Worksafe BC said when a tower crane operator had just finished hoisting formwork from the upper level of a concrete residential high-rise to its first level, and was hoisting the load block while advancing the trolley toward the mast, the empty hook, load block and rigging chains (about 454kg altogether) plummeted to the ground, with the load line spooling around them.

No workers were injured, but several were working in close proximity to the falling equipment.

Inspection of the hoisting gear box showed that a gear has broken in half during operation. Lab tests showed that the gear was made of defective metal and prone to cracking, breaking down, and failing during operation.

“Other tower crane gear boxes have failed, most recently during a list in Alberta in fall 2015. In this case, regular and thorough gear box inspections could have identified gears needing repair and replacement. Such inspections are key to preventing crane equipment collapses and serious or fatal injuries,” Worksafe BC said.

Worksafe BC outlined a number of tips for safe work practices, including the use of X-rays or magnetic particle testing to detect hidden flaws.