The LWF Blog

Fire Engineering Design and Risk Assessment – Sprinkler Heads – Part 18

October 26, 2017 12:24 pm

In LWF’s Fire Engineering and Risk Assessment blog series for Architects and others involved in building design, we have been looking recently at Fire Suppression and in particular, sprinkler systems. In Part 17, the basic design of a sprinkler head was outlined, along with operating temperature and Part 18 will continue from that point with sprinkler sizes.


The sizes of sprinkler head are given in millimetres – 10mm, 15mm, 20mm. The size refers to the apertures through which water will pass, not the size of the head itself. It is most common to find 10mm sprinkler heads used as part of a light hazard installation, 15mm in ordinary or high hazard and 20mm in high hazard installations. An early suppression fast response system (ESFR) may have size 20mm sprinkler heads, or more.


Each size of sprinkler head produces a different size water droplet, with the largest aperture indicating the largest droplet size.


The design of the sprinkler head from an aesthetic point of view can also vary significantly, to allow for use in varying types of design, from simple and practical, spray pattern sprinklers through to decorative recessed or concealed pattern sprinklers.


A decorative sprinkler head might be used in a suspended ceiling, so that it can be colour matched to the ceiling colour, or that the majority of the sprinkler can be hidden above the suspended ceiling with only the heat-sensitive detection element extending beyond the surface of the ceiling. A recessed pattern sprinkler is designed to work with all of the sprinkler head and all or part of the heat-sensitive element above the suspended ceiling.


A concealed pattern sprinkler is designed to be concealed in the ceiling and its installation hidden by a cover plate at ceiling level. The design is such that the plate is attached to the sprinkler with fusible elements which, when heated to a given temperature by a fire in the area, will detach and expose the sprinkler, which in turn reacts to the heat and becomes operational.


All ceiling installed sprinkler systems will react more slowly to a fire than a system where the heads are positioned more closely to the zone where the gases are hottest. The hottest gas layer of a fire is usually between 75 and 100mm below a flat ceiling.


There has been some debate over the use of concealed pattern sprinklers in the UK, some consider that there are risks affecting life safety. The delay in activation of such a system might allow the fire to develop at a faster rate for a slightly longer time and affect safe egress or the spread of smoke. However, this issue would also apply to concealed pattern sprinkler systems which are installed with the primary aim of protecting property too.


In Part 19, we will look at more concerns relating to the use of concealed pattern sprinklers. 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.


Share this post