04.03.2009

SafeWork SA issues tower crane safety alert

SafeWork SA - South Australia's Occupational Health and Safety (OHS) agency - has issued a safety alert warning owners, employers and suppliers of Liebherr 200 HC tower cranes to closely inspect, maintain and monitor the gearboxes and hoist tolerances of the equipment.

According to SafeWork SA, the safety alert was in response to a number of incidents involving Liebherr 200 HC tower cranes – the latest in Adelaide in August 2008 - in which the hoist drum goes into free fall. The incidents were caused by similar faults in the gearboxes.

Preliminary investigations of the hoist drive assembly exposed a broken output shaft (shaft 4), that is directly connected to the hoist drum. The hoist brake on this type of crane is located on reduction shaft 2.
Please register to see all images

Gearboxes need to be checked

When shaft failure occurs with this design of hoist gearbox, the hoist brake will be ineffective, allowing the crane’s load to free fall. Further investigation indicated that metal fatigue appears to have occurred, possibly due to a misalignment of the output shaft with the hoist drum.

SafeWork SA says the gearbox failures cannot be predicted by observing the gearbox in operation. Therefore, owners, employers and suppliers need to have a scheduled strip down, inspection and non-destructive testing programme for the gearbox shafts and bearings.

Additionally, owners need to immediately check the alignment of the output shaft with the hoist drum shaft, to the manufacturer’s specifications. This must include bearing alignment and condition, and fastener integrity.
If the alignment is out of tolerance, the gearbox must be removed, stripped down, and tested in a non-destructive manner for cracks.