The LWF Blog

Facilities Management – Fire Detection & Fire Alarm Systems – Alarm Devices – Part 12

August 25, 2016 9:42 am

In our blog series for those working in Facilities Management, we have recently been looking at fire detection and fire alarm systems. In the last edition, we discussed how the choice and positioning of alarm sounders must be considered when meeting sound level requirements for alarms.


The dB level emitted by the sounders should generally be 65dB(A), although this varies down a little in stairwells and very small areas to 60dB(A). Additionally, if the alarm is intended to wake sleeping occupants of the building, the sound level should be adjusted upwards to 75dB(A).


However, careful consideration should be given to the outcome of an alarm in the case of sleeping occupants. In a residential care home, the sleeping sound level of 75dB(A) should only be achieved in bedrooms if it is expected that those residents will wake and then evacuate themselves from the building in a timely fashion. Where it cannot be expected that the individuals will be able to do this without assistance, BS 5839:1, which relates to situations in England and Wales, states that levels of 60-65dB(A) would apply throughout, enabling staff to be alerted and then provide the relevant assistance to every occupant.


Standard recommended alarm sounder levels are not the only aspect of sounding alarms which should be taken into account. The level of noise in the area prior to the sounding of an alarm must be taken into consideration. In an area which has a high noise level, visual alarms should also be provided in the form of flashing beacons. In addition to these being used in areas of high noise level, they are also used to alert people who may be deaf or not have full hearing capacity.


Where flashing devices are used, the rate must be considered and not set too high, in case this might trigger an epileptic attack in people with photosensitive epilepsy. It should also be noted on this subject that whilst devices set to 30-130 flashes per minute as standard (and stated in BS 5839:1) should not trigger an epileptic episode, the provision of several flashers in an area which are not synchronised may do so.


Whilst visual beacons are helpful to those people with hearing difficulties, they are not the only fire alarm provision that can be provided. Vibrating pagers may also be provided to those people who have hearing difficulties and are resident in or attending a building with such a system installed. These are particularly necessary in those buildings where a deaf or hard of hearing person might need to sleep and so be unaware of flashing beacons. Indeed, in sleeping accommodation, vibrating pads may be provided in the bed itself, under mattresses or pillows, to wake the sleeping occupant in case of fire. BS 5446:3 provides specification of performance for such devices intended for use in domestic premises, however they are also useful for hotels, or any building in which people with a hearing impairment might sleep.


In next week’s blog, we will continue looking at fire alarm systems and in particular, voice alarm systems. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact Peter Gyere in the first instance on 0208 668 8663.


Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.


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