Smoke-making machines are used in a variety of settings. Live theatrical productions often use smoke machines to create fog effects in order to indicate an outdoor setting and create a sense of mystery. Smoke-making machines are used in still photography, filmmaking, and video production as well for the same purposes. Other events, such as music concerts or laser shows, may use smoke machines to produce a surface onto which lights or lasers are projected, creating a smoky or underwater effect.
Before smoke-making machines were widely used, smoke was created in other ways. Burning oils or pouring water over dry ice could create a limited amount of smoke that could then be fanned into the appropriate part of a stage or film set. However, such natural smoke can irritate the eyes or performers and leave an unpleasant odor. In the 1970s smoke-making machines that used a combination of water and natural glycols were developed to offer a more controlled, safe and environmentally clean alternative.
Many smoke-making machines rely on the principle of phase change to operate. The water-based fog fluid is exposed to a very hot surface inside the machine where it is quickly boiled and becomes water vapor. The expanding vapor flows out of a nozzle and condenses in the air, much like natural fog. Another category of smoke-making machines use dry ice or liquid nitrogen. By exposing these substances to hot water, they create a chemical reaction that forces moisture already in the air to condense a form a low-hanging cloud of fog.
Smoke-making machines of different sizes can be used to produce different quantities of smoke. Often the dense smoke coming out of the machine must be fanned until it spreads out and takes on the look of natural smoke or fog. Some smoke machines use compressed air to force the smoke out and diffuse it automatically. Smoke-making machines may either be plug-in electric or battery powered.
Smoke-making machines are electrical appliances and so may be prone to failure for a number of mechanical reasons. However, the biggest problem with some smoke machines are their potential negative effects on health. Certain types of smoke fluid have been cited as causing irritation to the eyes and lungs, though other brands of fluid claim to be safe. Machines that use dry ice offer the safest alternative, since the smoke they produce is composed entirely of carbon dioxide and water vapor.