The LWF Blog

Fire Safety Engineering for Design – Sprinkler Heads – Part 233

May 5, 2025 10:30 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 232, LWF discussed different types of sprinkler system with control mode specific application (CMSA) and concealed pattern sprinklers. In part 233, we continue talking about concealed pattern sprinklers and concerns over slower sprinkler reaction time.

The use of concealed pattern sprinklers for life safety purposes is considered inappropriate by some industry professionals. Concealed pattern sprinklers have a slower reaction time to a fire and also there is a possibility that a component could fail due to incorrect installation or post-installation interference. Component or installation failures, however, are not particular to a life safety usage of sprinkler system and could happen just as easily in a property protection scenario.

In addition to the slower reaction time and the two-stage operation of a concealed pattern sprinkler (in releasing the cover plate before the sprinkler is activated), there are other concerns about this type of system, as follows:

• Monitoring of the ceiling void space usage is important as any obstruction of the sprinkler casing vents can be detrimental to sprinkler operation.
• It is necessary to leave an air gap between the cover plate and ceiling in order for the sprinkler to operate, but this can cast shadows onto the ceiling and so the gap is often (inappropriately) sealed with paint or plaster which can delay sprinkler activation or cause the sprinkler to become active in the ceiling as the cover plate is stuck shut.
• Misalignment of the sprinkler during installation can lead to the shadow effect being more obvious.
• Unsafe installation of concealed pattern sprinklers can result in the casing being positioned too high, which means the deflector would be above the bottom of the ceiling.
• Use of the ceiling void for air conditioning or heating plenums could result in air movement away from the sprinklers.
• The concealed pattern sprinklers were originally restricted to cover risks up to ordinary hazard group 2 in the UK, as they may be unable to deal with a faster growing fire.

In part 234 of LWF’s series on fire engineering we will talk about other devices/sprinkler systems for particular uses. 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.