Fog/Smoke Coming Out of Grates

np18358

Active Member
I am currently trying to create an effect for Thoroughly Modern Millie. The Set Designer has two grates built into the set that he want smoke (really fog) to come out of. We don't have the budget to do anything with dry ice (nor do I really think the low-lying/rolling is what we are looking for) and other fog (we have used G300's in the past) has set off the smoke detectors. I am using haze (Unique 2.1 unfortunately) throughout the show, however I only have 1 hazer, and there are two grates, so I don't think I can pipe it to come out of the grates. I am also using footlights in the grates, and I thought that maybe if I install fans in the grates, the movement of the haze, plus the light coming through the grate will give an effect that appears as if the particle is coming out of the grate. Am I missing a better choice? Should I try computer fans?? Box Fans?? Box Fans may be too large.
Thanks.
 
If possible, run the fog into a large box [about 30" X 30"xx30"] then duct it to your grate put a ] pc fan or duct fan with speed control. This will act as a buffer to keep an even flow.
 
If possible, run the fog into a large box [about 30" X 30"xx30"] then duct it to your grate put a ] pc fan or duct fan with speed control. This will act as a buffer to keep an even flow.

That sounds like a grate idea ;).

I agree - doesn't sound like you want dry ice for this. It will "bubble" through the grates (at best) and won't really rise at all. A haze machine will also present its set of unique challenges in that haze is pretty thin and intended to be mostly translucent. I would recommend a using a fog machine with quick-dissipating fog fluid. If you need a lot of force (like a tall "jet" of fog), look in to Co2 jets. Of course then, you have to deal with the associated Co2 cylinders which will only get you about 45 seconds per 50-lb tank.
 
A haze machine will also present its set of unique challenges in that haze is pretty thin and intended to be mostly translucent.

What Les says. If you are looking for "steam out of a grate on a cold day" kinda thing, you'll be disappointed with a hazer I think. A straight up fogger will give you the thicker fog that you probably want for this effect, especially if it has some travelling to do. If you put the fogger at the midopint between the two grates, what's the distance from fogger-to-grate?
 
If possible, run the fog into a large box [about 30" X 30"xx30"] then duct it to your grate put a ] pc fan or duct fan with speed control. This will act as a buffer to keep an even flow.

If I may - What your set looks like is grates on the ground with the fog rising up?

If you saturate this box in haze / fog, there will be condensation: make sure you have exit holes at the bottom for the leftover fluid. Also, the fan has got to be left outside that box and can't be directly exposed to the fog. You and it to run very slowly not to disperse the rising fog effect, and using a very light fog fluid, like Low Lying Fog Fluid, without the refrigeration, is an excellent idea to get fumes up, quickly dissipating.
 

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