It is important that any outbreak of fire in premises is detected at an early stage in order that the occupants once alerted can commence evacuation of the premises as soon as possible. There should also be a means so that anyone in the building who discovers a fire, can alert others to the existence of the fire and this should include arrangements for calling the fire and rescue service. The benefit of early warning of a fire will increase the probability of the safe evacuation of the building and will assist owners and occupiers of buildings in formulating their fire safety policy and emergency fire action plan.
Risk assessment fire warning - in small single storey non-residential buildings the means of raising the alarm could be quite simple, e.g. where a shouted warning "FIRE" by the person discovering the fire may be all that is needed. In more complex buildings, a sophisticated fire detection and fire alarm system may be needed.
False alarms - around 97% of all automatic calls received by the fire and rescue service result in unnecessary attendance due to false alarms. This is normally attributed to poor, design, installation or maintenance of automatic fire detection and alarm systems. Guidance on how to assess the risks and reduce false alarms is provided in BS 5839: Part 1: 2002.
Special fire precautions are necessary within residential care buildings, hospitals and enclosed shopping centres and additional guidance is provided in the annexes. The intention is to help designers and verifiers find the information they require quickly when designing or vetting such buildings. It is important to remember that the guidance in the annexes is in addition and supplementary to the guidance to Standard 2.1 to 2.15. For additional guidance on:
residential care buildings, see annex 2.A
hospitals, see annex 2.B
enclosed shopping centres, see annex 2.C.
Evacuation methods affect the category of fire detection and fire alarm system that should be installed in a particular building. The type of occupancy and means of escape strategy should be determined at building design stage. For example evacuation may be:
Where the design of the means of escape is based on simultaneous evacuation of all occupants, then operation of a manual call point or fire detector should give an almost instantaneous warning from all the fire alarm sounders. However where the means of escape is based on phased evacuation, then a staged alarm system is appropriate. This enables two or more stages of alarm to be given within a particular area (e.g. alert or evacuate signals).
Building uses incorporating design for phased evacuation are often a fire engineered solution which will include the fire alarm specification. Dependant on the determined use at design stage, a category L1 to L5 with or without voice alarm should be installed.
The factors that should be considered when assessing what category of fire alarm or automatic fire detection system is to be provided, will vary widely from one premises to another therefore the type of system will need to be considered on a case by case basis.
An assessment of the determined use should be carried out at the design stage, taking into account the building evacuation factors in order to specify the appropriate alarm category for the circumstances concerned. The significance of various evacuation factors will depend on use and occupancy. These factors are:
In any building, some of the occupants may have impaired sensory, cognitive and/or mobility impairments which could create difficulties in perceiving or responding to a fire or in evacuating the building.
Compensatory features - buildings in which other fire precautions, such as means of escape, depart from the Technical Handbook guidance should have in place fire alarms systems to compensate for such departures. Category, L1, L2, L3, L4, or L5 systems should therefore be installed in the building.
Fire detection and fire alarm system is a term used in this handbook to describe any type of automatic sensor network and associated control and indicating equipment. Sensors may be sensitive to smoke, heat, gaseous combustion products or radiation. Normally the control and indicating equipment operates a fire alarm system and it may perform other signalling or control functions as well. Automatic sprinkler systems may also be used to operate a fire alarm system.
At the design stage it is important to take into account the building evacuation factors, in order to specify the alarm category. Life safety fire alarm systems installed in a building will be one or more of the following categories.
Category L systems are automatic fire alarm systems installed for the protection of life, incorporating detectors, sounders and manual call points installed in the building. Category L fire alarm systems are sub-divided from the most stringent L1 to the least stringent requirement L5, depending on the detector coverage in the building:
L1 detectors are installed throughout the building; the objective of a category L1 system is to offer the earliest possible warning of fire, so as to achieve the longest available time to escape
L2 detectors are installed in the building so as to give warning before escape routes are impassable owing to the presence of fire, smoke or toxic gases; but with enhanced coverage in specified areas of the building
L3 detectors are installed so as to give a warning of fire at an early enough stage to enable all occupants, other than possibly those in the room of fire origin, to escape safely, before the escape routes are impassable owing to the presence of fire, smoke or toxic gases
L4 detectors are installed in those parts of the escape routes comprising circulation areas and circulation spaces, such as corridors and stairways
L5 detectors, sounders are installed in specified locations where the designed is to satisfy a specific fire safety objective (other than that of a category L1, L2, L3 or L4 system).
Categories L1 to L5 should be installed in accordance with BS 5839: Part 1: 2002 which specifies various categories of life safety fire alarm systems.
Category M is a standalone manual fire alarm system that includes manual call points and sounders at specific locations in the building. Automatic detection is not part of the system. Nevertheless category M systems should be installed in conjunction with L1, L2, L3, L4, L5 and voice alarm systems.
BS EN 54: Part 11: 2001 covers two types of call points. Type A (direct operation) in which the change to the alarm condition is automatic (i.e. without the need for further manual action) when the frangible element is broken or displaced and Type B (indirect operation) in which the change to the alarm condition requires a separate manual operation of the operating element by the user after the frangible element is broken or displaced.
Manual call points as specified in BS EN 54: Part 11: 2001 (Type A) should be installed in buildings and sited in accordance with BS 5839: Part 1: 2002.
Voice alarms - in complex and multi use buildings the installation of a voice alarm should be considered. For example, where a building is designed for phased evacuation or where occupants might not respond quickly to a fire warning, or where occupants are unfamiliar with the fire warning arrangements. Voice alarms systems may be used to alert staff or give a coded message explicit to those having responsibility for taking action in a fire. They can form part of a public address system and give both an audible signal and verbal instructions (which may be pre-recorded) in the event of fire. A voice alarm system should be installed to comply with BS 5839: Part 8: 2008.
The fire warning signal should be distinctive in sound from other sounds which may be in general use and be accompanied by clear verbal instructions.
In some circumstances visual alarm signals should be used to either supplement or replace the audible alarm, such as where hearing protection is likely to be used or in situations where occupants have a hearing impairment. Buildings such as hospitals and residential care buildings for example may incorporate a combination of audible, visual and voice alarm in the overall system.
A residential care building should have a communication system designed and installed in accordance with the guidance set out in annex 2.A. This is to give occupants and staff the earliest possible warning of an outbreak of fire and allow time for assisting occupants in an emergency to evacuate the building or for horizontal progressive evacuation initially to an adjacent compartment which leads to a compartment exit.
A hospital should have a communication system designed and installed in accordance with the guidance set out in annex 2.B. This is to give occupants and staff the earliest possible warning of an outbreak of fire and allow time for assisting occupants in an emergency to evacuate the building or for horizontal progressive evacuation initially to an adjacent sub-compartment which leads to a compartment exit.
Shared residential accommodation is designed to provide sleeping accommodation for not more than 10 persons, entered from open air at ground level and having no sleeping accommodation at a storey height of more than 7.5m. At least a category LD2 (Grade D) should be installed.
The threat posed by a fire in Residential buildings such as hotels and boarding houses in which occupants may be asleep, is much greater than that in buildings where the occupants are normally awake and alert. Guests may not be aware that their lives are at risk and are also likely to be unfamiliar with their accommodation or escape routes.
A category L2 system is likely to be appropriate for the majority of sleeping accommodation premises. However it is important that the choice of system category is based on a risk assessment of the particular circumstances.
Early warning of fire significantly increases the degree of safety provided to occupants. In order to minimise false alarms, a variation from the category L1 system may be justified regards the siting of smoke or carbon monoxide detectors in bedroom areas. Detectors are typically installed in most other rooms and few if any areas should be left unprotected and a category L1 or L2 system should be installed.
The occupants will be alert but could be unfamiliar with the building; nevertheless they should be able to respond to an outbreak of fire in their immediate area. Certain events, such as some pop concerts, may attract large numbers of young, excitable persons and will require a greater degree of control and stewarding than for other events which, despite attracting similar audience numbers, will have an entirely different behaviour profile, such as a play performed in a large theatre.
A category L1, L2, L3, or M system, should be installed in the building. The category will be dependant on the use of the building, for example whether it is a cinema, restaurant or nightclub, an assessment should be carried out at the design stage to determine the appropriate category. The following is a guide only.
Where there are:
more than 300 occupants then a category L1 system should be installed
no more than 300 occupants but more than 100 then at least a category L2, system should be installed
no more than 100 occupants but more than 60 then at least a category L3 system should be installed, and
no more than 60 then at least a category M system should be installed.
In shops, the occupants will be alert but could be unfamiliar with the premises however they should be able to respond to an outbreak of fire in their immediate area. In department stores with restaurants or cafeteria a phased evacuation can be used where fire safety measures are provided to facilitate this strategy. A category M, L3 or L4 system should be installed, in shops where there are:
more than 300 occupants then a category L3 system should be installed
not more than 300 occupants but more than 100 then a category L4 system should be installed, and
not more than 100 occupants then a category M system should be installed.
In offices, the occupants will be alert and familiar with the building and are unlikely to be so engaged with the task at hand that they initially fail to perceive or respond to an outbreak of fire in their immediate area. In these circumstances, a manually operated category M system that can be heard throughout the building when operated from a manual call point may be all that is required.
Many educational buildings are also a community resource and serve a variety of functions. It is therefore important that the choice of system category is based on risk assessment of the particular circumstances. An example would be where a country school could consist of one large classroom with 14 pupils and a teacher, where the warning is understood, and can be heard throughout the building. More complex educational buildings, may contain different uses such as large assembly areas, auditoriums, or administration centres. In such cases, the guidance under the relevant building types should also be followed. In educational buildings with more than 60 occupants therefore, at least a category M, L3, L4 or L5 system should be installed dependant on assessment at the design stage.
In factory buildings (class 1), factory (class 2), storage buildings (class 1) and storage buildings (class 2) the occupants will be alert and will be familiar with the building, also the numbers of persons in the building will normally be low but can vary for example a large compartment with production lines such as clothes manufacturing. Due to the varied nature of use, some buildings may contain hazardous or dangerous materials or processes, with the potential for fire or explosion, posing an additional risk to persons, on or in the immediate vicinity of the building. Such factors should be part of the fire risk assessment to ensure that fire safety measures are provided to safeguard occupants who are so engaged with the task at hand that they may initially fail to perceive or respond to an outbreak of fire in their immediate area.
Normally a category M system should be installed, however occupants could work alone in remote areas of the building and this should be considered when determining the category of system.
Therefore dependant on assessment at design stage a category M, L1, L2, L3, L4, or L5 should be installed.
An enclosed shopping centre should have a communication system designed and installed in accordance with the guidance set out in annex 2.C.
These buildings may be small single-storey or large complex buildings which include mixed use occupancy such as airports, where the category of alarm system will normally form part of a fire engineering solution. Excluding large complex buildings and dependant on risk assessment at design stage, a category M, L4 or L5 system should be installed.
In small single-storey buildings where the occupant number is not more than 10 and the floor area is such that everyone can see each other, a shouted warning "FIRE" by the person discovering the fire could be all that is needed. In assessing the situation, it must be determined that the warning can be heard and understood throughout the building, or compartment, including those in remote locations such as toilets.