Rigging, Signaling, and Load Control
Rigging, Signaling, and Load Control
This domain tests the connection between the crane and the load: sling and hardware selection, hitch type, load weight and center of gravity, tag lines, signalperson duties, and communication. The exam expects you to calculate sling tension and to control the load, not just hook it.
Core rules
- A qualified rigger selects slings and hardware for the load, environment, and hitch. Inspect for broken wires, cuts, burns, distorted hardware, and missing labels; remove defective gear from service.
- Know the load weight and center of gravity. Use a spreader or multiple legs to keep the load level and to avoid crushing or slipping.
- Sling tension increases as the angle from horizontal decreases. For a two-leg bridle, each leg tension = (load weight / 2) ÷ sin(angle from horizontal). Do not use the angle from vertical by mistake.
- Protect slings from sharp edges with softeners. Never knot a sling or shorten it with a load-bearing hitch unless the manufacturer permits it.
- Use standard hand signals or a clear radio channel. One designated signalperson; anyone may give an emergency stop. The operator must stop when communication is lost.
- Control the load with tag lines where practical, but keep people out from under and away from the swing path.
Worked example
A 2,000 kg load is lifted with a two-leg bridle, each leg 60° from horizontal. Each leg tension = (2,000 / 2) ÷ sin 60° = 1,000 ÷ 0.866 = 1,155 kg. If the legs were 30° from horizontal, each would be 2,000 kg. Reasoning: a flatter sling angle multiplies tension, so the sling and hardware must be rated for leg tension, not half the load.
Traps
- Measuring the sling angle from vertical.
- Assuming a 2,000 kg rated sling is fine because the load is 2,000 kg total.
- Signaling with gloves or from behind the operator.
- Using a tag line to correct a load that is already unsafe.
- Hooking below the center of gravity.