Principal of Assembly buildings- fire protection engineering:

As assembly buildings accommodate members of the public they often accommodate people with disabilities. People may have impaired mobility or they may be deaf or blind or have other disabilities. If assembly buildings do accommodate such people they must have the ability to evacuate these people in an emergency. Often, these buildings will have an investigation period of several minutes after the fire alarm has activated and before the evacuation signal is given to the people in the building.

This allows the staff to check the cause of the fire alarm activation and to ensure that it is actually necessary to evacuate before commencing that evacuation. If the cause was a false alarm or a small fire that has been extinguished then no evacuation need take place. It is sometimes necessary to start evacuating disabled people during the investigation period before the general population is given the signal to evacuate. Management procedures can achieve this.