The LWF Blog
Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 168
January 29, 2024 11:51 amLWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 167, LWF talked about the requirements when NFPA 72 is the relevant standard and will look at how fire alarms connect with other fire safety measures. In part 168, we discuss the cabling used in fire alarm system installations.
The cabling for a fire alarm system installation can be divided into two categories – that which must continue to work while there is a fire, and the cabling which can be allowed to fail having already served its purpose.
Power supply cables and cables to fire alarm sounders and remote communication devices must continue to operate during a fire.
Cables to fire detectors and failsafe cables to auxiliary devices such as door release devices do not need to continue operating after activation of the fire alarm, as their purpose has been fulfilled.
Suitable cabling for a fire alarm system can be mineral-insulated copper-sheathed cable (MICC), which complies with BS EN 60702-2 and “soft skin” cables complying with BS 7629-1.
The performance of the latter type of cabling should be verified with the cable manufacturer prior to use for a fire alarm system.
It is possible to use other types of cable, the standards for which can be found in BS 5839-1 Section 26.
Cables are normally designated ‘standard’ fire resistance for general use or ‘enhanced’ fire resistance for use when they are required to continue to perform for extended periods during a fire, (i.e. for longer than the initial evacuation period).
Standard cables generally meet a PH30 classification to BS EN IEC 62232:2022 and additionally have a 30 minute survival time.
Enhanced cabling may be necessary for certain installations, e.g. in buildings with multi-phased evacuation, buildings without sprinkler systems, those without sprinklers and greater than 30 metres in height, or where a fire in one area does not instigate evacuation of other areas (for example, healthcare facilities).
Enhanced cables need to continue to perform for 120 minutes and thus should meet the PH120 classification and additionally, should meet a 120 minute survival time to BS 8434-2. This second test is especially onerous because the test temperature reaches 950 °C and the water spray duration increases to 60 minutes.
Appropriate fixings must be used, as the cables must stay in place and operational for the given duration. The use of plastic cable ties, for example, would not be appropriate.
In part 169 of LWF’s series on fire engineering we will discuss Radio-based systems. 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 since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 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.