Why do we need Voice Alarm?
There is some well documented research* into the human behaviour in the event of fire. Most striking is the variation in the response to alarm signals:
13% people react in a timely manner to bells
45% of people react to text information
75% of people react In a timely manner to voice messages
Further research shows that peoples behaviour varies dependant on the environment, and in an emergency may exit the building using the same door they used to enter. The use of a clear voice message greatly increases response time and provides the opportunity to advise occupants of the safest emergency route.
Management of Evacuation
Before deciding on a VA System design the evacuation requirements of the building must be established:-
ls the building to be evacuated all at once (one out all out)?
Does the building require a phased evacuation plan?
In the example shown below only part of the building is evacuated immediately.
Whilst other areas will have an alert or standby message.
Voice Alarm System Types
Once the evacuation strategy of the building is understood, the designer should assess the type of voice alarm system that should be used.
The level of manual control and the need for live messages versus automated messages will drive the decision on the type of system Installed. BS 5839 Part 8 defines 5 types of systems as summarised below:
Type V1: Automatic evacuation
This system offers automatic operation of the voice alarm system against a pre-defined evacuation plan. The system may also have facilities for the manual operation of non-fire emergency messages. provided that these are automatically overridden by emergency messages.
Type V2: Live emergency messages
In addition to the automatic facilities provided by the Type V1 system, the Type V2 system provides the facility for automatic message initiation as well as the facility to broadcast live emergency messages by means of an all-call emergency microphone situated at a strategic control point This allows supplementary live announcements to aid safe evacuation.
Type V3: Zonal live emergency messages
In addition to the functions of the Type V2, the facility to broadcast live emergency messages in pre-determined emergency zones. or groups of zones. This allows evacuation control in specific areas of the building where a pre-determined evacuation plan might not cover all eventualities.
Type V4: Manual controls
Type V4 system has the facility to select and direct stored emergency messages to individual zones as well as the ability to disable or enable emergency broadcast messages and display their status. This allows a well trained and disciplined staff to follow a pre-planned evacuation strategy when the automatic mode needs to be overridden.
Type VS: Engineered systems
Where the application falls outside the scope of type V1-V4, a type VS system allows the design of a tailored solution based on the assessment of special or mutable risks.
Voice Alarm and Public Address?
Is the system to be used only for Voice Alarm or a combination of Voice Alarm and Public Address? and maybe even music?
If so, the zoning requirements for Voice Alarm Evacuation may be different from Public Address.
In the example shown below there is a requirement for 3 separate paging zones and
2 areas for music, as well as 3 alarm zones. However there are only 2 evacuations zones.
Microphones & Other Inputs
How many microphones are needed and what are they used for?
Microphones may be used to broadcast live messages both in an emergency and in normal public address.
For emergency use, microphones must be operated and be monitored in accordance with BS 5839 Part 8 and be certified to the requirements of EN54-16.
Identify opportunities to broadcast miscellaneous announcements such as:-
Landlord input in shopping centres
Pre-recorded messages on a PC
Audio visual presentations
Background Music & Entertainment
Does the system need music, if so how many sources and how is it to be routed?
Different areas of a building may need to be linked to entertainment systems.
You need to identify the type and location of the music source.
What messages do I need to meet the needs of the building?
Recommended messages are defined in the standards, and meet the needs of most buildings. In some cases messages may be tailored to suit special applications and may even involve coded alerts to warn staff ahead of the public.
The system architecture may be selected depending on the type and size of the building where they are being installed. Three main variations of providing voice messages are available:
Stand Alone Voice sounders
Distributed Amplifier systems
Central Rack Amplifier systems
Although these devices can not be considered a true VA they do offer voice messages, with each device containing a ‘memory’ chip that has a number of pre-recorded standard messages, that are operated direct from the fire alarm control panel.
It is important that the control panel has a ‘synchronisation’ capability so all the independent recorded messages are delivered at the same time.
Central Rack Systems
Central Rack systems consist of a rack of amplifiers that control all the loudspeaker circuits that are radially wired. This rack can also contain facilities for zone selection, music input, emergency and general paging announcements.
Considerations when using rack systems:
The link between the fire control panel and the rack must be fully protected and monitored.
The correct cables sizes must be provided for the loudspeaker circuits particularly If they extend across many floors.
The battery standby capacity must be properly calculated with some capacity to extend in the future.
Distributed Rack Systems
Distributed Rack Systems allow the loudspeakers to be connected to local amplifiers.
* Guyiene Proulx, PhD ‘Misconceptions about human behaviour in fire emergencies’ published in Canadian Consulting Engineer, March 1997, pp 96, 38. David Cantor, ‘Studies of Human Behaviour In Fire: Empirical results and their implications for education and design’ published by BRE, July 1985.