A
fog machine or
smoke machine is a device which emits a dense vapour that appears similar to
fogFog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...
or
smokeSmoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...
. This artificial fog is most commonly used in professional
entertainment applicationsTheatrical 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...
, 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 vapourizing proprietary
waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
and glycol-based or glycerine-based fluids or through the atomization of
mineral oilA mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....
. 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.
It is recommended using the manufacturer's fog fluid. Fog machines are calibrated for temperatures of the fluid formulated for that particular model. Using incorrect fluid for the fog machine could result in a damaged machine due to overheating during the flashing process.
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
CO2Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
or
nitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
) 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 iceDry ice, sometimes referred to as "Cardice" or as "card ice" , is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue...
, liquid nitrogen, or more recently liquid 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 temperature and pressure, carbon dioxide is an unstable liquid, the carbon dioxide sublimates and instantly produces a gas, condensing water vapor and creating a thick white fog. A fan placed at the top of the container directs the fog where it is needed.
Liquid nitrogen (N
2) 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 air is an alternative to using liquid nitrogen in generating low lying fog effects. Liquid air is composed of N
2 and O
2 mixed in a ratio of 79% nitrogen and 21% oxygen stored as a liquid in insulated cylinders. This ratio of nitrogen to oxygen is the same as that of atmospheric air, and indeed liquid air may be fabricated by simply liquefying atmospheric air. Liquid air can 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. Its key advantage over liquid nitrogen is that it presents no asphyxiation hazard, since it contains oxygen. A disadvantage is that it supports combustion, whereas liquid nitrogen inhibits combustion.
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
DraculaDracula is an 1897 novel by Irish author Bram Stoker.Famous for introducing the character of the vampire Count Dracula, the novel tells the story of Dracula's attempt to relocate from Transylvania to England, and the battle between Dracula and a small group of men and women led by Professor...
,
A Christmas CarolA Christmas Carol is a novella by English author Charles Dickens first published by Chapman & Hall on 17 December 1843. The story tells of sour and stingy Ebenezer Scrooge's ideological, ethical, and emotional transformation after the supernatural visits of Jacob Marley and the Ghosts of...
and
MacbethThe Tragedy of Macbeth is a play by William Shakespeare about a regicide and its aftermath. It is Shakespeare's shortest tragedy and is believed to have been written sometime between 1603 and 1607...
. Fog machines are also frequently used in
HalloweenHallowe'en , also known as Halloween or All Hallows' Eve, is a yearly holiday observed around the world on October 31, the night before All Saints' Day...
displays such as
haunted houseA haunted house is a house or other building often perceived as being inhabited by disembodied spirits of the deceased who may have been former residents or were familiar with the property...
s or forests. Because of greater availability and reductions in prices between 2003 and 2005, fog machines have become widely used for domestic Halloween presentations.
Fog machines are also useful for industrial applications including visualizing the flow of air, such highlighting drag over a surface in a
wind tunnelA wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
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
reflectiveReflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
and
refractiveRefraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
qualities of the smoke created by fog machines, they are often used in
nightclubA nightclub is an entertainment venue which usually operates late into the night...
s and other entertainment venues to enhance the effects of
lightingModern stage lighting is a flexible tool in the production of theatre, dance, opera and other performance arts. Several different types of stage lighting instruments are used in the pursuit of the various principles or goals of lighting. Stage lighting has grown considerably in recent years...
and
laserA laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
arrangements, although they are being superseded by
haze machineHaze machines, or haze generators , are effects machines similar to fog machines, designed to produce an unobtrusive, homogeneous clouds suspended in the air intended primarily to make light beams visible or create a subtle diffusion.-Properties:Unlike theatrical fog, which is typically intended to...
s (see also
light beamA light beam or beam of light is a narrow projection of light energy radiating from a source into a beam. Sunlight is a natural example of a light beam when filtered through various mediums...
).
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
Security SmokeSecurity smoke is thermally generated white smoke specifically used as a security measure...
devices can produce between 300 and 1,000 cubic metres of smoke in 30 seconds and have been utilised in a wide variety of industries, including buildings requiring a high level of security, such as banks and jewellers, but also warehouses, offices, retail premises and in cash-handling chains. Concerns have been raised, that these devices may cause criminals to panic, causing them to become violent to customers or staff, however
Security SmokeSecurity smoke is thermally generated white smoke specifically used as a security measure...
now has its own European Standard EN50131-8 which specifically states that it must not be installed in such a way as to create a mantrap.
Industrial uses
Ultra Low Volume (ULV) fogging is used by pest control industry and cleaning companies. ULV refers to the droplet size (between 20-30 micrometres) generated by these fog machines. This fine droplet size is known as the optimum size for pest control. Traditional thermal fog machine technology has difficulty reaching crawling pests such as roaches, flea and rodents due to the droplet size being too fine (less than 10 micrometres). It is often found that small droplets are blocked by the "air-curtain" of insects and rodents.
Cold Fogging, in contrast, is heavy enough to penetrate these "air-curtains" as well as light enough to be evenly distributed within a room.
Military uses
For military uses see the articles about smoke screen,
smoke bombA smoke bomb is a firework designed to produce smoke upon ignition. Smoke bombs are useful to military units, airsoft games, paintball games, self defense and pranks...
and
smoke grenadeSmoke grenades are canister-type grenades used as ground-to-ground or ground-to-air signaling devices, target or landing zone marking devices, or as screening devices for unit movements. Smoke grenades are normally considered non-lethal, although incorrect use may cause death...
.
Adverse Health Effects
Atmospheric effects generated using water and dry ice or liquid nitrogen can present asphyxiation or breathing hazards. Both carbon dioxide and nitrogen displace ordinary air and the oxygen it contains, creating a risk of subtle anoxia (lack of oxygenation) for people working in these atmospheres. Adequate ventilation is essential to ensure that artists and technicians are surrounded by breathable air. Carbon dioxide has the added hazard of interfering with the normal breathing reflex, which is sensitive to carbon dioxide levels in the air. Nitrogen has no effect on the breathing reflex, but this creates its own hazard in that a person breathing pure nitrogen can lose consciousness from lack of oxygen without any premonitory symptoms.
Fog produced with liquid air does not present the hazards of carbon dioxide or liquid nitrogen because the liquid air has the same composition as ordinary atmospheric air (including the same level of breathable oxygen).
Fog machines which generate their effects solely using water, such as ultrasonic or pressurized technology, pose no special health risks, however it should be noted that "water based" fog fluid does contain glycol.
A number of studies have been published on the potential health effects presented by exposure to glycol based theatrical fogs and artificial mists.
Two studies, a
Health Hazard EvaluationThe Health Hazard Evaluation program is a workplace safety program administered by the National Institute for Occupational Safety and Health . It was developed by NIOSH to comply with a mandate included in the Occupational Safety and Health Act of 1970 to investigate occupational hazards reported...
completed in 1994 by the
National Institute for Occupational Safety and HealthThe National Institute for Occupational Safety and Health is the United States’ federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the Centers for Disease Control and Prevention within the U.S...
, and another one in 2000 by the Department of Community and Preventative Medicine at the
Mount Sinai School of MedicineMount Sinai School of Medicine is an American medical school in the borough of Manhattan in New York City, currently ranked among the top 20 medical schools in the United States. It was chartered by Mount Sinai Hospital in 1963....
and ENVIRON; both prepared for Actors Equity and the League of American Theatres and Producers, focused on the effects on actors and performers in
BroadwayBroadway theatre, commonly called simply Broadway, refers to theatrical performances presented in one of the 40 professional theatres with 500 or more seats located in the Theatre District centered along Broadway, and in Lincoln Center, in Manhattan in New York City...
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 simulated 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 AssociationThe Entertainment Services and Technology Association is a live entertainment industry organization. From their website:"ESTA is a non-profit trade association representing the entertainment technology industry dedicated to a core mission of Building the Business of Show Business...
(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
ESTAThe Entertainment Services and Technology Association is a live entertainment industry organization. From their website:"ESTA is a non-profit trade association representing the entertainment technology industry dedicated to a core mission of Building the Business of Show Business...
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.
Haze Machines
Haze machines, also called haze generators or hazers, produce atmospheric effects (haze) which tend to be less dense than that of fog machines, allowing them to be used in creating more subtle looks. Depending on a venue's or location's
ventilationVentilating is the process of "changing" or replacing air in any space to provide high indoor air quality...
, this haze can stay in the air for hours.
Because of the small particle size of the output from hazers, under 5
micrometreA micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s, a hazer typically takes longer to fill the same volume of space with a visible effect relative to a fog machine.
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