Fog Effects for Stage & Studio

The effects available range from wisps of smoke to impenetrable clouds, from mysterious low-lying fog to a thin mist in the air revealing dramatic shafts of light. The two prevalent "technologies" in use today for making theatrical fog effects involve 1) sublimating dry ice (frozen carbon dioxide) and 2) vaporizing a specially formulated fluid (typically glycol-water mixture).

Dry Ice Fog

How it works

Dry ice is dropped into warm water where the frozen carbon dioxide (dry ice) sublimates into cold carbon dioxide gas which mixes with the humid air resulting in condensation and the formation of fog. (For those who have forgotten their high school science, sublimation is the process whereby a solid becomes a gas directly, without passing through a liquid state.)

Characteristics of dry ice fog

• Low lying - because the fog is cooler than the surrounding air, it drops, curling off stage edges, down stairs etc, rather than rising
• Non toxic - however like any gas which displaces the amount of oxygen in a space, there is a risk associated with too high of a concentration
• Dissipates quickly - as the fog mixes with the surrounding air, it quickly warms and evaporates

Dry Ice Fog Machines

Typically, in a theatrical setting, a dry ice fog machine is a large closed barrel (traditionally a converted 55 gallon barrel) with a water heating element, a hose or vent outlet with an exhaust fan and a way to lower a quantity of dry ice into the water on cue. Large hoses or ducts are used to deliver the fog to the stage.

Applications

Dry ice fog creates a magical environment - not unlike the fog over a body of water on a crisp cool morning - as it swirls around the performers feet, swirling and shifting dramatically in reaction to movement on the stage.

Drawbacks

• Can require significant quantities of dry ice which must ideally be purchased daily as stored dry ice loses volume rather quickly. A short application can easily require 50 lbs of ice.
• Dry ice fog dissipates quickly. Virtually as soon as it is created, it starts to dissipate. This is countered by continuous creation of fog.
• Dry ice requires cautious handling. At -109.3 °F, even brief contact with skin can cause significant damage.
• Dry ice fog is somewhat less dramatically impacted by stage lighting. Since it is lying along the floor, it does not "reveal" beams of light "raining" down from overhead.
• Dry ice fog is not appropriate for scenes where an actor might be required to lie on the floor for an extended period of time. The heavy concentration of carbon dioxide at floor level displaces oxygen and as a result, could create a danger.

Positives

• Although, various manufacturers have developed solutions that attempt to simulate the effect produced by a dry ice fogger, none of these solutions really quite matches the magical, mystical effect of the low-lying fog produced by a dry ice fogger.

Fluid-base Fog Machines

How it works

Today, most fluid-based fog machines work by rapidly heating a mixture of water and glycol, producing a vapor. The expanding vapor is forced out of a nozzle where the warm, moist vapor mixes with the cooler air to form fog.

Characteristics of Fluid-based Fog

• Because the fog produced by this method is warmer than the surrounding atmosphere, it tends to rise as it disperses.
• The typical fog produced this way is somewhat heavier in appearance than the fog produced by dry ice - ie it does not swirl as readily when someone moves through it.
• By controlling the "on" time of a fog machine, the amount of fog can be controlled creating effects ranging from a wisp to a virtually opaque cloud.
• In general, fog generated by a fluid-based machine will remain - or linger - for a significant time.

Fluid-based Fog Machines

Fluid-based machines are manufactured by a number of companies including Rosco, Ultratec, and High End. While there are a number of innovations and minor variations, for the most part they are similar in that they consist of a fluid reservoir and a pump for moving the fluid to the heat exchanger and a nozzle through which the vapor leaves the machine. Many machines are smaller than a typical microwave oven, quite portable and operate off a single 15amp electrical outlet. The manufacturers have developed a number of accessories or modifications to adapt these machines to meet specific needs.

Applications

With the various accessories and adaptations (described below), fluid-based fog machines are used to create a wide range of effects from low-lying to thick clouds, from thin wisps to pervasive haze. In addition to theatrical use, they have many industrial applications including the training of emergency workers, wind tunnel testing of aerodynamics, etc.

Variations

Hazers

Haze makers use compressed air rather than heat to vaporize a specially formulated variation of the glycol-based fluids. Most frequently used in concert settings, they produce a thin, haze-like effect used to dramatically reveal the beams of lights and special effects.

Chiller Modules

Low-lying fog similar in effect to that produced by dry ice fog machines is achieved by passing the fog machine output through a cooling unit lowering the temperature of the vapor.

Permanent Installations

In addition to the easily portable versions of their fog machines, most manufacturers also produce larger, less portable units for theme park or arena concert applications. These machines are capable of producing enormous volumes of fog or haze continuously for extended periods of time.

Drawbacks

• The vapor from fluid-based foggers may be irritating or allergenic in some persons with sensitivities.
• Although there are a variety of similar fluids available from various manufacturers, it is advisable, and in some cases, essential to use the fluid for which a particular machine is designed.
• Although minimal, fog machines do require some periodic maintenance. For example, reduced output may indicate that the heat exchanger is beginning to clog and in need of cleaning.

Positives

• Fluid-based machines today are available in a range of sizes, capable of producing everything from a wispy puff of smoke to extraordinary volumes of fog or haze. In general, they are quite "shippable" making them good touring solutions, or accessible to productions away from major rental houses. The fluids are readily available by "mail order" and can be stored indefinitely.

Most orders for in-stock items, placed before noon, are shipped same-day.