The LMI Reading Was Taken With the Load Still on the Deck
A 60-ton all-terrain crane is lifting a skid-mounted pump from a flatbed trailer. The shipping papers list 9,800 lb, but the skid is packed with mud and an unmarked wooden crate is strapped to the top. The operator booms to a 43 ft radius, where the chart shows 11,200 lb. With the load still resting on the trailer deck, the load moment indicator reads 8,900 lb (79%), and the operator says, 'We have 21 percent left.' Wind is gusting 18 to 22 mph, and a 4 ft by 6 ft control panel on one side of the pump is not wrapped. The rigger wants to lift it a few feet, see how it hangs, and re-rig if it tips. A signal person is on the far side of the trailer, out of the operator's direct view, and wants to give hand signals. The crane was set up on mats that morning, and the LMI was checked at startup.
1. Evaluate the operator's 79% reading. Is the pick within capacity? Show the correct way to establish the load.
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No. The LMI is reading only the part of the weight the crane is carrying while the skid is still supported by the trailer deck. As the load breaks free, the reading will rise to the full gross load. The 79% figure is not the pick's capacity percentage.
Do the math from verified weights:
- Shipping weight: 9,800 lb
- Rigging: roughly 400 lb
- Gross: about 10,200 lb
- 10,200 / 11,200 = 91% of chart
That is already a high-percentage lift, and the weight is unverified: mud, water, and the unmarked crate could add several hundred pounds. At 10,800 lb gross the pick is at 96%. The correct sequence is to verify the weight (scale, load cell, or calculation), add all rigging, compare with the chart for the actual boom length and configuration, and only then make a trial lift of a few inches, after the load is fully free, to confirm the LMI reading. Never use a reading taken with the load on the deck.
2. What about the wind and the unwrapped control panel? How do they affect the lift, and what would you do?
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Wind and sail area are independent hazards the load chart does not solve. Load charts are based on still air or a manufacturer's stated wind limit; 20 mph is a common limit, and gusts of 22 mph already reach or exceed it. The 4 ft by 6 ft control panel (24 sq ft) acts as a sail: it increases the load's wind area, can rotate the load, and side-loads the boom in a way the chart does not account for.
Options:
- Suspend the lift until gusts are below the manufacturer's limit, measured at the boom tip, not the ground.
- If the manufacturer permits, reduce the sail area by wrapping or removing the panel and securing it.
- Use tag lines to control rotation, and keep personnel out of the fall zone.
I would not lift an unwrapped 24 sq ft panel in 22 mph gusts. The decision is the lift director's, not the rigger's.
3. The rigger wants to test-lift and 'see how it hangs,' and the signal person is out of the operator's view. How do you supervise the lift?
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Two separate supervision failures.
Signals: The operator must have a clear view of the load or be in continuous radio contact with one designated signal person. A signal person out of the operator's view giving hand signals is not acceptable. I would reposition the signal person or use radios on a dedicated channel, and stop the lift immediately if communication is lost.
The 'lift and see' plan: A load is not a test article. The correct order is verify the weight, verify the rigging and attachment points, check the wind, brief the crew, then lift a few inches only to confirm the load is fully free and the LMI agrees. If it tips after that, the rigging was wrong; the answer is to fix the rigging before the lift, not to experiment in the air.
I would stop the pick, verify the weight and rigging capacity, re-check wind, confirm one signal person, and re-brief before any load leaves the deck.