Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants
Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants



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Lawrence Webster Forrest
Legion House
Lower Road
Kenley
Surrey
CR8 5NH

Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
E-mail: fire@lwf.co.uk

Fire Engineering Design and Risk Assessment - Sprinkler Installation Design - Part 41

Posted by LWF: 11/04/2018 14:02

In LWF’s Fire Engineering blog series for Architects and others in the building design business, we have been looking at sprinkler installations. In part 40, the additional measures required for life safety sprinkler systems were reviewed. In part 41, we look at those enhancements necessary for property protection. 

Usually, a sprinkler system is designed to deal with a fire in one location, i.e. a fire which develops from at a single source point. It is possible, however, that a fire might have multiple sources. Fires which fall into an ordinary hazard risk group will be subdued or controlled with one to four sprinkler heads, and in cases where a multi-point fire starts on a single floor of a building, the standard sprinkler system is likely to be able to cope. 

If fires were to start on more than one floor of a multi-storey occupancy, an enhanced sprinkler system would be required. 

A standard sprinkler system, complying with British Standards, which is able to deal with ordinary group 2 risks will deliver sufficient water and provide an acceptable flow to between one and 18 active sprinkler heads. Where a fire has multiple start points or there is a failure in the distribution piping network, the system may become overrun and will be unable to maintain adequate water pressure to provide a flow rate to those sprinkler heads which have been activated. The fire would continue uncontrolled.

A failure condition is likely to be where a multi-seat fire ignites on one floor and requires the opening of more than 18 sprinkler heads, or where a partial failure of the sprinklers on one floor (through deliberate damage) can lead to the fire potentially spreading between floors of the building. In addition, a failure can be in the form of a sprinkler riser or main distribution main.

There are safeguards which can be put into place to guard against such failures in a live fire situation.

Where four pumps are provided instead of two, each pump will be capable of supplying the standard demand for a sprinkler system.

To safeguard power to the pumps, each should be connected to both the mains electricity and the secondary power source – such as a standby generator, diesel engines or similar.

The suction manifold positioned to permit two groups of two pumps to draw from it and subdivided by a motorised stop valve which will normally be left open.
A single full-capacity tank should be provided, subdivided into two equal sections with each section having an infill connection. Each infill connection should be sized and connected to provide maximum inflow from either two independent town mains or from a single town main fed from both directions.

In part 42 of this series, we will continue looking at those enhancements which should be undertaken for property protection in case of a multi-seat fire to avoid failures. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.

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.



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