[SML] Smoke vs Heat vs Rate of Rise detectors

[Dougherty, Jim]

George Davidson has it right - the camera system we used was best suited for a space like an engine room where there wouldn't be daylight changing the lighting conditions, audience members coming and going or scenery moving.  The computer in the system would analyze the video images over time to establish "normal" then react to flames or smoke in the image that distorted it from normal.  Our situation changed so constantly that it was always kind of panicking.  We weren't the correct application for what could have been a great system and I'm still grateful that they tried it in the first place, as the reason was to try to get a system that would work with our fog and haze.

Regarding water displacing oxygen, there are two great reasons water is a good extinguishing agent.  One, the phase change from water to steam absorbs a lot of energy, robbing it from the fire.  Two, the expansion rate as it changes to gas from liquid is 1700:1 and that steam displaces oxygen.  Two legs of the fire tetrahedron addressed.  As was also pointed out though, if you're in a room full of steam the displaced oxygen is the least of your worries.  You're going to cook.  Firefighters try to avoid filling a space with steam that they or any potential victims might be in, even with the right gear.  The mist will absorb heat more readily than a typical sprinkler system - smaller droplets equals more surface area.

- Jim Dougherty
Middlebury College Theatre Dept
(and former firefighter)