Here is a paper I wrote in 2017. I thought I would post it here because AVIXA Xchange has exactly zero articles on the topic. There is some newer information available so I may at some point update this, In the meantime, I hope you find this useful and I tried to cite sources as much as possible. Leave a comment or message me with questions.

Enjoy! - Dan

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In the entertainment industry, atmospheric effects such as fog, haze, and smoke are critical to creating the desired performance environment. These effects can dramatically influence the audience's perception, affecting whether the event is perceived as high quality and playing a crucial role in conveying the artistic vision of the designers. These effects can be vivid, as seen at the Super Bowl and Olympics, or subtle, where the only purpose is to refract a spotlight so that the audience can see the beam of light. These effects are often created by machines that place concentrated particles or droplets in the atmosphere, which become the desired effect as they expand and dissipate throughout the performance venue, illuminated by the lighting in the room. Compared to the audience, employees on stage are often exposed to greater levels of these effects due to their proximity to the source and the additional time exposure from multiple rehearsals and performances. This paper is a review of existing literature available on atmospheric effects, drawing heavily on research commissioned by the Actors' Equity Association (AEA). AEA represents performers on stage, who could be most adversely affected by atmospheric effects. Many jurisdictions have adopted the "Actors' Equity standards," either formally or informally, depending on the area.

Review

When working with atmospheric effects, there are a few basic types of effects that are widely used. Each effect can be manipulated based on intensity, quantity, duration, and/or temperature. Fog is perhaps the most common and dramatic effect, and anyone who has attended a professional show has likely encountered fog in use. Fog is the traditional "make a cloud" effect that people see. Another popular effect is haze, which often saturates the atmosphere with moisture droplets to enable lighting effects to be seen. The haze itself is rarely seen without a primary light, called a "key light," illuminating it. Smoke is a particle introduced into the atmosphere through combustion; it is used less frequently in entertainment due to the natural fire risk, greater clean-up required, and its limited effect possibilities (ESTA, 2016).

Similarities between fog and haze include each being composed of droplets suspended in the air. Fog can come from a variety of machines and, in most formulations, is dense and dissipates quickly. Low-lying fog is very similar to regular fog; however, the fundamental difference is that low-lying fog stays at knee height or lower. It can be extremely dense but dissipates quickly. Haze is less dense and lingers longer, allowing a stage light to be visible as it shines through. Smoke is vastly different from fog and haze because it is composed of particles rather than droplets. Because of this, smoke may be colored, whereas fog is only colored based on the lights shining through it. Smoke may also amplify respiratory effects due to the particulate nature (ESTA, 2016).

There are a few basic components to a good fluid, each with its advantages and disadvantages. The main component in most fluids is water (ESTA, 2016). The advantage of using water is its significant cost-effectiveness—it is inexpensive and contributes to only minimal health effects. Water also evaporates the fastest and most completely. However, water has a low refraction index, meaning light scatters the least, resulting in lower visibility. Water can also accumulate on the floor, contributing to potential slip hazards backstage (ESTA, 2016; Cooper, 2014). Many stage floors have a rubberized surface or are painted with special floor paint, such as Rosco Tough Prime, to help reduce slips and falls. This is particularly important considering many productions use dancers who are in near-constant motion, actors walking and running in dimly lit spaces, and technicians maneuvering backstage with little to no light during set changes. Some productions also utilize a vinyl dance floor to help provide the correct amount of friction for the dancers. However, when wet due to condensation or spillage, this can create a new fall hazard (Cooper, 2014; Rossol).

Alcohols are another basic component used in atmospheric effects. Several different alcohols may be used in the effect. These alcohols are all used to slow the evaporation rate and as a medium to refract light (ESTA, 2016; Cooper, 2014). The major differences between the alcohols used from a performance standpoint influence how much light needs to be refracted and how long the effect needs to linger before it dissipates. The glycol family is one of the most common types of alcohol used, and there are several variations of glycols used, including propylene, triethylene, diethylene, dipropylene, 1,3-butylene, and polyethylene (Ports, 2016; Moline, Highland, Wilmarth, & Kao, 2000; Environ International Corporation, 2001). These are the commonly used alcohols approved for use by the Actors' Equity Association (Environ International Corporation, 2001). Also approved is a hydroxyl formulation of glycerin, though it is not typically used in atmospheric effects and is not widely adopted by equipment manufacturers (Environ International Corporation, 2001; Ports, 2016; Moline, Highland, Wilmarth, & Kao, 2000).

Alcohols can be controlled based on how well they mix with water. Manipulating this relationship can create excellent effects, as the mixture will offer a higher refraction index while also increasing the evaporation time compared to a mixture of mostly water. Alcohols and water are not the only substances available; mineral oil is often utilized as it never actually evaporates, meaning the effects can last a long time. The high refraction index is ideal for many effects; however, it is not without its challenges. Mineral oil can be difficult to clear and tends to leave a slippery deposit behind, so people must be careful not to slip with this additional hazard present backstage (Cooper, 2014; Environ International Corporation, 2001; Burr, 1994; Ports, 2016; Rossol; Ruling).

Historically, dry ice has been a very common method of creating fog, especially low-lying fog. Dry ice is generally regarded as one of the safest mediums, and its availability and cost have made it one of the most widely used resources (ESTA, 2016). Dry ice is effective when it is submerged in a tank of 30-50 gallons of water, with about 30% of the tank available for the accumulation of gases at the top of the tank. Usually, a heating coil is added to the water to keep it warm enough to prevent freezing, otherwise, the water will form a shell of ice around the dry ice, naturally mitigating the desired effects. Dry ice vapors tend not to dissipate naturally, so a fan must be added if the vapors need to travel a significant distance or reach a significant height (ESTA, 2016; Rossol).

Liquid nitrogen is a favorite on cruise ships, although it is not used as often on land. This element can work well in a large tank-like space such as a horse trough, where it can expand and spill out of the area. It can be one of the quietest methods, requiring no fan, with the primary consideration being to ensure it does not heat above 325 degrees Fahrenheit (Ruling; Cooper, 2014; Rossol). In practical terms, this means keeping it a reasonable distance away from theatrical stage lighting fixtures. There are two markets where liquid nitrogen seems to be ideal: operas, where noise can be an issue, and cruise ships, where the infrastructure easily supports it. Another common application is as a propellant in confetti cannons (Rossol; ESTA, 2016).

When larger droplets are needed, mechanical fogs can be called upon. Pressurized water is perhaps one of the more common effects and can be seen in shows like Singing in the Rain and Beauty and the Beast, where the desired effect is more of a rainstorm and light needs larger surfaces to refract. There are several considerations, though, including ambient temperature and humidity. Using this incorrectly could result in slip and/or electrical hazards being created. The increased humidity can also be detrimental to scenery, and in some cases, it can cause the fire retardant on curtains and scenery to develop a white, chalky appearance, which indicates that a new application of retardant is needed (Cooper, 2014; ESTA, 2016).

Liquid Synthetic Air (LSA) is a nitrogen-oxygen mix that produces a low-lying fog. Temperature can be a factor for its use, and it is generally used interchangeably with liquid nitrogen, with the look of the overall effect being the primary consideration. Naturally, LSA is odorless, which is another advantage (ESTA, 2016).

A cracker effect is a process where mineral oil is broken down into smaller droplets. Crackers use an air compressor attached to a dispersion system, which offers additional control as the operator can adjust the size of the droplets expelled from the system as haze. This process capitalizes on the lower evaporation rate of mineral oil to produce a pure white fog. While it is possible to do this with a glycol-based fluid, designers do not often deploy this method, though it can be particularly effective for some shows (ESTA, 2016).

Sprayer fog can be used to distribute high-grade mineral oil into a very fine haze. Sprayers can be used as a self-contained machine, and the product will be in the form of an aerosol. This is extremely popular for haze machines and is the current industry standard for almost all touring concerts and performances. This effect allows the audience to view the beams of light while being blissfully unaware that any atmospheric effects are in use (ESTA, 2016).

Ultrasonic fog machines are a less common method of creating fog compared to other techniques like dry ice and glycol-based systems. They work by using high-frequency sound waves to break down fluids, typically a glycol-water mixture, into tiny droplets that are then dispersed into the air.

While ultrasonic fog machines are popular in residential settings as humidifiers, they have limited application in professional entertainment environments due to their lower fog density and potential for less-than-ideal performance. While they may be found in smaller, amateur events or in situations where cost is a major factor, larger professional productions typically opt for more robust and reliable fog machines.

Like haze, fog machines work in a variety of methods, with the most common being a pump propelling glycols diluted with water (ESTA, 2016). These are highly efficient, compact machines that have been in use for over 30 years. They operate by pumping fluid through a heater and exhausting it into a fan that disperses the fog (ESTA, 2016).

Gas-propelled machines work by heating the fluid to a vaporization point. This is one of the most versatile methods of dispersion as it can be used for mineral oil, glycols, and gases. However, caution must be used because when a fluid is heated too much, it is possible to change the chemical composition of the fluid and turn the gas into a toxic cloud (Teschke; Ports, 2016).

Pressurized water machines use water at high psi to create a mist of droplets. This method is ideal for ice shows where the effect can be used strategically on the ice, and an abundance of water will simply freeze as a layer of ice on the existing ice area. This method can also be used strategically for equestrian and rodeo events, where the water can be used as a method of dust control in addition to providing the visual effects desired for the production (Teschke; Ports, 2016; Cooper, 2014). One commonality among all fogs is that when they are cooled, the droplets tend to stay low to the ground, creating a low-lying fog effect. Dry-ice-based fog is naturally low-lying due to its low temperature; however, both mineral oil and alcohol-based fluids can capitalize on this effect through the use of a chiller attached to the output of the fog machine (ESTA, 2016).

Safety Considerations

Safety is paramount when using theatrical atmospheric effects. One of the most important considerations is to always use machines that comply with industry standards and to avoid using homemade machines. Glycols, in particular, can undergo heat denaturation, transforming into formaldehyde. Additionally, some glycols are toxic, such as ethylene glycol (Teschke; Ruling; Rossol; Cooper, 2014).

Conclusion

Since the initial study commissioned by the Actors' Equity Association conducted by Environ Corporation, awareness about the various exposures faced by performers has increased. The entertainment industry, unlike manufacturing or mining industries, does not have many health and safety professionals, so the risks are not as well understood by those within the industry. However, there is a movement to commission studies and identify the questions that need to be answered. This movement started with the 1994 report where 224 actors from nine Broadway productions were surveyed. "Of this group, 134 questionnaires (60%) were from actors appearing in the four productions using theatrical 'smoke,' and 90 questionnaires (40%) were from actors appearing in the five control productions. When compared to actors from the non-'smoke' productions, actors from two or more of the four productions utilizing theatrical 'smoke' reported experiencing a significantly greater prevalence of nasal symptoms (sneezing, runny or stuffy nose), respiratory symptoms (cough, wheeze, breathlessness, chest tightness), and mucous membrane symptoms (sore throat, hoarseness, dry throat, itchy/burning eyes, dry eyes) during their performances for the week prior to the survey." Through detailed follow-up data, it was ultimately determined that "based on the results of this study, there is no evidence that theatrical 'smoke,' at the levels found in the theaters studied, is a cause of occupational asthma among performers. Some of the constituents of theatrical 'smoke,' such as aerosolized glycols and mineral oil, could have irritative or mucous membrane drying properties in some individuals. Therefore, it is reasonable to minimize exposures by such means as relocating 'smoke' machines to avoid exposing actors to the direct, concentrated release of the aerosols, minimizing the amount of 'smoke' necessary for the production, and using only fog fluids approved by the manufacturers of the machines. The glycols used should be at the level of 'food grade' or 'high grade.' Glycol-based systems should also be designed to heat the fog fluids only to the lowest temperature needed to achieve proper aerosolization. This would help to avoid overheating the fluid and minimize the generation of decomposition products" (NIOSH, 1994).

This landmark study marked the first time the industry commissioned a major study, and it established the mechanism to start evaluating the equipment and processes used. Environ Corporation was commissioned to create two reports (Environ International Corporation, 2014; Environ International Corporation, 2001), which established what equipment should be utilized and how it could be calibrated to operate within the guidelines. With the Actors' Equity Association publishing the guidelines, production companies now have a reference point for standards. ESTA, the trade organization for theatrical equipment dealers, has adopted these standards and published additional reports as well as follow-up surveys to monitor the enforcement of the standards (Ruling). Additionally, because these standards are being established, there has recently been an awareness of the need to monitor compliance with the procurement of monitoring equipment (Union acquires monitoring device to measure compliance, 2003).

References

- Actor's Equity Association. (2001). Landmark theatrical "smoke and fog" study completed. Theatre News.
- Cooper, D. C. (Ed.). (2014). The event safety guide: A guide to health, safety and welfare at live entertainment events in the United States [Kindle].
- Entertainment Services and Technology Association. (2016). Introduction to modern atmospheric effects (5th ed.) [PDF]. Retrieved from [http://tsp.esta.org/tsp/documents/docs/IntroToModernAtmosphericEffects5a.pdf](http://tsp.esta.org/tsp/documents/docs/IntroToModernAtmosphericEffects5a.pdf)
- Environ International. (2014, September). Calibration factors and time-and-distance guidelines for use of theatrical haze equipment. Everett, WA: CITC.
- Environ International. (2001, May). Evaluation of short-term exposures to theatrical smoke and haze air sampling protocol.
- Moline, J. M., Golden, A. L., Highland, J. H., Wilmarth, K. R., & Kao, A. S. (2000, June). Health effects evaluation of theatrical smoke, haze, and pyrotechnics. Retrieved from Equity-League Pension and Health Trust Funds website: [http://www.actorsequity.org/docs/safesan/finalreport.pdf](http://www.actorsequity.org/docs/safesan/finalreport.pdf)
- NIOSH. (1994, August). HHE report no. HETA-90-0355-2449, Actors' Equity Association/The League of American Theatres and Producers, Inc. (Research Report No. HETA-90-0355-2449). New York, NY: CDC.
- Ports, D. (2004, May). Safety issues for glycol/glycerol water-based atmospheric effects. Retrieved from [https://ocw.mit.edu/courses/music-and-theater-arts/21m-735-technical-design-scenery-mechanisms-and-special-effects-spring-2004/assignments/drkp_tn10.pdf](https://ocw.mit.edu/courses/music-and-theater-arts/21m-735-technical-design-scenery-mechanisms-and-special-effects-spring-2004/assignments/drkp_tn10.pdf)
- Rossol, M. (n.d.). The health and safety guide for film, tv, and theatre (2nd ed.) [Kindle].
- Ruling, K. (2000, July). Fog safety still a concern for users and manufacturers. Entertainment Design, 34(7), 20-23.
- Teschke, K., Chow, Y., Netten, C., Varughese, S., Kennedy, S. M., & Brauer, M. (n.d.). Exposures to atmospheric effects in the entertainment industry [PDF]. Journal of Occupational and Environmental Hygiene, 2(5), 277-284. [http://dx.doi.org/10.1080/15459620590952215](http://dx.doi.org/10.1080/15459620590952215)
- Union acquires monitoring device to measure compliance. (2003, February 26). Theatre News. Retrieved from [http://www.actorsequity.org/theatrenews/smoke-haze_02-06-2003.html](http://www.actorsequity.org/theatrenews/smoke-haze_02-06-2003.html)