A fog machine or smoke machine is a device which emits a dense vapour 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 as well. Typically, fog is created by vapourizing proprietary water and glycol-based or glycerine-based fluids or through the atomization of mineral oil. This fluid (often referred to colloquially as fog juice) vapourizes or atomizes inside the fog machine. Upon exiting the fog machine and coming into contact with the moisture in the outside air the vapour condenses, resulting in a thick visible fog.
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Types of Fog Machines
Heated Fogs
Heated fog machines use either an inert gas or an electric pump to propel mineral oil, glycol, or glycol and water mixture into a heat exchanger, where the solution is vapourized.
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 vapourizes 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 CO2 or nitrogen to propel either mineral oil or a glycol based fluid into a heat exchanger where it is vapourized 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.
Chilled Fogs
Chilled fog machines are designed to create thick clouds of fog that lay close to the ground and dissipate as they rise. They are typically created by using either dry ice, liquid nitrogen, or more recently liquid synthetic air.
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. Because, at standard pressure, dry ice is an unstable liquid, the carbon dioxide sublimates and instantly produces a gas, condensing water vapour and creating a thick white fog. A fan placed at the top of the container directs the fog where it is needed.
Liquid nitrogen (N2) is used to create low lying fog effects in a manner similar to dry ice. A machine heats water to at or near the boiling point, creating steam and increasing the humidity in a closed container. When liquid nitrogen is pumped into the container, the moisture rapidly condenses, creating a thick white fog. A fan placed at the output of the container directs the fog where it is needed, creating a rolling fog that lies low to the ground.
Liquid Synthetic Air (Liquid Air) was developed as an alternative to using compressed nitrogen in generating low lying fog effects. Liquid air is composed of N2 and O2 mixed in a ratio of 79% nitrogen and 21% oxygen stored as a liquid in compressed cylinders. Liquid synthetic air was developed to be used as a direct replacement for liquid nitrogen in chilled fog effects and is intended to be used in the same manner in the same equipment.
Uses of fog machines
The versatility of fog machines make them appropriate for a wide variety of applications:
Fog readily assists in creating a specific mood or feeling for a theatrical moment, and is often used in plays, such as Dracula, A Christmas Carol and Macbeth. Fog machines are also frequently used in Halloween displays such as haunted houses or forests. Because of greater availability and reductions in prices between 2003 and 2005, fog machines have become widely used for domestic halloween presenations.
Fog machines are also useful for industrial applications including visualizing the flow of air, such highlighting drag over a surface in a wind tunnel or testing for leaks or filter effectiveness in air conditioning installations.
Emergency services personnel and militaries also use fog machines in their training regiments.
Because of the reflective and refractive qualities of the smoke created by fog machines, they are often used in nightclubs and other entertainment venues to enhance the effects of lighting and laser arrangements, although they are being superseded by haze machines (see also light beam).
Several companies in Europe and Canada have developed rapid deployment fog machines for use as intrusion and hold-up security systems, intended to disorient an intruder by filling a room with fog when triggered by a panic button or other security device. These devices can produce between 300 and 1,000 cubic metres of smoke in 30 seconds and tend to be installed in buildings requiring a high level of security, such as banks and jewellers. Concerns have been raised, however, that these devices may cause criminals to panic, causing them to become violent to customers or staff. [1]
Adverse Health Effects
A number of studies have been published on the potential health effects presented by exposure to theatrical fogs and artificial mists.
Two studies, a Health Hazard Evaluation completed in 1994 by the National Institute for Occupational Safety and Health [2], and another one in 2000 by the Department of Community and Preventative Medicine at the Mount Sinai School of Medicine and ENVIRON [3]; 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 [4] 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 [5], 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."[6] This standard was based primarily (though not exclusively), upon the findings of a report commissioned for ESTA by the Cohen Group[7] 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[8], although this is not always practical.
Haze Machines
Haze machines, (also called haze generators or hazers), are taking over the job of fog generators for highlighting lighting or laser effects. The fog produced with haze machines tends to be much lighter and less dense than that of fog machines, allowing it to be used in venues without creating an overly-dense and distracting cloud. Depending on the venue's ventilation, this haze can stay in the air for hours in turn reducing operational costs. Thus, haze machines are often seen with bands and large venues that need a certain lighting effect more visible. Most haze machines use an oil-based fluid, however, there are some machines that use a glycol based fluid.
See also
References
- ^ "What is a fogging device?". BBC News. 8 June 2009. http://news.bbc.co.uk/1/hi/magazine/8089678.stm. Retrieved 2009-07-02.
- ^ Burr GA, Van Gilder TJ, Trout DB, Wilcox TG, Driscoll R. NIOSH Health Hazard Evaluation HETA 90-0355-2499. Actor's Equity Association.
- ^ Moline JM, Golden AL, Highland JH, Wilmarth KR, Kao AS. Health Effects Evaluation of Theatrical Smoke, Haze and Pyrotechnics. Prepared for Actor's Equity Pension and Health Trust Funds. June 6, 2000.
- ^ Wieslander G, Norback D, Lindgren T. Experimental exposure to propylene glycol mist in aviation emergency training: acute ocular and respiratory effects. Occup Environ Med. 2001 Oct;58(10):649-55.
- ^ Varughese S, Teschke K, Brauer M, Chow Y, van Netten C, Kennedy SM. Effects of theatrical smokes and fogs on respiratory health in the entertainment industry. Am J Ind Med. 2005 May;47(5):411-8.
- ^ ANSI E1.5 - 2003, Entertainment Technology - Theatrical Fog Made With Aqueous Solutions Of Di- And Trihydric Alcohols F&S/1997-3017r7.5
- ^ Gregory E. Raymond, Joel M. Cohen. Recommended Exposure Guidelines for Glycol Fogging Agents, Project No. 6070-1001
- ^ Teschke K, Chow Y, van Netten C, Varughese S, Kennedy SM, Brauer M. Exposures to atmospheric effects in the entertainment industry. J Occup Environ Hyg. 2005 May;2(5):277-84.
External links
- Rosco U.S. - How Fog Machines Work
- Actor's Equity Study on Health Effects from the use of Theatrical Smokes and Fogs in Broadway performances
- [1] Article examining the pros and cons of Fog machines as security devices.
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