of fire. Most common causes of system failure are vandalism, theft, blockages, or problems of connection between pipework and outlets.
Both dry and wet riser systems are indispensable parts of modern high-rise buildings. These systems enable firefighters to do their job efficiently and confidently with adequate water supplies at any level of the building on fire.
