6.11.3.2 Alarm Devices

Taken from BS 8458 6.11.3.2 for Alarm devices:

...Whilst in some residential and domestic buildings, the actuation of the fire alarm triggers immediate and total evacuation of the premises, other residential buildings are designed so that the initial alarm is sounded only in the dwelling where the fire starts, as only this dwelling needs to evacuate immediately. It is important that the configuration of the watermist alarm is matched to the building’s fire evacuation strategy.

If a building or dwelling has comprehensive automatic fire detection and alarm provision that provides adequate fire alarm and warning arrangements to initiate evacuation, additional watermist alarms to initiate evacuation might be unnecessary. 

A watermist system may be interfaced with the fire detection and fire alarm system (e.g. by means of a flow switch), so that a fire alarm signal is given by the building’s fire alarm system when a watermist nozzle operates.

Alarm system designers need to take account of the fact that the watermist alarm might have more than one function, e.g. to initiate evacuation, to alert management and/or alert the fire and rescue service...

It goes on to say:

...The alarm device should meet one of the following recommendations.

  1. The alarm device should be connected to an internal audible alarm.

  2. Provided that the property is fitted with an automatic fire detection and alarm system meeting at least the minimum grade and category recommended in BS 5839, the watermist alarm device can be interlinked to this system. The automatic fire detection and alarm system should be in accordance with the recommendations of BS 5839-1:2013 or BS 5839-6:2013 as appropriate.
    NOTE BS 5839-1:2013, Table A.1 and BS 5839-6:2013, Table 1 provide guidance on the category of system for the relevant property types.

  3. The alarm device should initiate a watermist alarm signal that should be configured and acted upon in accordance with the fire strategy for the building.

Therefore, as a default the alarm referred to in the standard is an additional alarm to the detection used to trigger Automist.

There are examples where the fire strategy dictates a Grade D LD1 standard fire alarm system as described in BS 5839 Part 6 is required to sit alongside Automist. Such a configuration will have smoke detectors sited in hallways and landings at all floor levels and they must also be sited in all habitable rooms and areas where a fire might start that communicate with the stair enclosure. In certain instances, Automist can also be upgraded to perform this function with compatible alarms with a volt-fire relay to initiate the scanning of Automist. The selected alarms must meet the requirements of BS 5839-6:2013. There are six grades of system ranging from Grade A to F, whereby a higher grade generally represents a greater risk of fire in the premises, so a higher level of fire safety system is needed to be installed. However, the nature of the premises and the characteristics of the occupant are also important factors.

The majority of standard housing in the UK falls within the D-F category - whereby mains or battery-powered alarms are installed. This progresses in complexity until grade A is reached, where a full fire detection system with control and indicating equipment is installed. Please refer to BS 5839-6:2019 for further details.


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