A bolt projectile incident has resulted in a key recommendation for people undertaking maintenance on certain machines.
Two bolt heads sheared off from the outer casing of a final drive and became projectiles during the routine servicing of a Caterpillar D11T dozer at a Queensland coal mine, according to inspector of mines Pat Hurley.
The dozer was being relocated out of a workshop when the right-hand final drive locked up and subsequently failed, splitting the outer case.
The dozer locked as it began reversing and was unable to move forwards or backwards.
The operator jacked the machine up to see if it would rotate, and it was during this attempt to move the track backwards that the right final-side drive casing split. The bolt heads were ejected, travelling 4.6m before striking a nearby toolbox.
The technique to remove the plugs contributed to the incident, as the plug was struck prior to being loosened before being removed by an impact wrench.
The Resources Safety and Health Queensland Coal Inspectorate has identified defective magnetic plugs in some final drives and has been working with Hastings Deering to identify the part numbers and communicate the information to the industry.
The magnet in the defective plugs can seperate from the plug body due to insufficient crimping during their manufacture.
If the magnet separates when installed it can cause extensive component damage, which may cause the planetary retaining bolts to shear and become projectiles.
The key recommendation stemming from this incident is to treat all plugs as suspect, especially if it has been replaced with a new magnet since January 2021.
It is advised that under no circumstances should the plugs be struck prior to being loosened. The use of an impact wrench is not recommended.
Queensland chief inspector of coal mines Peter Newman authorised a number of recommendations following the incident, to ensure on-site maintenance on the D11T dozer is performed safely.
Site senior executives (SSEs) must:
- ensure the mine site has access to and has actioned Hastings Deering Customer Information Bulletin – HDCIB 2022 Bulletin 09 Revision 1 Defective Material Plugs.
Supervisors must:
- ensure the mine site has access to and has actioned Hastings Deering Customer Information Bulletin – HDCIB 2022 Bulletin 09 Revision 1 Defective Material Plugs
- ensure that all defective plugs are identified and replaced as soon as possible
- ensure an exclusion zone should be implemented when performing maintenance activities, and that coal mine workers are not in close proximity
- ensure that under no circumstances are plugs struck prior to be loosened, and that the use of an impact wrench is not recommended.
Coal mine workers must:
- ensure they adhere to – Hastings Deering Customer Information Bulletin – HDCIB 2022 Bulletin 09 Revision 1 Defective Material Plugs
- ensure they never strike a plug prior to attempting to loosen it, and that the use of an impact wrench is not recommended
- ensure that you remain within the established exclusion zone, out of the line of fire, as a mitigating critical control measure.