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SCIENCE FILE / An exploration of issues and trends
affecting science, medicine and the environment | Science
in Brief

I Didn't Know That...

March 29, 2001

Q. How do they make fog (or smoke) in a theater?

A. The most common way is to heat a mixture of water and mineral oil or ethylene glycol, the same chemical used in antifreeze. When the water evaporates, it takes with it small droplets of of the organic liquid, which produces the fog of smoke effect. Manufacturers of the evaporators say that the fog thus produced is safe and nontoxic, but there have been scattered reports that it can be a problem for people with asthma. A company called Praxair Inc. received a special Academy Award for technical achievement in 1998 for developing an artificial fog produced by a mixture of nitrogen, oxygen and steam. Low-lying or ground fog is produced by chilling the fog so that it doesn't rise.

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