"People who always insist that where there's smoke there's fire probably haven't spent much time in the theatre," is how the New York Times' Ben Brantley opened his review of the Broadway revival of Jesus Christ Superstar. The April 7 edition of Back Stage reported that fire trucks were called twice during the show's first preview when smoke detectors raised the alarm. One savvy theatregoer remarked, "That's the first time I've walked out of a theatre saying, 'That's a fog show!'"

Jesus Christ Superstar may be making the news because of its heavy fog, but it is certainly not unusual in using it. Fog is ubiquitous in pop music concerts and Broadway musicals, and is also used in many straight plays, industrials, and theme park rides. It's used because it works. It can be a theatrical effect, like a puff of smoke to help advance the plot, or it can be used as a subtle atmospheric effect to make beams of light visible, and to turn a visually mundane scene into a magical one.

Fog is a handy tool for the designer, but its use in professional productions has been controversial for at least 10 years. In July and August 1990, the National Institute for Occupational Safety and Health (NIOSH ) was asked by the Actors' Equity Association and the League of American Theatres and Producers to investigate the possible health effects of theatrical "smoke" on Broadway. The results of that study were reassuring to those using fog. The researchers found lots of complaints from the performers, but no objective evidence that the fogs were doing anyone any harm. Peak expiratory flow rates were used as a measure of respiratory disease, and the researchers found that restricted airflow was just as likely to be found in performers working on shows without fog as on shows with it. Based on this finding, NIOSH concluded that there was no evidence that theatrical "smoke" is "a cause of occupational asthma among performers."

The NIOSH study didn't end the controversy about theatrical fogs, but the theatre industry has matured in the subsequent years and responded to the continuing concerns in a variety of ways. The performers' unions have worked to limit their members' exposure to fog, while also trying to establish scientifically if there is actually a problem. ESTA's Fog and Smoke Working Group has been working to set standards for glycol and glycerin fogs and to help educate the public on how to use fog responsibly. The specifiers and users of fog equipment have also become more sophisticated in their choices of fog effects and fog technologies. The fog machine manufacturers have tried to serve their customers by offering a range of machines that use a variety of fog-making materials.

One objection to the NIOSH finding was that asthma was only one of the performers' concerns. If fog and pyrotechnic smoke irritates a performer's vocal apparatus, that is also a problem because it threatens the performer's ability to work. To investigate this possibility, Actors' Equity and the League of American Theatres and Producers embarked on a jointly funded epidemiological study in 1997. This joint Equity/League study, conducted by the Mount Sinai School of Medicine and the Environ Corporation, attempts to measure any changes in the upper respiratory tracts of actors from before a show to after it that might be caused by theatrical fog or pyrotechnic smoke. It also attempts to measure any changes in lung vital capacity. The final report on the study was due in December of 1999, but, as of this writing has not been published yet.

In the meantime, fog is permitted on Broadway productions, as Superstar shows, but Actors' Equity has restricted its use under many of its other collective bargaining agreements. According to Equity field representative Keith Sklar, while the study is going on, it only makes sense to limit the use of fog to the technologies Equity believes are virtually harmless, which are dry ice and liquid nitrogen. The standard Letter of Agreement Equity offers many theatres also limits fog effects to these methods. However, the LOA is subject to negotiation, so some theatres have responded to the restrictions by crossing out the anti-fog text before signing the letter. The American Guild of Musical Artists also has tried to limit its members' exposure to fog. Many opera houses are working under an agreement that allows only "water-based" fogs. This, of course, permits dry ice and liquid nitrogen fogs, but it has been interpreted in some cases to allow glycol and glycerin fogs in which a substantial portion of the fog fluid is water.

ESTA's Fog and Smoke Working Group--which has members representing users, specifiers, and distributors of fog equipment, as well as fog machine manufacturers--has been addressing the controversy in two ways: by working to educate the public on the differences between types of atmospheric effects and how to use them safely and effectively, and by working on a draft of an American National Standard for glycol and glycerin fogs. The education project was started first, with the working group publishing the first edition of the Introduction to Modern Atmospheric Effects in April of 1996; however, the projects have become intertwined with the research conducted in support of the standard adding a lot of information that has been put into the current third edition of the book and on the ESTA website (www.esta.org).

The first step in trying to set any standard, particularly one that affects health, is to find out what is already known about the subject. Fog machine manufacturers had done their research and found results that made them confident they could make and market fog machines without unreasonable liability, but the standards-making body needed to do its own research. ESTA issued a request for quotations for a survey of the relevant literature on the toxicity of the components used in glycol and glycerin fogs. The RFQ was sent to 51 companies that have a certified industrial hygienist (CIH) on staff, and a dozen bids were received. Two companies were selected to conduct independent literature surveys: the Cohen Group of San Mateo, CA, and HSE Consulting and Sampling of Omaha, NE. Their reports are posted on the ESTA website.

The Cohen Group report and the HSE Consulting report are substantially the same in their findings. Both reports state that glycerin and the five dihydric alcohols studied are of low toxicity. Some of the chemicals are of such low toxicity that no maximum allowable concentrations have ever been established for them, even though they are used in a wide variety of industries. A few of the chemicals have exposure limits defined by governmental bodies in the US, UK, and Germany, but these exposure limits are higher than the levels needed to produce a reasonably foggy theatrical environment.

The CIH studies gave the working group good information on what a long-term, time-weighted average exposure limits for glycol and glycerin fogs might be, but they were little help in trying to determine appropriate short-term limits. That is, sometimes a show needs a burst of fog for an effect--such as the burst that is used at King Herod's entrance in Superstar--and that burst will be at a higher level than the general level of fog, but for a very short time. What might an appropriate short-term, higher level be? Finding that answer requires the expertise of a group more experienced with setting occupational exposure limits than the Fog and Smoke Working Group is, so the F&S Working Group has asked the American Conference of Governmental Industrial Hygienists to help in the project. The ACGIH is the group that sets the voluntary exposure standards on which most of the OSHA Permissible Exposure Limits are based. The F&S Working Group has not received an official reply to its proposal yet, but there has been some correspondence that indicates interest.

The fog machine manufacturers have not been idle while the above has been going on. Over the past five years, customers have become more particular about the fog effects they buy or rent. While there is nothing to suggest that one fog technology is safer than any other when used according to the manufacturer's instructions and with a reasonable amount of care, some customers are looking for fog-making technologies that they can call "the safest" or "the best" and will have a preference for one over another. This has led to experimentation and product development with the general results of simplifying the fog fluid formulas, reducing the total quantity of chemicals in the air, and increasing the use of chemicals that have published exposure limits.

"Rosco Clear is a market response," notes Rosco product manager Eric Tishman. "People were telling us, 'I don't like the smell of your fog,' so we made an unscented fog. It just so happens that the scent is built into the color." Thus, Rosco Clear Fog Fluid was born. The intent may have been to give customers an unscented fog fluid, but the result also has been to give them one that is part of the trend toward simpler fog fluids with few or no proprietary ingredients. Rosco Clear contains no chemicals that were not part of the F&S Working Group's CIH literature search, and no chemicals that are not likely to be covered by the working group's standard when it is finally issued.

High End Systems has modified its fog fluid formulas to make them produce a longer-lasting effect while using less fluid. "If you can make a machine that uses the slower-evaporating glycols in a better way, then perhaps you don't need to put as much in the air for the same level of haze," explains High End Systems' vice president of engineering Mike Wood. "That was the intent [with the Nebula]." The Nebula machine made a fine haze of triethylene glycol or PEG 200, two glycols that evaporate very slowly. In contrast, propylene glycol, another popular component of fog fluids, "evaporates almost immediately, so you have to keep pumping it out there to keep anything going at all," says Wood.

Ultimately the Nebula machine was not a popular product, but the work on it led to changes in the fluids for the F-100 fog machine. "We've reduced the amount of propylene and increased the amount of triethylene to try to produce effects that last longer with less glycol in the air," explains Wood. "That's the way our sales have gone: the fluid with that mix is by far our best-selling fluid. People have realized they don't have to use as much of it."

Le Maitre's haze fluids are an example of two responses combined: simplification of the fluids and the use of materials that have published standards. "All of our haze fluids use a glycerin particulate," says Randy Segeren, Le Maitre Special Effects' research and development manager. Glycerin has exposure limits set for it in the US, and the UK and Australia as well. The Neutron machine uses a fluid that is almost entirely glycerin, while Le Maitre's haze fluid for the G300 and H150 is a mixture of glycerin and over 50% water.

Another fog fluid component that has a well-recognized exposure limit is highly refined mineral oil. "So far all the tests that have been done show that if you stay under the government mandated 5mg per cubic meter, there are really no ill effects whatsoever," says Jim Gill, vice president of Reel EFX, the manufacturer of the DF-50 haze machine. The atmospheric effects used on the Broadway production of Jesus Christ Superstar are oil fogs created by machines from MDG Fog Generators. MDG's machines are relative newcomers to the Broadway market, but are proving particularly popular for a variety of reasons, among them that oil fog has virtually no odor and no taste, and the machines use relatively little fluid. "That's because of the way that we do it," says Martin Michaud of MDG.

The mineral oil machines in the MDG product line mix an inert gas with the oil and then vaporize it, which results in droplets 0.5 to 0.7 microns in diameter, according to the company's literature. Most heated fog droplets are on average one order of magnitude larger. The smaller the droplet size, the more light scattering per liter of fluid, so smaller droplets reduce the amount of fluid put into the air for a given sized fog effect. The trick of adding gas to the fluid is not MDG's alone--Rosco's Model 1600 has a compressed-air input port, and CITC's Hi-Lo DigiFogger also mixes CO2 with the fluid--but MDG has been perhaps the most successful in marketing the reduced fluid consumption that results from the technique.

Of course, some people are not going to be happy with the notion of breathing any chemical, no matter how benign it is. For them, water is the fog fluid of choice. Pure water fogs are dry ice fog, liquid nitrogen fog, liquid synthetic air fog, and high-pressure water mists.

The latter two are where the most action has been over the last five years or so. Liquid nitrogen machines are preferred for many applications, because among other things, a lot of nitrogen fog can be added to the air before it displaces enough oxygen to cause a problem. However, this can happen, for example, on extended movie shoots in a closed studio. To address the problem, Liquid Synthetic Air (LSA) has been developed for use in liquid nitrogen machines. It's a cryogenic mixture of nitrogen and oxygen that mimics natural air. The mixture must be monitored to make sure the nitrogen does not boil off and leave an oxygen-enriched mix, but as long as this is done, an unlimited amount can be used in a venue.

High-pressure water mists are not new, having been developed to make fogs in 1969. However, most of the time their use has been confined to ice shows and equestrian spectacles where the wet fallout from the mists is not a problem. Recently CITC has been successfully marketing the portable Jungle Mist system to theatres and opera companies. Mists have large droplets, so they tend to fall rather than hang in the air, but the falling particulate is a powerful atmospheric effect, particularly when back-lit, and some people appreciate the added water in the air. "Opera singers and people who are hard on their voices really love the higher humidity," says CITC president Gary Crawford.

One thing that all the fog manufacturers are doing is trying to educate their customers on the safe and responsible use of their equipment. "We put the safety information on our website; the information about oxygen-deficient atmospheres and guidelines for safe use of CO2 and dry ice," says Gary Fails, president of City Theatrical, the manufacturer of the Aquafog dry ice machine. "Of course, we give away the ESTA booklet with our fog machines, and encourage people to read it."

"If you provide information, people are less concerned," says Four Star Lighting's Lee Iwanski, a member of the F&S Working Group. "The unknown is the most frightening."