Large-scale stage productions frequently utilize mechanical equipment - such as the stage lifts often seen at concerts-to enhance the visual impact of the performance. While the use of such large-scale machinery undoubtedly lends a sense of grandeur and magnificence to a show, the inherent safety hazards associated with it cannot be overlooked. Naturally, whenever feasible, hazards should be eliminated or risks mitigated through the application of "inherently safe" design principles.
How, then, can the risks posed by stage machinery be reduced? Solutions can be found in both the mechanical design and operational techniques. Examples include designing protective guards for shear points, specifying steel wire ropes with a safety factor exceeding 10, or designing gearboxes with a service life of 400 hours and a torque capacity of twice the characteristic load. These methods serve to permanently eliminate hazards or significantly reduce risks. Consequently, when designing a hoist intended to lift a 500 kg load, one could theoretically design it to handle a 1000 kg capacity to mitigate previously identified risks. However, for economic reasons, designers rarely adopt this approach. Furthermore, technical constraints play a role: consider, for instance, how the structural design of the building itself would need to be altered if every rigging batten were designed to handle a 1000 kg load instead of the required 500 kg.
If inherently safe design methods are not feasible - or if they fail to fully reduce risks to an acceptable level - then technical protective devices or alternative protective solutions must be introduced to further mitigate those risks. Typically, this involves incorporating specific safety functions into the control system. In certain examples provided by Waagner-Biro Luxembourg Stage Systems (hereinafter referred to as "Waagner"), a pressure sensor is installed to continuously monitor the load and verify the safety of the equipment's lifting operations. "Waagner" designates this overload detection capability as a specific safety function. The most common safety function is the limit switch, which can halt equipment operation both within the normal range of travel and during emergency situations, thereby providing a user-friendly and reliable method for ensuring overall safety. However, none of these solutions can completely eliminate hazards; they merely reduce the *probability* of a hazardous event occurring, contingent upon the technical solution functioning correctly. This raises a critical question: how high must the reliability of these safety functions actually be?
If neither inherently safe design measures nor technical solutions - or economically viable alternatives - are available to mitigate risks, then the only remaining option is to simply provide users and operators of the equipment with information regarding the *residual risks* that remain. This typically involves posting warning signs or providing detailed operating instructions (stipulating, for instance, that the equipment may only be operated by trained personnel). Of course, this method of risk reduction is the most fragile and should be employed only when no other options are available.