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Fire Safety for Facilities Management Personnel – Drencher & Water Spray – Part 244

March 18, 2024 12:04 pm

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 243, LWF looked at the types of sprinkler systems known as drencher systems and water spray systems. In part 244, we continue discussing water spray systems, in particular medium-velocity spray systems.

A medium-velocity spray system is used for fire risks involving water-miscible flammable liquids, or low-flashpoint non-water-miscible liquids. The spray heads of a medium-velocity spray system emit fine water droplets of less than 0.4 mm diameter. The fine spray of water is then able to extinguish the fire by diluting the liquid which raises the flashpoint of the mixture. For liquids with low flashpoints this method may prove more difficult, but allows a measure of control.

When using a fine spray, heat can be extracted from the flames and the fire is controlled. This principle may be used for low flashpoint non-water-miscible liquids, but it may be that an element of control is all that can be achieved. For example, this might mean that the fire did not grow or that the rate of growth was slowed sufficiently for the Fire Service to attend and extinguish the fire before significant damage was sustained.

Medium-velocity spray heads are normally open and are operated in the same manner as high-velocity spray heads (see part 243 for more information on high-velocity spray heads). A medium-velocity spray is often seen in use for cooling exposed structural steelwork in certain circumstances, such as a fire in a flammable liquids plant. It may also be used to cool flammable liquid or gas storage tanks which are threatened by an adjacent fire. The cooling and wetting of potential fuel or combustive elements helps to slow fire progress.

Practical applications for medium-velocity spray systems are normally confined to flammable liquid plants. However, they may also be used when protecting installations such as an oil-fired boiler that burns fuel with a lower flashpoint than would be appropriate for a high-velocity spray system.

The BS 8489 series of standards provides guidance on fixed fire protection systems for industrial and commercial use and is a code of practice for design and installation.

In part 245 of this series, LWF will begin to discuss water mist systems. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

 

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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