The LWF Blog

Fire Safety for Facilities Management Personnel – Voice Alarm Systems – Part 215

August 21, 2023 10:59 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 214, LWF discussed emergency microphones and message sources. In part 215, we will talk about how to avoid the numerous potential sound pitfalls when designing a voice alarm system.

In addition to background noise being a challenge when installing a voice alarm system, there are other factors which will need to be assessed and any issues dealt with prior to commissioning.

One such potential issue is that the intelligibility of the voice alarm system message can be affected by the presence of a solid element between the nearest loudspeaker and building occupants. Any form of solid construction, such as a door or partition, acts as a high frequency filter. This means that only the low frequency part of the message will pass through the obstruction and will not be sufficiently clear for the hearer to understand.

For this reason, it is likely to be necessary for a loudspeaker to be placed in every room in a building, whereas with a conventional fire alarm system with sounders, that would not be required (as the sound would travel through partitions sufficiently to alert all building occupants to a fire situation).

Although the real proof of intelligibility of a voice alarm system will be that all occupants in all areas of a building can clearly hear and understand the message given, there are other methods of quantifying intelligibility. Test equipment designed for that purpose is available which can be useful in case of a dispute between the voice alarm installer and the user or enforcing authority, provided the required intelligibility level had been specified at the design stage.

In some buildings and environments, the ambient noise level can vary significantly. An airport terminal is one such example. At peak hours, the ambient noise will be very high, but at night, the sound level is much lower. Voice alarm systems can utilise ambient noise sensing and compensate accordingly, so that the voice alarm broadcast levels are adjusted as the background noise varies.

For routine maintenance and testing purposes, a voice alarm system can be treated in much the same way as a standard fire alarm system and the recommendations for fire alarm systems can be used, with two additional checks:

• Weekly, all microphones should be checked for correct operation
• Quarterly (not more than 13 weeks) all loudspeaker zones should be checked for correct operation, including a subjective assessment of message intelligibility.

In part 216 of this series, LWF will begin to look at fire extinguishing appliances. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

 

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.