How Smoke Machines Work

Dry Ice, Liquid Nitrogen, Glycol, and Water Smoke Machines

Smoke machines or fog machines produce visible vapor.
Smoke machines or fog machines produce visible vapor. Crispin, Alexander / Getty Images

Smoke, fog, haze, and mist machines create some exciting special effects. Have you ever wondered what makes the smoke? Have you ever wanted to create the effect yourself? If so, you are in luck, as we will reveal these mysteries. However, we will warn you that a little knowledge is a dangerous thing! If used incorrectly, the equipment and chemicals used to generate simulated smoke can be dangerous (toxic, burn hazard, asphyxiation hazard, fire hazard, etc.). Also, all types of smoke generators will trigger smoke alarms. I'm telling you how the effects are created, not advising you to make your own smoke. If you are a serious do-it-yourself type, read the article and then please follow the links I have provided to the right of this article, which include specific instructions and warnings from professionals and experienced amateurs. 

Dry Ice and Water Make Smoke (Fog Really)

Aside from using a smoke machine, this method is the simplest for most people, both in practice and obtaining materials. Dry ice is solid carbon dioxide. You can make a dense fog by adding dry ice to hot water or steam. The carbon dioxide is vaporized, making a fog, and the rapid cooling of the surrounding air condenses water vapor in the air, adding to the effect.

Important Points

  • Dry ice fog sinks to the floor.
  • Water temperature affects the characteristics of the fog. Hotter water or steam vaporizes the carbon dioxide more quickly, yielding lots of fog and using up the dry ice more quickly, too. If fresh hot water or steam isn't added, the remaining water will cool quickly.
  • An easy 'smoke machine' can be made using a styrofoam cooler. Simply add hot water and dry ice. Machines that use dry ice work by continually heating water, to keep the fog flowing. Simple machines are also available to make dry ice or to solidify air.
  • Dry ice is cold enough to cause frostbite - use protective gloves when handling it.
  • Remember that use of dry ice increases the level of carbon dioxide in the air where it is used. This can present a respiratory hazard low to ground (or downstairs, if applicable), in enclosed spaces, or with large quantities of dry ice.

Liquid Nitrogen Makes Real Water Fog

One of the big advantages of liquid nitrogen is that nothing extra is needed to produce fog. Liquid nitrogen works by evaporating and by cooling the air, causing water to condense. Nitrogen is the primary component of air and is non-toxic.

Important Points

  • Nitrogen fog sinks to the ground.
  • Smoke can be made by either letting the nitrogen off-gas naturally or by using a fan to blow the 'smoke' where it is wanted.
  • Liquid nitrogen presents a serious hazard to the user. Although dry ice can give you frostbite, liquid nitrogen is cold enough to cause considerable tissue damage and death. Do not use nitrogen unless you have had the proper cryogenics training. Never use liquid nitrogen in a situation where other people can access the nitrogen source.
  • As the nitrogen concentration increases, the oxygen concentration in a room decreases, presenting a potential asphyxiation hazard.

Atomized Glycol Smoke Machines

Most smoke machines use water with a glycol mixture to produce special effects. Many commercial smoke machines use 'fog juice' that consists of glycols, glycerine, and/or mineral oil, with varying amounts of distilled water. The glycols are heated and forced into the atmosphere under pressure to create a fog or haze. There are a variety of mixtures that may be used. See the reference bar to the right of this article for Material Safety Data Sheets on some example types. Some homemade recipes for fog juice are:

  1. 15%-35% food grade glycerine to 1 quart distilled water
  2. 125 ml glycerine to 1 liter distilled water
    (glycerine creates a 'haze' at concentrations of 15% or less and more of a fog or smoke at concentrations higher than 15%)
  3. Unscented mineral oil (baby oil), with or without water
    (we can't vouch for the safety of using mineral oil for fog juice)
  4. 10% distilled water: 90% propylene glycol (dense fog)
    40% distilled water: 60% propylene glycol (quick dissipating)
    60% water: 40% propylene glycol (very quick dissipation)
  5. 30% distilled water: 35% dipropylene glycol: 35% triethylene glycol (long-lasting fog)
  6. 30% distilled water: 70% dipropylene glycol (dense fog)

The resulting smoke should not smell "burnt." If it does, likely causes are too high of an operating temperature or too much glycerine/glycol/mineral oil in the mixture. The lower the percentage of organic, the less expensive the fog juice, but the fog will be lighter and will not last as long. Distilled water is only necessary if a heat exchanger or other tubing is used in the system. Using a homemade fog mixture in a commercial machine will almost certainly void the warranty, possibly damage the machine, and possibly pose a fire and/or health hazard.

Important Points

This type of fog is heated and will rise or disperse at a higher level than dry ice or liquid nitrogen fog. Coolers can be used if low-lying fog is desired.

  • Changing the mixture or conditions of dispersion of atomized glycols can result in many special effects that are difficult to achieve with other simulated smokes.
  • Glycols can undergo heat denaturation into highly toxic substances, such as formaldehyde. This is one of the major problems with homemade smoke machines - they may operate at a temperature that is incompatible with the substances being used. Also, this is a danger with homemade fog juice used in commercial machines.
  • Glycols, glycerine, and mineral oil can all leave an oily residue, resulting in slick or sometimes slightly sticky surfaces. Be aware of the potential safety hazards, especially since the smoke may limit visibility. Also, some people may experience skin irritation from exposure to glycol fog.
  • Some glycols are toxic and should not be used to create smoke. Ethylene glycol is poisonous. Some glycols are sold as mixtures. Medical or pharmaceutical grade non-toxic glycols only should be used in smoke machines. Do not use antifreeze to make a fog mixture. The ethylene glycol types are poisonous and the propylene glycol types always contain undesirable impurities.
  • If water is used, it needs to be distilled water, since hard water deposits can damage the atomizer apparatus.
  • Some of the chemicals that can be used for this type of smoke are flammable.

Real Water Vapor Fog

In some cases, this type of simulated smoke is created by finely dispersing hot water or steam. The effect is similar to what happens when water is poured on a hot rock in a sauna. In other cases, water vapor machines act by condensing water vapor out of the air, such as may be seen when a freezer door is opened. Many commercial smoke machines use water vapor in some fashion.

Important Points

  • This type of 'smoke' is best generated in a cool room.
  • Water vapor is non-toxic.
  • Hot vapor will float, so chillers may be employed when a ground effect is desired.
  • A fogger essentially makes a cloud, so water condensation on objects is possible and may present a safety concern.
  • Water vapor, like all simulated smokes, will set off a smoke alarm.