Evaluation of Whole-Body Vibration, Seat Design and Performance, and Sitting Posture in Large Mobile Equipment
| Principal investigator(s): | Alan Salmoni (University of Western Ontario);
Tammy Eger (Laurentian University);
Paul-Émile Boileau (Institut de recherche en santé et en sécurité du travail du Québec) |
| Co-investigator(s): | Andre Plamondon, Alain Delisle (Institut de recherche en santé et en sécurité du travail du Québec); Joan Stevenson (Queen's University); Christian LaRiviere (PRIVICAP); Peter Vi (Construction Safety Association of Ontario); Sylvain Grenier (Laurentian University/Occupational Health Clinics for Ontario Workers) |
| Sponsoring Institution: | University of Western Ontario |
Objective
This study was an extension of previous RAC-funded research. In that study, pieces of equipment -- including LHD vehicles, haulage trucks and scrapers -- were found to expose the operators to WBV levels above the health guidance caution zone defined in the ISO 2631-1 standard. The purpose of this study was to carry out a more comprehensive investigation on the pieces of equipment in mining and construction that appeared to expose the operators to WBV levels above the ISO 2631-1 health guidance caution zone. The study had three broad objectives:
- To investigate comprehensively LHD vehicles, haulage trucks and scrapers identified in the first study as causing unsafe exposure levels (Phase 1).
- One of the primary manifestations resulting from unsafe exposure to WBV is lower back problems. Sitting posture can also cause lower back problems as well as affect the level of exposure to vibration. Thus, the second broad objective of the present research was to assess the sitting postures and comfort of LHD vehicle drivers when operating under typical working conditions (Phase 2).
- The third broad objective was to investigate seat design characteristics that might be employed to minimize exposure to WBV (using Phase 1 data to simulate the vibration exposure for LHD vehicles) during LHD vehicle operation. Since the seat on which the operator sits represents the transmission point between the vibrating equipment and the person, proper seat design has the potential to play a major role in minimizing exposure to WBV (Phase 3).
Method
In Phase 1, 17 LHD vehicles (8 small & 9 large), 6 haulage trucks (3 small & 3 large) and 34 scraper vehicles were evaluated. Vibration signals were collected at both the seat-vehicle (this data was used in phase 3) and the operator-seat interfaces. In Phase 2, sitting postures were assessed during the operation of a sub-sample of LHD vehicles. In Phase 3, the acceleration vibration response of the LHD vehicle category corresponding to the mean and upper bound spectra were determined from the Phase 1 data. These vibration spectral class characteristics were reproduced on a WBV vehicular simulator to study the biomechanical response of subjects submitted to vibration on a currently-used seat and to identify subject response characteristics to the WBV.
Results
In Phase 1 it was found that many of the vehicles exposed operators to potentially harmful levels of vibration, particularly in the vertical axis. This conclusion was consistent no matter if the ISO or European Union safety standards are applied to the data. Clearly action is warranted. Since it is very difficult to change the work structure (i.e., shift length, breaks, etc.), one of the most promising protective strategies is to design seats that can be installed in these vehicles that will minimize the magnitude of the vibration exposures. In Phase 3 seat characteristics were identified, which if used during seat design and seat installation could help reduce vibration exposure significantly. Cooperation with vehicle and seat manufacturers is necessary for this to be implemented.
In Phase 2 the postures of the LHD operators, many of which were quite awkward, were identified so they could be used in the laboratory testing to be carried out in Phase 3. A major portion of the time spent in Phase 3 was spent attempting to identify the correct protocol to use to test the body’s biomechanical response to vibration. This proved to be challenging. At the time of writing this report study 3, which was to assess the biomechanical response using various postures was not completed. This work will, however, be finished over the next few months.
Conclusions
- The present research (Phase 1 field testing) has confirmed what the research team had suspected concerning seat design, namely, that the seats being manufactured and used in the LHDs and scrapers are not effective in decreasing WBV exposure (many are in fact amplifying the vibration as found in both Phase 1 and 3). This is not surprising since vibration dampening has not been one of the major criteria used when purchasing seats for these vehicles. Two issues make an immediate fix unlikely. First, the seats are often purchased separately from the vehicles. Second, a solution would need full cooperation of the manufacturers. If the latter condition could be met, there would almost certainly be increased costs passed on to the purchaser. An immediate solution for existing vehicles is not obvious.
- Phase 2 was designed to study the working postures used by LHD operators. While this work is potentially very useful for WBV exposure research, it is also very important for all types of musculoskeletal injuries. The LHD cab environment is an incredibly challenging one in which to gather work posture data — simply collecting the data took months of discussion and preparation; this knowledge, however, can now be transferred to other projects.
- The research conducted in Phase 3 to measure the biomechanical response to WBV proved to be very challenging. Through the laboratory testing, the reliability of the measurement techniques was determined, but significant biomechanical responses to 60 minutes of vibration exposure in the vertical axis were not detected. Further research in this area should consider the limitations mentioned above. This line of research is very important if the human body (biomechanical) response to WBV is to be understood more clearly. More research is obviously recommended.
- The spectral analysis and seat testing conducted at the IRSST in Montreal as part of Phase 3, confirmed the findings reported above for Phase 1. It is only by pursuing this line of research can we begin to understand optimal seat design. Much more work will need to be completed (and it is noted that WSIB is currently funding the VibRG to do more of this research) in this area. A strong recommendation would be for WSIB to help in finding a manufacturing partner for this very important work. Seats with vibration damping capabilities will need to be built into the design and installation stages.
- Since this was a jointly funded research project (WSIB and IRSST) between Ontario-based researchers and researchers based in Montreal at the IRSST, it is important to comment on the efficacy of this strategy. From the perspective of the researchers this strategy was incredibly valuable. The research team’s strong recommendation is for WSIB to continue facilitating such partnerships. Much is to be gained, not least of which are research cost efficiencies (the work done in Montreal could not be done in Ontario) and the expansion of expertise to address an important worker safety issue. The skills, workplace access, and knowledge of the combined team of researchers are quite impressive and in the area of WBV, matched in few other places in the world. Ten researchers and six graduate students played a significant role in the research program, including the reporting of the results and submission of research articles:
Publications
For more information:
asalmoni@uwo.ca
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