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THE 4 MINUTE EVACUATION, EGRESS TIME
THE 4 MINUTE EVACUATION, EGRESS TIME
Fig.1©NFPA, Fig. 2© Medline Plus, Fig. 3 ©BSI
All international standards make reference to 4 minutes time for evacuation from a certain compartment, incase of fire.
(Here we are only discussing the 4minute criteria (Not the 6 minutes to point of safety), and to note that in Hong Kong, the criteria is increased to 4, 1/2 minutes).
The above medical report highlights the time limit under oxygen depletion condition, when our body starts to fail. At the same time the BS Standard to the right charts the time that is required for people to start to evacuate themselves from danger, in which case the actual evacuation required may be more than 4 minutes?
Caveat: This is not a Fire Engineers Report. Hence the details of the actual ASET (Available Safety Egress Time), Radient Flux of the fire, ppm of CO, etc. are not discussed. Meaning that a much more detailed, engineered paper related to the NFPA 130 fire and smoke effects in a metro station is benificial, and would underpin the simplistic discussion that I am making herein.
The above datas shows the triangle of Combustable material, fire and Oxygen.
If there is a fire (Assuming there is materials that will ignite/burn).
The fire will sap the O2 out of the immediate surrounding
If the O2 drops below 19.5% we will begin to have cognitive & other failure, etc.
The fire will automatically stop when the O2 is around 16%.
However by this time we may have lost consciousness, etc. + if we have been in this condition for 4 minutes, we would not be alive.
The above datas highlight the need to suppress the fire and also to manage the smoke, in case the fire rages on.
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