5. System Actuation BS 8458

Here are the critical differences between Automist and a traditional watermist system:

	Traditional watermist system	Automist
Activation	Glass bulb or fusible link (mechanical thermal)	Electronic trigger based on smoke detection and thermal sensing
System design	Wet pipe (i.e. one that is permanently charged with water)	Non-pressurised (open) dry pipe
Nozzle location	Ceiling (or close to the ceiling) mounted	Wall mounted at 1.3m height
Discharge performance	The system should be capable of providing pressures and flow rates to permit all the watermist nozzles in the fire test room or largest compartment, whichever is the greater, up to a maximum area of operation (AMAO) of 64 m2, to operate simultaneously at not less than the greater of: a) the nozzle pressure given by the pass criteria determined by the test in Annex C if BS 8458; or b) the approval listed discharge performance.	The electronic activation ensures only one watermist nozzle activates with not less than the pressure and flow given by the pass criteria determined by the test in Annex C of BS 8458.
Minimum run time	10 minutes	30 minutes (connected to mains water)
Ceiling height	3.5m or 5.5m height depending on fire test results according to Annex C of BS 8458	3.5m height depending on fire test results according to Annex C of BS 8458. Higher ceiling heights, if supported by fire engineering justification

We have chosen to deviate from the Standard because it means we can activate much earlier for certain types of fires, before the build-up of significant heat. These options can reduce the chance of burns for someone very close to a fire and minimise the production of life-threatening toxic gases, which are still the biggest threat in domestic fires.