From the desk of ETC Technical Service Manager David North:
A Wisconsin-based rigging accident
Okay, so now I have your attention.
Last winter, a nearby ski hill [we have no mountains in WI], suffered a frightening accident that rigging-equipment designers, rigging specifiers and rigging operators should all take note of, as it applies directly to what we do every day. Harvey Sweet, senior technical product manager, one of several resident rigging specialists and a key member of the ESTA Standards Committee on Rigging had the following comments on the situation:
AN ACCIDENT IN WISCONSIN
The good news is that the accident did not involve theatrical rigging equipment. The bad news is that at least 14 people were injured.
A ski lift was in use during the Christmas holiday in 2009, when suddenly the lift stopped moving forward and quickly reversed, gaining speed. People on the lift were rapidly dragged downhill and eventually fell off of the lift or were bruised and injured by lift chairs slamming into them as the chairs stacked up at the bottom of the ski lift system.
What happened and why is this important to stage rigging?
The gear box on the lift motor sheared its teeth and could no longer move the load. The load brake that should have stopped the hoist was on the power input side of the motor/gear box and could not control the load because the brake was dependent upon a functional gear box to transmit power to the moving load.
This is a cautionary tale for power hoist rigging for the theater.
When a load is suspended above the stage and the machinery fails, the equipment should be designed to prevent the kind of accident that occurred with this ski lift.
Placing a load brake on the hoist so that it directly controls the motor output side of the machine (and its load) will prevent a failure in the gear box or motor from causing scenery or any other lifted load from falling uncontrolled out of the stage loft. Short form: machines with load brakes on the output shaft of a stage power hoist system are safer than machines that control the load through the motor or gearbox.
There are several lessons to be learned here.
1. The lift had an inadequately designed and maintained load-side brake, independent of the viability of the gearbox. Lesson: Hoist products should have a load brake mounted to the output shaft of the gearbox.
2. The lift was to have had a daily and weekly inspection of safety devices, which that day had only partially been completed and had rarely been performed previously. Also, no training records were available to verify who was trained on what procedures. Lesson: Have established procedures for operating stage machinery, have qualified people following those procedures, and have documentation of training on file.
3. Additional safety equipment had been suggested on a yearly inspection and had not been installed. Lesson: Get yearly inspections and follow the recommendations or shut down the equipment until such time as they can be followed.
Imagine the sinking and horrific feeling that dozens of people had as the machinery they relied upon reversed direction without warning.
Harvey has some other tasty tidbits of advice, standards and policy on rigging that we'll get to in the coming months. Also look over the Prodigy webpages to see how we've taken care of that fear factor. http://www.etcrigging.com/