25 Million in the Mississippi River

During the load test of the ship unloader, on June 11, 1998, the crane tumbled into the Mississippi River.

Built in Slovenia and shipped to Louisiana on barges, the 9 million dollar ship-loading crane was finally assembled and being put through its final qualification testing. Placing a maximum load suspended by the boom and then trolley out to the farthest reaches of the boom would test the capacity for the crane. This was an extreme case that would qualify the crane as required by the standards for its intended use. As the load was almost to the end a large bang was heard and the crane tilted toward the river, back, and then fell over into the Mississippi with the operator still inside.

This ship-loading crane has an extendable boom with a hook/hoist and trolley for transferring heavy quantities of materials on and off of barges along the Mississippi. It runs along the shore, parallel to the river on wide railroad tracks. It was designed with rail clamps, which were very strong spring loaded brake shoes that would extend to contact the rails and stop any movement of the crane if power was lost.

SEAL’s role in this engineering investigation was to determine why the crane fell into the river and whether there were any contributing factors such as wind or other outside influences to cause the failure.

During the final test as the load was being trolleyed near the end of the boom, the trolley stopped moving.  This is because it reached a limit switch, which was installed to stop the load before it reached the end and so the trolley would not hit the hard stops.  In order to extend the travel to the end of the boom, the limit switch was bypassed by pressing the emergency stop button; this disabled the safety feature provided by the limit switch.  The testers were intending to inch the trolley manually to the end of the boom.

Apparently not much thought had gone into the plan for this test since as the stop button was pressed all power was cut to the crane and that activated the rail clamps. Since the crane was at its extreme limit, when the spring-loaded clamps slammed against the rail (the big bang) it lifted the landside wheels off of the rails. This set up a slow oscillation of the crane and suspended load which then tilted over and into the river. One of SEAL’s Engineers determined what really happened based on the examination of the recovered parts of the crane, the design of the crane, operating and control systems and the description of the sounds and actions of the crane provided by the surviving witnesses.