The LWF Blog

Fire Engineering Design and Risk Assessment – Fire Suppression & Sprinklers – Part 5

July 27, 2017 9:46 am

In this Fire Engineering Design and Risk Assessment blog series, we have been looking recently at the use of sprinklers to suppress incidences of fire in buildings. Part 4 looked at the merits of using sprinkler systems and talked about how their use can save lives and extensive property damage. In this blog, we are going to discuss those instances when sprinklers fail to control a fire and what contributory factors lead to such situations.


The National Fire Protection Association (NFPA) collect data on fires in the US and published information indicating that in around 7% of fire situations, sprinkler systems had failed to operate. The majority of those sprinkler failures were due to the sprinkler system having been shut off prior to the fire, perhaps because a part of the system was leaking and required maintenance.


Because human error, lack of maintenance and upkeep etc. all contribute towards the correct use of a sprinkler system, sprinklers cannot be claimed to be 100% effective.


Sometimes the case is argued that because of the lack of a 100% effective tag for sprinkler systems, that they should be traded-off in favour of other fire protection measures. However, a correctly installed and maintained sprinkler system is extremely effective and certainly, any other fire protection method used in lieu would also have to be maintained in order to ensure fire protection was consistent.


One example is that fire doors can fail in their duty to ensure fire does not spread between compartments for the adequate amount of time (FD30 provides 30 minutes protection, for instance). If a door is left open, propped open or poorly fitted, then they also cease to be 100% effective.


For an optimally protected building, a balance must be achieved between active and passive fire protection measures that fulfil the needs of the building and its occupants.


The reliability of sprinkler systems in comparison to passive fire protection measures can be found in PD 7974 Part 7 – Application of fire safety engineering principles to the design of buildings.  The document offers probability figures for successful sprinkler activation between 0.75 and 0.95, which tallies with data from the US of 0.93.

Further probability figures can be gained from the British Automatic Sprinkler Association’s Sprinklers for Safety, which states that:

‘These figures compare favourably with passive fire system figures which include the following:

Probability of fire doors being blocked open = 0.3

Probability of self-closing doors failing to close correctly on demand = 0.2

Probability that fire resisting structures will achieve at least 75% of the designated fire resistance standard = 0.25 for suspended ceilings and 0.65 for partition walls.


Probability that fire-resisting structures will achieve at least 75% of the designated fire resistance standard, for partition walls = 0.65.’


In Part 6 of this series, we will look at the tangible benefits of sprinklers as a part of a building’s fire protection measures. 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.






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