The LWF Blog

Fire Safety for Healthcare Premises – System Technology for fire alarms – Part 142

August 24, 2020 1:22 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 141, LWF considered the system technology available for healthcare buildings and started with conventional systems. In part 142, we look at addressable systems.

An addressable system contains circuits of fire and smoke detectors, where some form of communication exists between the control and indicating equipment (CIE) and each detector. Each circuit acts as a simple data-communications circuit rather than simply a circuit providing electrical current, as is the case with conventional systems.

Communication consists of “polling” where the CIE pings each detector or manual call point on the system and the devices respond to the CIE with their current state. The time taken for the CIE to poll all units within the system must be sufficiently short to ensure an acceptable delay between the operation of a call point and the sounding of the fire alarm, for example. Definitions of what is an acceptable amount of time can be found in BS 5839-1.

The principal and most useful difference between a conventional and an addressable fire alarm system is that when a detector or call point in an addressable system operates, the identity and therefore, the location of the fire alarm signal is known at the CIE. A conventional system cannot distinguish between the operation of one device from another on the same circuit.

The software of the CIE of an addressable system can convert the signal from the uniquely identified detector into a pre-programmed location and this can then be displayed in plain English to aid with clarity and speed of response.

While having the pre-programed location is most useful, in order to comply with British Standards, the signal must also contain the code for zone indication. In a conventional system, each zone is defined by an individual circuit. In an addressable system, devices in many zones may be connected on a single circuit, but configured into different zones for each detector or call points within the system software. This allows greater flexibility in zoning and allows extra zones to be created at minimal cost.

In Part 143, LWF will continue to discuss addressable system by considering wiring, short circuits and how some systems can transmit instructions to 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 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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