What Is The Difference Between Dry Riser And Wet Riser System?
A riser system is part of safety devices installed in modern tall buildings to prevent fire outbreak. It can be a wet riser system or dry riser system installed in the building design. This riser system helps firefighters to easily supply water through a building in case of fire outbreak. This article will equip you with the knowledge of the difference between the two systems.
Dry Riser System
The Building Regulations requires that any building above 18m tall must have a dry riser system. Structures such as hospital basements, limited access environments, and multi-level basement buildings must also possess a dry riser system. It is a system that makes use of interconnected pipes that allows the passage of water to the upper floor of a building.
It is also a connection of water inlets and outlets. The water inlet pumps water into the building, while an outlet allows the flow of water to each floor of the building. The firefighters attach their hose to the outlet and direct the water into the building on fire.
The dry riser system is made up of three elements, and these elements are instrumental to the effectiveness of the riser system. They are the pipework, the external inlet, and the internal outlet. They must be designed in line with BS 5041, BS 5306, BS 9990, and Building Approval regulations.
The following are features and criteria for the dry riser system;
- The external inlet is enclosed in an enclosure with the inscription ‘Dry Riser Outlet’ written on it.
- The enclosure contains a cave which drains down the water in the dry riser after the fire occurrence.
- The enclosure must be able to provide immediate access for the fire brigades. As such, it must be vandal proof.
- The pipework in a dry riser system is placed in a fire-resistant enclosure. It has an air valve at the top which expels the air in it as soon as the water enters.
- In a dry riser system, the pipework must be galvanised steel and free of water. As demanded by the building regulation, buildings over 18m tall should use a pipe with an internal diameter of 100mm and 150mm for taller buildings.
- The internal outlet consists of BS instantaneous female outlet, which can be either single or double. The gate valve controls the BS instantaneous female outlet.
- The outlets are also enclosed with a breakable door. It is usually placed in the building’s fire escape staircase or a lobby.
- For every 900 meters square floor, there should be one outlet except for the ground floor. No part of the floor should be more than 60m away from an outlet.
Wet Riser System
Buildings with a height above 50m usually make use of the wet riser system. The design is similar to that of the dry riser system. However, unlike the dry riser, the wet riser is continuously charged with water. The water supply into the wet riser is from a storage tank which makes use of pressurised supply into the wet riser.
Wet riser system is needed in buildings above 50m tall because fire brigade appliances cannot supply the required pressure that can charge the riser to provide water to such height. However, the fire brigade water supply can be used as a supplement in case the water in the riser storage tank is exhausted.
The design of a wet riser system and dry riser system has certain similarities. Features of a wet riser system are as follows;
- The minimum running pressure needed in a wet riser system is 22.7I/S flow rate at the rooftop outlet of 4 bar.
- For an outlet, the maximum running pressure permitted in operation is 5 bar.
- Wet riser system installation must be within the fire fighting shaft and the escape stairs. It can also be located in an enclosure, within protected lobbies and stairs.
Maintenance of the Dry Riser and Wet Riser System
It is advisable that routine testing and maintenance should be carried out annually for both riser systems. This maintenance is solely the responsibility of the building owner or the managing agent. British standard regulations also require that the system should be visually inspected every six months. It helps to build assurance that the riser system is available for use in case of emergency. A full wet test must also be carried out, and the wet pressure must be a maximum of 150 PSI or 10 bar.
A wet riser should be inspected regularly to ensure it is in good condition. A check for vandalism, theft, failure in pipework connections, blockage, or open outlets should be done to avoid system failure.
As an essential and integral part of modern tall buildings, dry and wet riser systems should be maintained appropriately. It will complement the effort of firefighters in reaching the higher parts of the buildings in emergencies.
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