Sorry to be the bearer of bad news, but this issue is coming up more and more in the newly constructed high school theatres that I’m working in, and administrators aren’t that keen on shutting down the smoke detectors (or putting them in test mode) for plays. In the last 3 theatres I managed we simply had a No Fog Machine policy.
All is not lost though – we did allow ground fog (mostly dry ice). You can find a suggestion for policy wording in my High School Theatre Safety Manual, but in short, here it is (feel free to appropriate):
Fog Machine Policy
Most smoke detectors are designed to measure particles in the air and risk being set off if the smoke level from a fog machine gets too high on stage. Therefore smoke machines and hazers are not permitted in the theatre.
Dry ice and ground fog may be safe as they tend to gravitate downwards, but if you chose to use dry ice and/or ground fog, you do so at your show’s own peril. If they set off the fire alarm, the theatre must be completely evacuated (performers, crew, staff and audience), and permission must be given by the Fire Department before anyone can re-enter the building. In that case, your show will most likely be shut down for the remainder of that performance.
_____________________________________________ ____________________Signature of User Representative Date
You may want to have a conversation with the administration / construction department about the installation of the smoke detectors. The NFPA has shifted to requiring Rate-Of-Rise Heat Detectors over stages for the very reason you have described (smoke detectors false tripping). Specifically, if you have a Fire Curtain it is to be tripped (released) by the detection of a thermal gradient from a Rate-of Rise Heat Detector (not from a smoke detector). The alarm system installer should have known this, but like many other things, they just aren't aware of the special circumstances of a theatre.
If they are just dead-set on detecting smoke, then a good option is to have the smoke detectors replaced with a "multi-criteria" type detector similar to the ones manufactured by System Sensor company (https://www.systemsensor.com/en-us/Pages/Spot-Multi-Criteria-Multi-Sensor-Detectors.aspx). They have a combination of Smoke Detection, Rate-of-Rise Heat Detection, and (optionally) CO2 Detection. The detector won't signal an alarm condition until it registers a condition on both parts of the detector device, thus preventing false trips (http://www.systemsensor.com/en-us/Documents/EgyptianTheatre_CaseStudy_SSCS005.pdf).If your system has smoke detectors in air ducts that draw air from the stage, the in-duct sensors sometimes false trip on atmospheric effects. One way to thwart this problem is to shut-down the air handler temporarily during the part of the show where the atmospherics are used, and then restart the air handlers after the effects have had a chance to dissipate. This approach also keeps the atmospheric effect on the stage rather than having it sucked / blown away.