Posted By Zaphod I've seen several Hollywood films where someone puts a lighter up to one sprinkler and they all go off - sending the occupants of the building into disarray. Can anyone tell me, do sprinklers behave like this? I thought that each individual sprinkler head needs to be activated by heat. However, a colleague recons that with one sprinkler going there is a drop in pressure which activates a burst of high pressure to start off all the other sprinklers. Can anyone tell me which is correct.

Posted By Dan Malone Hi Zaphod, You are correct in the assumption that only the head under the fire will activate. However that are other systems out there that will activate an area(these are the one in the movies). Heads that activate one at a time have a liquid filled bowl. As the heat from the fire rises causing the liquid to expand. This releases a plug allowing the water to escape. Other sprinkler heads will activate if the head continues to rise. The other type of sprinklers are the deluge style. Here an area or building sprinkler system activates when one of the heads goes off. Not really the one to have in case of a false activation??? Need I say more. Hope that this helps. Regards Dan Malone

Posted By Glyn Atkinson Not so good if an inept flt driver accidentally catches one of the heads, makes it activate and you have thousands of pounds worth of white goods directly underneath - including the pallet full he was moving ! 27,000 gallons of water goes a long way !! Some spectacular photos and investigation evidence for my old NVQ file, mind !

Posted By Ashley Wood So far everything that has been said is correct. Normally only deluge systems have one or more heads that operate and these are activated, not by a glass bulb, but by a detection system or by manual means. However, some manufacturers (typically the ones dealing with water mist systems) have developed a 'burst disc nozzle'. this is a device that sits behind the glass bulb of each nozzle. When one nozzle is ruptured by heat, the pressure within the flow is detected by a sensor that then starts the fire pump. When this happens the burst disc that is behind all the other glass bulbs breaks (due to pressure)allowing the water to bypass the 'plug'. This type is used to protect say for example a hotel room where you may also want the nozzle in the room lobby and the corridor to operate. Also, some manufacturers have developed control valves that have a glass bulb built into them. When heat ruptures the glass bulb the valve opens allowing water into all deluge nozzles.