Theatrical & Special Effects
Special Effects with Dry Ice
When Dry Ice is combined with hot water it will produce vigorous bubbling water and voluminous flowing fog. A theatre fog machine is generally a 30 to 55-gallon metal or plastic water barrel with a 110-volt or a 220-volt hot water heater to keep the water hot. Dry Ice is placed in a bucket with holes to allow hot water to enter. When the bucket is lowered into the hot water fog is instantly produced. The resulting water vapour fog is gently blown by a fan and directed to the desired area by an air duct tube. Fog stops whenever the bucket of Dry Ice is pulled out of the water. More modern fog machines pump heated water over a tray holding the Dry Ice.
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How to Create Dry Ice Fog
Adding dry ice to hot water produces bubbling water and flowing fog. Adding 2.3 kg of dry ice in 15 to 19 litres of hot water produces the greatest amount of fog in the first 5 to 10 minutes. The amount of fog diminishes as the water temperature cools. Dry Ice makes fog because of its cold temperature, -78.5°C, immersed in hot water, creates a cloud of true water vapour fog. When the water gets colder than 10°C, the dry ice stops making fog, but continues to sublimate and bubble. The fog will last longer on a damp day than on a dry day.
How Much Dry Ice Do I Need?
For each 15-minute period of a fog effect, put 2.3 to 4.5 kgs of dry ice into 15 to 30 litres of hot water. Hotter water will make more fog. Very hot water will add its own rising steam to the vapour cloud. If there is no steam the fog will flow down hill and in the direction of any air movement. A small fan can help control the direction of the fog. Smaller pieces of dry ice with more surface area produce a greater volume of fog but also cool the water down much faster. In both cases the result is more fog for a shorter amount of time.
Keep the water hot with a hot plate, electric skillet, or some other heat source to produce fog for a longer time. Otherwise when the water gets too cold it must be replaced to continue the fog effects. If the container is completely filled with water the fog will flow over the sides the best.
Note that the bubbling water may splash out of the container so be mindful of the surface it is placed on may become or slippy. The water vapour fog will also dampen the area it flows across.
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