In the last years, in the field of fire safety, alongside the now well-known prescriptive approach, the new performance-based approach – known through the international term Performance Based Design – has begun to spread in Italy.
Before the advent of this new methodology, the fire professionals, with the support of the code writers, could see the length of the escape route as the only measure on which to intervene to ensure life safety. In fact, the moment when the alarm is activated has always been considered as the evacuation start up.
But, is it really what happens in reality?
Try to imagine being in a situation where a fire alarm is operated, and the answer is immediate. Several studies have highlighted how, once heard the alarm, individuals occupy their time in activities other than evacuation; all these actions can also cover two thirds of the time it takes to leave the building. The English expression “milling” (stroll around like a mill) stands for social interaction in the early alarm phases: individuals try to check and seek for a confirmation, with other people, about the seriousness of the message or warning they received; or try to go and retrieve personal possessions or to bring together all individuals with whom they have an emotional connection.
These activities can be measured in tens of minutes. This time interval that elapses between the alarm and the beginning of the evacuation takes the name of pre-movement time, which is only one of the elements that constitute the Required Safe Escape Time (RSET).
In conclusion, we might wonder: can we consider life safety as guaranteed in an exit way 30 meters long, although before starting evacuation even 30 minutes could pass?