A fog machine or a smoke machine, is a device which uses a superheated mixture of glycol and water to generate a supply of fog-like smoke. It is usually used in professional entertainment applications, but there are also smaller fog machines for personal use. The simplest form of fog machine does not involve heating elements or the water/glycol mixture called ‘fog juice’. Once exiting the fog machine and coming into contact with the moisture in the outside air the vapour condenses, resulting a thick visible fog.
It is indicated to use the manufacturer’s fog fluid. Using different fluid than indicated, could result in a damaged machine due to overheating during the process.
Chilled fog machines
Chilled fog machines are designed to create thick clouds of fog that lay close to the ground and dissipate as they rise. They are usually made by using either dry ice, liquid nitrogen or more recently liquid air.
By heating water to or near boiling in a suitable container and then dropping in one or more pieces of dry ice, the dry ice effects are produced.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.
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.
Liquid air is an alternative to using liquid 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 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 such as creating a specific mood or feeling for a theatrical moment and is often used in plays (like Dracula, Macbeth), in Halloween displays such as haunted houses or forests or in clubs (a DJ might use a fog machine to enhance the lighting display behind and above the dancers). Other users of the fog machines may be emergency services personnel and militaries (in their trening).
Several companies in Europe and Canada have developed interesting security systems that rapidely spread fog (using these fog machines). They were created in order to disorient an intruder by filling a room with fog when triggered by a panic button or other security device. These Security Smoke 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. Concerns have rapidly developed, considering that these devices may cause criminals to panic, causing them to become violent to customers or staff.
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 knownas 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.