The LWF Blog

Fire Safety for Facilities Management Personnel – Fire Service Facilities – Part 267

August 27, 2024 11:09 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 266, LWF discussed the facilities that should be provided in a building design for the fire service, including rising and falling mains. In part 267, we continue talking about rising and falling mains, and the differences between wet and dry fire mains.

A dry fire mains that serves the upper floors of a building is known as a dry rising main. A dry fire main that serves basement levels of a building (below main entrance level) is known as a dry falling main. A dry rising main may be seen in a building of multiple levels, but in a very high building, the rising mains are kept permanently charged with water, supplied by water pumps, and these are known as wet rising mains.

Wet rising mains are required in tall buildings (currently those over 50 metres) due to the limitations of Fire Service pumps. Pumping water vertically and overcoming gravity requires larger pumps as the height increases. Fire Service pumps can provide adequate pressure in buildings up to around 50 to 60 metres, however above this height requires larger pumps to be housed within the building.

The landing valves of fire mains are located in firefighting lobbies. However, in blocks of residential flats, it’s acceptable to treat the protected corridors as firefighting lobbies.

BS 9990 gives detailed guidance on the design of wet and dry fire mains. Where mains are required, dry mains are recommended except in the case of buildings with floors more than 50 metres above firefighting access level, where wet rising mains are recommended.

A dry rising main is normally 100 mm in diameter. A wet rising main should be capable of supplying two firefighting jets for a period of at least 45 minutes, where total water demand is 1500 litres/minute. Such demand for water would be too great directly from a town main. A separate water supply is usually necessary and this is likely to comprise a tank holding at least 45,000 litres capacity, drawn from the town main. Domestic water tanks are not suitable for this purpose, unless it can be demonstrated that the quantity required will always remain and can’t be used to meet the needs of domestic supply.

Every six months, rising mains should be inspected for continued suitability by a competent person. Each year, dry rising mains should be charged with water to check for potential leaks and repaired as appropriate.

In part 268 of this series, LWF will talk about foam inlets and private water supplies. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

 

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.