Further guidance regarding escape routes
This section provides further guidance on the general principles that apply to escape routes and provides examples of typical escape route solutions for a range of common building layouts. The guidance is based on premises of normal risk so if your premises (or part of your premises) are higher (or lower) risk you should adapt the solution accordingly.
Widths and capacity of escape routes and stairways
Once you have established the maximum number of people likely to be in any part of the premises, the next step is to establish that the capacity of the escape routes is adequate for people to escape safely in sufficient time to ensure their safety in case of fire. The effective usable width of an escape route is the narrowest point, normally a door or other restriction such as narrowing of a corridor due to fixtures and fittings. The capacity of an escape route is measured by the number of persons per minute that can pass through it, so to establish the capacity of a route, it is first necessary to measure the width of the route at the narrowest point. The effective width of a doorway when the door is open at right angles to the frame. The effective width at any other point is the narrowest clear unobstructed width through which people can pass.
The time available for escape depends on several factors. Studies of human behaviour in an emergency situation have shown that about two thirds of the time available to escape is taken up by the initial reaction to the developing situation. For example, people will decide whether the situation is real or false, often waiting to see the reaction of people around them, and generally gathering information to decide whether to act or not.
The final third is taken up by the actual movement away from the area of fire. Throughout this time the fire may be growing and spreading. Therefore to account for the limited available time for people to travel to a place of reasonable safety, the length of escape route needs to be restricted. The following guide can be used to determine the general capacities of escape routes;
A width of at least 750mm can accommodate up to:
80 people in higher risk premises.
100 people in normal risk premises.
120 people in lower risk premises.
A width of at least 1050mm can accommodate up to:
160 people in higher risk premises.
200 people in normal risk premises.
240 people in lower risk premises.
An additional 75mm should be allowed for each additional 15 persons (or part of 15) Note: The minimum width of an escape route should not be less than 750mm (unless it is for use by less than five people in part of your premises) and, where wheelchair users are likely to use it, not less than 900mm. The aggregate width of all the escape routes should be not less than that required to accommodate the maximum numbers of people likely to use them. When calculating the overall available escape route capacity for premises that have more than one way out, you should normally assume that the widest is not available because it has been compromised by fire.
If doors or other exits leading to escape routes are too close to one another you should consider whether the fire could affect both at the same time. If that is the case, it may be necessary to discount them both from your calculation. As a general rule stairways should be at least 1050mm wide and in any case not less than the width of the escape route that lead to them. In all cases the aggregate capacity of the stairways should be sufficient for the number of people likely to have to use them in case of fire. Stairways wider than 2100mm should normally be divided into sections, each separated from the adjacent section by a handrail, so that each section measured between the handrails is not less than 1050mm wide.