Theatrical smoke and fog, also known as special effect smoke, fog or haze, is a category of atmospheric effects used in the entertainment industry. The use of fog can be found throughout motion picture and television productions, live theatre, concerts, at nightclubs and raves, amusement and theme parks, and even in video arcades and similar venues. These atmospheric effects are used for creating special effects, to make lighting and lighting effects visible, and to create a specific sense of mood or atmosphere. Recently, smaller, cheaper fog machines have become available to the general public, and fog effects are becoming more common in residential applications, from small house parties to Halloween and Christmas.
Theatrical fog and theatrical fog machines are also becoming more prevalent in industrial applications outside of the entertainment industry, due to their ease of use, inherent portability, and ruggedness. Common popular applications for theatrical fog include environmental testing (such as HVAC inspections) as well as emergency personnel and disaster response training exercises. Militaries have historically used smoke and fog to mask troop movements in training and combat, the techniques of which are technologically similar to those used in theatre and film. Health harms can be caused by short- and long-term exposure to artificial fogs. Some types of fog are less healthy than others. Handling the generating equipment also has health risks.
Types of effects There are generally 4 types of fog effects used in entertainment applications: smoke, fog, haze, and "low-lying" effects.
Smoke Smoke effects refer to theatrical atmospheric effects produced either by pyrotechnic materials, such as Smoke Cookies, and pre-fabricated smoke cartridges; or other flammable substances such as incense or HVAC smoke pencils or pens. Smoke is differentiated from other atmospheric effects in that it is composed of solid particles released during combustion, rather than the liquid droplets that fog or haze are composed of.
Fog
Fog is created by pumping one of a variety of different glycols (such as propylene glycol, triethylene glycol, and glycerol) or glycol/water mixtures (referred to as fog fluid) into a heat exchanger (essentially a block of metal with a resistance heating element in it) and heating until the fluid vaporises, creating a thick translucent or opaque cloud. Devices specifically manufactured for this purpose are referred to as fog machines. An obsolete method for creating theatrical fog on-stage (although the technique is still used in motion pictures) is to use a device known as a thermal fogger, initially designed for distributing pesticide, which aspirates a petroleum product (typically kerosene or propane), ignites the fuel to create a flame, and then heats a mixture of air and pesticide to create a dense fog. This technique is similar to the smoke generators used by military forces to create smoke screens, and is generally only used outdoors due to the volume of fog produced and the petroleum fuel required. For theatrical purposes, the pesticide is typically replaced with glycol, glycol/water mixtures, or water.
"Low-lying" fog effects can be created by combining a fog machine with another device designed specifically for this purpose. As the fog exits the fog machine, it is chilled, either by passing through a device containing a fan and ice, or by passing through a device containing a fan and compressor similar to an air conditioner. The result is a relatively thick fog that stays within a few feet of the ground. As the fog warms, or is agitated, it rises and dissipates. Several manufacturers of theatrical fog fluid have developed specially formulated mixtures specifically designed to be used with CO2, intended to provide thicker, more consistent fog effects. Although these chilling devices do not use carbon dioxide, the specially formulated fog fluid does create denser fog than regular fog fluid.
Haze
Haze effects refer to creating an unobtrusive, homogeneous cloud intended primarily to reveal lighting beams, such as "light fingers" in a rock concert. This effect is produced using a haze machine, typically done in one of two ways. One technique uses mineral oil, atomized via a spray pump powered either by electricity or compressed CO2, breaking the mineral oil into a fine mist. Another technique for creating haze uses a glycol/water mixture to create haze in a process nearly identical to that for creating fog effects. In either case, the fluid used is referred to as haze fluid, but the different formulations are not compatible or interchangeable. Glycol/water haze fluid is sometimes referred to as "water-based haze" to avoid ambiguity. Smaller volumes of haze can also be generated from aerosol canisters containing mineral oil under pressure. Although the density of haze generated and the volume of space that can be filled is significantly smaller than that of a haze machine, aerosol canisters have the advantages of portability, no requirements for electricity, and finer control over the volume of haze generated.
Carbon dioxide and dry ice
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