Too Much Fog?
I was astonished to read that The Alley Theatre's production of Treasure Island (Live Design, July 2007) used 20-liters of haze fluids and 600lbs. of carbon dioxide a week. While it's only to glamorize moving light beams here, our current production of Gypsy uses about 0.3 liters of fluid and 6lbs. of carbon dioxide a week (MDG Atmosphere). What does Equity have to say about Treasure Island? Were there any health complaints from the cast and crew? Aside from the particulate issue, what about the gas itself? I understand that the air in the theatre is changed during a show (how many directors have I heard asking to have the AC turned off for one reason or another?), but here's a cocktail-napkin calculation: 75 one-show pounds of CO2 make about 652cu-ft. of pure gas, or 130,400cu-ft. of 5,000 PPM (or 0.5% concentration) CO2, the TLV-TWA used by OSHA. But a 50'×100'×20' theatre has a volume of 100,000cu-ft. Whatever the actual size of The Alley, what about the concentrations on stage? Safetygram-18 of the AirProducts Corporation says, “At concentrations in excess of 1.5%, carbon dioxide may produce hyperventilation, headaches, visual disturbances, tremor, loss of consciousness, and death.” This is not a matter for cocktail-napkin calculations.
— Timothy H. Buchman, mainstage light booth
City Center Theatre
New York NY
Response From The Alley Theatre
We test atmospheric effects following Equity's Air Sampling Protocol guidelines using our PDR 1000 aerosol monitor. These tests include calibrating our monitor to machine specific guidelines, logging tests that follow actors blocking, and submitting those results to equity. For the majority of Treasure Island's fog, we used Le Maitre™ PFI-9D low-fog generators, which uses a calibration factor of .75 mg/m3. With the PDR 1000 calibrated correctly, we traced blocking in time across the stage and above the stage for flying actors. Our resulting highest concentration level was 14.762 mg/m3. Equity's maximum level for glycol fluid is 40 mg/m3. We use the Air Sampling Protocol and our PDR 1000 in order to ensure that the specific areas our actors inhabit comply with the guidelines. The monitor and air sampling protocol give much more control over defining what is acceptable than the time based guidelines.
Concerning the amount of CO2 used in our production, I would like to be a little more specific. Our theatre is roughly 734,160cu-ft. Our air handler moves 30,000cu-ft. per minute (CFM) of fresh air into our theatre. Therefore, our air is completely recycled every 25 min. The amount of CO2 in natural air is .033%, which means we have 242cu-ft. of naturally occurring CO2 in our space. The LSG unit releases 34.8 CFM of CO2. Since we used two LSG machines, we were adding 69.6cu-ft. of CO2 into our theatre every minute. This raised our total level of CO2 in the theatre to 312cu-ft. every minute the machines were on. This took our percentage of CO2 from .033% naturally up to .042% for every minute that the machines were on. This is well below the .5% recommended TLV-TWA by OSHA. In the worst-case scenario, if we assume that no new air was coming into the theatre and we used 100lb of CO2, after 11 minutes we would have a concentration of 0.15% (or 30% of OSHA's maximum recommended level), and the tanks would be empty. Since our air handlers exchange 4% of the total air in the theatre every minute, we will always be below 96% of this maximum possible concentration of .15%, giving us a maximum of 0.14% total CO2 concentration in the theatre's air. I hope this clarifies the cocktail napkin calculation.
— Clint Allen, lighting supervisor