Open Cut » Health and Safety
Recent Whole-Body Vibration (WBV) research indicates the degeneration of the human spine is caused by the accumulation of vibration shocks (or 'peaks') rather than many hours of low level vibration. Operators of heavy coal mining equipment are exposed to WBV transmitted through the vehicle to the seat, and often incur shock loading. Compliance with current seating standards can result in seat characteristics not satisfactory for operator impact protection.
Vipac Engineers and Scientists Ltd (VIPAC) was commissioned by ACARP to develop a specification defining acceptable impact performance of operator seating in selected mining vehicles. The mining vehicles are dozers, graders, loaders and trucks. The specification is a laboratory test and assessment method that will allow seat manufacturers to supply seating tested for the requirements of coal mine vehicle applications.
WBV measurements were conducted on 60 vehicles at three open-cut coal mine sites located in the Hunter Valley and Bowen Basin regions. Six types of operator seats were extensively tested in purpose-built laboratory facilities.
Key project objectives have been achieved and general findings are summarised as follows:
- A test method ('specification') for seats for dozers, graders, loaders and trucks is presented along with acceptability criteria. The criteria include a ranking system so better performing seats are identified.
- Most seats were found to be acceptable, although few achieved the best ranking. Generally, large suspension stroke air seats were best, although the research indicates that seats most suitable for a vehicle class have properties 'matching' the characteristic vibration of the vehicle. For dozers, two seats provided very good protection. For graders, one seat was better than the others. For loaders, most seats were similar in performance. For trucks, one seat was better than the others, but also two seats failed because of the large displacement inputs for these vehicles.
- The benefit to long-term operator health of a seat with good vertical impact protection is expected to vary depending on the vehicle class:-
- For trucks and graders the benefit is significant. A good seat is expected to keep these vehicles well below the ISO 2631-5:2004 Health Limit.
- For loaders, the benefit is minor. This is because, loaders found to exceed the health limits were strongly influenced by side-to-side vibration, which is not reduced by seats with good vertical impact protection.
- For dozers, the benefit is usually minor, although on occasion it can be significant. This is because, dozers found to exceed the health limits were usually strongly influenced by side-to-side vibration, which is not reduced by seats with good vertical impact protection. However, some dozers have high vertical vibration, in which case a seat with good vertical impact protection is beneficial.
The following items list recommendations for further research related to the current project:
- The deterioration of seat performance with service loading is an important practical issue related to the findings of this project. Seat maintenance and replacement are required for adequate long-term protection of operators. Proposals to address this aspect are being prepared.
- The scope of this project was limited by considering only a selection of commercial suspension seats and coal mining vehicles. The research program can be extended to consider other vehicles, such as underground vehicles, and light and medium vehicles. Commercial seat models not laboratory tested within this project can be tested as further work. The research findings indicate that testing an almost 'non-suspension' seat for application in rubber-tyred vehicles is of interest. Furthermore, only one seat of each type was tested, whereas the specification recommends at least two of the same type be tested.
- Seats with the best impact protection rating for each vehicle class have not been 'road tested' to show their benefit using field comparison trials. Testing of this nature is considered to be worthwhile, in order to quantify the in-service improvement expected of these seats.
- A dedicated evaluation of the influence of lateral seat motion on operator health and potential for seat modifications to improve this is considered worthwhile. Operators are susceptible to fore-aft and sideways vibration as well as vertical vibration. Of these lateral directions, ISO 2631-5:2004 rates sideways vibration as most important by a factor of two. Seats generally provide minimal effective protection in these directions, but do not create impacts due to suspension over-travel. The research indicates that to reduce the long-term spinal degeneration health risk for loader and dozer operators, the side-to-side vibration must be attenuated. Further research is recommended in this area for these vehicles.