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
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?
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 article: Special Forestry Hazard Alert Bulletin: Beware the danger zone