Support heavy machinery attachments when servicing – even when the power’s off

Friday, February 07, 2014

Hydraulics can fail – even in zero energy state 

WSN Special Forestry Hazard Bulletin: Beware machinery danger zone - please post and encourage discussion in your workplace 

WSN Bulletin spécial forestier : Gare à la zone de danger

What happened?

Mobile head of mechanical harvesting equipment on a winter's day in northern Ontario bush.

A worker and a maintenance contractor were in the process of changing a broken topper knife on a delimber. The machine was placed on level ground, booms extended slightly, mobile grab arms closed, and mobile head left in a raised position. The ignition was turned off, key removed, hydraulic shut-off arm raised, and the master switch was closed and locks applied. 

The maintenance contractor went for tools as the worker stood in front of the mobile head facing the machine. The boom suddenly dropped, the angle moving it forward toward the worker, knocking him over and pinning his legs under the mobile head. 

Why did it happen?

Worker legs pinned in snow under mobile head of equipment

Although the equipment power was shut off, the attachment had not been blocked or supported – in case of mechanical failure – to ensure that no movement could happen, i.e. a zero energy state. 

How could it have been prevented?

If an attachment can’t be lowered to the ground it must be blocked or supported to achieve a zero energy state. As well, in the case of a delimber, a chain attaching the mobile head to the stationary head must be applied. Use extreme caution while operating around logging machinery. 

Related articleSpecial Forestry Hazard Alert Bulletin: Beware the danger zone