The LWF Blog
Fire Engineering Design and Risk Assessment – Sprinkler Installation Design – Part 42April 16, 2018 10:17 am
In LWF’s fire engineering blog series for Architects and others in the building design industry, we have been looking at sprinkler installation design. In part 41, we started looking at how an enhanced sprinkler system in case of multiple-point fires would differ from a standard sprinkler system in design. The safeguards which must be considered for such a system including pump, electrical supply and water ‘fail-safe’. Part 42 continues from that point.
Each division of the water tank should have an emergency refill connection to be accessed by the fire service and the pump delivery manifold should be arranged in a way that allows each group of two pumps to serve an independent manifold. Each manifold will then distribute to an independent riser location.
Each riser should be arranged to serve alternate floors and be fitted with a pressure switch to signal to the pump suction manifold motorised stop valve when there is a sudden drop in pressure. The alternate floor arrangement provides an additional level of redundancy, should a failure occur in one riser, the next, alternate riser should still operate.
A standard sprinkler system is designed to function typically using 18 sprinkler heads for up to an hour, whereas the enhanced sprinkler system possible for property protection enhancements could have 36 sprinkler heads operating on a fire floor, even when flashover has occurred, which could use up the water supply within 30 minutes. When sprinklers on other floors become operational, the water supply will run out even sooner.
In order to combat the problems raised by using so much more water than a standard sprinkler system in a much shorter space of time, the infill to the water tank should be sized to maximise the potential of the water main. This means that although the tank will not be dependent on the rate of inflow to operate under normal conditions, the option is available for extraordinary circumstances if required.
As the mechanical failure of a sprinkler riser or distribution main is a possibility, the pump suction manifold’s motorised valve will be set to close if a sudden drop in pressure is identified in any riser. This precaution allows for at least 50% of the water to remain available to the second riser.
Even when considering the possible failures or issues which may be encountered in the operation of a sprinkler system and attempting to mitigate them, there are still problems which could be encountered which would jeopardise the whole system, and in the case of a large fire, potentially the building too. The sprinkler plant room itself could potentially be breached and if the decision is taken to mitigate this risk, it would mean separate plant rooms where each room would house half of the stored water and two of the four pumps. The suction manifold would still connect the two tanks, but each set of two pumps would require separation by compartment.
In part 43 of this series, LWF will discuss domestic and residential sprinkler systems. 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.
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.