In the event passengers must be rapidly evacuated from the airplane, reduction of personal injury and damage may be enhanced by early notification of the evacuation. When evacuation is required, the aircraft must be first secured against movement and all external hazards. This means that it is necessary to stop the aircraft and set the parking brake, as nay accidental movement during evacuation could cause serious injuries to those sliding out of the aircraft or those under it on the ground. Engines, including the APU, must be switched off to prevent people from being sucked in or burnt by hot exhaust gases. These steps are crucial and will ensure the area is safe prior to leaving the aircraft.