106 Part 2 · Entertainment Discipline Overview This category contains a variety of production elements, some usually found only in theme parks: fog, flammable gas, water fountains, and such. Most of these systems (other than fog) are generally purpose-built, with a custom interface to other show systems. This category is sometimes also called "process control," but this term has other specific meanings in indus- try. 1 F OG AND S MOKE E QUIPMENT The Entertainment Services and Technology Association's (ESTA) Introduction to Modern Atmospheric Effects 2 defines fog as "A mixture of liquid droplets in air that reduces visibility and reflects light," and "smoke" is "Small, solid particles produced by burning and dispersed in the air. In the context of atmospheric effects, `Smoke' is used to refer to any aerosol made of solid particles rather than liquid droplets." While smoke effects are occasionally used in per- formance, fog effects are typically more easily controlled, and will be the focus here. A large variety of off-the-shelf fog machines are available that use glycol-based solutions, frozen liquid or gaseous carbon dioxide, liquid nitro- gen, or other materials. In theatrical-style live shows, fog generation usually falls under the jurisdiction of the electrics department, and in these situations, fog machines are often inter- faced to lighting control systems. F IRE AND W ATER S YSTEMS Most fire and water systems are custom-designed and built from the ground up to create spec- tacular effects for theme park or similar attractions. Water systems are generally custom and use standard process, industrial, and machinery control components, such as PLCs. See "Pro- grammable Logic Controllers (PLC)," on page 91. Because of the obvious danger, safety concerns are of utmost importance with any flame effect, and safety standards, such as the National Fire Protection Association's "NFPA 160 Standard for Flame Effects Before a Proximate Audience" should always be followed. Flame 1. In industry, "process control" means the control of processes in chemical, wastewater, refinery and other facili- ties. 2. Introduction to Modern Atmospheric Effects, 4th edition See http://www.esta.org/tsp/documents/ published_docs.php Courtesy Rosco Laboratories