An Introduction to Phased Evacuation

One of many functions of a voice alarm system is to provide the means to enable the phased evacuation of a building.

Phased evacuation is literally the systematic removal of people from an area, floor or building during an emergency such as a fire. By phasing the evacuation of a building, it is possible to ensure that those in the most danger are able to escape first.

In many buildings it is not possible to use a lift in the event of a fire; lifts are often programmed to travel to the ground floor the instant the fire alarm is raised. This means that the stairwells and other evacuation routes will be used in order to escape the building. In a high rise or any multi-level building, expecting everyone to leave the building at the same time could potentially lead to panic and blockage on these evacuation routes. The ability to initiate a controlled, area-by-area evacuation of a building – known as phased evacuation – helps prevent this.

Imagine if a fire starts on the fifth floor of a multi-level building. It is clear that the people on this floor are most at risk, also those immediately above and below (i.e. on the fourth and sixth floors) are at a high level of risk. With phased evacuation, everyone on these three floors will be instructed to leave the building immediately. It is not unusual to evacuate the basement and top levels of a building too. Depending on the nature of the fire and the structure/layout of the building, evacuation can continue on a floor by floor basis until all have been led to safety.

In our scenario (see diagram), whilst the third and fifth floors are being instructed to “leave the building immediately”, people on the other floors can be warned of a possible call to action. Multiple messages to different areas can all be broadcast simultaneously. At the same time, via a priority microphone, live announcements can be made to any selected areas, or all areas of the building.

Another benefit of the phased evacuation method is the fact that on occasion (although very rarely), alarms turn out to be false. By delaying the evacuation of some areas of the building there is much less disruption, should the alarm prove to be a non-event.

A voice evacuation system uses clearly understood, spoken instructions, via pre-recorded, digitally stored messages. The system is not reliant on a person (or persons) to relay the message, in a potentially rushed or panicked way.

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