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Everyone Goes Home Safe: Furthering The Rigging Safety Discussion
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Rigging Risks Exposed (16 photos)
Do you have a rigging safety plan in place? Does your rigging exhibit any of these signs critical signs? Click through to find out!
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  Ken Deloria, Rigging

The bottom line is that a wide range of solutions need to be considered, adopted, and implemented.

The alternative, which I fear we’re close to, is the cancellation of all future outdoor events until safety guidelines are drafted by a government agency, and a method of policing the guidelines is put in place. That could take years.

So more than ever, I believe that we desperately need to establish a safety charter that governs all 50 of the United States.

If we don’t, it will be done for us and we probably won’t like the results.

Fault Conditions
Now let’s pick up where we left off last month: bridling and reeving. This is more than incidental knowledge because these two practices, while often misunderstood, are two of the most likely culprits for inadvertently setting up potential fault conditions.

Bridling doesn’t refer to horses, as you may have guessed. It refers to angular loads. When a load is suspended by two or more suspension points that are not directly in line with the mass of the load, the resultant rig is said to be bridled.

As you can see in Figure 1, the vector force of a bridle can create loads within the rigging parts that far exceed the actual load of the object itself. This does not mean that the 100-pound object used in these four examples will ever weigh more than 100 pounds. Of course not.

Figure 1: The vector force of a bridle can create loads within the rigging parts that far exceed the actual load of the object itself. (click to enlarge)

But the load on the rigging parts can greatly exceed 100 pounds due to the vector loading of those parts (which might be wire rope, Spansets, slings, chain, or other materials).

Because this is counterintuitive, I like to show the effect in real time by using three 30-pound fish scales - which I do when teaching classes in person. I’ll actually rig up a 10-pound load with a sliding spreader bar. I put one fish scale on the top-most hang point – which is always going to read 10 pounds – and then put the other two scales on each of the two bridle parts of the rigging.

Then, as the angles of the bridle are adjusted, everyone can see how the load on each of the bridle parts varies. It’s particularly dramatic when the angles are acute in either compression or expansion, and the fish scales quickly max out at 30 pounds - then suddenly the light bulb goes off!

As the bridle angle approaches 90 degrees (full horizontal) the loading on each bridle part mathematically approaches infinite. In real life that doesn’t happen because of material elasticity and other factors. But it’s worth knowing that the true force in a bridle part can exceed the actual mass of the suspended object by a very large factor.

Source: Live Sound International

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