Here are a number of different ways to analyse evacuation of buildings.
Standard fire safety guidance documents typically specify the width of exit routes (such as doors and stairs) based on the number of occupants. Some, more sophisticated documents, such as BS 9999, also incorporate factors such as the occupant characteristics and the fire risk within the building to modify those figures. These methods are useful, simple approaches that give reasonable results for most buildings.
However, in certain situations it is necessary to predict the amount of time needed to evacuate a building (in fire engineering, this is referred to as the Required Safe Egress Time or RSET). This can be used in combination with smoke modelling, which can predict the time available before untenable conditions are reached (knows as the Available Safe Egress Time or ASET).
The combination of these methods is often useful in unusual or complex buildings where the standard design guides would be inappropriate or compliance is impractical to achieve. By demonstrating that the evacuation is complete well before untenable conditions occur (i.e. the RSET is shorter than the ASET), IFC engineers are capable of demonstrating that building designs are safe for occupants.
Computer Evacuation Modelling can combine these elements by way of a 3D model demonstrating evacuation of persons in real time, with the travel distances, exit routes and widths. This tool is particularly useful when the means of escape are complex, exit widths are difficult to achieve and the client wishes to maximise the occupancy. This method is often used to demonstrate evacuation in complicated buildings where ADB is difficult to comply with and occupancy is required to be maximised.