Absence of conflict of interest.
Citation
Kim, J. H., Marin, L. S., & Dennerlein, J. T. (2018). Evaluation of commercially available seat suspensions to reduce whole body vibration exposures in mining heavy equipment vehicle operators. Applied Ergonomics, 71, 78-86. https://doi.org/10.1016/j.apergo.2018.04.003
Highlights
- The study’s objective was to examine the impact of seat suspension systems on mine worker health and safety outcomes.
- The study was a randomized controlled trial conducted in a laboratory setting. The authors examined differences in whole body vibration (WBV) exposure between different seat suspension systems for three mining heavy equipment vehicles.
- The study found that seats with active vertical suspension were significantly more effective in reducing WBV exposure compared to the passive suspension seats.
- The quality of causal evidence presented in this report is high because it was based on a well-implemented randomized controlled trial. This means we are confident that the estimated effects are attributable to the different seat suspension systems, and not to other factors.
Features of the Study
The study used a laboratory experiment to assess whole body vibration (WBV) exposure. The authors created 24 minutes of floor vibrations collected and replicated from three mining heavy equipment vehicles (HEV)—a 240-ton haul truck, a bulldozer, and a scraper—with eight minutes of floor vibrations per HEV. To test WBV exposure, the authors used two types of seats with different vertical suspension systems and with features turned on and off resulting in six unique seat combinations:
- Seat 1: electromagnetic active suspension seat with fore/aft suspension
- Seat 1: electromagnetic active suspension seat
- Seat 1: electromagnetic passive suspension seat with fore/aft suspension
- Seat 2: passive air suspension seat with lateral suspension
- Seat 2: passive air suspension seat
- Seat 2: passive air suspension seat with air bladder cushion
Both types of seats were mounted on top of a platform and two participants were tested in the seats simultaneously.
Study participants included eight healthy adults with past heavy equipment driving experience. Each participant was pain free in the seven days prior to the study and without a history of musculoskeletal disorder. The authors randomly assigned participants to Seat 1 or 2, where each participant experienced three conditions. Participants then switched seats and experienced the three other conditions. The order of the three conditions per seat were counterbalanced across the eight participants to minimize order effects. The study evaluated various combinations of fore/aft, lateral, and vertical suspensions, grouped by the three HEV types. Using laboratory-collected acceleration data, the authors conducted statistical analyses to examine the impact of the seat suspension combinations on the outcomes. Outcomes included WBV exposure metrics: RMS weighted average acceleration, vibration dose value, and static spinal compression.
Findings
Health and safety
- The study found that seats with active vertical suspension significantly reduced vertical vibrations. However, passive fore/aft (x-axis), lateral (y-axis), and vertical (z-axis) seat suspensions did not significantly reduce corresponding axial vibrations.
- The study also found that seats with active vertical suspension were significantly associated with a 50% reduction of floor vibration, as compared to the 9% reduction by the passive air suspension system and the 10% reduction by the passive air suspension with air cushion system in all three vehicle types.
- Alternatively, the study found that fore/aft and lateral seat suspensions significantly amplified floor vibration.
- The study found that seats with active vertical suspension significantly reduced static spinal compression dose values for the 240-ton truck and scraper vehicles but not for the bulldozer.
- The study found no significant reductions in static spinal compression dose values for seats with fore/aft or lateral suspensions for any HEV.
Considerations for Interpreting the Findings
The authors did not explicitly provide information to calculate attrition. However, the authors conducted the experiment in a laboratory setting where all eight participants completed all six conditions, implying no attrition. The study was conducted with only eight participants so the findings should be interpreted with caution.
Causal Evidence Rating
The quality of causal evidence presented in this report is high because it was based on a well-implemented randomized controlled trial. This means we are confident that the estimated effects are attributable to the different seat suspension systems, and not to other factors.