In case of fire, don’t run; walk instead
The Sunday Nation
Nairobi,
31 October 2010
After the stampede that killed eight people at the Nyayo Stadium, we must turn the spotlight on other situations that are disasters in waiting. Banking halls come to mind immediately.
Every time I see customers queuing at a bank I worry that even a minor incident, like a fire in an office litter bin, can kill people as they attempt to run away. The question that bothers me is this: Are the doors of a bank wide enough to evacuate everyone in case of an emergency? Indeed, how wide, is wide enough?
To get the answer, we need to consider the relevant information. First; the average person measures about 50cm across the shoulders. Second; a normal door is about 75cm wide but banks usually have larger ones with a double-swing entrances making it about 2m wide. Therefore, three people can comfortably pass through a bank’s door without interfering with each other’s private space.
How fast can people go through such a doorway? When people are walking normally in a crowd, they maintain about one metre of space in front and behind each person. If they moved through the 2m-door in this manner and at the average speed of one metre per second, the evacuation rate would be three people per second.
Thus if there were 100 people in the bank, they can be evacuated in about half a minute. Now that is quite fast, but it not how crowds behave. If there is a loud “bang!” everyone rushes for the door and in a few seconds, they block it.
The blockage occurs when more than four people attempt to pass through the 2m-wide door at the same time. They simply won’t fit! From that moment onwards, the number leaving the banking hall drops from four per second to less than one per second.
Thus evacuating 100 people can take more than three minutes, instead of just 30 seconds. The problem is not only the slow evacuation rate, but also the injuries sustained by people pressing against each other and against the door frames.
Two lessons come out of this. First: banks must find out the maximum number of people that can be safely evacuated from their halls. This depends on the size of the door.
Once the maximum number is found, it must be strictly enforced by counting the number of people entering and leaving the bank. This can be done quite easily using plastic discs similar to the ones used in parking lots.
Customers pick one disc at the door when entering and surrender it when leaving. Once the maximum number is reached, then the additional people are asked to queue outside and wait for space.
The second lesson is that, if you hear a loud bang when inside a crowded banking hall, don’t rush for the door – walking calmly will get you to safety faster than running.
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