A fog machine creates artificial fog (" stage fog ") by evaporating fog fluid . Hence the full name of the classic fog machine is evaporator fog machine . Systems based on dry ice are also still in use to generate ground fog . Depending on the machine type and fluid, the properties of the mist can be changed in terms of service life and density.
For centuries, fog and smoke have been produced for various purposes using steam or pyrotechnically . The development was driven by the need for methods that are less harmful to health and easier to control.
Paraffin and heated oils were used in film and theater, as well as in nightclubs, until the mid-1980s. Oil-based fluids for use in specially designed smoke machines are still mostly used in the professional sector. However, these systems have little in common with historical oil mist machines (which are no longer permitted due to the flammability of the mist, the precipitation on surfaces and the harmfulness of the oils in the lungs).
In 1973 Günther Schaidt, who lives in Schenefeld near Hamburg, developed the fog fluid that was still used in this form and the associated machines. He received a technology Oscar for this development in Hollywood . Almost all subsequent fog machines copy the operating principle of these Safex machines.
Fog machines are used in film, television and on stage to create a mysterious atmosphere. They are often used at parties and in discos to increase the spatial effect of spotlights and laser beams (haze machines). By scattering on the fog droplets, light rays are visible from the side. Fog gives the room depth by gradually covering it up.
In addition, fog serves as an aid for technical purposes such as speed measurement (via LDA ) or the visualization of air and gas flows ( streamlines in wind tunnels ). The fire brigade uses fog as a smoke substitute during exercises to create an artificial visual obstruction. In model construction, smoke rising from chimneys and steam locomotives is simulated.
The fog from smoke machines can trigger optical smoke alarms . If a fire alarm system is connected , this leads to incorrect use by the fire brigade. The associated loops must therefore be deactivated. In the case of fire alarm systems and some automatic fire extinguishing systems that do not have any technical facility for functional testing, artificial fog is therefore also used to test functionality.
Fog machines were also used to make military installations or weapon systems "invisible" to enemy aircraft. They are also used to prevent intruders from seeing.
Ordinary fog machines use a mixture of double-distilled water (to prevent mineral residues) and high-purity glycols or glycerine . The fog fluid is pressed by a pump into a heating element with a narrow diameter, where it evaporates by heating. The result is the fine aerosol, which is later perceived as a mist.
Artificial fog, like natural fog, scatters the light from headlights . For theater performances or concerts, fog machines are therefore used together with suitable lighting to achieve a dramatic effect.
Since fog machines are often installed in hard-to-reach places (e.g. on ceilings or behind protective grilles), they are usually controlled via remote controls or DMX . In addition, a trigger is attached to some smoke machines. A remote control is also available for almost all fog machines, whereby a control option via DMX is also increasingly found in the lower price ranges.
The lifetime of the mist depends to a large extent on the relative humidity . The higher this is, the more durable the fog.
If the fog fluid contains glycerine, it should not be heated to 200 ° C or more, otherwise the carcinogenic substance acrolein can be formed. Common fog machines have a temperature control, which should prevent too high temperatures and thus the formation of acrolein. In addition, it should be noted that the smoke machine and smoke fluid form a single unit. Therefore, only smoke fluids that have been approved by the manufacturer of the smoke machine should be used. Fog with glycols is harmless to health as long as it does not completely replace normal breathing air (inhalation directly from the fog machine)
Other ways of working
In the case of hazers, special fluids based on glycols or highly refined mineral oils are usually vaporized or atomized in order to create an almost transparent haze. This happens either similar to the principle of the classic fog machine or by means of atomization using, for example, ultrasound or compressed air. In addition, a fan is often used to distribute the generated haze evenly in the room.
The generation of ground fog was originally mostly achieved by dry ice (solid CO 2 at around −78 ° C) with condensation of existing humidity. Due to the poor availability and high storage costs, cryogenic liquid nitrogen or liquid carbon dioxide is now often used . A riser pipe to the bottom of the standing bottle allows the rapid removal of the liquid phase, which evaporates very quickly at ambient pressure, cools down and sometimes turns into solid carbonic acid snow , which continues to absorb heat when sublimating . While all of the CO 2 becomes gaseous, water mist (and possibly some snow) is formed from the moist ambient air when it cools down. Cooling down conventional fog from fog machines also creates fog close to the ground. Processes are also used in which the mist from conventional machines is made heavier with water mist from ultrasonic atomizers. The resulting ground fog remains close to the ground due to the larger and heavier particles, although the fog itself is warmer than the surroundings. The disadvantage here is the high water consumption and the risk of residues forming on the floor. However, dry ice fog is still considered the “most beautiful ground fog” because it is snow-white and due to its high density (due to the reduced temperature and enrichment with CO 2 ) it “flows” over the ground.
In another type of machine, two chemicals are mixed from pressurized gas containers , usually similar to a spray can, and burned at a nozzle. The advantage is that the machines are compact and no power supply is required, the disadvantages are the high operating costs, the risk of fire and the fact that the mist is harmful to health. They were used until around the mid-1980s, particularly in the field of film production .
CO 2 jet
With CO 2 jets, liquid CO 2 under pressure is pressed out of a nozzle and evaporates immediately. This creates a short-lived fog, similar to a flame made from bear moss spores . They are therefore also referred to as a "cold flame". With appropriate lighting, it can also be used to create non-hazardous flames of different colors.
- stolen property is fogged - the smoke machine is supposed to protect Mechernich train station from break-ins. In: Kölner Stadtanzeiger online , September 24, 2016