The LWF Blog

Facilities Management & Fire Safety – Sprinkler System Design Principles – Part 10

June 2, 2017 9:51 am

In this blog series for those who work in Facilities Management and who have an interest in or responsibility for fire safety, we have been looking recently at sprinkler system design principles. While most facilities managers might not require an in-depth knowledge of how sprinkler systems work, it is important to understand the basics so that an input into the design of new builds or the maintenance of existing ones is possible.

 

In Part 9, we looked at equipping a sprinkler system through various key design elements to deliver an adequate amount of water to the point of the fire. In this blog, we will be discussing where the water that is delivered will come from.

 

A sprinkler installation is normally either connected to a water authority main, or a pump and tank which is supplied by a water authority main. However, not all systems are average and some might require an alternative form of water supply such as a gravity tank or a pressure tank. Water can even be obtained from sources such as an elevated private reservoir, a river or a canal.

 

The British Standard – BS EN 12845 – does impose some limitations on how water can be obtained for a sprinkler system. It describes three types of water supply as follows:

 

– A single supply such as a single town main or a single pump drawing from a tank of water.

 

– A superior supply, such as a town main fed from both ends or duplicate pumps drawing from a tank of water.

 

– Duplicate supplies, which might be two independent town mains or duplicate pumps and tanks fed from a potable water supply.

 

In every possible case, water for the sprinkler system should be obtained from a superior or duplicate supply source. Single supplies are unacceptable for high-risk hazard cases.

 

In addition, the building insurer will need to know about the water supply for the sprinkler system in order that they can classify it according to their own system – grade I, grade II and grade III. The lower grade the water supply is deemed to be, the lower the premium discount that will be given.

 

The LPC Sprinkler rules have recently been republished to incorporate BS EN 12845 in addition to relevant technical bulletins.

 

The LPC water grades are as follows:

 

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

 

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

– Grade III supply is a single supply, such as the single town main or a single automatic pump and tank(s).

 

As a failsafe, pumps for sprinkler systems are often installed as one diesel and one electrically driven. Two electric pumps can be used in theory, but each would have to be powered by a different source.

 

In Part 11 of this series, we will look at sprinkler heads and how they operate. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact Peter Gyere in the first instance on 0208 668 8663.

 

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

 

 

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