The LWF Blog
Fire Engineering Design and Risk Assessment – Sprinkler Heads – Part 19November 2, 2017 3:05 pm
LWF’s Fire Engineering Design and Risk Assessment blog series for Architects and others in the building design business has been looking recently at sprinkler heads; the different types and suitability for certain purposes. In Part 18, it was established that concealed and ceiling-set sprinkler heads are likely to react more slowly to fire conditions and that this can be an issue to both life safety and property protection. In Part 19, we will discuss further concerns about concealed pattern sprinklers.
In addition to the triggering of concealed pattern sprinklers taking longer because of their position in relation to a fire, it also has a slower reaction time because it requires the cover plate to react and then the sprinkler head itself.
The design means that while it is usual for the cover plate trigger to achieve the required temperature and activate prior to the sprinkler head, on some occasions it can activate incorrectly.
The obstruction of the sprinkler casing plates can be detrimental to operation and makes the monitoring of the ceiling void space usage important particularly if sprinklers are used as the main source of fire detection. Should a sprinkler become ineffective due to a plate being covered, the fire could develop and enter the ceiling void space.
There is an air gap between the cover plate and the ceiling which is necessary if the sprinkler is to operate correctly, but this gap often results in a shadow which can lead to the space being filled with paint or plaster; it is important this does not happen. Particular care should be taken if the area is to be redecorated too.
The sprinkler must be installed carefully to avoid misalignment of the cover plate which can make the shadow effect more obvious.
The sprinkler deflector should be positioned correctly and in this case, that means with the plate just below the ceiling height. It is not acceptable for it to be just above the ceiling height, ie. within the ceiling cavity.
If the ceiling void is used as a supply plenum (meaning it is used to facilitate air circulation for heating and air conditioning systems) this can prove detrimental to the performance of the sprinkler system as it can move air away from the sprinkler heads.
For these reasons, sprinklers are sometimes viewed as an option where the fire is unlikely to grow to above an ordinary hazard group 2, but not for larger or faster growing fires. However, sprinkler manufacturers are working to reduce the issues raised and are implementing changes such as a lower activation temperature for cover plates than for the sprinkler heads, to remedy errors in activation order. Also, such systems are available as fast response devices and with the deflector on extending chains or struts to ensure correct installation and operation.
In Part 20, LWF will look at the role of the sprinkler in terms of life safety in buildings. 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.