Making The Right Choice - Fire Alarm Systems
For complex premises, choosing the right system can be a very complicated task, with many different parameters to be considered and balanced. Specifiers are too often content just to quote the British Standard, believing it must be a good system if it complies with BS 5839. Some will even mention Part 1: the Code of practice for system design, installation, commissioning and maintenance, and the year of publication, but in truth the Code of Practice does no more than state a range of possibilities and options and in the recent edition addi
Perhaps it is best to start by writing down the needs of your business, what has driven you to think about a system. If it is because of fire authority requirements pay careful attention to their wording. Some people are convinced that paying more for something guarantees that you get the best, if there are add-ons to be had they will buy them. With a fire alarm system it may well be better to leave the add-ons on the shelf. Extra components can increase installation costs dramatically. Whole life costs will also be greater, as there is more to maintain, and replace. With a fire detection system false alarms can almost certainly increase in line with the number of detectors on the system. The best advice must be to keep the system as simple as possible commensurate with risk. It must further be remembered that a fire alarm is an information provision system, if you do not need or are unable to respond to a high level of information, why pay for it?
A small to medium business will probably expect little from their system. They may well just want a means to raise an alarm in the event of a fire, in order to comply with basic legislative requirements. In this case a simple system comprised of standard break glass call points and bell type sounders will meet the need and is most unlikely to give any trouble. This is called a 'Category M' or 'Manual system' in the British Standard. In a larger building it may be necessary to divide the building into a number of zones, so that the approximate location of an incident can be quickly identified. In this case a simple, but clear zone plan must be displayed near the control panel, principally to help the fire service find the incident quickly.
A simple manual system is really designed for life protection only, but human beings are very good fire detectors, no-one has yet invented better. If the means are provided for them to raise the alarm quickly, an improved level of property protection will also follow by default. This can be enhanced by the addition of an auto-dialling system on a dedicated telephone line, so that a message is automatically sent to summon the fire brigade should a call point be operated. Such a system can save valuable minutes when needed, for relatively little cost. Auto-dialling systems are very reliable, but should nevertheless be backed up by a confirmation call in all cases.
In larger and more complex buildings, a life protection system may require some automatic fire detection to supplement the manual call points. It is not always necessary to place detectors throughout the building. The simplest system will have detectors on exit routes and stairwells, with, perhaps, any high risk rooms adjoining corridors also covered. In this context a high risk room would be a room where there is a high risk of an undiscovered fire starting. Rooms which are permanently occupied, or regularly visited when the building is in operation, need not have detection, remember fewer detectors mean fewer false alarms. These partial systems still comply with the British Standard, and are identified within it as categories L2, L3 and L4.
Premises where persons sleep present the greatest threat to life, and should be given the highest level of cover by automatic detection. The British Standard designates total cover life safety systems as type L1. Hotels and boarding houses and hostels, are all places where such systems will almost certainly be required. Houses in multiple occupation also present a higher than average life risk, and have their own special system type designated in the code. However, an L1 system can seldom be justified in premises which do not have sleeping accommodation, over specification will be costly, and may lead to a system which gives unnecessary trouble all its life.
If property protection is your prime concern it is likely that you will need detection throughout your premises. Insurance companies tend to favour sprinkler systems as a property protection measure, and if these are fitted they will often consider a smoke detection system superfluous.
The problem with property is that it cannot evacuate when the alarm is raised, and it must be remembered that, on its own, a detection system can do no more than give an early warning. A sprinkler system will raise the alarm, and fight the fire. However, there are many premises where property is an important consideration, but sprinkler systems are not a practicable option, historic properties usually fall into this category. In such cases a full property protection system, category P1, will give the earliest warning, allowing contingency plans to be put into operation, and the fire brigade to be alerted.
Partial systems for property protection are rare, but it may be that all your valuables can be stored in an area which is separated from the remainder of the building by substantial fire resisting construction. In this case the cost of a full P1 system would not be justified, as such the current British Standard allows a category P2 system for partial coverage.
Article provided by Lawrence Webster Forrest Limited
Lawrence Webster Forrest Limited is a fire safety engineering consultancy with over twenty years experience in the development of fire engineering technology and the application of fire safety standards.
As the UK's leading independent fire consultants. LWF specializes in helping businesses meet the requirements of fire safety legislation through cost effective fire safety consultancy services.
For further information please contact
Peter Gyere Marketing Manager on 020 8668 8663
www.lwf.co.uk
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