The LWF Blog

Fire Engineering Design and Risk Assessment – Fire Attack Time Line – Part 61

September 30, 2019 1:16 pm

In LWF’s Fire Engineering blog series for Architects and others involved in building design, we have been looking at the provisions which should be made for firefighting activities. In part 60, we began a worked example of how the time line for a fire attack would be worked out and we will continue from that point in part 61.

When considering the positions for the stopping jets, we assume a floor configuration that makes it necessary to attack the fire from two directions, involving utilising two firefighting shafts.

Access routes on each floor area have been established by the use of protected corridors.

Firefighting lifts are provided which can access all floors within a minute. As the firefighters will exit the lift two floors below the floor of fire origin, it is necessary to use two flights of stairs. A base time of 30 seconds per floor which increases by 15 seconds per floor is used as the basis for calculations.

Upon arrival at the building, the fire alarm system, indicator board and fire safety management systems should provide information such that the firefighters are aware which fire attack access door they need to use and the firefighting lift should be waiting for them at fire attack access level.

The officer in charge will need to spend a little time at the fire alarm panel or talking to the fire marshal, which should take no more than three minutes. During that time the crew can collect all necessary equipment from the fire pump.

It is important to note that the method of calculation and elements of the time line of firefighting activities have been provided but in no way do the seconds and minutes mentioned reflect all scenarios. Every figure used should be determined accurately for each building individually.

Using the walkthrough, we can assume the fire attack time line to be as follows:

Fire ignition to detection – 120 seconds
Detector becomes operational to alarm activation – 10 seconds
Central alarm monitoring station processing – 60 seconds
Fire Service receives the call – 10 seconds
Call is transmitted to fire station and they respond – 60 seconds
Travelling time to fire location – 600 seconds
Officer in charge prep & equipment collection – 180 seconds
Lift travel to floor two floors below fire – 60 seconds
Two flights of stairs to travel to floor of fire origin – 75 seconds
Sub-total of time taken from fire ignition to arrival at scene – 1175 seconds (20 minutes approx.)

In this case, the worst-case scenario adjusted by a factor of 3, suggests a time limit of beginning the fire attack within 40 minutes of discovery of the fire. This indicates that the horizontal distance from the fire pump to the lift and from the staircase landing to the point at which the jet begins its work must be completed within 20 minutes.

In part 62, LWF will look a little more closely at the second 20 minutes and what must happen during that time before summarising the subject of firefighting. 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 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.

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