Written by Troy Reit
Do a quick search for rigging failures and you’ll be amazed! There are a lot of people who think they know what they’re doing, but don’t. The really scary part is that they didn’t know what they didn’t know, and in some cases, their ignorance has cost people their lives.
In my 25+ years as an installer and production guy, I’ve seen some pretty scary rigging “techniques” where well-meaning people have done their best but fail to comprehend the forces at work, the tools for the job, or just don’t have a proper respect for the task they’re undertaking. Here are a few of my favorite examples:
- I was doing some consultation in the chapel of a prestigious university when I noticed the speaker hang. The speakers were suspended from the ceiling with decorative chain and hooks, like you’d use to create art on a wall, not even worthy to hang a chandelier. The hooks had spread to the point that the small piece of metal holding the speaker up was level with the ground. Any small vibration (remember, this is a speaker) could have caused it to slip off and crash into the chairs below.
- While mixing a show in a local performing arts venue, I looked up at the lighting/video truss hung over the crowd in the center of the room. The 40’ span was made up of 10’ sticks of truss, and right in the middle the webbing didn’t line up (continue the pattern in the diagonals). Come to find out, it was also hung over an upright steel rib in the structural steel with wire rope and no burlap or other means of deflecting the sharp angle.
- I was in a conference facility recently to hang some projectors and screens. When I asked the venue manager how much I could hang from his trusses, he said, “A lot.” That was his official answer because he truly didn’t know, and he was the guy responsible for what and where shows were hanging in there. He justified his estimation by saying that nothing has fallen yet.
If those examples make perfect sense to you, then you may be well on your way to making good rigging decisions. If you don’t know why they’re bad examples, keep reading. Knowing enough to know that you don’t know enough is the best first step to safe rigging. My goal here is to help you understand some of the major pitfalls and get you to the point that you know how much you don’t know, as well as how to find people that can help.
Common Rigging Pitfalls
- It must be rated. Rigging materials are rated for a specific load. You might see something like WLL (Working Load Limit) stamped on a piece of hardware, which means that it is rated to hold that amount of weight. That’s typically at a safety factor of 5:1 or 8:1, meaning that it will break at 5 or 8 times the WLL. That doesn’t mean you can hang 5 or 8 times what it says, but that it has been overbuilt to provide an extra layer of safety when using it at the rated capacity. Unknown loads, shock loads or movement (dynamic loads) can change the actual load, and the safety factor takes that into consideration. If something isn’t rated, then it can’t be used to rig with. Decorative chain, dog chain, non-forged eye bolts (where there’s a gap in the eye), or anything that is not installed according to the manufacturer’s specifications have no rating. This also applies to building structure. If you’re hanging things in a building, either the building has to have plans that specify that the structure will hold it, or you need a stamped engineering drawing saying that it can be installed the way you plan to.
- Equipment must be designed to hang. I can’t tell you how many times I’ve seen speakers with lag eyes screwed into their particle board exterior and hung over people. If the device is not designed by the manufacturer, and equipped with a specified means for hanging it, then you can’t hang it! There are many parts of a speaker box that are not structurally sound, and a lag bolt or eye screwed into wood has no rating (other than shear) because of the variability of the composition of the wood. Even if you drill a hole in a box and put a bolt all the way through it, you can’t guarantee that the speaker enclosure is solid enough in that one spot to hold the entire weight. Handles of speakers are not meant for flying, but for carrying, so they also can’t be trusted as rigging points.
- Bends matter. Tying a simple overhand knot in a rope reduces its strength by 50%. Bending a piece of wire rope, even to wrap it around something, reduces its strength and at a small enough bend radius, its strength drops to zero. As a rule of thumb, the bend around the thimble of a piece of wire rope is the minimum safe bend for that rope. Wrapping wire rope around a piece of structural steel requires that a material be placed between the two to keep the bend radius from approaching 90°.
- Devices have specific uses. Crosby Clips are a common way to secure wire rope, but did you know that there is a correct and incorrect way to install them? They’re built to bite into the wire rope so they have to be installed correctly or they will derate the load capacity of the wire rope. There are rules with shackles, too, governing where loads can be placed, how many, and even the orientation of the shackle to the load. Even sticks of truss have rules. When assembled, the diagonal members must continue the pattern from one stick to the next or all load rating drops to zero. There aren’t a lot of different tools in the riggers arsenal, but each one is designed for specific purposes and may only be used according to how it was designed or all bets on load capabilities are off.
- Moving a load increases forces. If you have a point rated to hold 200lbs and you have a 150lb load, how do you get it up there? Simple, right? Hang a pulley off the point and pull it up with a rope? Wrong. The load itself applies 150lbs to the point (because that’s what it weighs) and to pull it up, you have to apply an additional 150lbs to the same point for a total effective load of 300lbs. More than that, rope stretches, so the actual force may exceed 300lbs as you’re pulling. When loads move, the act of starting and stopping those loads applies additional forces called dynamic loads. You see the same thing when loads are moving while hung, like acrobats on a trapeze. This is why all gear involved in flying people requires a 10:1 safety factor even after we’ve taken the dynamic loads into consideration. When they move unexpectedly, such as free-fall or jerky motion, the dynamic loads can increase exponentially, even within a few inches of movement. We call that a shock load. This is why it’s important to check every connection and make sure it’s solid. An improperly loaded shackle that suddenly shifts under load can create enough shock load to bring the entire rig down.
- Inspections are mandated by law. Performing arts venues (that includes schools and churches) are required to do annual rigging inspections, and the new ANSI standard for chain hoists require an annual inspection with load testing. If you don’t follow these standards, it is considered criminal negligence. Performing arts venues should also do annual training on rigging equipment and techniques to improve and maintain a safe working environment. There are lots of classes available and a few organizations dedicated to improving safety in the industry through training and certification.
Any surprises? If you have a load in the air right now where you know you’ve violated even one of these principles, you have a legal obligation to correct it. Do not try to take it down on your own, which could increase the risk, but reach out to a qualified rigger to get it inspected and develop a plan to make it safe. Even equipment that has been hanging for years with no incident should be corrected as soon as possible. Just because it hasn’t fallen yet doesn’t mean it can’t or won’t. It may be as simple as taking pictures and sending them to an engineer who can provide a stamped drawing.
I know what you’re thinking: You don’t have the budget to take care of it right now. Compare the cost of fixing it now to the cost of cleaning it up when something fails. If you think it’s expensive now, multiply that cost by a factor of 1000 and you’ll be in the right ballpark. Your choice.
Who do you call? Companies that do this kind of stuff regularly are a good place to start. If you’re hanging audio gear, check with a audio installation company. These companies work with riggers and engineers all the time. You can also look for an ETCP Certified Rigger. The Entertainment Technician Certification Program was developed to test and demonstrate that a technician knows what he or she is doing, so finding one to help is a big step in the right direction. You can search for ETCP Certified Technicians at http://etcp.esta.org/findtechnicians/search.php.
There is no one that knows everything about rigging, but by collaborating with professionals that do it for a living, you can make your venue significantly safer. Even seasoned riggers will double-check their work and bring in other professionals in their field to make sure what they’re doing is safe. It is never a bad idea to ask questions.