Sling Tension & Lifter Compression Dangers
All Qualified Riggers and Crane professionals are taught to consider sling angles in tension calculations. But we are taught in a way that misses a critical point. Our concern is centered on the sling surviving the tension we are going to apply. But what if we are lifting isn’t ready for the compression that sling tension will deliver? That tension isn’t gravity. It’s pulling in. Is that job built wood box really up for thousands of more pounds of compression?
Common wood box on a construction job site. Can barely withstand 150 lbs of plywood leaning on it.
Crane Materials Bins Are A Calculated Risk
Crane Materials Bins that are rated for crane use have so many factors calculated in the design. Factors not calculated in job boxes. Compression and tension are calculated in all directions. One way this is controlled is with dedicated lifting points and maximum ratings. It controls for the tensions and compression involved. If you go to slings, on a box, these items can’t be controlled. Is it one sling? What’s the final angle? Is it it basketed? Choked? What’s the spread from other structural members? These are all unknown in a job built box. We can calculate the risk in our crane materials bins. Not only can we run the calculation and ensure it’s delivering the 3:1 safety factor, we can test for it. In our case under the German standard, we test to that 300%. If you lift it as we instruct you, then you’ll have your risk calculated instead of guessed at. Maybe one should take a guess at the method OSHA requires under 1926.251?
Rigging poses human error problems and unknown tensions.
Controls are Built Into Materials Handling Equipment
Materials Handling Equipment has controls built in. Four lifting points ensure the same forces happen over and over. If you have a bin that relies on a human to decide where the slings go on, does it end up uneven like the lift above? Do you have the potential for cutting since we no longer have the good D:d ratio? What’s the compression force involved on the bin if the sling is down under 45 degrees and the load is 2000 lbs? Can we effectively say 30% of the stress is in crush? If that’s the case, I would ask it this way… Would you stand this bin on it’s side on the ground and place a V8 motor on the side of it with your head in that bin? This is the sort of clarity of thought we need in crane and rigging decisions. How certain are you it can take 600 lbs of crush from the sides?
When do you end the service life of a job built box?
Standards Save Lives
The problem with not adhering to a standard isn’t limited to ratings or operations. It also comes down to what criteria do you use to decide safely when it’s time to stop using a bin? If you have wood bins that are banded for rigidity, does anyone say “corrosion” is a rejection criteria? Does anyone say dry rot is a reason to remove them? Or do you run them until you see a failure and then reassess? Is Jimmy at the yard the final arbiter of safe?
When you have a standard, it’s overseen by experts in the field with hundreds of combined years of experience. They gather to review the data and combine their experiences with setting the standards. Seeing these makeshift load containers has forced their hand in updating ASME B30.20 2025 to adopt Load Containers under their standard. Now we have a consensus standard that rejects wood boxes. No more plastic boxes. OSHA and the states haven’t advised anyone to change quite yet. But let’s be clear. If it’s in the ASME now and it’s released, any incident after this would consider the ASME and the General Duty Clause. Do you know it’s a hazard, or should you have known that it was a hazard to lift the wood bin that failed structurally? If the answer is yes, then they will cite you and it becomes a headache. We can prevent the headache. And more importantly, our work saves lives.
If you are ready for professional and efficient load container, we’ll be ready to help.
Let’s prevent this sort of accident together with good engineering practices.
