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6.11.3.2 Alarm Devices

It is important to note that guidance for Automist on alarms is through BS 8458:2015 (the domestic an residential water mist standard), not BS 5839-6: 2019 (the early warning, means of escape, detection and alarm devices). When detectors or alarms are linked directly to the Automist system as the scanning initiation device, they are not operating as an early warning device, only as part of the suppression system. Still, the devices used for Automist are certified to their relevant standards: BS EN 54-1 for detectors and BS EN 14604:2005 for alarms. They work as an analogous to the frangible bulb. It is only when the initiation of the Automist scanning is done by an existing early warning detection and alarm system is that the requirements of BS 5839-6:2019 apply to the alarm system in place, which would apply regardless whether Automist was present or not.

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 5839-6:2019 as appropriate. NOTE BS 5839-1:2013, Table A.1 and BS 5839-6:2019, 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. Typically, Automist will also have its own detectors to initiate the scanning procedure as below but these systems are not necessarily linked.

Standard fire alarm system alongside Automist.

 Automist connected to alarm system as confirmation of early warning

 

In accordance to BS 8458:2015 6.11.3.2, the water mist system may be connected to the alarm system as a confirmation signal of fire from the suppression system. This is optional, desirable, and especially useful when alarm panels are used as it can separately identified as a confirmation signal beyond and above what the detection system might already be providing. The confirmation signal leverages Automist’s second knock from the thermal sensing in the spray head to confirm suppression is in progress. An example of this installation is seen below:

 Automist connected to alarm system as confirmation of early warning

 

In certain instances, Automist can also be configured to operate from the alarm system already specified. This is common in applications where an aspirating system is being used and the presence of detectors (early warning or Automist) is not desired. A volt-fire relay output from the fire panel (or interlinked alarm system) is used to initiate the scanning of Automist. The selected detection and alarm system must meet the requirements of either BS EN 54-1 (detectors) or BS EN 14604 (alarms) and their installation, that of BS 5839-6:2013. What type of alarm system is required for the premises is not part of the Automist installer specification scope, this will have been previously determined. Automist just allows the possibility for these to be integrated or not, depending on their specification. The example below shows how this integration takes place:

Automist triggered by existing early warning alarm

 

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