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Types of Smoke and Fogs The following discussion of the various types of smoke and fogs isbased upon an accumulation of information from a variety of studies, andfrom actual experience in use.1. Dry Ice: Dry ice is one of the earliest types of materials used tocreate fog effects. Dry ice is frozen carbon dioxide, and when exposed toair it sublimes directly from a solid to a gas. The cold gas causesmoisture to condense into a thick, low-lying fog. Dry ice is the safestway to generate fog except in enclosed spaces where the carbon dioxide canaccumulate and reduce the oxygen concentration in the air. This couldcause asphyxiation if the oxygen concentration falls below 19.5%. Therewould also be a hazard if someone was lying down in the dry ice fog.2. Petroleum Distillates: Many of the earlier types of fogs were based onkerosene, fuel oil or other petroleum distillates. These were vaporized byheating to generate a fine mist. Unfortunately, inhalation of these chemi-cals caused eye and respiratory irritation, chemical pneumonia, andnarcosis (dizziness, headaches, nausea, etc.). In addition, the mist ofthese petroleum distillates is a fire hazard. I definitely recommendagainst any fog product containing fuel oil or other petroleum distillates.3. Zinc Chloride Smoke Generating Devices: A number of companies sellsmoke generators based on zinc chloride (e.g. smoke cookies, smoke pots,smoke candles, smoke bombs). Some of these also contain chlorinatedhydrocarbons such as perchloroethylene, a probable human carcinogen. Thesmoke is generated by heating or burning the product, which is classifiedas a Flammable Solid, D.O.S. by the Department of Transportation. Theseare available in sizes that generate small to very large amounts of smoke. The Material Safety Data Sheets on many of these products are notadequate and do not reflect their hazards. Use of these smoke devices infire fighter training exercises has resulted over the years in complaintsof breathing problems, chest pains, hot and cold flashes, headache, fever,fatigue, sore throat, nausea, cough and even some fatalities. Some ofthese symptoms might be due to chlorinated hydrocarbons, but most are dueto the generation of high concentrations of hydrochloric acid from thereaction of the zinc chloride with water. In some studies, hydrochloricacid concentrations have been many times higher than OSHA PELs and evenapproach levels considered immediately dangerous to life or health. Evenlower levels of smoke have caused symptoms. I recommend against the use of zinc chloride smoke devices, ordevices based on titanium chloride and similar materials indoors or inoutdoor situations where either film crew or actors could be exposed to anysubstantial amount of the smoke.4. Ammonium Chloride: Ammonium chloride (sal ammoniac) is a common methodof generating smoke on stage and outdoors. The smoke is created by heatingthe ammonium chloride. Air sampling studies have found largeconcentrations of ammonium chloride, in some instances near the OSHA PELfor nuisance dusts. Air sampling studies have also shown that somedecomposition of the ammonium chloride to hydrogen chloride occurs duringthis heating. The hydrogen chloride dissolves in water in the respiratorysystem to produce hydrochloric acid, a respiratory irritant. The levels ofhydrochloric acid are much smaller than those caused by the zinc chloridesmoke devices, but are still high enough to cause concern. It is notrecommended that ammonium chloride be used indoors or in enclosed spaces.5. Mineral Oil: This includes oil crackers and diffusion foggers. Oilcrackers involved bubbling air through a drum of mineral oil. The airbubbles reaching the surface contained "cracked" oil of particle size 1-50microns. This oil is not "cracked" in the sense of chemically breakingdown the oil, but is merely creating smaller droplet size. This has alsobeen used in combination with dry ice. The diffusion fogger produces amineral mist of less than 1 micron size by using a compressor to forcemineral oil through fine filters. Air sampling studies by California OSHA in an enclosed sound stage90' by 75' by 30' found that ten minutes of fogging produced mineral oilconcentrations for almost 2 hours that were 50% to 90% of the OSHA 8-hourPEL for mineral oil. However this PEL for mineral oil is based on its useas a cutting oil in industry; no toxicological studies have been made oninhalation of mineral oil of particle size less than one micron. There isconcern about long term health problems such as lipid pneumonia, since thevery fine mineral oil mist gets deep into the lungs and stays there. Thisis not recommended for use indoors.6. Vegetable Oils: Corn oil and similar vegetable oils are used in thesame manner as mineral oil above. Although vegetable oils are suitable foreating, little information is available about effects of inhalation. Definitely, only food-grade oil should be used to ensure there is nocontamination by molds like aflatoxin, which is carcinogenic. Use withcaution.7. Glycol Fogs: During the last decade, a whole range of products havebeen developed that use mixtures of water and polyfunctional alcohols,including ethylene glycol, propylene glycol, diethylene glycol, triethyleneglycol, polyethylene glycol and glycerin. With some exceptions, theseappear to be safer than most of the other fogs and smokes, except for dryice. Ethylene glycol and diethylene glycol are toxic by ingestion, causingkidney damage and possible death; the other glycols mentioned areconsidered only slightly toxic. Ethylene glycol has been removed from mostfogs after studies showed that it is a teratogen (can cause birth defects). Unfortunately long-term studies have not been done on inhalation of themists of most of these glycols, although respiratory irritation issometimes listed on Material Safety Data Sheets. A more serious concern is how the fog is generated. These mixturesare heated in a fog machine to a temperature near 600 F. One air samplingstudy found significant levels of acrolein in the mist generated, about 20%of the OSHA PEL. Acrolein is a strong respiratory and eye irritant. NIOSHis conducting studies on various fogs to determine the extent of thisdecomposition product. It is likely that some chemicals could generatemore decomposition products than others. Reformulation and finding ways toreduce the temperature needed to create the mist are possible solutions. Despite these problems, at this time, the glycol fogs are probably theleast hazardous fogs to use, although some will most likely turn out to besafer than others.8. Burning Organic Materials: The burning of gums such as olibanum gum(frankincense), paper, and other materials can also generate smoke. Thesesmokes are irritating and considerable amounts of carbon monoxide may alsobe generated. In addition to the smoke hazards, there is the concern aboutthe open flames. These materials should not be burned inside or wherepeople would be exposed to substantial amounts of smoke.Regulations Although not as hazardous as pyrotechnics or fire, smoke and fog onmotion picture sets is regulated by many Fire Departments. In New YorkCity, for example, you need a fire permit to use smoke or fog, just as youdo for pyrotechnics.