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Short Summary
Main recommendation: Use a sling as the only connection between a crane hook and a load, and calculate its rated capacity carefully, since most rigging failures come from overloading slings due to uneven load distribution, sling angle, or abrasion. The video explains that rigging errors, not crane structural failures, can cause serious lifting accidents, including a 2008 New York collapse that killed six workers and one civilian.
Key Points
- Rigging means all the steps used to attach a load to a crane so it can be suspended and moved, and it is prone to human error.
- The tag on a rated sling shows its capacity for the three basic hitches: vertical, basket, and choker. A basket hitch roughly doubles capacity because two legs hold the load, while a choker hitch has less capacity due to stress at the choke point.
- Uneven center of gravity can overload individual slings. Dividing total weight by sling count is only safe when attachment points are equidistant from the load's center of gravity.
- Shallow sling angles greatly increase tension. At a 30-degree angle from horizontal, each sling feels roughly double the force of a vertical sling, because horizontal components must be canceled by opposing slings.
- Synthetic slings are vulnerable to abrasion and melting from friction when sliding under high contact pressure, so they must be protected from sharp edges.
Details Worth Noting
- Concrete instructions:
- Stop and do not lift if a sling has no load rating tag. Every rigging sling, whether synthetic, wire rope, or chain, must have one.
- Choose the hitch by load type: use a vertical hitch when the load has a hook or shackle attachment, a basket hitch when the load has no attachment point and is balanced and easy to control, and a choker hitch when a snug grasp is needed, accepting its lower rating.
- For multi-sling lifts, find the load's center of gravity, calculate each sling's share of the load based on its horizontal distance from that point, and confirm each sling can handle its portion.
- Secure a load before lifting if it could slide when one sling stretches more than the others.
- When sling angles are not vertical, reduce capacity according to the angle using the video's formula. The video notes the formula is simple but requires knowing when to apply it.
- Protect synthetic slings from sharp edges, corners, and burrs.
- Use a spreader bar to distribute the lifting force among attachment points that are farther apart, reducing sling angle, increasing capacity, and reducing sliding and abrasion.
- In the video's demonstration, two slings holding a steel bar read about 800 grams each when vertical, but about 1200 grams each (roughly 50 percent more) when their tops were brought together so the tops touched, simulating a shallow angle.
- The video states it is not a training resource and that rigging is a dangerous job requiring much more study before involvement in heavy lifts. The companion video covers crane failures above the hook.
Bottom Line
Most crane lifting accidents discussed here stem from misjudging how load weight, angle, and friction affect a sling's real capacity, so rigging requires careful calculation and professional training before any heavy lift.
