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Alert: Truck-Mounted Mobile Cranes

  • ISSN: 1195-5228
  • Issued: June 1995
  • Content last reviewed: January 2011

Hazard Summary:

A construction accident investigated by Ministry of Labour officials involved the failure of a 22-ton truck-mounted mobile crane.

The failure appears to have begun at the inner bolts that secured the slewing ring (the gear assembly that rotates the boom assembly) to the crane's pedestal. These bolts had been improperly torqued, which led to bolt failure and, eventually, to the complete failure of the boom assembly.

On truck-mounted cranes, failure to make sure that the torque values on bolts are equal and as prescribed in the manufacturer's specification can result in uneven distribution of stresses on the mounting bolts. This can cause bolt failure, which will ultimately allow the crane assembly to come off the truck chassis.

Required Action:

  • Mobile cranes should be inspected to make sure that each fastener is of the size and grade specified by the manufacturer.
  • The fasteners must be torqued, to the values set by the manufacturer, with a torque wrench that is properly calibrated at intervals not greater than those specified by the manufacturer.
  • Owners, suppliers and operators of mobile cranes must observe the precautions outlined in the manufacturer's maintenance and repair manual.

For additional information, please call the Ministry of Labour Health & Safety Contact Centre.

This Ministry of Labour Alert has no legal effect and does not constitute and is not a substitute for legal advice. If you require specific assistance with respect to the interpretation of a legislative provision and its potential application to you please contact your legal counsel.

Remember that while complying with occupational health and safety laws, you are also required to comply with applicable environmental laws.

Please photocopy Ministry of Labour Alerts, distribute them widely and post them where people will see them.