Description of Driving Event:
During a crane disassembly, a cable sling broke, dropping a 10 ton crane counterweight. The crane crew was removing the front counterweight from the crane to place it on a flat bed trailer when the mishap occurred. The sling used was a rusty, 4 leg, 5/8 inch diameter cable about 15 feet long. Only two legs were used during this lifting operation. The investigating committee found that calculations made from a standard table published by U.S. Steel showed that the allowable working load for a new cable of this size using 2 legs was only 5.28 tons. The crane operators, based on their experience and intuition, grossly underestimated the strength of the sling.
Lesson(s) Learned:
Improper choice of lifting slings can occur if only intuition obtained by experience is used.
Recommendation(s):
Instruct crane operators to use calculations made from standard ANSI publications to determine safe sling working loads.
Evidence of Recurrence Control Effectiveness:
N/A
Documents Related to Lesson:
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Mission Directorate(s):
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