Fire Show Controls Designer Must Consider Every Possibility
BIRKET Engineering News, May/June 1995
Page one of the Control Engineer’s Handbook might say, “In order to maximize personnel safety, minimize personnel contact with moving equipment or related controlled functions.” In other words, keep people away from things that might hurt them. In the entertainment world, this kind of thrilling man/machine or man/special effect interaction is encouraged, equating to popular attractions and money in the bank for park owners.
The designer of a ride or show control system that involves fire effects must make guest and cast safety his primary design criteria. Fire control system designers are concerned with the occurence or presence of explosive mixtures, the potential of fire/people interaction, and the show area’s air quality. The concern for air quality introduces the need for environmental monitoring.
The objective of environmental monitoring is to safeguard the air quality offered to attraction guests or personnel and to provide early alarming of unacceptable conditions. While the specification of gas system and environmental monitoring components and their locations are left to the gas specialists, the controls designer is responsible for how they are implemented within the overall show control system.
Typical gas system items of interest to the controls designer are gas sniffers, oxygen deficiency sensors, carbon monoxide excess sensors, air flow sensors, and temperature sensors. Each of these sensors perform a specific function and therefore not all sensors are required in a particular installation.
The most universally used sensors are gas sniffer sensors. Gas sniffer sensors are used to detect a percentage of the lower explosive limit (LEL) concentration. These sensors provide warning and alarm signals to the fire system controller in the event of a gas leak that produces concentrations great enough to permit ignition. Remembering that natural gas rises and propane sinks, sensor placement is all important.
Oxygen deficiency and carbon monoxide sensors are installed in enclosed places where operators or guests may spend long periods of time. In the event of unacceptable air quality, the sensor will transmit warning and alarm signals to the fire system controller. For example, too much oxygen in the air may indicate a leak in an oxygen feed line, while an oxygen deficiency may indicate excessive fire. Too much fire may consume the oxygen available for breathing.
Temperature sensors are sometimes required to monitor ambient temperature. As an effect is operated, the surrounding temperature may reach levels that are unacceptable for a human. The temperature sensor transmits to the show controller the entire range of temperatures. Setpoints are chosen for warning and alarm signals. Upon reaching an unacceptable temperature, the heat source is shut down and cooling fans are turned on. In addition to ambient air and surface temperature sensors, radiant heat sensors may be necessary. They detect radiated heat (like light) as opposed to conducted or convected (moved via air) heat.
Air handlers are required in shows that have enclosed show space areas. Air handlers are responsible for getting fresh air in and the products of combustion (sulfur, smoke) out. The volume of air moved by these systems is dependent on the size of the show area. These systems may be controlled directly by the show control system or they may be part of the building facility. In either case, this environmental monitoring element must have the the capability of transmitting a “flow OK” signal to the fire system processor. Many shows require constant ventilation.
Finally, it is not enough to just monitor all of these devices and stop the show when an overlimit condition is detected. What if a sensor fails in a state that indicates that conditions are safe? If the sensing system is important, then it is important to know that sensing system is working correctly. Sensors must be routinely validated. For example, if a certain temperature shows an increase of 30 degrees at the midpoint of every show, then if this normal behavior is not observed, the sensor is marked as bad. The error is reported and the next show is disabled until the problem is addressed. Another approach is to periodically create an artificial overlimit condition while observing the resultant emergency stop. The system can be designed to disable the show if this test is not performed on schedule. Sensor validation is a critical aspect of fail-safe design.
Contributing to this article are Sr. Systems Analyst Dan Birket and Director of Projects Marcial Godoy, whose résumés of fire and effect control systems include Buccaneer Bay for Treasure Island at the Mirage, EFX for the MGM Grand Hotel Casino and Theme Park, Escape from Pompeii for Busch Gardens Williamsburg, the Viking Adventure Stunt Show for Wakayama Marina City in Japan, the Wild Wild Wild West Stunt Show for Universal Studios Florida, and Backdraft and the upcoming Waterworld Stunt Show for Universal Studios Hollywood.