Panel axis is critical for single crane rotation

Background

A rigger recently sustained serious injuries when struck by shards of concrete that shattered from a precast panel which fell after being lifted from a semi-trailer. The semi-trailer was also extensively damaged.

This incident happened when both the auxiliary head sheave assembly (also known as the 'rooster') and its hoist rope failed catastrophically during an attempted single crane rotation of a 13.5m x 1.7m x 15 ton precast panel. WorkSafe's preliminary enquiries into the incident found:

• An erection design engineer (EDE) had not been engaged to plan the erection works.
• Safety critical EDE functions had not been assigned to or completed by another suitably competent person.
• Space to set-up the crane and unload panels was restricted due to narrow street width, power lines and adjacent structures.
• The panel delivery semi-trailer was unable to deliver the panels in-line with the crane's boom (due to the above space restrictions).
• Panels were delivered at right angles to the crane's boom.
• The panel's orientation in relation to the crane's boom resulted in 'side-loadings' to and collapse of the auxiliary head sheave assembly (see Figure 1), severing of the auxiliary hoist rope, and loss of the load.

Work involving lifting or hoisting precast panels is high risk construction work and has the potential to cause serious or fatal injuries to workers and members of the public in the vicinity of works.

Prevention measures

The builder should:

• Before the manufacture of precast elements, consult with all relevant persons involved in the construction process (eg the project design engineer (PDE), EDE (if independent of the PDE) and the erection contractor) to ensure there is agreement that the planned structure can be safely constructed in the manner proposed.
• Consider site specific factors and constraints (eg space restrictions) and whether it is necessary to change the size of proposed elements or use specialised or multiple cranes in order to complete the job safely.
• Ensure contractors are provided with safety-critical erection design information such as panel-specific rigging and bracing instructions and the erection sequence.

Contractors undertaking single crane, multiple hoist precast panel rotation should:

• Pre-inspect the work site and review the panel specifications to identify any factors or constraints that may impact on proposed panel rotations or selection of appropriate crane/s.
• Obtain safety-critical erection design information such as panel-specific rigging and bracing instructions and the erection sequence.
• Ensure crane operators and rigging crews are instructed and aware of the increased danger of equipment failure if the panel's main axis is not kept in-line with the boom throughout the rotation process; including the initial lift off truck (see Figure 2).
• Ensure the maximum rope angles on head sheave assemblies remain within the manufacturer's safe use specification, otherwise the lift should be treated as a designed lift (see AS 2550.1-2011 for guidance on designed lifts).
• If the auxiliary hoist rope is reeved for increased capacity, seek approval of such configuration and the capacity of the termination point (becket) from the crane's manufacturer or a suitably competent person (eg engineer).

When the panel's main axis is in-line with crane's boom, both hoist ropes are aligned with the sheaves and exert minimal side loadings (ensuring a safer lift).

If the panel's main axis is at right-angles to the crane's boom, the main and auxiliary hoist ropes may exert hazardous side-loadings to boom head sheaves.

Further guidance

The following publication provides additional guidance on the rotation of precast concrete panels:

• WorkSafe Victoria Industry Standard - Precast and tilt-up concrete for buildings

The following publication provides additional guidance on multiple hoist operation and designed lifts:

• AS 2550.1-2011 Cranes, hoists and winches - Safe use - General requirements.