The LWF Blog

Facilities Management & Fire Safety – Drencher & Water Spray Systems – Part 15

July 6, 2017 10:43 am

In this blog series for those who work in Facilities Management and who have a responsibility for or interest in fire safety, we have been looking at fixed fire-fighting systems. In Part 14, we looked at the relevant checks and maintenance to be undertaken on sprinkler systems to ensure it stays in good working order. In part 15, we’re going to look at two different types of water systems – Drencher Systems and Water Spray Systems.


A Drencher system is one that is designed to work on the outside of a building rather than the inside. It is used most commonly in situations where one building is closely adjacent to the protected building and the transfer of fire from one to the other is a possibility. A drencher system discharges water over the outside, over windows and any other wall opening which may allow fire to get inside the building and continue to spread.


The Drencher system heads can be either sealed or open, depending upon how the design works along with additional systems inside the building. Sealed heads operate in the same manner as sprinkler heads and work as an extension of an existing sprinkler installation. Open heads can be used as a separate system, which would then be activated manually or automatically through a separate detection system. Which type of system is appropriate depends upon the results of the fire risk assessment.


Water Spray Systems are designed for use where there is a particular fire risk from the use or storage of flammable liquids in a building. A Water Spray System comes in high and medium velocity sprays, for different uses. Although most of these systems are installed for use on an automatic basis, it is possible that manual control over discharge could be appropriate for some circumstances.


A high-velocity spray system is one for use in extinguishing fires in non water-miscible liquids with relatively high flashpoints (66˚C and above). If a substance was water-miscible, it would mean it would mix with the water, in this case, it does not.


The system will include high-velocity spray nozzles which produce large water droplets of around 1.5-2.5mm. The large droplets are able to penetrate the up draught from a fire and cool the liquid until it is extinguished. The nature of its operation is referred to as ‘deluge’, because a small group of nozzles discharges their water load simultaneously over the relevant area. You are most likely to find this type of spray system in use where there are oil-filled transformers, diesel generators and oil-fired boilers.


The second type of water spray system – medium-velocity will be discussed in our next blog, Part 16 of this series. 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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