Fire Evacuation Strategies Explained
When people picture a fire evacuation, they tend to imagine a single moment, an alarm sounding and everyone leaving at once. That picture fits a great many buildings, but it is only one of several recognised approaches, and the right choice depends on the size and layout of the premises, the number and needs of the people inside, and the risks that a fire risk assessment has identified. Choosing the wrong strategy, or applying a complex one without the systems and training to support it, can be just as much of a problem as having no plan at all.
The evacuation strategy should always come out of the fire risk assessment, taking account of who is at risk, where they are in the building, the risks that cannot be removed or reduced any further, and the size and layout of the premises. For the overwhelming majority of buildings in this country, one of a few long established and well proven arrangements will be entirely suitable, and the guiding principle throughout should be to keep things as simple as the building allows.
Single stage, or "one out, all out"
The simplest option, and the one most people will recognise, is single stage evacuation. When any detector is triggered or any call point is operated, every sounder and visual device in the building signals at the same moment, and everyone makes their way to the assembly point at a safe distance from the building, where a roll call can be carried out and further instructions given. A clear fire evacuation plan is what turns this from a general intention into something staff can follow without hesitation.
This suits the large percentage of UK premises that have a limited number of occupants and storeys and no unusual evacuation requirements. In a very small building, where the floor area across all the storeys is 300 square metres or less, the fire alarm only needs a single zone, and even the simplest non addressable panel will manage the task. Staff can be briefed in advance on what to do, which is one of the reasons this arrangement remains so dependable, since there is very little that can be misunderstood.
Staged evacuation, where leaving all at once is too disruptive
As the number of occupants grows in a building that still has a limited number of storeys, evacuating everyone at the first sign of an alarm can become unduly disruptive, particularly given how many alarms turn out to be false. Where there is adequate escape provision, especially at least two separate staircases, a staged approach becomes possible. Any procedure other than single stage is, slightly unhelpfully, grouped under the heading of "staged" evacuation.
Two stage
The commonest staged arrangement is a two stage system. The building is divided into several fire alarm zones, each confined to a single physical space such as one floor, staircase or wing. When the alarm is triggered, only the devices in the affected zone give a full evacuation signal, usually a continuous tone, while the remaining zones give an alert signal, often one second on and one second off, to indicate that something is happening somewhere in the building. Trained responders then investigate the originating zone and decide whether it is a false alarm or whether to escalate to a full evacuation, which means a two stage system is also a form of staff alarm.
This calls for an alarm system a few notches above the single stage minimum, since each zone needs to be a separately controllable alarm zone, and larger buildings of this kind usually have other functions to manage, such as fire door retainers, which makes an analogue addressable system the more sensible choice in practice.
Staff alarm only
In some premises of this size, even the alert tone is felt to be disruptive, or it confuses staff about whether they should be leaving. A staff alarm avoids this by paging nominated responders with the location of the fire signal, with no audible alarm in the building other than at the panel itself, or by broadcasting coded messages over a public address system where one exists. One responder goes to the panel and at least two go to the location of the signal.
BS 5839-1 sets out how to operate this safely in clause 19. A maximum delay before the evacuation signal starts automatically cannot be set at more than six minutes, in case responders are too slow to investigate, although many fire advisors consider that too long for their building and commonly set two to three minutes instead. As a further safeguard, a second smoke device activating, or any call point being operated, will start the evacuation signal regardless. Reliable communication between the responders matters a great deal here, since a false alarm needs to be confirmed and the panel reset before the countdown expires, and handheld radios are the most dependable option for this.
A practical point worth knowingA staff alarm carries a further advantage. Many fire and rescue services in England and Wales now require commercial premises to visually confirm a fire signal from an automatic detection system before they will mobilise, so having trained responders on hand to do exactly that fits neatly with how the service already operates.
Simultaneous evacuation in taller buildings
The two stage protocols remain viable for premises up to around ten storeys, where the staircases are usually large enough to allow a complete evacuation in one go, known as a simultaneous evacuation, if a fire is judged to be serious. The investigation stages described above still come first, in the hope that a quickly identified false alarm allows a full evacuation to be avoided, but the building retains the capacity to clear everyone at once when that is the safer course.
Phased evacuation in reduced staircase buildings
Taller offices are often designed with reduced staircase capacity, on the reasoning that the stairs would otherwise be expensive and very much underused, since few journeys within the building are made on foot beyond nearby floors. In any building of this kind, a phased evacuation must be used, signalling the evacuation to floors in a pre set sequence according to where the fire signal originates. This depends on each floor being a separate fire compartment capable of holding a fire for an enhanced period, usually with lobbied staircase entrances. Where any floor may be occupied by people who cannot readily use the stairs, the plan also needs to address how they will be assisted, which is where measures such as evacuation chair training become part of the wider strategy.
Standard fire sounders are unsuitable here, because the tone can bleed into the floors directly above and below and prompt people to start leaving too early. A voice alarm system designed to BS 5839-8 is used instead, delivering a preset message relevant to each floor so that occupants know precisely when their area needs to be evacuated. The usual sequence evacuates the fire floor first, followed closely by the floors immediately above and below, after which the floors higher up the building take priority. The panel managing all of this has to handle a considerable array of tasks, the cause and effect programme, from voice messaging to releasing door retainers and shutting down air handling plant, with no facility to give a simultaneous signal by mistake.
Why commissioning matters hereWith a system this complex, correct programming and commissioning before handover is what makes the difference between a strategy that works for every possible activation and one that does not. Using a third party accredited organisation for this work gives access to a certification body's complaints and rectification scheme, and it carries real weight if a serious problem ever has to be examined in court, since it helps demonstrate that the building owner exercised due diligence.
The strategy is only as good as the training behind it
Whichever approach is chosen, the training of the people who respond to the fire signal is central to it working, since they make the early decisions on whether a signal is genuine and they do so while keeping their own risk to a minimum. A well trained team of responders can cut disruption considerably by identifying false alarms quickly, dealing with a small fire at an early stage where it is safe to do so, and keeping an eye on contractor work that might otherwise set the alarm off. Every other member of staff should have the evacuation procedure explained at induction and a copy provided with the fire safety policy.
Ongoing training needs to match the complexity of the procedure in place, which is one more reason to choose the simplest protocol that meets the needs of life safety and business continuity. Beyond refresher sessions, well organised fire drills at suitable intervals, followed by honest feedback to staff and responders, remain the most effective measure of all, and they routinely bring evacuation times down once the lessons are acted on. The temptation to add features simply because the panel offers them should be resisted, and the strategy kept firmly in charge of the technology rather than the other way around.
For most organisations, the value of a fire risk assessment lies partly in arriving at the right evacuation strategy in the first place, one that suits the building and the people in it rather than one borrowed from somewhere larger or more complex. As independent assessors covering the North West, North Wales and the West Midlands, we look at the building as it actually is, and recommend the approach that gives genuine protection without unnecessary cost or disruption.
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Get in touch Fire Risk AssessmentsThis article is provided for general guidance and does not constitute professional advice for any specific premises. Evacuation strategies should be determined by a competent fire risk assessment and, where relevant, the applicable British Standards. Considerable care has been taken to ensure accuracy at the time of writing, but legislation and guidance change over time. Fletcher Risk Management Limited provides Fire Risk Assessments, Fire Door Inspections and Fire Safety Training across the North West, North Wales and the West Midlands.