The difference between dry riser and wet riser systems
The main difference between the dry riser and wet riser systems, is that one contains water at all times, whereas the other is an empty system that can be flooded with water when needed to get it to a specific place.
Dry riser and wet riser systems are found in buildings, as a method of supplying water for fire fighting emergencies. Wet riser systems are the more common of the two and can be found in many buildings worldwide. They are a system of pipes that are kept full of water at all times that may be quickly dispensed in the event of an emergency. The water supply for a wet riser is usually pumped from a central storage tank, to specific valves on each floor. It may use a dedicated fire pump or pressurised gravity tank. Although they already contain water, it is also possible for fire fighters to supplement the water supply in a wet riser system with their own water, if the supply is running low. This is unusual but could happen if the water level in the tank is not adequate, or the system is in use for a long period of time and more water is needed.
A dry riser, as the name suggests, is the system that does not contain water except when needed i.e. when the system is in use.
It is an empty pipe, or network of pipes, that may be connected to an external water source and used to distribute water, usually to upper levels of a building. A dry riser can be linked to multiple levels of a building, making it a quick and easy option for distributing water quickly and safely in the event of a fire. The system consists of the pipes, external inlets and outlet valves. When they are not in use the dry risers pipes are filled with compressed air that is only released when water is pumped in.
Dry risers are commonly used when the water pressure of a building is deemed inadequate for the purpose of fire suppression, or in buildings that have pipes likely to freeze in colder weather. They must have an access area large enough for a fire engine to get close enough to connect them to the water supply and should be within a fire resistant shaft, usually the buildings fire escape. Wet risers should also be in a fire-protected area.
The size of a building can also have an impact on what system is used.
Dry risers can be found in low-level buildings and those up to 18 metres above ground level, whereas wet risers are found in higher buildings. Both systems require regular maintenance to ensure they remain in full working condition. This includes visual inspections for both, and for dry risers testing them with water on a regular basis to determine whether there are any areas prone to leakage, or any drops in pressure during the test – if there are, the system is not in full working order. Wet risers require regular flow tests and should also be regularly checked to ensure the system pressure is working.
Both systems have benefits and drawbacks that make them suitable for different situations. Wet risers are needed in buildings over a certain height as the pumping pressure required may be more than can be provided by the fire service, and of course the higher the building is the longer water pumped from the ground will take to reach the top levels.
If a wet riser system is used then water is immediately available where it is needed.
Dry riser systems, however, are still more efficient than the use of manual hoses as they allow water to be pumped to multiple places from one source, and eliminate the time and effort it would take to run hoses to different parts of a building. They still enable a quick response in the event of an emergency and can be easily installed in buildings and easily accessed.