Mobile Tower Crane
Crashes To Ground

During 1997 a 36-year-old employee for a crane service company was killed while charging a battery on top of a portable tower crane. The crane (30-ton capacity, built in 1979) was set up at a wind farm, to assemble a large wind turbine. It was positioned adjacent to a 140-foot metal windmill column, and its outriggers were extended. The 2-man crew carried out a routine compaction procedure to hydraulically compress dirt under each outrigger, then inserted railroad ties and other 4x4 timbers. Both men were certified union operators. The length of each outrigger was 91/2 feet, making the distance between outriggers ~27 feet. The men were placing a 20-ton generator on top of the windmill column while workers from the windmill company were inside the column ready to attach the generator. The victim was working on top of the crane platform, fixing the diesel-powered winch engine, which had recently stalled. Suddenly, in a shower of hydraulic oil, one outrigger slid off its 4 x 4 wooden footing, and the entire tower crane, extended to its maximum height of ~180 feet, fell away from the windmill and crashed in a cornfield, carrying the 20-ton generator and worker with it. The man clung to the crane and was killed instantly when he hit the ground. The outrigger that failed was setting on fresh, packed dirt immediately adjacent to the new concrete footing for the windmill column. It is assumed this soil caved in allowing the outrigger to slide off its base. There was no wind that day.

1. Tower cranes must be set up with extreme care--all outriggers must be on solid ground!

—Improper setup of mobile tower cranes results in >50% of crane accidents.
—Sudden ground shifting can lead to disastrous results, as in this case.
—Both adjustable outriggers should have been placed on solid, undisturbed soil.

2. Workers must be diligent to regularly check and re-check alignment of crane equipment.

—As work progressed, the extra weight of the generator may have shifted the crane.
—With heavy loads alignment is more critical, and should be frequently checked.

3. Additional means to anchor or secure portable tower cranes should be considered.

—Simple guy wires could have provided significant lateral stability to this crane.
—In certain situations, however, they may create additional hazards at the worksite.