dry ice effects

[mr_sound]

Well I just found out I've been put in charge of trying to pull off an effect the concert promoter wants for our halloween show. Basically, he wants to fill the orchestra pit with fog and put some red lights down there. I do have a fog chiller...one of those cheaper ones that uses ice to do the trick, and it didn't work. The pit is about 3 feet deep, and maybe 28 feet wide at it's widest point. My fogger didn't have a high enough output to get the job done right, plus the fog kept warming up too fast and wouldn't stay in the pit.

I've never used dry ice before, so I don't know if using it will be the solution. Does dry ice fog linger longer than regular ice chilled fog? And how much dry ice do you think I'd need to keep this going all night? We can't afford to rent an actual dry ice machine, so the plan is to put it in a small tub of warm or hot water. And how much does dry ice usually cost and where can I get it?

I'm doubting we can pull this off...the show is saturday...but I told him I'd look into it.

[Peter]

It has been my experience that this is a very hard trick to pull off!

That being said. I have had the best experience using a homemade fog chiller (I'll try to describe it below). I have tried dry ice in the past, but it never made enough fog to do anything. If you plan on using dry Ice, i would plan on buying alot of it. Another thing you have to watch out for with dry ice is the CO2 that comes of of it. If you start using too much of it, and it has an easy way to leak out of the pit (CO2 is heavier then air, so it will tend to say low, which is why the "smoke" it makes stays low) you might have to consider how much CO2 people in the front rows of seats will be breathing.

My homemade smoke cooler consists of a piece of ductwork ligned with foam to inslulate it. I filled gallon bags with ice (lucky for me our school has an ice machine that I got permission to use) and loaded a bunch of the bags into the shaft. I then ducttaped the top two-thirds or so of the ouput end of the shaft so only the cooler air at the bottom could get out. I put the smoke machine pointing into the other end of the shaft (having left some room before the first bag of ice) and ontop of the smoke machine I placed several computer fans blowing air into the tube. This prevented the smoke from coming out the wrong end and provided a draft through the tube to push the cooled smoke out the other end. (Computer fans can be easily riged up to run off of an AC to DC converter or off of batteries, just make sure you read the lables on everything so you put the right voltage and amperage everywhere it is suppsto go and nowhere it isnt!)

This whole rig worked fairly well, but of course, fairly quickly the smoke warmed back up to room temperature and rose. I am thinking now in retrospect, I maybe could have found an old cooling unit from an old freazer or refridgerator and used that to cool down the smoke ever more. I guess another option would be to run an air conditioner somewhere and pipe that cold air in and blow it into the pit from right behind your smoke machine, that cold air should cool down your smoke and maybe keep it cold longer.

Tomorow we are starting our unit on Gases in AP Chemistry, and I have been bugging the teacher to show me a way to make a safe, lasting, and heavy (sinks) gas to use in a situation, but I guess if he could show me it and it isnt too expensive, lots of other people would be doing it already!

[Mayhem]

I cannot comment on dry ice but I am wondering if you could perhaps extend the length of your chiller to keep the smoke cooler for longer.

I am thinking along the lines of using a large cheap Styrofoam cooler box (or a couple joined end-to-end). Place some bags of ice (I would double bag them) or even frozen plastic bottles of water.

Try placing a short hose from the output of the chiller into the cooler box and you will need to make up a little fan/box to draw the smoke from one cooler into the next.

With the second cooler, you could try leaving the lid half off or placing some cling wrap over it and then adding holes. This is where trial and error is going to come into it and you may not have enough time. But once you have the cooler boxes in place cutting the vents in the last one shouldn't be that difficult.

The other thing to try is placing some pedestal fans in each corner of the pit, so they are just out of sight. Angle them to the centre of the pit and see if this will keep the smoke in the pit for longer.

Just some random thoughts off of the top of my head - which I hope may be of some help!

Good luck and what ever solution you come up with, please post it here.

[ship]

High End Systems produces a smoke called "Cold Flow" which should be a little more heavy than normal fog juice and should work in most smoke machines. Perhaps your chiller or one of the others above might work better with a smoke type that is more designed to linger low. Search the various websites such as the brand you use, Rosco, High End, LeMaitrie, Celco and others to see if there is other types of fog solutions available than the standard ones or for more details on Cold Flow.

I used a 50/50 solution of HES Stage and Cold Flow solution over the weekend, it did a fairly decent job of lingering low at least without a chiller. Straight cold flow and a chiller should work even better.

I do agree with the cautions about CO2 gas and the audience, much less the cost of a lingering effect. While in the pit, breezes sweeping it off stage will be less, you are still without a doubt going to have it disperse within say a half hour.

Another idea might be to add some haze to the fog especially if there is any low lying haze on the market. This will supplement or replace the need for fog.

[Radman]

From the sounds of your fog chiller it might be cheapest and easiest to buy or rent a better fog machine and use either ice or better yet dry ice in it. Dry ice will last longer. In my experience dry ice fog disappears very fast. I thing a fog machine with a decent chiller should work fine. I know our chiller (which we never use) has a built in fan to move the fog better, maybe it is the same on yours?

[mr_sound]

Well thanks for all the advice, and I will certainly keep those ideas in mind if I ever need to do this again, but for the show tomorrow..it's pretty short notice. It was pretty much going to be either dry ice, or nothing. We don't have the available power to run any commercial quality chiller..or even a heavier duty fog machine, not to mention there's no budget for it.

Since the pit actually has vents that dump into the ventillation system, under the pit, I think using dry ice could actually prove to be a really big problem. I had never even considered the fact that it's still CO2 when it warms up...just one of those details you overlook. So that's out...we'll just do without it. He's not paying me enough to go all out just to fill the pit with fog. Frankly I don't think anyone is going to care anyways....the lighting will be cool enough as is.

[Peter]

As a super low tech alternative, go out to the local craft store and buy a bunch of cotton batting and strech it over the top of your pit (the kind made to make large fake spiderwebs might be best for the long crossing spans, and thinner stuff better for in between). With some work, and the right angles on your lights you might be able to get a neat effect.

Just a random idea I just thought of while reading your last post!