Drivers of residential solid waste collection trucks are exposed to a wide variety of physical and health hazards. Automated robotic arm collection methods are intended to eliminate physical and ergonomic hazards associated with manual waste collection. However, whole-body vibration (WBV) exposure is a hazard that may be significant and greater than being found in semi-automated or manual methods. WBV is measured in a pilot field study of automated waste collection trucks during normal operation for nearly eight-hour periods on two consecutive days. All four trials are run under similar route conditions. Vibrations are measured at the seat-driver interface using a tri-axial accelerometer seat pad and portable vibration monitors. Measured WBV levels are compared with prior published data from waste collection trucks and health standards. The average WBV exposure value, corresponding to 0.99 m.s -2 for frequency-weighted r.m.s. acceleration, is above the ISO 2631-1 action value of 0.50 m.s -2 and below a limit value of 1.15 m.s -2 as given in the European Parliament Directive 2002/44/EC. This exposure level suggests the presence of potential health risks.
Human exposure to whole-body vibration (WBV) is recognized as an occupational health risk factor, especially for lower back pain (LBP). Directive 2002/44/EC of the European Parliament recognizes worker risk from exposure to vibrations and the effects on the muscular/skeletal, neurological, and vascular systems [
Laboratory studies had demonstrated WBV effects on the vertebra, intervertebral discs, and supporting mus- culature. Both experimental and epidemiologic evidence suggested that WBV might act in combination with other work-related factors such as prolonged sitting, lifting, and awkward postures to cause increased risk of back disorder (p. 6-33).
Guidelines for human WBV exposure could be found in Annex B of ISO 2631-1, Mechanical vibration and shock―Evaluation of human exposure to whole-body vibration [
Solid waste collection was recognized as a hazardous occupation. The 2012 lost-time and restricted-work accident rate for U.S. solid waste collection was over 2.7 times greater than the combined private industry sector rates [
Residential solid waste collection is typically performed with trucks possessing a haulage capacity sufficient to reduce frequent trips to a landfill for off-loading, yet small enough to be maneuverable in urban traffic. These vehicles are likely to expose operators and passengers to WBV. Residential solid waste collection methods range from manual to semi-automated to automated (or mechanized) loading of waste. Manual collection and loading are typically accomplished by a work crew of two to three persons physically moving waste containers from a collection point and then lifting and dumping these into the hoppers of trucks. Semi-automated systems still require the manual movement and placement of the waste containers at the truck hopper by a work crew; however, a hydraulic or mechanical device lifts and empties the waste containers into the hopper. In the fully automated system, a driver operating a joystick controls robotic arm collects solid waste from containers, without leaving the vehicle cab. In this situation, the collection container is positioned at the curbside by the resident [
Manual and semi-automated solid waste collection vehicles expose drivers to similar WBV as with other commercial vehicles, such as delivery trucks. In the automated method, operators drive the truck,
Solid waste collection management eliminated manual material handling, walking, and direct contact with the solid waste by the implementation of the robotic arm collection system; however, the change may have introduced new ergonomic stressors due to joystick manipulation, neck and trunk-turning posture, and possible increases in WBV. While ergonomic stressors due to continuous poor posture (neck and trunk turning) and joystick maneuvering are fairly well recognized, few safety and health professionals in the US have an adequate awareness or understanding of WBV to assess the potential risk to workers [
http://resource.isvr.soton.ac.uk/HRV/VIBGUIDE/2008_11_08%20WBV_Good_practice_Guide%20v6.7h%20English.pdf
waste collection drivers is warranted.
Three prior studies evaluated solid waste collection trucks and WBV levels [
The objective of this study was to obtain measurements of WBV exposure to operators of automated residential solid waste collection vehicles at the contact interface between the driver and seat and compare these measurements with health risk guidelines. If a WBV health risk is apparent, further study of WBV source generation will be conducted to propose remedial actions.
The trucks monitored in this study were representative of the types used for automated collection. On Day 1, a 2007 Sterling Condor (#1) and a 2003 Peterbilt (#2) truck were monitored. On Day 2, the test was repeated on two 2007 Sterling Condors―one was the same vehicle and driver (#1) as Day 1 and another 2007 Sterling Condor with a different driver (#3). All trucks were equipped with the McNeilus 31-yard side loader compactor,
The trucks were run on their regular routes with no deviations from normal operation. The pre-trip inspections performed by the drivers indicated normal operating condition for all trucks. The four residential routes were within the same geographic area and shared level terrain, asphalt-paved roads in the residential area, similar spacing between homes, and similar distance from the landfill. The phases of the route included the start of the route at the garage/yard, travel to and from the collection area, collection, travel with a full load to the landfill, idling in queue to dump, dumping, travel return unloaded back to the collection area, and break time. Trips to the landfill for dumping were repeated up to three times during the workday.
Two Quest Technologies (Oconomowoc, WI) HAVPro Human Vibration Meters were used to obtain WBV measurements. The meters comply with ISO 8041:1990(E) (including Amendment 1:1999(E)) and ISO 2631- 1:1997 requirements [
・ wk weighting for the vertical (Z) axis;
・ wd weightings for the horizontal (X and Y) axes;
・ a 1.4 multiplier for the horizontal axes.
The accelerometers were Quest Technologies Model 5313AQ tri-axial LIVM seat pad accelerometers connected via cable to the HAVPro instruments.
The HAVPro time history buffer is limited to 240 samples in a set; therefore it can hold up to a 20-minute total of continuous 5-second interval data in its time history. If data collection continues past the full-point of the buffer, the initial 5-second datum is eliminated to enter the newest incoming 5-second datum while still maintaining an on-going time weighted average. The HAVPro instrument will hold up to 100 data time history sets. To maintain datum, upon reaching the 20-minute storage limit of the time history buffer, the data set is saved as a data time history set and a new buffer data set is begun. In this manner, a continuous record of recordings of approximately eight hours can be achieved.
WBV data from the HAVPro meters was downloaded via an RS232 port and USB adaptor to a computer. This data was entered into the Quest Technologies Quest Suite Professional II software, Version 3.7.2269, for storage and analysis.
The experiments were carried out over a two day period, July 31 and August 1, 2007, with three different trucks and drivers. As previously stated, one driver and truck pairing was repeated on the second day. Each trial run recording time limit was approximately eight hours.
For Day 1, a series of 24 individual 20-minute sets were recorded during the workday to allow viewing of 5-second interval data for the different phases of the collection task to avoid the overwriting of data on the HAVPro memory buffer. On Day 2, this setting was maintained for one truck and changed for the other. The setting change entailed a reduction of the interval time to 1-second, with the intent of increasing resolution of vibration data during the collection tasks. With 1-second intervals, each time history set was four minutes long; a total of 99 4-minute time history sets were recorded for a total of 6.6 hours.
During daylight hours on the day prior to the experiments, an initial survey of the truck cabs was conducted to determine optimal equipment layout to avoid interference with the driver during normal duties. As shown in
hours during the driving to the collection route and actual solid waste collection times. Truck logs were obtained to provide driver-recorded times of landfill delivery and unloading. The logs were compared with the graphic WBV results and verified the modes of operation during specific time periods. The instruments were retrieved from the trucks at the end of the workday. Data was downloaded into two separate computers, to assure backup in the event of one computer’s failure.
To create a composite of the full-day individual time history sets, each data set for a given truck and day was combined to give a more accurate assessment of the total workday exposure. This was accomplished by using the data-combining feature of the Quest Technologies Quest Suite Professional II software. The individual time history sets were retained in original form to allow further detailed analysis of specific phases of the waste collection task such as during collection, unloading, etc.
A summary of the frequency weighted r.m.s. Aeq values in the X, Y, Z, and XYZ-sum axes is presented in
During waste collection which is approximately 75% of the workday, the X, Y and Z axis values are relatively close to each other ranging from 0.36 to 0.58 r.m.s., with WBV only slightly higher in the Z axis. Also during collection, three of four Y and Z axes data sets were equal to or greater than the 0.50 m・s−2 action level. The meter settings of 5-second and 1-second averaging yielded similar results. Figures 4(a)-(b) graphically present a representative two-minute segment showing vibration during of the container collection process, measured on Truck #1, Day 1. The heavy bold graph lines on top in
Truck and day | Measured time (hr:min) | X | Y | Z | XYZ sum | VDV XYZ sum | CF XYZ sum |
---|---|---|---|---|---|---|---|
1 - 1 | 7:43 | 0.36 | 0.41 | 0.61 | 0.98 | 3.31 | 2.84 |
2 - 1 | 8:23 | 0.36 | 0.35 | 0.65 | 0.95 | 8.53 | 3.04 |
1 - 2a | 6:36 | 0.38 a | 0.44a | 0.59a | 1.01a | 5.92a | 8.04a |
3 - 2 | 8:13 | 0.40 | 0.46 | 0.56 | 1.02 | 9.77 | 7.33 |
Average | 0.38 | 0.42 | 0.60 | 0.99 | |||
SD | 0.02 | 0.05 | 0.04 | 0.03 |
a1-second interval averaging.
Segment | Day/Time | X | Y | Z | XYZ-sum |
---|---|---|---|---|---|
Collection | 7 - 31/2:20 a.m. | 0.36 | 0.50 | 0.57 | 1.03 |
Collection | 8 - 1/7:17 a.m. | 0.44a | 0.54a | 0.58a | 1.13a |
Driving | 7 - 31/9:00 a.m. | 0.20 | 0.32 | 0.89 | 1.03 |
Unloading | 7 - 31/9:20 a.m. | 0.27 | 0.31 | 0.65 | 0.85 |
a1-second interval averaging.
It would be expected that the WBV levels should be relatively similar for the four experiments as trucks were operated on or with identical seats, similar terrain, equivalent spacing of containers, and same distance from the landfill. Truck #2 is of a different manufacturer than Trucks #1 and #3; however, all trucks were equipped with the identical McNeilus 31-yard side loader compactor. Truck #3 has the highest X and Y axis value, the lowest Z axis value, and the highest XYZ-sum value. The very slight differences in Y and Z axis values for Truck #1 on Days 1 and 2 are explained by minor differences in collection conditions. Truck #1―Day 2 data was recorded using 1-second averaging, resulting in a total data collection time of only 6.6 hours versus 8 hours for the three other experiments; however, results appear to be similar to the 5-second averages.
Study author | X | Y | Z | XYZ sum | Waste Collection type |
---|---|---|---|---|---|
Bovenzi | 0.08 | 0.12 | 0.21 | 0.31 | Semi-automated |
Maeda | 0.76 | 0.79 | 1.1 | Manual | |
Melo | 0.17 | 0.19 | 0.43 | 0.60 | Semi-automated |
Paschold | 0.38 | 0.42 | 0.60 | 0.99 | Automated |
exposure and may reflect a waste collection method in which the driver frequently exits the truck to move and position the container at a hydraulic lifter. The Melo [
In the absence of a U.S. regulatory standard, a comparison of findings is made with European minimum requirements for the protection of workers from exposure to mechanical vibration. European Directive 2002/44/ EC presents a daily exposure action value of 0.5 m・s−2 and a limit value of 1.15 m・s−2. All four measurements showed exposure to be above the action value and below the limit value. According to ISO 2631-1:1997(E), values in the action level zone present potential health risks that require attention. Precise assessment of risk within the action level zone is currently not possible; however, it should be noted the average XYZ-sum value, 0.99 m・s−2, was only 15% below the limit value that suggests health risks are likely.
The ISO standard states that the WBV assessment is made independently for each axis and the health risk evaluated according to the highest single axis value. However, section 7.2.2 explains when two or more of the axes vibration magnitudes are similar (not defined in the standard), the vector sum can be used for health risk assessment.
The four CF values are below the 9.0 threshold contained in ISO 2631-1:1997(E). If the 9.0 threshold were exceeded, the r.m.s. values could be considered invalid and exposure would have to be determined by the VDV method.
This study measured four vehicles, a small sample size relative to the number of trucks. However, the results were fairly consistent. The 1997 ISO standard requires an adequate monitoring duration to assure precision and representation of typical exposure. This study differs from the prior solid waste collection truck and many other WBV studies, as an entire work day of monitoring was completed and has many combined sample sets of WBV data (up to eight hours).
Many other variables in a full scale study should be recorded and included such as driver anthropometry, seat type and adjustment, vehicle conditions (tire pressure, shock system, differing models, etc.), roads, driving speeds, variations in residential waste loads, and so on.
This study finds that automated residential waste collection drivers are exposed to WBV levels associated with an increased health risk while working in a seated position [
HelmutPaschold, (2015) Whole-Body Vibration in Automated Residential Solid Waste Collection. Open Journal of Safety Science and Technology,05,85-92. doi: 10.4236/ojsst.2015.54011