Technical Focus: Visual Alarm Devices (VADS)

This month in our Technical Focus, Steve Snoddon, Joint MD of Diamond discusses Visual Alarm Devices (VADs) and their appropriate use within  Fire Detection and Alarm Systems.

Q: Can you tell us what VADs are and why they are necessary?

A: A fire detection and alarm system that is well installed, used and maintained can provide a fast response to a fire outbreak, therefore greatly reducing the risk to life and limiting damage to property. Whilst the primary means of alerting people to fire remains the use of audible warnings, there may be circumstances when the usual audible fire warnings, sounders and voice alarms are not sufficient.  In these circumstances those responsible for the design and installation of the fire detection and alarm systems will have to consider alternative approaches to giving warning of fire. One such approach is the use of visual alarm devices (VADs), which as the name suggests, offer a visual warning of fire.

Q: So under what circumstances should the use of VADs be considered a necessity?

A: Broadly speaking there are two main instances where VADs will be appropriate-

(1) Based on the environment:

Where the person may not be able to hear the audible warning due to the environment – an example of this would be on a factory floor where there is high ambient noise and where hearing protection is required; or in buildings in which the initial warning of fire may be restricted to staff – an example would be certain public assembly buildings.

Also environments where audible alarms would not be appropriate due to the nature of the activities ongoing at those establishments – eg broadcasting studios, in which audible alarms would cause interruption to live broadcasts, or in hospital operating theatres where an audible alarm may be disruptive, or interrupt operating procedures.

(2) Where there may be people with a hearing impairment:

Under The Equality Act 2010, VADs are needed as a means of giving warning to deaf or hard of hearing people – examples might include hotel bedrooms, student accommodation, public washrooms etc.

Q: Who determines if VADs are needed?

A: The need for VADs in any specific building will always be determined at the design stage.  All VADs should be selected, installed and maintained to the relevant standards, these being BS 5839-1 and BS EN 54 part 23.

Q: What are the design considerations for VADs?

A: BS 5839-1 gives a number of recommendations to assist in the effective design and installation of VADs –

• Visual alarm signals should be provided in areas where ambient noise levels exceed 90 dB and in other areas where hearing protection is likely to be used under normal circumstances (e.g. factory floor)
• VADs should be sufficient in number and distribution to be readily visible from all normally accessible locations throughout the area in which they are provided, under normal ambient light levels. Siting of sensors is critical, consideration needs to be given to the height at which the sensor is to be installed, any fixed obstructions need to be factored into the design in terms of the reflectivity of adjacent surfaces
• The signal should be distinguishable from any other visual signals used in the premises, it should flash at a rate within the range of 30-130 flashes per minute and should be at an intensity sufficient to attract attention but not so high to cause difficulty with vision due to glare
• Where restrictions on the ability to hear are in place e.g. ear defenders or hard of hearing people, siting should ensure that there is not undue dependence on direct line of sight. For example, people spending their time looking at computer screens or focusing closely on a specific activity.

Design Considerations, including the use of visual alarm devices forms part of the Diamond Systems CIBSE approved CPD training on Fire Detection Design Considerations.  If you would be interested in booking this event, please contact us to discuss further. Email design@diamondsystems.co.uk.