Ryan P. Blood

Whole body vibration exposures in forklift operators: comparison of a mechanical and air suspension seat.

Using a repeated measures design, this study compared differences in whole body vibration (WBV) exposures when 12 forklift operators drove the same forklift with a mechanical suspension and an air suspension seat. A portable PDA-based WBV data acquisition system collected and analysed time-weighted and raw WBV data per ISO 2631-1 and 2631-5 WBV measurement standards. Tri-axial measurements of weighted vibration (Aw), crest factor, vibration dose values, time-weighted average-peak, raw (+) peak, raw (–) peak and static compression dose (Sed) were compared between seats. There were significant differences in z-axis WBV exposures with the air suspension seat, yielding lower WBV exposures. In addition, there were differences between seats in how they attenuated WBV exposures based on the drivers weight. In the mechanical suspension seat, WBV exposures were weight-dependent, with lighter drivers having higher WBV exposures, whereas with the air suspension seat, the same trends were not as prevalent. Statement of Relevance: This study contributes to the understanding of how different seat suspensions can influence WBV transmission and how some components of vibration transmission are dependent on the weight of the driver. Additional systematic studies are needed to quantify how various factors can influence WBV exposures.

Whole-body Vibration Exposure Intervention among Professional Bus and Truck Drivers: A Laboratory Evaluation of Seat-suspension Designs

Long-term exposure to seated whole-body vibration (WBV) is one of the leading risk factors for the development of low back disorders. Professional bus and truck drivers are regularly exposed to continuous WBV, since they spend the majority of their working hours driving heavy vehicles. This study measured WBV exposures among professional bus and truck drivers and evaluated the effects of seat-suspension designs using simulated field-collected data on a vibration table. WBV exposures were measured and compared across three different seat designs: an air-ride bus seat, an air-ride truck seat, and an electromagnetically active (EM-active) seat. Air-ride seats use a compressed-air bladder to attenuate vibrations, and they have been in operation throughout the transportation industry for many years. The EM-active seat is a relatively new design that incorporates a microprocessor-controlled actuator to dampen vibration. The vibration table simulated seven WBV exposure scenarios: four segments of vertical vibration and three scenarios that used field-collected driving data on different road surfaces—a city street, a freeway, and a section of rough roadway. The field scenarios used tri-axial WBV data that had been collected at the seat pan and at the drivers sternum, in accordance with ISO 2631-1 and 2631-5. This study found that WBV was significantly greater in the vertical direction (z-axis) than in the lateral directions (x-and y-axes) for each of the three road types and each of the three types of seats. Quantitative comparisons of the results showed that the floor-to-seat-pan transmissibility was significantly lower for the EM-active seat than for either the air-ride bus seat or the air-ride truck seat, across all three road types. This study also demonstrated that seat-suspension designs have a significant effect on the vibrations transmitted to vehicle operators, and the studys results may prove useful in designing future seat suspensions.

Evaluating whole-body vibration reduction by comparison of active and passive suspension seats in semi-trucks:

Truck drivers have one of the highest injury rates in the US workforce with the majority of injuries occurring in the low-back. Exposure to Whole Body Vibration (WBV) is thought to be a significant factor. This study compared difference in WBV exposures in sixteen drivers who drove a semi-truck over a standardized test route with a passive (air suspension) and electromagnetic vibration cancelling (active suspension) seat. Tri-axial WBV measurements of average weighted vibration (Aw), Vibration Dose Value (VDV), and Static Compressive Dose (Sed) were collected and compared between the two seats. Vehicle speed and location was collected with GPS loggers. The results show when compared to the passive suspension seat, the active suspension seat reduced Aw (p<0.001) and VDV (p<0.001) vibrations exposures by roughly 50%, with impulsive exposures (Sed) being reduced by approximately 20% (p=0.02). Based on the results the active suspension seat appears to have the potential to substantially reduce an operator’s exposure to WBV.

Quantifying whole body vibration exposures in metropolitan bus drivers: an evaluation of three seats

The objective of this study was to evaluate three seats amongst a population of metropolitan bus drivers as they drove a standardized test route including city streets, old and new freeways, and a street segment containing ten large speed humps. Three comparisons were made: 1) comparing seats made by different manufactures (Seat 1 and Seat 2), 2) comparing seats with a standard foam (Seat 2) and silicone foam (Seat 3) seat pans, and 3) comparing WBV exposures based on road types. Whole body vibration (WBV) exposures were measured using a tri-axial seat pan accelerometer and the attenuation capabilities of each seat were evaluated by comparing the vibrations measured at the floor and seat of the bus. There were significant WBV exposure differences between the various street types, which were shown across all seat types. The city street and older freeway segments had the highest WBV exposures with both segments producing WBV exposures slightly above the action limit for Vibration Dose Value (VDV(8)). Relative to Seat 2, Seat 1 performed better at attenuating impulsive and shock related WBV exposures, however, neither seat performed significantly better when Average Vibration (Aw(8)) and VDV(8) WBV exposures were compared. In addition, no performance differences were seen between the standard foam (Seat 2) and silicone foam (Seat 3) seat pans. This study provided a unique opportunity to explore WBV exposures among bus drivers and potential ergonomic interventions in the way of seat options to reduce WBV exposures and potentially reduce workplace injuries.

Vehicle Design Influences Whole Body Vibration Exposures: Effect of the Location of the Front Axle Relative to the Cab

Using a repeated measure design, this study compared differences in whole body vibration (WBV) exposures among 13 drivers who drove a truck with the cab over the front axle (cab-over design) and a truck with the cab situated behind the front axle (non-cab-over design). The drivers drove both trucks over a standardized route that comprised three distinct segments: a freeway segment, a city street segment with stop-and-go driving (traffic lights), and a city street segment without traffic lights. A portable WBV data acquisition system collected tri-axial time-weighted and raw WBV data per ISO 2631-1 and 2631-5 standards. Simultaneous global positioning system (GPS) data were also collected to compare vehicle speeds. The GPS data indicated that there were no speed differences between the two vehicles. However, average and impulsive z-axis vibration levels were significantly higher for the cab-over design than for the non-cab-over design. In addition, significant WBV exposure differences between road types were found, with the freeway segments having the lowest exposures and the city street segments without traffic lights having the highest exposures. Vehicle type and the associated WBV exposures should be considered when purchasing vehicles to be used by full-time professional vehicle operators.

Whole Body Vibration Exposure and Seat Effective Amplitude Transmissibility of Air Suspension Seat in Different Bus Designs

A number of studies have shown that whole body vibration (WBV) exposures contribute to low back pain in vehicle operators. Bus design may be an important factor in determining the WBV exposures that a driver receives. The purpose of this study was to determine whether differences exist in WBV exposures among three buses commonly used in long urban commuter routes: a high-floor coach bus, a low-floor coach bus, and a low-floor articulating bus. Each bus had the same new air-suspension installed and was driven over a standardized test route which included four road types: a smooth freeway, a rough freeway, a city street segment, and a road segment containing several speed humps. WBV exposures were evaluated per ISO 2631-1 action limits for acceptable WBV exposure levels. In this study, there were statistically significant differences among buses in WBV exposures. The high-floor coach bus had the highest fore-aft (x-axis) exposures, the low-floor articulating bus had the highest lateral (y-axis) exposures and the low-floor coach bus had the highest vertical (z-axis) exposures. With respect to ISO action limits, the z-axis WBV exposures did not exceed the 8-hour action limit (0.5 m/s2). The study also found that the air suspension seat did not perform well in the coach buses. The air suspension seat transmitted 92% of the floor measured vibration to the seat of the operator on the high-floor coach bus, 88% on the low-floor bus, and 76% on the low-floor articulating bus. Due to the low vibration attenuation performance of the air suspension seat, an evaluation of the different types of seats and seat suspensions may be merited in future research.