What happened?
On July 8, 2015, at 0857 local time, the bulk carrier Asia Zircon II was offloading a cargo of wind turbine towers in the Port of Galveston, Texas, when the lifting wire rope for one of the ship’s deck cranes parted while hoisting a tower section out of the cargo hold. The wire failure caused the tower to fall back into the hold, damaging the tower and other tower sections still in there. Two of the five longshoremen inside the cargo hold suffered non-life-threatening injuries. No pollution was reported. Damage was estimated to exceed $1.5 million.
The Asia Zircon II had 84 wind turbine tower sections on board and cargo hold no. 4 held 10 base sections weighing 66 metric tons each. The longshoremen were offloading these base sections when a “popping” sound occurred. Recognizing that the sound meant a wire rope splitting, a foreman shouted to the longshoremen in the cargo hold to “hit the deck!” Because the longshoremen were between sections of the tower bases, which absorbed the impact from the falling cargo, they were protected. Numerous items of debris were ejected from the tower base sections as a result of the impact and the compression forces from the falling section.
The debris was mostly broken pieces of metal, sheered nuts and bolts, parts of the towers’ footings, and securing structures. One of the longshoremen in the cargo hold reported that he was hit by the flying debris; another said he was injured while taking cover. Both injuries were minor.
Post-accident Examination
It was found that the incident was precipitated by the failure of the wire rope from the vessel’s crane no. 4. Pieces of the failed wire rope and the cargo slings used in the lift revealed, in part, that the four sections of the failed wire rope (from the drum, the free end, the failure end, and the shackle end) showed signs of inadequate lubrication; the lubricant was not distributed down into the inner wire surfaces. The lack of lubrication caused excessive wear on the wire contact surfaces, particularly those not near the surface where the lubricant was applied. Cracks propagated out from the areas of excessive wear into the individual wire strands, creating stress concentrations and gradually reducing the load capacity of the rope.
The ship company’s SMS detailed maintenance and inspection procedures for crane wires, requiring pre-operation checks of lifting equipment before arrival in port. Investigators were informed that these checks were conducted before arrival in port at about the same time as wire rope greasing was ordered, but no documentation identified which equipment and components were checked. The SMS manual also highlighted, “When lubricating crane wires, it is necessary to remove old grease and residue to inspect the strands, with particular attention to those areas of any wire which are not visible. . . . [It is] completely unsatisfactory to lubricate merely the [immediately visible and accessible] parts of the wire.”
The NTSB determined that the probable cause of the failure of the lifting wire rope of crane no. 4 on the bulk carrier Asia Zircon II was inadequate lubrication due to ineffective maintenance resulting in excessive wear of the wire rope.
Lessons To Takeback
Maintenance of Lifting Gear
- Inspection, maintenance, and management of wire ropes are essential to the prevention of accidents.
- A deteriorated wire rope directly affects the ability to safely and reliably handle loads up to the rated capacity of the crane.
- Crane operators, signalmen, riggers, safety observers, and crewmembers should adhere to manufacturer operating guidelines, design limitations, safety precautions, and inspection and maintenance procedures.
Crane Operations
Workers participating in crane operations should ensure that they remain in a safe area during a hoist. Entering the drop zone while the hoist is in progress puts them at risk.
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Source: NTSB
