The LWF Blog

Fire Safety Engineering for Design – Sprinkler Heads – Part 229

April 7, 2025 10:23 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 228, LWF began to talk about sprinkler heads. In part 229, we continue discussing sprinkler heads with the five key attributes of a sprinkler head that are important to sprinkler design.

Research has shown that there are five key elements of a sprinkler head which are important when undertaking sprinkler system design. This is especially the case for storage protection, to ensure the necessary quantity of water is delivered to the fire area (actual delivered density). The five key areas are:

• RTI
• K-factor
• Temperature rating
• Orientation
• Spacing

To accommodate these five factors, there has been a move away from traditional area/density design specification for storage sprinkler systems and an uptake in designs based on number of operating sprinklers heads at a given minimum operating pressure.

Sprinkler droplet size is determined by the orifice size, with larger droplets formed by larger orifices. In this way, it supports the use of 10 mm sprinkler on low-output fire risks and 20 mm orifice on larger/faster developing fires.

Sprinklers come in various different types to ensure there is a type fit for purpose. Conventional and spray pattern sprinklers are commonly seen, but there are also more decorative, recessed or concealed pattern sprinklers for circumstances requiring them.

The client may wish for a decorative sprinkler system to be used on a suspended ceiling, with colour-matching to the ceiling shade. Alternatively, the body of the sprinkler may be concealed within the ceiling itself, with only the heat-sensitive element protruding through.

A recessed pattern sprinkler is one where the sprinkler body and all or part of the heat-sensitive element are concealed above the plane of the ceiling.

Where appearance of the sprinkler system is important, it is essential that the choice made is for a colour-matched system or a recessed system as sprinklers cannot be painted under any circumstances. The application of paint to a sprinkler head could block the heat-sensitive element causing the sprinkler to fail completely in a fire situation, or the paint could block the orifices in the sprinkler head, resulting in less or no water from the head.

In part 230 of LWF’s series on fire engineering we will begin to look at conventional and spray types of modern 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 since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

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.