Crane drop incident

Purpose

The purpose of this safety alert is to remind duty holders of the need to prepare and follow detailed lifting procedures; especially when using synthetic lifting slings, slings in basket hitch configuration or when carrying out a single lift with more than one crane.

This alert does not detail the specific causes of this crane drop incident.

While this alert specifically applies to lifting a mobile crane by slinging its outriggers, the principles can be applied to lifting other loads.

Background

A large mobile crane weighing approximately 92 tonnes was dropped at a wharf in Queensland while being loaded onto a ship (refer Figure 1). The crane was dropped partly on the ship and partly on the wharf, causing significant property damage. It appears the crane was dropped when the lifting slings, that passed around the crane’s outriggers, failed.

_{Photograph 1 - Crane dropped on ship and wharf}

Synthetic lifting slings are versatile and are frequently used due to their high strength to weight ratio, along with being much less likely to damage the load being lifted. However, synthetic slings are more prone to damage and failure than chain slings of an equivalent rated lifting capacity. In particular, synthetic slings are much more prone to being cut around an edge of the load being lifted in comparison to chain slings.

The Tower and Mobile Crane Codes of Practice both caution against the use of basket hitch unless the slings are prevented from moving along the load to be lifted (i.e., to prevent the load falling). It is acknowledged that when lifting a mobile crane, the use of basket hitch could be used with the slings passing around the crane’s outrigger beams, unless the manufacturer of the crane being lifted states that this should not be done.

Contributing factors that can cause loads falling

A range of factors that can lead to loads falling.

In general, synthetic lifting slings can fail due to a whole range of causes including the following:

1. Slings not having adequate capacity for the slinging method being used,
2. Sling protection not provided,
3. Sling protection not being thick or strong enough to adequately cushion a sling around the edge of the load,
4. Slings being cut because the sling protection moves and/or the sling moves off the protection and is cut on the edge of the load,
5. The lifted load not being correctly balanced,
6. Damaged or otherwise defective slings, and
7. Slings not being manufactured and proof tested to a reputable design standard.

Action required

Lifting procedures

The more complex a load to be lifted the greater the need for specific documented lifting procedures (e.g., a lift plan) to be prepared and followed. Where one party is involved in developing the lift plan and another is carrying out the lift, it is important that the lift plan is agreed on by both parties and then strictly followed. Where a change is to be made to the lift, this should never be done “on the run” or without two-way consultation between both parties.

Sometimes it may be necessary to make changes to the initially agreed lift plan, but an additional risk assessment process is to be followed to identify and control any additional hazards that may arise from changing the lift plan.

Slinging method

The slinging set up for lifting a mobile crane should follow the instructions of the crane manufacturer or a suitably qualified professional engineer.

Wherever slings are used to lift a mobile crane it is very important that the slinging set up and crane configuration does not cause the sling to move off the sling protector and/or along the outrigger. This is more likely to occur when a basket hitch is used but can sometimes still occur when a choke hitch is used. A sling is more likely to move during a dual crane lift as non-vertical loads are applied to the sling. A small amount of non-vertical loading can be applied to a basket hitch sling perpendicular (at right angles to) to the outrigger. However, no horizontal loading should be applied along the length of the outrigger as this can cause a cutting action to be applied to the sling and/or may cause the sling being pulled away from the sling protection on the outrigger.

Where basket hitch is used, the sling protection should always be secured in place (e.g., by strapping), so that it cannot move out of position under any circumstances. Consider using sling protection with a lip that prevents the sling from sliding off the protection and being cut.

Where a choke hitch is used, the capacity of the lifting slings will be reduced and the lift plan needs to identify and recognise this factor. Where choke hitch is used, sling protection needs to be provided both around the top and bottom corners of a square or rectangular load.

Ensure that any reductions in lift capacities are calculated (e.g., angle or reeve factors) prior to the lift commencing, with the lift plan identifying and recognising these factors. Information on lifting capacity reductions for slings is provided in the relevant Australian Standard for the sling type being used.

Crane selection and control of the lift

Where wharf cranes exist and have adequate lifting capacity, they are generally a safer option than ship-based cranes to lift large and complex loads as they will not be affected by the ship’s movement.

Lifts involving two or more cranes nearly always introduce additional hazards compared to a single crane lift. While a single crane may not have adequate capacity to lift a single load, more can go wrong on a multiple crane lift and more stringent risk control measures generally need to be applied. Where multiple cranes are used, the lifting capacity of each crane also needs to be increased (refer section 11.3 of the Mobile crane Code of Practice 2024 (PDF, 2.29 MB) for further information).

While it is the aim to keep the hoist ropes on a multiple crane lift vertical, in reality, this is extremely difficult to do. For any multiple crane lift, the slinging system needs to allow for at least some unexpected horizontal loads to be applied to the lifting slings. These unexpected loads may necessitate the use of choke hitches instead of basket hitches.

In response to the greater risk associated with multiple crane lifts, an Intermediate or Advanced Rigger must be in control of the lift in accordance with the Work Health and Safety Regulation 2011. The Rigger should also have suitable experience. Prior to operating a crane involved in a multiple crane lift, it is advisable for a crane operator to receive training on a relatively straightforward load to be lifted. Crane operators are also required to follow all instructions of the Intermediate Rigger in charge of the lift. Communication between the rigger and crane operators should be carried out using two-way radios on a dedicated radio frequency to prevent interference.