Hazard, Keefe & Leane Engineering, Inc. 
Formerly Hazard Engineering 1974 - 1999

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Crane Collapse

 

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Overall View of Accident Site of Crane Collapse

A wire-rope sling that was supporting a mast, which was being removed from a crane, broke causing the mast to fall to the ground as strike a second crane. Our investigation revealed that the mast was being removed from the crane by means of third crane. The white colored mast was attached to the load hook of the third crane with the wire rope sling. That hook was not equipped with a safety catch, so that the sling had to remain in tension or it could have slipped off the hook. The mast was rotated to a vertical position by means of the third crane. At that point the mast was extending vertically upward from a crawler of the crane being disassembled, and was being supported only by the sling and the third crane. The third crane then began to creep forward, when the sling broke and the mast toppled to the ground, striking the second (red colored) crane. The lifting capacity of the third crane was 300 tons (600,000 pounds) and the weight of the mast and crawler of the crane being disassembled was approximately 270,000 pounds. As a result, the third crane was capable of picking up the entire mast and crawler of the crane being disassembled. The sling was rated at approximately 80,000 pounds with a safety factor of 5, so that its breaking strength would have been approximately 400,000 pounds. However, a detailed examination of the sling revealed that it was not in good condition prior to the occurrence. The condition of the sling would have reduced its breaking strength. Consequently, as the mast was being moved, and was vertical, the load applied to that sling evidently exceeded its breaking strength, causing it to break and release the mast.

 

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