In April 2021, a mobile crane tipped over at a residential construction site falling onto three houses. No one was injured. The mobile crane was a hydraulic slewing crane with a maximum rated capacity of 80 tonnes.
Early investigations indicate the crane was to be used to lift a water tank into position at one house, when for reasons yet to be established it tipped over and the boom struck the houses. Investigations are continuing.
These findings are not yet confirmed, and investigations are continuing into the exact cause.
Stability is one of the most important safety considerations for mobile cranes. Issues include:
- the stabilising moment of the crane—the crane counterweight generally provides the primary stabilising moment
- the overturning moment applied by the suspended load, the part of the crane boom that is outside the tipping point of the crane, the crane hook and lifting gear
- the ground conditions and means of supporting the outrigger pads or the crane tyres
- the slope of the ground—both side slope and slope in line with the crane
- wind conditions—this will vary depending on the size and shape of the suspended load and crane boom
- dynamic factors caused by the crane motion and the load (e.g. for boom movement, application of brakes, swaying of the load)
- rapid slewing.
Ways to manage health and safety
Taking steps to manage risks is a condition of doing business in Queensland. Effective risk management starts with a commitment to health and safety from those who manage the business. If an incident occurs, you'll need to show the regulator that you’ve used an effective risk management process. This responsibility is covered by your primary duty of care in the Work Health and Safety Act 2011.
Use the hierarchy of controls to help decide how to eliminate and reduce risks in your place of work. The hierarchy of controls ranks types of control methods from the highest level of protection and reliability to the lowest. It’s a step-by-step approach to eliminating or reducing risks. You must work through the hierarchy of controls when managing risks, with the aim of eliminating the hazard, which is the most effective control.
Possible control measures to prevent similar incidents
Planning and coordinating mobile crane operations
Planning for mobile crane operations should start as early as possible. This involves:
- consultation with people engaged in the work, such as the principal contractor or crane hirer, crane supplier, engineer and crane operator
- ensuring the type and number of mobile cranes selected suit the particular needs of the lift to be carried out
- determining the size of the crane crew by undertaking a risk assessment and implement appropriate controls, especially in relation to minimising the risk of collision between the crane and other plant, and loads contacting other structures, overhead powerlines or workers
- not siting a mobile crane until carefully considering if it:
- has adequate capacity to lift the load at the maximum radius
- could collide with other plant and structures at the workplace
- using a reliable method of signalling between the crane operator and dogger
- using documented lifting procedures to help to define responsibilities and approach the crane lift in a logical, systematic way. Safe work method statements must be prepared for a range of high risk construction work associated with cranes
- establishing exclusion zones around mobile cranes and adjoining areas to prevent people from entering the area. The size of the exclusion zone should be based on a written risk assessment. If the exclusion zone requires closure of a public footpath or roadway, approval must be obtained from the relevant authority.
- Manufacturers of mobile cranes should provide documented information on the maximum load applied by the outrigger foot to the ground for the different boom configurations supplied with the crane.
- Outriggers should be set up according to the manufacturer’s operating instructions for the specific type of mobile crane. If provided by the crane manufacturer, outrigger pins must be used to lock the outriggers in place. The outriggers should also be used to help level the crane.
- Timbers, pads, bog mats or other means of distributing the load should always be placed under the outriggers, irrespective of the ground conditions.
- Timbers, pads and bog mats should be of dimensions and materials as specified by the crane manufacturer. If the manufacturer has not provided this information, a competent person should specify the minimum size of the material to be used.
Ground conditions and crane support
Different ground types will have different ground bearing capacities. Factors to consider:
- Harder ground, such as rock, is capable of withstanding higher ground pressures than softer ground, such as dry sand.
- If there are different ground types, the poorer type should be used for determining the maximum ground pressure that can be applied when the crane is set up on outriggers.
- Examine nearby excavations or trenches at the site. Rock that extends far below the surface provides a good indication of the ground’s integrity. However, this will only provide a reasonable indication of the ground’s strength when the excavation is not too far from the crane.
Roles and responsibilities
Several people have different roles and responsibilities for crane stability:
- The crane operator:
- has the primary responsible for crane stability to ensure a crane will not overturn
- must have a comprehensive knowledge of the crane’s operating capabilities and be competent to carry out the lifting operation to ensure it does not overturn
- should be able to determine adequate ground conditions to support the crane setup to prevent the risk of it tipping.
- should carry out a visual inspection and functional test before each work shift commences, including inspecting and testing
- should have the final say about whether a lift should proceed.
- The crane manufacturer:
- must ensure that the crane complies with the strength and stability requirements of the design standard to which it has been manufactured
- should ensure instructions are provided that clearly show the operator the area and type of timbers or pads to be placed under the outrigger feet.
- A principal contractor or person conducting a business or undertaking:
- should supply the crane crew all information on the location of trenches, backfilled excavations and covered penetrations at the workplace
- should give the crane supplier any geo-technical reports on the bearing capacity of the ground.
- The crane owner:
- should ensure all safety features and operating aids on the crane are functioning correctly
- should supply enough timbers or pads with the crane to enable the operator to provide sufficient support under the outrigger feet.
- The dogger:
- is responsible for safely slinging the load and providing accurate directions to the crane operator on load movement to ensure crane stability
- communicates the weight of the load to the crane operator, where this is known, to help ensure the SWL of the crane is not exceeded
- calculates the SWL of the ropes, slings, chains and other lifting accessories to be used in the lift
- provides the crane operator with clear and accurate directions.
Information, training, and instruction for mobile crane operations should include:
- documented work procedures to be used in the setting up and safe operation of mobile crane activities. Safe work method statements must be prepared for a range of high risk construction work associated with cranes.
- documented familiarisation training for crane operators for the specific make and model of mobile crane
- methods for inspection and maintenance of mobile cranes
- knowledge of the crane manufacturer’s operation and service manuals
- only persons with the appropriate mobile crane licence class operate the mobile crane.
The control measures put in place should be reviewed regularly to make sure they work as planned.
- Mobile crane Code of Practice 2006 (PDF, 1.34 MB)
- Safe support of mobile plant guide (PDF, 3.42 MB)
- Alert - Support of mobile plant on outriggers
- How to manage work health and safety risks Code of Practice 2021 (PDF, 0.65 MB)
Have you been affected by a workplace fatality, illness or serious injury?
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