Wow. It seems installers down here think a lot more about how spaces are going to be used. The normal thing in a
venue is to get the
venue techs to go and isolate the relevant zone of the alarm. So you might isolate the sensors inside the
auditorium but leave all others turned on. This may however cause you grief if you have leakage to a backstage corridor
etc that is non isolated. The bigger venues have documented procedures in place that
cover the process they go through when a sensor is triggered. This usually involves some form of verification. Sure I would expect fire and
smoke doors to have their electromagnetic holds released the moment something went off, but in a big enough
venue, people will be assigned to check the source of an alarm and then the
venue's emergency management (normally security and other such parties) will make a decision on the best way to proceed. If it's found to be a false alarm, they won't evacuate. If it can be managed, they will manage and if they need to evacuate then they will.
It is important to remember that in some cases the panic
etc caused by an evacuation can cause problems. In large venues, having a
system in place whereby staff are alerted first and then open the outer exit doors and position themselves before a calm announcement is made can be the difference between an evacuation that is successful and one that is a complete shambles, potentially involving injuries from
tripping or whatever.
The whole idea behind a
fire curtain and in most cases associated
smoke vents in the roof is to literally turn the
stage and
fly tower into a chimney. The
stage will
flare up, get out of there FAST but it will provide negative pressure to the
auditorium which should then allow enough time to evacuate the
auditorium safely. In some cases, dependent on the original design, the
fire curtain may not come all the way to the floor. In some cases it is designed to come all the way down and to seal the
stage in which case it is not creating a chimney, it's acting as a fire retarding wall.
In any case it is important to have documented procedures in place to
cover what happens in the event of a fire and what options are available for isolating the fire alarms in part or full. These documents should be signed off on by the relevant people in your organisation for OH&S, insurance
etc as well as the relevant people to your organisation for fire compliance, which varies from country to country, state to state and more locally. Very few venues have the luxury of being their own Authority having Jurisdiction, though I do know of one in my part of the world.
I recall vaguely having written on this or a very closely related topic before. It should be in the archives somewhere.
Oh and you should want more sensitive detectors, but with a control
system coupled with relevant procedures to allow for them to be temporarily isolated. People discussed
laser systems. It is important to note there are 2 types. One relies on an
infrared beam across the space, be sure to have these isolated before getting a ladder out. The other is a good
bit more sensitive and expensive. It's known as a VESDA, an acronym for Very Early
Smoke Detection Apparatus. I think it may also be known as an aspirating
smoke detector in some circles. It works by continually drawing air in from the space through a pipework
system and using a
laser to
monitor that air for so much as
trace amounts of
smoke. These can be sensitive enough to
pick up a smouldering fire that has not yet progressed to the
stage of producing easily visible
smoke. But you pay for this extra warning time...
As always, consult someone experienced / qualified / licenced / insured as appropriate when working these things out. It then becomes their behind on the
line not yours should anything go wrong...
