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Fogging your Haunt with Dry Ice
updated September 20, 2005
Double, double toil and trouble, Fire burn and cauldron bubble the witches sang in Macbeth and that's the vision you have for your home haunt but how bring it into reality? Fire is nice but it tends to burn down your home not to mention what a cauldron full of boiling liquid could do to you or the neighbor's over inquisitive children. What to do, what to do? The solution is just two words, DRY ICE!
What is Dry Ice?
Dry ice is frozen carbon dioxide or CO2. This is the same gas we exhale, plants inhale, and is the carbonation in our soda and beer. Dry ice is both denser and colder than ice made from water. Dry ice doesn't float in water and whereas water freezes at 32° F (0° C) CO2 freezes at -109.3° F (-78.5° C). That's mighty cold!
But what makes it "dry"? Well, a particularly interesting thing about dry ice is that it doesn't melt, it sublimates. This means that it goes directly from its solid frozen state to gas without first becoming a liquid. (At standard pressure and temperature of course) This recently sublimated super cold gas expands and lowers the air temperature it comes in contact with. Water vapor in the air condenses and forms fog. Because it is much cooler and denser than the surrounding air this fog flows downhill till it finds the lowest spot. The result, a spooky ground fog guaranteed to set the right mood for your haunt.
Using Dry Ice
Because dry ice is so cold it's important to handle dry ice with care. Wear protective gloves or use tongs to avoid frostbite burns.
To make fog with dry ice is as simple as placing it in water. The warmer temperature of the water will cause the dry ice to sublimate vigorously and produce fog. However, just because it's so simple doesn't mean there there aren't tricks to improve the show.
To get the most out of your dry ice you should remember that the warmer the water is, the more fog will be produced. Also, the warmer the water is, the quicker you will use up your dry ice. Keeping the water warm can be tricky. Because the dry ice is so very cold it will chill warm water quickly. To overcome this you have several options.
First, you can start with hotter water. Boiling water will produce lots of fog but you will have to add more boiling water on a regular basis to keep the level of fog constant.
Second, you could add heat externally. While a nice roaring fire may add authenticity to the boiling cauldron scene we envisioned at the beginning of this article it really isn't a suitable option. Fire can be very dangerous in a home haunt. There are lots of flammable materials around a typical haunt not to mention it's a danger to the little trick-or-treaters with their flowing costumes. Finally, CO2 smothers flames! You're bubbling cauldron becomes one giant fire extinguisher! A better option is electric heating. This can be in the form of a hotplate under the cauldron if it's made of metal or for the more electrically savvy an electric element mounted in it. Electric heating elements can usually be purchase for a reasonable amount from your local hardware or pulled from a hot water heater. From what we've been told the "low watt density" types are best as the heating demand is low.
Third, and simplest, is to start with a larger volume of hot water. Imagine what that heated spa of yours would look like with spooky fog pouring out of it!
Another way of getting more fog out of your dry ice is to break it into smaller chunks. The increased surface area means the dry ice will sublimate more quickly. This of course means that the water will cool more quickly as well.
Ideally, the container you choose for your display will have a large enough capacity to hold enough water so that you are not constantly changing it or be made of a material that can be heated.
Remember that we said when you put dry ice into the water it will sublimate vigorously. This means you also need enough room for the water to splash or have it sit on or in a waterproof surface.
It's always better to err on the side of too much rather than too little. For a cauldron sized display expect to use 10 lbs of dry ice per hour. Plan on using more if you electrically heat your cauldron.
Transporting and Storage
It's a good idea to plan on picking up your dry ice as close to the time you will be using it as possible. You don't want it to sublimate away when it's not adding to the spookiness of your haunt. A rule of thumb is that dry ice sublimates at 10%, or 5 to 10 pounds every 24 hours, whichever is greater. It's important to transport and store your dry ice in a well ventilated area. Carbon Dioxide in too high a concentration can cause suffocation. Pets and small children who are lower to the ground are at greater risk so they should not be left unsupervised near dry ice.
After you pick up your dry ice you should store it in a well insulated but not airtight container (as the dry ice sublimates pressure can build in sealed containers) such as an ice chest or if this is not possible you can wrap it in extra layers of newspaper and towels. It is not recommended to store your dry ice in the freezer or refrigerator. Dry ice is much colder than the freezer and will sublimate much faster than if stored by itself in a cooler.
Dry ice should not be left on stone, tile, or other ceramic countertops nor in contact with many types of glass. The difference in temperature can cause them to crack. Plastic, metal, and Pyrex containers are suitable but you should be careful when handling containers that have held dry ice because they can get very cold.
In the event that you have dry ice left over, as if it was possible with such a fun thing as dry ice, disposal is a snap. Just unwrap and leave your leftover ice in a well ventilated area and it will sublimate into a gas. When it's all gone, toss the wrapping into the trash and you're done.
Haunted Bay would like to thank Mary of Airgas in San Carlos for providing information for this article and we highly recommend them as your source for dry ice in the San Francisco Bay Area. Airgas will be open weekdays through and including Halloween. Airgas is charging $13.55 for 25 lbs. of dry ice at their San Carlos location. To find an Airgas location near you or to find a retailer that carries Penguin brand dry ice (available at many Safeway and Albertson's Supermarkets) please visit the Airgas website or consult your local phone book.
Happy foggy haunting!
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