The LWF Blog

Fire Safety for Facilities Management Personnel – Sprinkler Installation Design – Part 238

February 5, 2024 12:23 pm

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 237, LWF discussed high-hazard occupancies, classifications and the resulting design of the sprinkler protection installation. In part 238, we will talk more about water supplies for sprinkler systems.

Sprinkler installations are normally fed by one of two water sources – a water authority main or a pump and tank system supplied from a water authority main. Other sources of water are possible, however, including gravity tanks, pressure tanks, an elevated private reservoir or even nearby rivers or canals in some circumstances.

BS EN 12845 imposes some limitations on water sources for sprinkler installations and provides guidance. There are three forms of water supply described within the standard:

• A single supply – single town main or single pump drawing from a tank
• A superior supply – town main fed from both ends or duplicate pumps drawing from a tank
• Duplicate supplies – two independent town mains or duplicate pumps and duplicate tanks fed from a potable water supply

Wherever practical, a sprinkler installation should be drawing from a superior or duplicate supply. A single supply sprinkler system is not considered suitable for high-hazard risks.

The LPC rules provide a technical bulletin which defines three grades of waters supply for insurer classification. The summary of grade I, grade II and grade III are as follows:

Grade I – a supply that is either superior or duplicate (the total number of heads and the number in any fire compartment is limited if a superior supply is used)

Grade II – a superior supply in which the limitations imposed under Grade I are not satisfied

Grade III – A single supply, comprising a town main or a single automatic pump and tank(s).

The potential premium discount offered by insurers is based on the grades and, obviously, grade I attracts the highest rate of potential discount.

The pumps used for sprinkler systems may be driven electrically or by diesel. Where a superior or duplicate water supply is used, it is common practice to install one diesel and one electrical pump. The use of two electrical pumps would mean they required independent power supplies (in case one fails) or may be driven by the same electrical supply, provided there is automatic changeover to an alternative supply if the first fails.

In part 239 of this series, LWF will discuss sprinkler heads. 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