A new Safety Alert was published on WorkCover Queensland (Australia) December 22, 2015, following a fatal accident involving a mobile crane. The safety alert information matches what DICA advocates and advises users of outrigger enabled equipment around the world to be aware of and know. In particular, the following sentence is important to understand and apply to daily operations”
“Manufacturers and/or their agents in Queensland have a duty to supply information on any conditions necessary to ensure the plant is safe, this includes information on the loads imposed on the ground by outriggers and wheels.”
Accidents like these are what DICA is in the business of helping prevent. Our part, as the manufacturer, is to provide outrigger pads and crane pads that support and stabilize, and guidance as to their use and limitations (please see our safe pad handling and top 10 tips for a safe crane setup pages for more information on guidance and usage). Ultimately, it is the users responsibility to know what they need in specific situations to prevent accidents from occurring.
For assistance with specific questions or needs on this topic, please contact our fitting specialist team at 800-610-3422.
Below are additional excerpts from the Safety Alert. This information can be viewed in it’s entirety at WorkCover Queensland.
There can be several reasons why this type of incident occurs, but they often include one or more of the following factors:
- Soft ground – as a result of fill, ground water, reclaimed ground.
- Ground subsidence caused by nearby excavations and trenches, underground services and close proximity to creeks and other water courses.
- The area of timbers or other pads under the outrigger feet not being adequate for the ground conditions.
- Outrigger feet not being level or timber or pads being slippery, contributing to feet slipping off the pads.
- Uneven pressure being applied to the ground, such as when outrigger pads or timbers bend.
- An increased loading on the outrigger when the boom is directly above it or the boom is being loaded.
- Subsidence of the ground while the unit is being operated.
Soft ground can be disguised by a relatively thin crust on the surface where the ground has dried out, however, under the surface crust the ground is still soft. The hard crust can give the false perception that the ground has adequate bearing capacity, but when the load on the outrigger increases, one of the feet can suddenly punch through the crust and little can be done to stop the plant overturning.
Photograph 1 is an example of an outrigger pad sitting on the ground where a crust has formed without any indication that the ground is soft (i.e the pad has not sunk). Photograph 2 shows a view of an outrigger and pad that have punched through the crust deeply into the ground, causing the plant to overturn. Photographs 1 and 2 apply to the same incident scene.
The operating instructions from the mobile plant manufacturer should always be followed. Manufacturers and/or their agents in Queensland have a duty to supply information on any conditions necessary to ensure the plant is safe, this includes information on the loads imposed on the ground by outriggers and wheels. Where the information is no longer readily available, a competent person such as a geotechnical engineer should be engaged to assist in developing appropriate information on ground support for the unit.
It is often left to the operator of the mobile plant to decide on the type and size of timbers or pads provided under outrigger feet. Employers should provide operators with sufficient training instruction and supervision for them to make an informed decision as to what ground support is required.
Where there are any doubts or obvious signs that the ground may be suspect (i.e. soft ground, fill, underground services, etc), the operator should seek direction from their employer. There may be a need to engage the services of a competent person, such as a geotechnical engineer, to make an assessment of the ground and then to specify suitable control measures (i.e. ground preparation with crushed rock or the use of steel bog mats under the outrigger feet).
There is a particular need for caution where the ground is made up of fill. Indicators that the ground is fill include the presence of rubble (i.e. broken concrete, bricks, metal, timber) and that the ground doesn’t appear to be natural. Where the ground is fill, the operator should not assume that just because there are no obvious signs that the ground is soft that it is able to safely support the plant.
Continual monitoring of outriggers during operation is needed so that the unit can be stopped if the outrigger or pads show any signs of sinking.
Further information can be obtained from the following: