How much dry ice do I need? (Hallowe'en)

So for Hallowe’en, we’ve built a “monster under the porch”. It’s set up so as you push open a gate, long, stringy, gremlin-monster arms reach out from under the stairs. I would like to have spooky mist oozing our from under the porch. I have room for a bucket near the creepy green light, so I figured dry ice would be the easiest.

I’m not thinking of generating a lot. At most, I only want it to look like maybe twice the amount you see coming from this Jack O’Lantern’s mouth. Basically, for a time frame of about two hours, I want it to look like the monster may be a fire-breathing porch troll.

Anyone have any idea how much dry ice that takes?

wow. two hours? you’re gonna need A LOT. a single cake which is about 5x5 inches from my local meijer store will disapear in a handful of minutes.

why not invest in a small, non-glycerin-based fog machine? they won’t break the bank cost-wise and you won’t be handling dry ice, which can bite you hard if you don’t take the right precautions. i’ve used it in theater productions and safe to say i hate the stuff. use some aluminum foil to channel the ‘smoke’ where you want it, and presto, you’re in business.

keep us posted. i’d like to know what you decide to do. :slight_smile:

Part of the problem is that as the dry ice cools the water, less fog is emitted. Once the water is cool hardly any fog will be produced. Ideally you’ll want the water to always be warm or hot; warmer = more fog, but it will also sublimate faster. If you put a 5-lb chunk in a 5-gallon bucket, you’ll get a decent amount of fog for maybe 30 minutes, then you’ll have to switch out the cold water and/or add more ice. You might be able to experiment with occasionally adding small chunks to ~1-2 gallons of water, and changing/heating the water periodically, but my guess is that you’ll need at least ~15 lbs to get a decent effect over the course of 2 hours. It also would depend on if you get blocks (which would produce fog at a slower rate for a longer time) or pellets (which would give you lots of fog for a short amount of time).
If I were you I’d pick up a 5-lb block and do some experimenting, if nothing else it’s a good excuse to play with dry ice!

I think the place I’m getting it from sells in in 12 kilo bags. I don’t need a large area covered and I don’t need it to be dense.

I don’t need it for two hours straight, it’s more that I need enough for the waves of kids. I’m know how to handle the dry ice without burning myself, but in the few theaters I’ve worked in we couldn’t use dry ice much because the musicians in the orchestra pit kept passing out (no, really).

We play with dry ice all the time.

A 1 pound chunk in a bowl, bucket or pitcher, then quickly topped with a gallon or so of HOT water will give you an instant, thick response that will last for several minutes. Good enough for occasional trick-or-treaters. When they’re gone, dump the water, add a bit more ice, and repeat as necessary. If you want it hidden, you have some logistical work to do. I’d just get a big plastic cauldron from the HW store and use it in plain view.

As stated above, the water will get cold in a few minutes, so you’ll need to replace it.

We have a cheap-ass fog machine from Wal Mart that takes 6-10 minutes to heat up, fogs for 30-60 seconds, then heat again. That’s what you get for 20 bucks. Plus the fog rises instead of laying on the ground.

Theseguys have some interesting options…

yep. something about the loss of oxygen molecules or something similar. i’ve been warned about that in the past. k. now i gotta go find it.

:::hunting down the answer:::

here it is: ‘Because it sublimates into large quantities of carbon dioxide gas, which could displace oxygen-containing air and pose a danger of asphyxiation, dry ice should only be exposed to open air in a well-ventilated environment’ - wiki.

A 12 kilo bag will last you all night and then some. I was going to suggest a mere ten or fifteen pounds.

As noted above, the key is to keep the water hot. If you can replace the water just before the kids get there, you’ll be golden. A very industrious person could probably modify and enlarge an electric teakettle to keep the water hot, and just plunk in more dry ice when necessary.