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 System Installations - Part 24

Posted by LWF: 05/12/2017 11:28

In LWF’s Fire Engineering blog series for Architects and others in the building design business, we have been looking recently at Sprinkler Systems. In Part 23, we discussed methods of water delivery to the sprinkler heads and ascertained that ‘wet installations’ were the most commonly used type of sprinkler system, meaning that the system is constantly charged with water, ready for operation. In Part 24, we will give an overview of alternate wet and dry installations and dry installations.

As mentioned, a wet installation sprinkler system is most appropriate where there will be no substantial changes in temperature, i.e. the temperature will not go below zero or above 70°C, whereas an alternate wet and dry installation is a sprinkler which is designed for use where the temperature is expected to be below freezing in the Winter months. 

During the milder weather, the system operates as a standard wet installation, where the water is charged in the pipes ready for use. Prior to the colder weather, the system should be drained and the control valves set to Winter operation. It is important that the draining is done thoroughly, as any water left in the pipes can freeze and could cause a blockage when water is sent through them to the sprinkler heads. 

When the valves are set to Winter, the pipework of the sprinkler system is charged with a small amount of air pressure. If a fire is detected and a sprinkler head operates, the air pressure reduces and the control valve is activated, allowing water through the pipes to the sprinkler head. Once the weather is more consistently warm, the system should be switched back to wet operation.

One potential issue with the operation of an alternate wet and dry installation is the slight delay caused by the water reaching the sprinkler head in the colder months. It is the case that the amount of sprinkler heads which may operate from this type of system are restricted to less than that of a wet installation. To help overcome this issue, in some cases an exhauster or accelerator is fitted to the valve set which helps to charge the system with water more quickly when detecting a drop in air pressure.

Wet and dry installations are not suitable for high hazard storage risks and conditions where the temperature may exceed 70°C.

A dry installation works in largely the same way as a wet and dry installation does during the Winter months, with the exception that they are suitable for operating conditions which exceed 70°C. They should only be considered for use in areas where neither a wet nor a wet and dry installation can be used.

In Part 25 of this series, LWF will look at other types of sprinkler system installation and the types of use they can be put to. 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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