As the evacuation of tall/complex buildings draws increasing attention, Mike Floyd responds by explaining current strategies and how to match the fire alarm specification to their needs
IN RECENT years, there has been a lot of interest in the evacuation of tall and/or complex buildings – especially with such premises being prime terrorism targets – as well as in their potential fire problems.
The fire evacuation strategy should come out of the fire risk assessment findings. It should have taken into account the people at risk, where they are in the building, the risks that cannot be removed or reduced any further and the size/layout of the building.
In very tall or complex buildings, this might have involved a full fire engineering process through BS 7974 by a competent fire engineer. The strategy might itself need to be complex, such as keeping escape routes clear with smoke control systems or with the use of firefighting lifts for evacuation. In such cases, the fire alarm would need to be a hub both of signalling to occupants and of liaising/controlling various hardware systems, possibly via a building management system (BMS) and therefore of high specification and reliability.
However, Britain has a limited number of premises requiring such unusual measures, so most could use an off-the-peg arrangement, ie one of a few proven systems that are relatively easy to set up and manage. These solutions do not require excessive planning, training or justification as to their use, as they have worked for many decades.
A large percentage of UK premises have a limited number of occupants, storeys and unusual evacuation requirements. In all premises, the guiding principle should be ‘keep it simple, stupid’ (KISS), which should ensure that all persons likely to be in the building will correctly follow the chosen procedure. The simplest suitable option here is single stage evacuation, sometimes termed ‘one out – all out’.
If any detection is activated or a call point operated, all the fire alarm sounders and any visual devices will signal simultaneously. In a very small building where the floor area across all the storeys is 300m2 or less, there only needs to be one zone on the fire alarm system. On this activation, staff can be easily briefed in advance to make their way to a fire alarm assembly point. This should be set up at a safe distance from the building, and evacuees will await further instructions there and possibly assist with a roll call.
All types of fire alarm systems could be used in such premises, including the simplest non-addressable panel driven arrangements. There might still be many benefits in choosing a budget addressable system in larger buildings using such a strategy, such as simpler faultfinding and continuous monitoring of all devices, plus the obvious pinpointing of the location of activations.
As the number of occupants increases in a building with a limited number of storeys, the single stage system might be deemed too disruptive to the business. If adequate escape provision is available, especially via at least two separate staircases, a couple of other options are available.
Staged evacuation: two stage
Any procedure other than single stage is slightly unhelpfully termed a ‘staged’ evacuation. The commonest of these is a two stage arrangement, of which there are at least two variations. As the building is now larger, it has been divided up into several zones on the fire alarm system, with each zone limited in size and being confined to a single physical space such as one floor, staircase or wing. If the fire alarm is activated, only the sounders/visual devices in that zone will give an evacuation signal, usually a continuous tone. The devices in the remaining zones would usually give an alert tone such as one second on, then one second off, to indicate there is an activation somewhere in the building. Responders would need to be trained to investigate the initial zone and decide whether it is a false alarm, or to escalate the signal to a full evacuation if necessary. Therefore, this arrangement is a form of staff alarm, as well as a two stage.
The alarm system needs to be at least a few notches up from that which could only manage a single stage. As well as the zones having their own detection devices and call points, each zone must also be a separate alarm zone, so that alarm devices can be set off in the manner described. Some simple panels only have a single output circuit for sounders/visual devices, so these can only be used for single stage premises.
There are many non-addressable panels that do have a number of sounder outputs and could manage the correct signalling up to a certain number of zones. However, it is likely that other functions any fire alarm would need to manage in these larger buildings, such as fire door retainers, would make a more sophisticated panel and system a better choice.
On an analogue addressable panel, door retainers and other hardware can be controlled by a locally sited input/output (i/o) unit. These are added to the loop wiring that the detectors, call points and sounders/visual alarms share. As each loop can usually communicate with quite a large number of devices, this means additional tasks can be added as they arise in the evolution of the building’s use. Some manufacturers of two wire systems also have the option to add i/o units.
On non-addressable panels, wiring has to run to each device – which is required to be separately controllable from the panel.
An analogue addressable system also has the primary benefit of directing responders to a precise location of activation rather than just a zone, as do a few two wire systems.
Staff alarm only
In many premises of this largish size, but with a moderate number of storeys, the alert signal is still considered disruptive to the business and also occasionally confuses staff about whether they should evacuate the building immediately.
A staff alarm avoids this by having the responders paged with the fire signal location on activation, and no audible alarm given in the building other than at the panel. Another approach is to broadcast coded messages over a public address system, where available. This is more commonly used in larger premises with public access.
One responder would be nominated to go to the panel and at least two would go to the location of the fire signal. In premises mainly occupied by staff – such as offices and industrial – call point activations, heat detectors and sprinklers would result in an evacuation alarm, as these should be very reliable warnings. BS 5839-1: Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises has clear guidance on how to safely operate this protocol in clause 19. Primarily, this recommends that in case responders are too slow to investigate the signal, a maximum delay time before the evacuation signal starts automatically cannot be set at more than six minutes. Many fire advisors feel this is too long for their particular building, therefore two to three minutes is commonly used.
A further safeguard is set, in that any second smoke device being activated would commence the evacuation signal, as would a call point.
Training for the responders would need to be fairly detailed, including on the operation of the alarm panel, but principally on safe searching the fi re zone or location and potentially tackling a small fire, if safe to do so.
If a false alarm is found, it is vital that this can be quickly communicated to the responder at the panel so that it can be reset. Otherwise the countdown time might expire and the evacuation signal commence, thus negating the whole staff alarm purpose. Handheld radios are the most reliable option, but mobile phones might be acceptable.
Operating a staff alarm has another advantage. Many fire and rescue services (FRSs) in England and Wales require most commercial premises to visually confi rm any fire signals originating from fire detection systems before they will send appliances to the premises. The Scottish FRS usually despatches at least one appliance to all calls, as does Buckinghamshire and Milton Keynes FRS.
The protocols for two stage are viable for premises up to about ten storeys, in which it is likely that staircases are of sufficient size for a complete evacuation in one go (simultaneous evacuation) if a fire condition is deemed serious.
Offices from around this height can be designed with reduced staircase capacity, where a simultaneous evacuation would cause congestion in lobbies and staircases. The thinking behind such a design is that few journeys within the building are done via the stairs, other than to fl oors very close by. As the staircase would need to be quite large to accommodate a simultaneous evacuation, at most other times the staircases are very much under used, despite being expensive to have included.
All the investigation aspects of the staged alarms described above would be the fi rst stage of action in these buildings, where hopefully the evacuation may be fully avoided if a false alarm is found quickly.
In any reduced staircase capacity building, a phased evacuation arrangement must be used. This involves signalling the evacuation to fl oors in a pre-set sequence, according to where the fire signal originates. To ensure this is carried out safely and smoothly, a number of additional measures are needed. Each floor of the building has to be a separate fire compartment capable of containing a fire in that floor for an enhanced period, usually with lobbied staircase entrances.
As for the signalling arrangements, it has long been considered unsuitable to use standard fire sounders with or without visual alarms. This is because occupants of floors directly above or below where a tone type sounder is operated may hear some of that sound ‘bleed’ into their floor and cause them to begin evacuating their floor too early. Therefore a fire alarm system connected to voice type sounders should be used, usually designed and installed to BS 5839-8: Fire detection and fire alarm systems for buildings. Code of practice for the design, installation, commissioning and maintenance of voice alarm systems. This type of alarm can be configured to deliver a preset message relevant to each floor or area, so that occupants will know when their location needs to be evacuated.
The commonest signalling sequence is to evacuate the floor on which the fire signal originated, followed closely by the ones directly above and below. After that, it would usually be considered that persons in any additional floors above the fire level should be the higher priority. Although a complete evacuation might swamp the staircases and lobbies, a limited number of floors’ occupants descending in reasonably close succession can be handled.
The fire alarm must have a high level of management ability, in addition to outputting the signals to a voice system. No control must be available to give a simultaneous evacuation signal on the panel, as would be normal on other systems. As before, there would be a number of interfaces for the fire alarm to control at various times during the evacuation. As well as the fire door retainers, security interfaces might need to be de-activated and air handling or other plant shut down. Such an array of tasks, termed the ‘cause and effect’ program, is easily handled by one of the higher specification analogue addressable panels.
Although there is a good selection of panels that can manage this level of complexity, a key aspect of achieving the required outcome for every possible activation is correct programming and commissioning of the system before handover.
It would be prudent to choose a third party accredited organisation to carry out this work, in order to have the most confidence that all will be well. Full recourse to the certification body’s complaints and rectification scheme comes in such a package, as well as duplicate paperwork and ongoing monitoring of the supplier. An often overlooked benefit is that if any serious problem occurs in relation to the system, such as an injury, courts would normally accept that the building owner has exercised due diligence and the liability will fall on the supplier.
Choice of technology
These addressable systems have steadily dropped in cost and are available from a larger range of suppliers. Unfortunately, the biggest selling point still seems to be the identification of the exact fire location. Unless the premises experiences fairly frequent fires, this feature is not quite as important as it is claimed.
Useful on a day-to-day basis is the quick identification of various faults and their location, as well as reduced servicing requirements. Most panels now offer a ‘pre-alarm’ feature, which identifies any unusual condition in a monitored space that might or might not be a fire. This gives extra time for response such as searching, before a full alarm condition triggers. A wider selection of devices is usually available in addressable systems, with multi-sensors or multi-criteria type being extremely useful.
These devices generally help to reduce the incidence of false alarms if they are transient in nature, but also offer improved response to genuine fire signals if properly commissioned. It is possible to fit multi-sensors onto conventional systems, but it is usually more expensive and the full benefit is not obtained.
So far, the training of responders to the fire signal has been emphasised. This is key to ensuring the initial decisions that need to be taken are correct, but also that risks to such volunteer personnel are minimised. Few buildings have large numbers of fires each year, but many have disruptive numbers of unnecessary evacuations due to false alarms and poor control of contractor work. A well trained team of responders – such as I was fortunate to manage at a large government facility – can minimise the disruption by speedy identification of false alarms or tackling any small fire at an early stage that other trained staff in the area have not dealt with. They can also keep an eye on any work starting in their area without a permit in place, as can fire marshals who have been correctly briefed.
All other staff need to have the evacuation procedure explained on induction and to have a copy of this and the fire safety policy handed over in their work contract package.
Ongoing training needs to match the level of complexity of the evacuation procedure in place. This is the advantage of choosing the simplest protocol that meets the needs of life safety and any business disruption avoidance – KISS.
Apart from a programme of refresher training, such as talks with a relevant video, the most effective measure is well organised fire drills at suitable intervals. These should be followed by feedback to all staff via staff message systems and to responders/fire marshals, in order to improve things in future.
In my own case, the evacuation time was halved from eight to four minutes, following newly formatted evacuation drills and feedback sessions.
As we have seen, a successful evacuation system is achieved by an amalgamation of several areas in fire safety: a competent fire risk assessment leading to a practical fire strategy; the simplest evacuation procedure that will meet the needs of the occupants and business; a fire alarm system that can manage such a procedure; an ongoing training programme to match staff needs; and finally management of all the above, ideally by a dedicated fire manager in larger premises.
It can be tempting to add bells and whistles to the strategy because the fire alarm panel offers enhanced abilities, but beware of the tail wagging the dog!
Mike Floyd is an associate trainer and technical author with the Fire Protection Association