The LWF Blog

Fire Engineering Design and Risk Assessment – Fire Alarm Control Equipment – Part 21

October 20, 2016 9:21 am

In our blog series for Architects and those involved in the design and production of buildings, we have been looking at fire safety provision through fire alarms. In part 20, we began to explore the requirements in relation to audio and visual warnings and will continue here.


We established previously that the minimum sound level for a fire alarm sounder should be 65dBA, or alternatively 5dBA above any persistent background noise. However, if the premises in which the alarm is placed involve people sleeping – such as hotels, then the sound level should be 75dBA at the site of each bed.


Because of the practicalities of sound being muffled by walls and doors, in practical terms this might mean the installation of a sounder in each bedroom.

Of course, there are some types of premises which would be too loud for any sounder level to be heard clearly, such as a nightclub. In these instances, it is important that triggering of the fire alarm also immediately cuts off sound from the musical equipment.


When considering fire alarms for people who may be deaf or have limited hearing capability, the circumstances matter. In a nightclub, for instance, a deaf person with a group of friends would likely be evacuated along with them. They would be able to see that the situation had changed, with staff ensuring all persons have received the ‘fire signal’. However, where a deaf person might be working alone within the building, radio paging can be an additional safety measure. This would be triggered by the alarm system and then vibrate to alert the holder.


Flashing beacons which are triggered by the fire alarm are another measure which would help people who are deaf or have limited hearing. And in cases where a deaf person may be sleeping on the premises, a vibrating disk can be placed under their pillow to ensure they are woken if a fire breaks out. In the UK, further guidance on this can be obtained from the Equalities Act and Building Regulations Approved Document M.


Flashing beacons should be red or white (unless this conflicts with other visual warnings already in place) and care should be taken that the flash rates are not sufficient to trigger seizures in those people who suffer from photosensitive epilepsy.


Some systems support the use of a voice alarm, this means that instead of an alarm siren or horn, a human voice is played over the system at the same sound level. Care will be needed to ensure that the high volume does not distort the message quality. Equally, the zoning of these warnings must be matched to the evacuation zones.


In our next blog, we’ll talk more about fire alarm systems in terms of audio and visual devices. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.


Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.


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