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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Technical Advice => Topic started by: David Rooney on March 03, 2015, 05:56:49 PM
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Evening all ....
It has been decided an "automatic" drenching system is to be installed to cool an "iron curtain" in a theatre.
The theory being that the water will keep the curtain cool and prevent it from buckling in a serious fire condition.
There is a manual release obviously but out of hours there is a concern.
Smoke detection can't be used for obvious reasons so the proposal is to use heat detectors mounted either side of the curtain and connected to a coincidence detection panel so any two detectors are required to activate to allow the drenching valve to open.
The problem is the height of the detectors is going to be around 12 - 15 metres.
We are thinking this would be an acceptable variation on the assumption a fire would have to be very close and very large to threaten the integrity of the curtain and therefore in all likelihood they will react long before the curtain integrity is threatened.
There is ASD installed already that will signal the FB via RedCare long before the heat detectors react (in theory!)
Any thoughts please ???
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I am puzzled. The purpose of the safety curtain is to protect the audience from a fire on the stage for sufficient time to ensure their safe escape.It is unlikely to offer signifiant integrity to make a significant contribution for property protection. Why would it need to operate autmatically when the theatre is not in use? Manual control should suffice in my view.
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I believe the object of the curtain is to compartmentalise the building and help contain a fire whether it begins rear or front of house.
Having done a bit more research it appears (generally) the deluge system is not necessarily to cool the curtain so much but to flood the stage to extinguish a fire - which could be a problem with all the electrics !!!
I don't know who has asked for this, I'm assuming at this stage it's Insurance related.
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Usually sprinkler and deluge systems are controlled by a fusible link either glass bulb or solder strut and would not be controlled by a fire alarm and detection system. This would appear to be the best way forward.
However I would be very surprised if the fire curtain can provide any significant degree of fire compartmentation for property protection purposes, the fabric used is typically certified to a one hour fire resisting standard but integrity is always going to be weakest at the edges and the supports. A properly designed sprinkler system could represent a major reduction in fire risk.
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Imagine the scene, fire eater doing his big finale.
Triggers the heat alarm............
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From what I've seen of theatres the deluge system is simply a manual handle, there is no fusible link.
Imagine the scene, fire eater doing his big finale.
Triggers the heat alarm............
:) there is an interlock - when the curtain is up it's not allowed to rain ... !
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These old fire curtains are usually associated with a haystack lantern light above the stage that vents the space in case of fire.
[For general info: The vent opens in the event of fire, on a fusible link or manually for example, and raises the neutral pressure plane above the stage to a position somewhere above the gaps, that kurnal referred to above, between the curtain and the proscenium arch. The neutral pressure plane rises because there is very little inlet air at low level but the buoyancy of the smoke drives a lot of gases out of the vent at the top. This means that there is a drop in pressure in the space immediately behind the fire curtain and so the gaps will allow air to pass from the auditorium to the stage but will not allow smoke to escape from the stage to the auditorium.]
If there is no haystack lantern light above the stage in this case or if there is one but it has been decommissioned then the neutral pressure plane will stay low and smoke will escape round the curtain to the auditorium. So the curtain won't do a very good job.
If there is a haystack lantern light then the opening of the vent(s) might adversely affect the operation of the heat detectors, though, as you say, they're bound to go off by the time the fire reaches a size where it might start to buckle the fire curtain.
I would initially be inclined to recommend keeping it manual only but I do understand that if this is an old theatre then there might be some heritage value in the auditorium that deserves protection when the theatre is empty.
I would check to see if the ventilation is there. If not then integrity could be provided either by ensuring that the fire curtain shuts tightly onto fire resisting stops all around the arch with cold smoke and intumescent seals (which would be very unusual) or by providing an additional, modern fire curtain in front of the old one. I imagine the old one will have some historical value and will not be able to be removed.
As for the drencher, fusible links/glass bulbs would offer the most resilient and simple solution if the owners (or their insurers) are determined to make the system automatic, but in this day and age why keep things simple when you can over-complicate them? Also, I do not think that the drenchers are normally there to put the fire out. If that was their purpose why would they be directed at the curtain? Maybe in this case they're not...
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Thanks for the info .... I'm on site tomorrow and will check out the ventilation situation ......