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. If an individual is at an entertainment venue and beams of light are visible cutting across the room, that most likely means smoke or fog is being used. Theatrical smoke and fog are indispensable in creating visible mid-air laser effects to entertain audiences. 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 displays.
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 in 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, and the techniques and technology used for generating smoke and fog in theatre and film are similar.
Fog is created by pumping one of a variety of different glycol 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 vapourizes, creating a thick translucent or opaque cloud. Devices specifically manufactured for this purpose are referred to as a fog machines.
An obsolete method for creating theatrical fog on-stage (although the technique is still commonly 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, and then mixes in air and pesticide to create a dense fog. For theatrical purposes the pesticide is typically replaced with glycol, glycol/water mixtures, or water. This technique is similar to the smoke generators used by militaries to create smoke screens, and is generally only used outdoors due to the volume of fog produced and the petroleum fuel required.
"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 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 fluids.
Haze effects refer to creating an unobtrusive, homogeneous cloud intended primarily to reveal lighting beams, such as the classic "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" for the purposes of disambiguation.
Smaller volumes of haze can also be generated from aerosol canisters containing mineral oil under pressure. Although to 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 (CO2) liquid, stored in compressed cylinders, is used in conjunction with theatrical fog machines to produce "low lying" fog effects. When liquid CO2 is used to chill theatrical fog, the result is a 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. Effect duration is determined by the heating cycle of the theatrical fog machine and consumption rate of liquid CO2.
Carbon dioxide can also be used as an atmospheric effect on its own. When liquid CO2 is released into the air, typically through an electric solenoid valve to control timing and duration, the carbon dioxide liquid expands to a vapour and condenses the moisture in the air, creating large billowing plumes. When the solenoid valve is closed, the CO2 vapour rapidly disperses in the air, ending the effect nearly instantaneously. This effect can be used for a variety of applications, including simulating geysers of steam, in place of pyrotechnics, or to create an instant opaque wall for a reveal or disappearance during magic acts.
Dry Ice (solid carbon dioxide) effects are produced by heating water to or near boiling in a suitable container (for example: a 55 gallon drum with water heater coils in it), and then dropping in one or more pieces of dry ice. This makes the carbon dioxide sublime (transition directly from solid to gaseous states) very rapidly. The gaseous carbon dioxide condenses water vapour and creates a thick white fog. A fan placed at the top of the container directs the fog where it is needed, creating a rolling fog that lies low to the ground. As the submerged dry ice cools the water, the amount and duration of fog produced will be reduced, requiring "rest" periods to reheat the water.
Dry Ice can also be used in conjunction with a fog machine to create a low lying fog effect. Dry Ice is placed inside an insulated container with an orifice at each end. Fog from a fog machine is pumped in one side of the container, and allowed to flow out the other end. Although this technique does allow an individual to create low lying fog "on the cheap" (when compared to the cost of renting cylinders of liquid CO2 or watertight containers with integral heaters), the volume of low lying fog produced is typically less, and is more susceptible to atmospheric disturbances.
In 1992 the Academy of Motion Picture Arts and Sciences presented a Technical Achievement Award to Jim Doyle for the design and development of the Dry Fogger, which uses liquid nitrogen to produce a safe, dense, low-hanging dry fog.
On January 4, 2008, the Academy of Motion Picture Arts and Sciences presented a Technical Achievement Award to Jörg Pöhler and Rüdiger Kleinke of OTTEC Technology GmbH for the design and development of the battery-operated series of fog machines known as “Tiny Foggers.”
The operating characteristics of this compact, well-engineered and remote-controllable package make possible a range of safe special effects that would be totally impractical with larger, more conventional fog units.
Carbon dioxide is heavier than, and displaces, air and as such can present a serious hazard. Unsafe concentrations of carbon dioxide will initially cause headaches, nausea, blurred vision, dizziness and shortness of breath. Higher concentrations will result in loss of consciousness and death due to suffocation. When using compressed carbon dioxide or dry ice, care should be taken to ensure there is sufficient ventilation available at all times, and that procedures are in place to rapidly evacuate CO2 from any enclosed space in an emergency.
Liquid carbon dioxide (−56.6 °C) and dry ice (−78.5 °C) present a significant risk of frostbite or cold burn if mishandled. Proper protective clothing, such as long sleeves and gloves, should always be worn when handling these products. Liquid carbon dioxide, stored in compressed cylinders, also presents all the hazards attendant to gases under pressure and should be handled accordingly.
Nitrogen itself is relatively non-toxic, but in high concentrations it is heavier than air and can displace oxygen, creating a suffocation hazard. Liquid nitrogen (−195.8 °C) presents a significant risk of frostbite or cold burn if mishandled. Proper protective clothing, such as long sleeves and gloves, should always be worn when handling these products. Liquid nitrogen is stored in compressed cylinders, and therefore presents all the hazards attendant to materials under pressure and should be handled accordingly.
A number of studies have been published on the potential health effects presented by exposure to theatrical fogs and artificial mists.
Two studies, one completed in 1994 by the National Institute for Occupational Safety and Health (NIOSH) , and another one in 2000 by the Department of Community and Preventative Medicine at the Mount Sinai School of Medicine and ENVIRON ; both prepared for Actors Equity and the League of American Theatres and Producers, focused on the effects on actors and performers in Broadway musicals. The conclusion of both studies was that there was irritation of mucous membranes such as the eyes and the respiratory tract associated with extended peak exposure to theatrical fog. Exposure guidelines were outlined in the 2000 study that, it was determined, should prevent actors from suffering adverse impact to their health or vocal abilities.
Another study focused on the use of theatrical fog in the commercial aviation industry for emergency training of staff in stimulated fire conditions. This study also found eye and respiratory tract irritation.
In May 2005, a study published in the American Journal of Industrial Medicine , conducted by the School of Environment and Health at the University of British Columbia, looked at adverse respiratory effects in crew members on a wide variety of entertainment venues ranging from live theatres, concerts, television and film productions to a video arcade. This study determined that cumulative exposure to mineral oil and glycol-based fogs were associated with acute and chronic adverse effects on respiratory health. This study found that short-term exposure to glycol fog was associated with coughing, dry throat, headaches, dizziness, drowsiness, and tiredness. This study also found long-term exposure to smoke and fog was associated with both short-term and long-term respiratory problems such as chest tightness and wheezing. Personnel working closest to the fog machines had reduced lung function results.
The Entertainment Services and Technology Association (ESTA) has compiled a standard for theatrical fogs or artificial mists compositions for use in entertainment venues that "are not likely to be harmful to otherwise healthy performers, technicians, or audience members of normal working age, which is 18 to 64 years of age, inclusive. This standard was based primarily (though not exclusively), upon the findings of a report commissioned for ESTA by the Cohen Group and applies only those fog fluid compositions that consist of a mixture of water and glycol (so called "water based" fog fluid).
Short term exposure to glycol fog can be associated with headaches, dizziness, drowsiness and tiredness. Long term exposure to smoke and fog can be related to upper airway and voice symptoms. Extended (multi-year) exposure to smoke and fog has been associated with both short-term and long-term respiratory health problems. Efforts should be made to reduce exposure to theatrical smoke to as low a level as possible. The use of digital effects in post production on film and television sets can be considered a safer practise than using theatrical smoke and fog during filming, although this is not always practical.