The LWF Blog

Fire Safety for Healthcare Premises – System Technology for fire alarms – Part 143

September 1, 2020 1:26 pm

In LWF’s blog series for healthcare professionals, our aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 142, LWF discussed addressable systems. In part 143, we continue to look at addressable systems, considering wiring, short-circuits and how home systems can transmit instructions to other devices.

Most addressable systems contain wiring in the form of a loop or ring circuit which initiates and terminates at the control and indicating equipment (CIE). If an open-circuit fault occurs, a warning is given, and one signal path between each device and the CIE remains, instead of the original two. Radial circuits may be used and can be wired directly from the CIE.

A short-circuit event on an addressable loop serving many zones could result in a loss of protection to all the zones affected. Short-circuit isolators are installed to avoid this and they work to isolate the section of the loop involved. The use of short-circuit isolators at zone interfaces allows the loss to be limited to the protection of one zone (or the maximum permitted area for a zone).

To limit potential loss, some systems have short-circuit isolators fitted to each detector base, so there is no loss of protection in the event of a short-circuit.

Some addressable systems are able to transmit instructions to addressable devices on the loop, in addition to receiving information from detectors or call points. This means that if a fire is detected, the addressable relay may receive instructions from the CIE to operate and thus be able to close doors, shut down plant etc. These actions will be designed to limit the spread of fire and the potential for injury or further danger to building occupants.

Occasionally, a system is designed so that alarm sounders are addressable, which allows economies in wiring by installing sounders on the same addressable loops as fire detectors and call points.

A fire alarm system used in a healthcare building must be suitable for purpose and designed for the building(s) in which it will operate. It should be installed as per the manufacturer’s instructions and by a suitably qualified and third-party certified installer.

In Part 144, LWF will begin to look at the types of addressable system available – two state, analogue and multi sensor. 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 LWF on freephone 0800 410 1130.

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.

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