Most guidance documents on fire safety recommend standard simple methods for calculating exit capacity (such as standard stair capacity tables). These methods are simple to use, but do not give a real indication of the evacuation. More complex analyses allow a more accurate picture of the evacuation to be determined. Comparing this with smoke flow modelling, the exits can then be sized to ensure that the occupants have sufficient time to evacuate before conditions become untenable. This can be used either to reduce the sizes of the exits that may be required (as appropriate) or to give more confidence that the exit capacity is sufficient. There are several ways to carry out means of escape analyses for buildings, ranging from relatively simple methods to detailed, computer-based simulations. The main options are:
Calculation of Evacuation Times – Maze Fire Consulting can carry out fire engineering analyses of the actual time taken to evacuate a building. The time required once the people start to move (known as the ‘movement time’) is only one component of this analysis because other factors such as the alarm time and the pre-movement time can significantly affect the overall evacuation time. This type of analysis may therefore contain a number of elements such as a calculation of the activation time of the smoke detection system.
Computer Simulations – Maze Fire Consulting use a computer-based evacuation analysis program called Pathfinder to model evacuations from a wide range of building designs. One of the benefits of the model is that it provides a more visual demonstration of the predicted evacuation and that it can be used in conjunction with associated CFD models.