The LWF Blog

Facilities Management & Fire Safety – Water Spray Systems – Part 16

July 12, 2017 8:49 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, how they are used in buildings and their effects upon fire. In Part 15, we began looking at Water Spray Systems and how high and medium velocity systems are used for fire risks due to flammable liquids. In Part 16, we will talk about medium-velocity systems and their uses.


A medium-velocity spray system can be used in situations where water-miscible flammable liquids are present, that being those liquids which can mix with water, and also for flammable liquids with a low flashpoint of less than 66˚C but which are not water miscible.


With a medium-velocity spray system, the spray heads are able to produce very fine droplets of less than 0.4mm in diameter and this fine spray is able to extinguish a fire by diluting the flammable liquid with water. This has the effect of increasing the overall flashpoint temperature of the mixture so that it is less likely to ignite in a short space of time.


Where a liquid has a low flashpoint temperature, it is less likely that this method will be successful, but it is possible that a system design can take that into account.


When the water spray is operational, if it is sufficiently fine, heat is extracted from the flames and the fire can be controlled or subdued. While this system is effective at providing an element of control for low flashpoint non-water miscible flammable liquids, it is likely that this will simply allow more time for the arrival of the Fire Service, rather than extinguishing the fire altogether.


A medium-velocity spray system has other uses too. It can be used to cool structural steelwork and therefore help to maintain building viability during a fire in a flammable liquids plant, or to cool flammable liquid or gas storage metal tanks which are in danger from nearby fire.


It would be unusual to find a medium-velocity spray system outside of a flammable liquid plant, but could be found where there are oil-fired boiler installations, which contain oil with a lower flashpoint than would be appropriate for a high-velocity spray system.


British Standards covering water spray & misting systems are relatively new, the principles and adoption of the systems is generally accepted. US standards, such as NFPA 15 can be referred to where applicable.


In Part 17 of this series looking at Water Spray Systems, we will discuss Water Mist Systems and their potential for use. 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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