Fire alarm and detection systems


Mr Lawrance noted that it was often a ‘challenge trying to find what a building is used for’, with quite a lot having ground floor shop units, offices above and then sleeping accommodation above that, accompanied by common areas throughout. This requires ‘mixed systems’ to be used in terms of grade and category, which ‘quite often have to be interconnected’, and the ‘real challenge lies in defining premises’. The standard was updated in 2019 and withdrew the B and E grades while subdividing the D and F grades. Grades include A, B, C, D1, D2, E, F1 and F2, and the standard says what each system needs via a description – grades PD1 and PD2 are separate and cover property protection, with guidance available on installation. Showing a revised table


of categories and grades, Mr Lawrance said that the standard shows testing and servicing by grade, as well as recommendations and whether delays should be set up or not. Other amendments reflected supported and sheltered housing, ‘revised and expanded’ recommendations for grade C, and a recommendation that communal systems ‘should not normally be installed’ in purpose built blocks of flats. He presented the first table from


the standard covering categories and grades, and gave examples of how the table functioned and how those using the standard can discover the class of a premises, and then the minimum grade and category of each system for installation. This is divided into new or materially altered premises or existing premises, with each category and grade having key supplementary information that proves ‘quite important when designing a fire detection system’. One such example was for a D1


grade system, in which detectors may be incorporated within a system installed in communal areas, so this can be attached to an addressable system. Category LD1 detectors meanwhile, as another


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example, can be omitted from roof voids unless there are specific, significant fire hazards such as gas boilers present. Finally, another example was that in common areas of HMOs, heat detectors should be installed in every communal kitchen, while heat and smoke detectors should ‘as appropriate’ be installed in every communal lounge.


Panels and cabling Returning to grade A systems, a fire alarm control panel is required to have met BS EN 54-2: 1997+A1: 2006: Fire detection and fire alarm systems. Control and indicating equipment, as the system is addressable. For grade C, a panel meeting BS EN 54- 4: 1998: Fire detection and fire alarm systems. Power supply equipment is required with a power supply, or can be run off an intruder control panel. A and C systems require battery


standby capacity of 72 hours, though this can be reduced to 24 if a warden is on site, or there is a link to an alarm receiving centre (ARC). Cabling is also covered, with grade A material to comply with BS 5839-1: 2002 + A2: 2008 Fire detection and fire alarm systems for buildings. Code of practice for system design, installation, commissioning and maintenance requirements for fire rated cable; while grade C cable should meet BS 7671: 2018 + A1: 2020 Requirements for Electrical Installations. IET Wiring Regulations. This means that such a cable should be suitable for the current and voltage of the circuits on site


and ‘distinguishable from other services’, and monitored for open and short circuit connections. Should such a wire not be ‘sufficiently robust’ to withstand ‘likely damage’, additional protection must be provided, such as placing the wire in ceilings or floor voids, or mechanically protecting it. Grade D cables can be


connected into lighting circuitry or directly to a distribution board, with such cables for mains supply to smoke and heat alarms – and ‘any interconnected wiring between’ those – ‘suitable for domestic mains wiring’. Conductors used for interconnections should be ‘readily distinguishable’ from those supplying power as well. Grade F detectors need to be interlinked and battery operated, with the most suitable cables adhering again to BS 7671.


Audibility levels and siting With noise levels required to wake adult occupants from sleep, audibility levels are key and smoke alarms provide 85 decibels at three metres, while bedroom door open position should be achieved. Fitting units in hallways is ‘generally adequate’, and audibility should also be based on frequency, with a frequency of 570Hz more ‘likely’ to wake a young or intoxicated person than a higher level – generally, you should ‘certainly look’ to have one of between 500 and 1,000Hz. This may need to be increased in sheltered housing, and grade A


www.frmjournal.com JUNE 2020 23


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