Revisions in BS5839-1 2002 put greater emphasis on the responsibility of specifiers
and designers of fire alarm systems to reduce the incidence of unwanted alarms.
These alarms accounted for the fire brigade being unnecessarily called out nearly
700 times a day in the year 2000 alone. The incurred cost, misallocation of
resources and inconvenience should all be in the forefront of a specifier’s
mind. Indeed the revised BS5839-1 2002 now requires that fire alarm system designers
must be able to demonstrate on the design certificate the measures incorporated
in their design that limit the incidence of false alarms.
False alarms can be categorised into 4 types: equipment false alarms, malicious false alarms, false alarms from good intent i.e. someone wrongly suspects a fire and raises the alarm and lastly unwanted alarms – by far the largest occurrence when the system has responded to a fire-like phenomenon. Typically this is steam from cooking fumes, showers etc. or cigarette or cigar smoke. It is impossible to eradicate all these occurrences from places where people live day to day so alarms resulting from this type of source are difficult to overcome.
So how can a system designer attempt to limit the amount of these unwanted alarms? Firstly, care must be taken in design to appropriately position detectors so they still give optimum detection performance but are not sited in places exposed to high concentrations of steam and smoke in the normal course of daily events. Secondly, a system designer must take into consideration using equipment that has been designed to discriminate against nuisance alarms. BS5839-1 2002 advises that “analogue” equipment offers better immunity to unwanted alarms. Analogue detectors, such as the “Multipoint” detector, have distributed intelligence by means of an in-built microprocessor in every device. This means detectors are capable of making a more accurate fire decision as they are constantly storing analogue values and self-calibrating. Detectors reliably conclude whether or not a “real” fire situation is present thereby significantly reducing the number of unwanted alarms.
As well as the use of analogue devices, it is recommended that the best type of detectors to use are “multi-sensors”. The Multipoint detector has 3 smoke modes, 3 heat modes and a combination heat/smoke mode so can cater for any environment. These 7 different modes of detection enable the designer to use the ideal setting for a particular room. This setting can even be changed at any time if necessary. Therefore, the system designer benefits from versatility when specifying which type of detector to use and allows for a lower instance of unwanted alarms.
The Multipoint offers all the advantages of being an analogue detector whether used on a conventional or addressable system. It also has the unique feature of a built-in 90dBA sounder. Designers can be assured that audibility levels can be easily achieved with sound spread evenly throughout a building. This feature also means that the Multipoint can be easily and cost effectively installed.
Unwanted alarms can also arise from environmental factors. There are systems
that have been ergonomically designed to counteract these types of alarms and
minimise the disruption they can cause. Rafiki Protection, the manufacturers
of the Multipoint detector, has used the technology in the Multipoint to offer
a pre-alarm feature. What this means in practice is that the designer has an
opportunity to allow an alarm confirmation period on certain zones. If a Multipoint
detector senses smoke or heat in a zone that has been programmed to have a confirmation
period, then only the local sounder in that particular sensor sounds to warn
the room occupant. If the occupant realizes that they have caused this alarm
(by cooking, showering etc) they have the opportunity to clear the source of
the alarm before the rest of the building goes into full alarm and disturbing
all the occupants. If the source of the alarm is found to be genuine then the
rest of the building immediately goes into full alarm. This type of system is
ideal for HMO type applications or anywhere that suffers high incidents of unwanted
alarms. Rafiki offer this feature even on conventional systems providing a cost
effective solution to an age-old problem. Specifiers can be sure that they are
doing as much as possible to limit the incidence of false alarms and occupants
won’t be unnecessarily disrupted in their daily life.
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Rafiki Protection Ltd.
Springvale Industrial Estate,
Cwmbran NP44 5BD (UK)
Tel: 01633 865558 Fax: 01633 866656
Website: www.rafikiprotection.com
Email: sales@rafiki.biz