The LWF Blog

Fire Safety Engineering for Design – Sprinkler Heads – Part 232

April 28, 2025 10:19 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 231, LWF discussed sidewall sprinklers and early suppression fast response sprinklers (ESFR). In part 132, we continue to discuss types of sprinkler system with control mode specific application (CMSA) and concealed pattern sprinklers.

Control Mode Specific Application Sprinklers

At the end of March 2025, a new British Standard was published, BS EN 12845-2:2024 Fixed firefighting systems. Automatic sprinkler systems – Design and installation of ESFR and CMSA sprinkler systems.

CMSA or control mode specific application sprinkler systems are mainly designed and installed in high hazard storage scenarios where other sprinkler solutions are unsuitable. The CMSA approach to sprinkler protection utilises special designs of sprinkler heads, designed and tested to protect risks in specific configurations.

This type of sprinkler system is reliant on precise design for the purpose intended and appropriate installation, as a successful outcome can only be relied upon when correctly applied.

Concealed Pattern Sprinklers

A concealed pattern sprinkler system may be one of the slowest to react in a fire situation. A sprinkler of this type features sprinkler heads and sensors that are fully recessed into the ceiling with a cover plate at ceiling level. The cover plate is attached to the sprinkler with a fusible element, so when a set temperature is reached, the cover plate falls away and the sprinkler itself will react to the thermal conditions and become operational.

Because the hottest gas layer above a fire is 75 – 100 mm below a flat ceiling, the location of the sprinkler relative to this layer will have a bearing on the response time. The same is true of all ceiling-style sprinklers, except with concealed pattern sprinklers, the plate has to fall away before the sprinkler can become operational.

In the UK, there has been some discussion on the use of concealed pattern sprinklers in situations where life safety is the priority. The term life safety in relation to a sprinkler system is somewhat undefined. The Building Regulations cover aspects of building design and fire safety ranging from warning of fire, fire spread and access and facilities for the Fire Service, with the overall aim being to provide an acceptable standard of life safety.

In part 233 of LWF’s series on fire engineering we will continue to talk about concealed pattern sprinklers and the concerns over a slower sprinkler reaction time. 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.