<P> A fog machine, fog generator, or smoke machine is a device that emits a dense vapor that appears similar to fog or smoke . This artificial fog is most commonly used in professional entertainment applications, but smaller, more affordable fog machines are becoming common for personal use . Fog machines can also be found in use in a variety of industrial, training, and some military applications . Typically, fog is created by vaporizing proprietary water and glycol - based or glycerin - based fluids or through the atomization of mineral oil . This fluid (often referred to colloquially as fog juice) vaporizes or atomizes inside the fog machine . Upon exiting the fog machine and mixing with cooler outside air the vapor condenses, resulting in a thick visible fog . </P> <P> Heated fog machines use either an inert gas or an electric pump to propel mineral oil, glycol, or glycerin and water mixture into a heat exchanger, where the solution is vaporized . The most commonly encountered form of heated fog machine is the pump machine . Very basic models of this type of machine consist of a fluid reservoir, an electric pump to move the fog fluid and heat exchanger which vaporizes the fluid . More complex models may include a variety of other features, including variable speed pumps to control the output of fog, timer modules, or components for remote operation and monitoring of the fog machines' status . Some manufacturers have produced accessories and fluids that when combined with an ordinary heated pump machine, create fog effects similar to chilled fog machines . Gas propelled fog machines use an inert gas (most commonly CO or nitrogen) to propel either mineral oil or a glycol based fluid into a heat exchanger where it is vaporized into particles, creating a fog . Some models of gas propelled fog machine provide control over the output of fog by varying the volume of gas used to propel the fluid . </P>

Do you put water in a fog machine