Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC

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1 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL Pages Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Tammy R. Eger. a, Michael S. Contratto b, and James P. Dickey c a School of Human Kinetics, Laurentian University, Sudbury, ON, Canada, P3E 2C6 b Applied Research Laboratory, Caterpillar, Peoria, Il, USA c University of Western Ontario, 1393 Western Road, London, Ontario, N6G 1G9, Canada teger@laurentian.ca Received 1 st August 2011 ABSTRACT Operators of load-haul-dump (LHD) vehicles are commonly exposed to wholebody-vibration (WBV) levels above ISO and EU Directive 2002/44/EC guidelines. WBV was measured at the floor and seat while the same operator drove two LHDs on a controlled test track while driving speed, bucket load, ride control, terrain type, driving task, and seat optimization were varied. Frequency-weighted RMS acceleration was calculated and A(8) values were modeled for six driving scenarios. Vibration exposure was lowest when the LHD was driven at the lowest speed, forward, over smooth terrain, with ride control on and the bucket loaded (0.20 m/s 2 ). The A(8) decreased from 0.84 m/s 2 when driving with ride control off, over mixed terrain using all gears, to 0.53 m/s 2 when driving with ride control on and an optimized seat. The estimated daily exposure decreased but remained just above the ISO and EU Directive 2002/44/EC guidelines. Keywords: Whole-body vibration, ISO , EU directive 2002/44/EC, speed, terrain, LHD 1. INTRODUCTION Operators of mining vehicles are exposed to whole-body-vibration (WBV) and shocks during the course of their work [1,2,3]. Exposure levels previously reported for load-haul-dump (LHD) vehicle operators suggest vibration frequencies are in a range that is harmful to human health [1,3,4]. Negative health outcomes associated with long-term exposure to WBV include lower-back pain, spinal degeneration, gastrointestinal tract problems, sleep problems, headaches, neck problems, autonomic nervous system dysfunction, hearing loss, and nausea [5,6,7,8,9,10]. LHD vehicles are used in underground mining to transport ore to dump locations, crushing stations and/or haulage trucks. In 1989 Village and colleagues measured vibration at the operator/seat interface from eleven LHD vehicles that ranged in size from m 3 bucket haulage capacity. The authors reported that vibration exposure was greatest when smaller (versus larger) LHDs were driven at higher speeds (versus lower) with an empty bucket (versus full) 3. In 2011, Eger et al., reported vibration at the operator/seat interface for nine large LHDs (> 3 m 3 bucket haulage capacity) and eight small LHDs (<3 m 3 bucket haulage capacity) under loaded and unloaded haulage conditions [11]. Semi-controlled measurements were conducted as each vehicle was driven over typical terrain while going forward (30 sec.) and then backward (30 sec.) ten times. The authors did not report a significant Vol. 30 No

2 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC difference in vibration exposure between small and large haulage capacity vehicles; however, vibration was significantly higher when the LHDs were driven with an empty bucket [11]. Eger and colleagues (2011) also evaluated the benefits of using ride-control to reduce vibration transmitted to the operator. Ride-control is available on some new LHD models, and is designed to act as a shock absorber in order to dampen bucket forces. The authors did not find a statistically significant difference in vibration at the operator/seat interface with ride control engaged or not engaged; however, the sample size was small and the authors suggested further measurement was warranted [11]. In order to prevent the negative health outcomes associated with WBV exposure, a risk assessment, based on published standards, can be conducted. The most widely accepted standard for measurement and evaluation of human exposure to WBV is the ISO report [12]. Another method for the evaluation of negative health effects associated with WBV exposure is outlined in the European Union Directive 2002/44/EC [13]. The current state of knowledge offers ample evidence to support slower operating speeds [14,3] proper equipment maintenance [14,15,16] and regular road maintenance [14,16,17]. Literature also provides evidence that vehicle and seat suspension, when suited to the operating environment, can attenuate the vibration; however, there is also evidence that a poorly suited seat can amplify the vibration [15,18,19]. Despite this knowledge, the overall reduction on frequency-weighted r.m.s. acceleration at the operator-seat interface when controlling haulage load, driving speed, road maintenance, seat amplification and a vehicle design feature that is believed to help reduce vibration transferred to the operator cab (ride control), have not been collectively examined. Therefore, the purpose of this study was to carry out controlled testing to estimate the A(8) value under different operating conditions that manipulated driving speed, haulage load, terrain, ride control, and seat optimization. The first objective was to document differences in vibration exposure at the operator/seat interface when driving the LHD at different operating speeds, with a loaded/unloaded bucket, over maintained and rough roads, with ride-control on/off and with an optimized and non-optimized seat. The second objective was to determine if the estimated injury risk based on ISO HGCZ values and/or EU Directive 2002/44/EC daily exposure and action limit values could be reduced if driving conditions were optimized. 2. METHODS Whole-body vibration measurements were conducted at an above ground mining equipment testing facility in Burnie, Tasmania, Australia. All measurements were performed on two LHD vehicles driven by the same experienced equipment operator. LHDa had a height, width, length and bucket haulage capacity of 2886 mm, 3176 mm, mm and 7.2 m 3 respectively. LHDb was smaller (height 2557 mm; width 2894 mm; length mm) with a bucket haulage capacity of 5.7 m Test Conditions Several variables were controlled/manipulated during the testing including driving speed (gear 1, G1; gear 2, G2; gear 3, G3; auto-shift, AS), haulage (loaded bucket; unloaded bucket), ride control (RC on; RC off), terrain (RT, rough terrain typical of a new production zone; MAIN, maintained terrain typical of a graded surface; MT, combination of rough and maintained), driving task (F, forward; B, backward; M, mucking), and seat (no amplification (optimized), NA; amplification (not-tuned), A). The same test track was used for all forward and backward driving tests. The test track had portions of flat maintained road sections, flat rough road sections, left turns, right turns, and up and downward slope inclines. Forward driving trials involved 2-3 driving circuits of the test track and backward driving involved one circuit. Mucking involved loading and unloading the bucket with quarry rock. Ride-control is an engineering intervention that works on the LHD vehicle s bucket lift cylinder and is designed to act as a shock absorber to dampen bucket forces and reduce fore-aft and pitching motion. Both vehicles were equipped with ride control, which could be engaged or disengaged with a switch in the operator s cab. 292 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

3 Tammy R. Eger., Michael S. Contratto, and James P. Dickey The duration of measurement for each test condition is reported in Table I. The trials were completed in a randomized order with several repeats for most trials. 2.2 Measurement of whole-body vibration Vibration measurement was conducted in accordance with the regulations set forth in ISO for whole-body vibration [12]. Two series 2, 10g tri-axial accelerometers manufactured by NexGen Ergonomics (Montreal, QC), in conjunction with a P3X8-2C DataLOG II, datalogger manufactured by Biometrics (Gwent, UK), were used to measure WBV exposure at the vehicle floor/seat interface and the operator/seat interface. One tri-axial accelerometer was secured in a rubber seatpad and affixed to the supporting seat surface (with tape) between the ischial tuberosities of the seated operator in order to measure WBV exposure at the operator/seat interface. A second tri-axial accelerometer was secured, with a magnet, to the floor of the LHD directly under the seat with the accelerometer axes orientated in the same direction as the seat pad accelerometer. Acceleration was measured in three translational axes (fore-and-aft = x-axis; lateral = y-axis; and vertical = z-axis) with a sampling frequency of 500 Hz. Collected data were saved on an SD memory card and later transferred to a laptop computer for analysis Analysis of whole-body vibration exposure Vibration analysis was conducted in accordance with ISO guidelines and carried out with Vibration Analysis Tool-Set (VATS 3.4.3) software distributed by NexGen Ergonomics (Montreal, QC). Frequency-weighted root-mean-square accelerations (a wx ; a wy ; a wz ) were calculated using the appropriate weighting factors as described in ISO (x-axis = Wd; y-axis = Wd; z-axis = Wk). Scaling factors associated with the determination of health for seated exposure were also applied (x-axis, k=1.4; y-axis, k=1.4; z-axis, k=1.0). Frequency-weighted RMS vector sum values (a wxyz ), peak accelerations, crest factors (CF), and vibration dose values (VDV) for each axis were also calculated. Readers can refer to ISO for detailed information on the mathematical calculations Seat Effective Amplitude Transmissibility Vibration transmissibility through the seat was quantified by calculating the seat effective amplitude transmissibility value (SEAT): the ratio between vibration measured at the operator/seat interface to vibration measured at the vehicle floor/seat interface (multiplied by 100%). A SEAT value equal to or greater than 100% is indicative of a seat with dynamic properties that have not improved or reduced the ride comfort on the seat; a value greater than 100% is indicative of a seat that has reduced the riding comfort; a SEAT % value less than 100% indicates the dynamic properties of the seat have resulted in a ride comfort at the seat better than at the floor (i.e. the seat was effective at reducing vibration levels under the operating conditions evaluated) Estimated Health Effects In order to comment on health risks associated with WBV exposure both the ISO and European Union Directive 2002/44/EC require the eight-hour equivalent frequency weighted RMS acceleration value, (A8), to be calculated and in some cases the eight-hour equivalent vibration dose value (VDV total ). VDVs are considered when there is a high shock content in the vibration signal (i.e. if CF values are greater than nine, the ISO standard indicates the VDV should also be considered when determining health risks); however, this paper will only focus on predicted health effects based on a comparison of A(8) values to the HGCZ and EU directive values Driving Scenarios In order to calculate the A(8) values the research team used estimated work cycle values previously reported 11 which assumed seven hours of vehicle operation within an eight hour workshift. More specifically, the task of driving with a loaded bucket was estimated to occur for 2.75 hours, while the tasks of driving with an unloaded bucket, Vol. 30 No

4 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC mucking, and off the LHD vehicle (breaks and traveling to and from the production area) were estimated to occur for 2.25 hours, 2 hours and 1 hour respectively. These task durations were used to calculate A(8) values associated with six modeled driving scenarios that varied the percentage of time spent driving the LHD in gear 3 and 4, over maintained and rough roads, with ride control on and off and with an optimized seat in order to determine if the predicted injury risk could be reduced. Modeled driving scenario one assumed the LHD was operated with ride control on, using all gears, over mixed terrain with a loaded and unloaded bucket; scenario two assumed the LHD was driven with ride control off, using all gears, over mixed terrain with loaded and unloaded bucket; scenario three had ride control on, using gears 1-3 over mixed terrain with a loaded and unloaded bucket; scenario four was a repeat of scenario three, but ride control was off; scenario five had the LHD operating over maintained roads with ride control on using only gears 1-3; and scenario six was the same as scenario one except calculations were determined with optimized seat values (i.e. no amplification of vibration as it travelled through the seat). The A(8) value calculated for each scenario was compared to the ISO HGCZ values and European Union Directive 2002/44/EC daily exposure action value and daily exposure limit value. The ISO standard states that the a w values corresponding to the lower and upper limits of the eight-hour HGCZ are 0.45 m/s 2 and 0.90 m/s 2 respectively, while the daily exposure limit value and daily exposure action values established in the European Union Directive 2002/44/EC are 0.5 m/s 2 and 1.15 m/s 2. ISO states that for exposures below the zone, health effects have not been clearly documented and/or objectively observed; in the zone, caution with respect to potential health risks is indicated and above the zone, health risks are likely [12]. According to EU Directive 2002/44 EC workers should not be exposed to vibration above the exposure limit and employers should implement controls to reduce WBV injury risks to the workforce if daily vibration exposure is above the action limit [13]. 3. RESULTS 3.1 Frequency-weighted r.m.s. acceleration Frequency-weighted r.m.s. acceleration values, crest factor values, vibration dose values, and dominant frequency values measured at the operator/seat interface for the two LHD vehicles under all measurement conditions are presented in Table I (LHDa) and Table II (LHDb). Accelerations in the vertical axis at the operator/seat interface, a wz, were lowest when the LHDs were driven at the lowest speed, forward, with ride control on and the bucket loaded (LHDa, 0.20 m/s 2,Table I; LHDb, 0.21 m/s 2, Table II). The highest a wz values occurred when the LHDs were driven in the highest gear, forward, with ride-control off, and the bucket unloaded (LHDa, 2.06 m/s 2,Table I; LHDb, 1.52 m/s 2, Table II). Driving with a loaded bucket typically resulted in lower vibration exposure levels at the operator/seat interface. The decrease in vibration exposure magnitude with bucket load was particularly noticeable at higher operating speeds (Table I & II). For example, driving LHDa forward in autoshift, with ride control off, with a loaded bucket resulted in an average a wz value of 1.34 m/s 2 whereas driving with an empty bucket resulted in a value of 1.93 m/s 2 (Table I). Driving at higher speeds also resulted in higher vibration exposure at the operator/seat interface (Table I & Table II). For example when driving LHDb forward with the bucket empty and ride-control on the average a wz in 1st gear, 2nd gear, 3rd gear and auto-shift was 0.24, 0.51, 0.89, and 1.1 m/s 2 respectively. Driving with ride-control engaged also resulted in a decrease in vibration at the operator/seat interface. When LHDa was driven forward with a loaded bucket, in third gear with ride control engaged the average a wz at the operator/seat interface was 0.73 m/s 2, and increased to 0.95 m/s 2 when ride-control was turned off (Table I). Driving over maintained roads also resulted in less vibration at the operator/seat interface in all axes (Table III & Table IV). The initial seat installed in LHDa and LHDb amplified vibration in all axes as indicated by SEAT values greater than 100% (Table V & VI). Thus, measured vibration at the floor/seat interface was typically lower than vibration measured at the operator/seat interface. 294 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

5 Tammy R. Eger., Michael S. Contratto, and James P. Dickey Table I Summary of vibration information measured at the operator/seat interface from LHDa. Trial description, measurement duration, frequency-weighted r.m.s. acceleration values, peak frequency-weighted r.m.s. acceleration values, crest factor values, and dominant frequency values for each axis are presented Vol. 30 No

6 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Table II Summary of vibration information measured at the operator/seat interface from LHDb. Trial description, measurement duration, frequency-weighted r.m.s. acceleration values, peak frequency-weighted r.m.s. acceleration values, crest factor values, and dominant frequency values for each axis are presented. 296 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

7 Tammy R. Eger., Michael S. Contratto, and James P. Dickey Table III Summary of frequency weighted r.m.s. accelerations for LHDa, measured at the operator/seat interface when driving over maintained roads (maintained) and rough roads (rough). Maintained roads consistently resulted in lower vibration exposure levels at the operator/seat interface. Table IV Summary of frequency weighted r.m.s. accelerations for LHDb, measured at the operator/seat interface when driving over maintained roads (maintained) and rough roads (rough). Maintained roads consistently resulted in lower vibration exposure levels at the operator/seat interface. Vol. 30 No

8 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Table V Summary of overall SEAT % value for all trials shown for x, y and z axis for LHDa. A SEAT % over 100% indicates vibration is amplified as it travels from the floor through the seat. Table VI Summary of overall SEAT % value for all trials shown for x, y and z axis for LHDb. A SEAT % over 100% indicates vibration is amplified as it travels from the floor through the seat Determination of health risks Crest factor values were generally greater than 9 indicating both a w values and VDVs should be considered when determining predicted health risks (Table I & II). However, only the A(8) values, associated with the six modeled driving scenarios are presented (Table VII; Appendix 1 and 2) and illustrated (Figure 1 and 2). The A(8) value for LHDa associated with driving scenario one (RC off, MT, G1- AS) was above the ISO HGCZ but below the EU Directive 44/EC Action Limit Value (Figure 1). However, the A(8) value decreased when auto-shift gear was avoided (driving scenario 2), when ride-control was engaged (driving scenario 3 & 4), when driving occurred over maintained roads (driving scenario 5) and when an optimized seat was modeled (driving scenario 6). Although the interventions resulted in a lower A(8) value the estimated daily exposure was still within the ISO HGCZ and above the EU Directive 44/EC exposure limit boundary for both LHDa (Figure 1) and LHDb (Figure 2). For example, the A(8) for LHDb decreased from 0.84 m/s 2 when driving with ride control off over mixed terrain using all gears to 0.53 m/s 2 when driving with ride control on, over mixed terrain, using all gears, but with no vibration amplification through the seat (Figure 2). 4. DISCUSSION This study found that driving an LHD vehicle with a loaded bucket, at a lower operating speed, with ride control engaged, over maintained roadways, and with an optimized seat resulted in lower vibration at the operator/seat interface than when driving with an unloaded bucket, at higher operating speed, without ride control engaged, over rough roadways, without an optimized seat. Furthermore, vibration levels measured at the operator/seat interface were in the range known to indicated health risks were likely to develop [12,13]; however, overall risk, based on the A(8) value was reduced when the LHD was operated under optimized conditions. Vibration exposure in the vertical axis at the operator/seat interface measured in the current study ranged from m/s 2 for the LHD with the 7.2 m 3 bucket and m/s 2 for the LHD with the 5.7 m 3 bucket. These values are in-line with previous reported a wz values for large LHDs ( m 3 bucket), performing typical duties in an underground mine (0.98 m/s 2 3 and 0.52 m/s 2 1, and 1.0 m/s2 ). [11] Reduction in vibration, associated with changes in haulage capacity, driving speed, terrain and seat optimization are also in line with previous research. Driving with a loaded bucket versus an unloaded bucket also result in less vibration in 298 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

9 Tammy R. Eger., Michael S. Contratto, and James P. Dickey haulage trucks used in above-ground mining [2]. Kumar went on to conclude that driving terrain, and speed of travel had a great affect on the magnitude of the vibration exposure, and that the decreased vehicle mass and increased driving speeds associated with unloaded travel contributed to the higher vibration acceleration values. Village et al., 1989 and Anttonen and Niskanen, 1994 have also reported lower vibration levels when driving mobile equipment at lower speeds. In a previous study, ride-control did not appear to result in a decrease in vibration exposure in the z-axis at the operator/seat interface; however, only four vehicles were evaluated for a limited period of operation [11]. In the current study, ride control was evaluated with a loaded and unloaded bucket under all operating speeds: consistently resulted in less vibration at the operator/seat interface. Driving over maintained/smoother terrain also resulted in less vibration exposure and is in line with findings reported by Cann and colleagues for long-haul transportation [21], and Rehn et al., for forwarder vehicles [22]. Moreover, poor road maintenance continues to be a problem [23] that results in higher levels of WBV exposure. Table VII Summary of A(8) values for six driving scenarios (Appendix 1 & 2) and an estimated value based on a modification of scenario 5. * all driving scenarios include the same percentage of time spent driving forward, backward, and mucking with the bucket loaded and unloaded ** this scenario was estimated by decreasing the A(8) value calculated in scenario 5 by 20% Vol. 30 No

10 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Figure 1. LHDa - A(8) values compared to the ISO Health Guidance Caution Zone (top) and EU directive action limit and exposure (bottom). Six scenarios are illustrated; driving with ride control off over rough and smooth terrain using all gears (RC OFF; MT; G1-AS); driving with ride control off over rough and smooth terrain using gears 1-3 (RC OFF; MT; G1-3); driving with ride control on over rough and smooth terrain using all gears (RC ON; MT; G1-AS); driving with ride control on over rough and smooth terrain using gears 1-3 (RC ON; MT; G1-3); driving with ride control on over primarily maintained terrain using gears 1-3 (RC ON; Main; G1-3); and driving with ride control on over mixed terrain using gears 1-AS with no vibration amplification through the seat (RC ON; MT: G1-AS; No seat amp.). The initial seat installed in the LHD vehicles tested in this study amplified the vibration at the operator/seat interface (Table V & VI). Research by Boileau and colleagues [18] also showed that seats installed in LHD vehicles amplify the vibration at the operator/seat interface as the measured SEAT values ranged from 1.25 for large LHDs to 1.35 for Class II small LHDs. Tested in a lab environment, they also found the natural frequency of the subject/seat combination was 3.2 Hz, which was in the range of the dominant frequency produced by the LHD vehicle when operating in an underground mine [18]. There is also evidence that some seats installed in construction vehicles are also poorly suited for the operating environment resulting in SEAT values greater than 1 [24]. However, studies by Blood et al., with forklifts [25] and urban buses [26] have also showed that vibration at the operator seat interface can be reduced if a seat, tuned for the dominant vibration exposure, is installed in mobile equipment. Moreover, Paddan and Griffin, 2002, compared 100 models of seats from 14 different types of vehicles including on-road vehicles (cars, vans and trucks), heavy machinery (dumpers and excavators) and military vehicles (helicopters and armoured vehicles). They found a wide range of SEAT values within vehicle categories (e.g., for the 4 excavators they report a range from %). Of particular interest, they conclude that 94% of the vehicles investigated might benefit from changing the current seat to a seat from one of the other vehicles investigated [27]. 300 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

11 Tammy R. Eger., Michael S. Contratto, and James P. Dickey Figure 2. LHDb - A(8) values compared to the ISO Health Guidance Caution Zone (top) and EU directive action limit and exposure (bottom). Six scenarios are illustrated; driving with ride control off over rough and smooth terrain using all gears (R C O FF; M T; G1-A S); driving with ride control offover rough and smooth terrain using gears 1-3 (R C OFF; MT; G1-3); driving with ride control on over rough and smooth terrain using all gears (R C O N; MT; G1-A S); driving with ride control on over rough and smooth terrain using gears 1-3 (R C O N; MT; G1-3); driving with ride control on over primarily maintained terrain using gears 1-3 (R C O N; Main; G1-3); and driving with ride control on over mixed terrain using gears 1-AS with no vibration amplification through the seat (R C O N; M T: G1-A S; No seat amp.). Six driving scenarios were modeled to illustrate the benefits of intervention strategies aimed at decreasing vibration exposure and injury risk prediction based on ISO and EU directive 2002/44 (Figure 1 & 2). The highest A(8) values occurred when the LHDs were driven in all gears (higher speeds), with ride control off (more vibration transmitted to the operator), over mixed terrain. When ridecontrol was used, the modeled A(8) values decreased from 0.84 to 0.71 m/s 2 (LHDb). Avoiding the use of fourth gear (autoshift), which is a control strategy used by some mines in Ontario Canada, resulted in a further decrease to 0.67 m/s 2. When driving over maintained roads were added to the model the A(8) values decreased to 0.58 m/s 2. Although the decrease did not result in predicted exposure levels below the EU daily action limit or the ISO guidelines, the exposures did approach the lower boundaries. When an optimized seat was modeled the A(8) value decreased from 0.71 to 0.53 m/s 2. This large decrease illustrates the importance of installing an optimized seat in all mobile equipment. Moreover, if we estimated the impact of including an optimized seat with the other interventions modeled in scenario five (gears 1-3; ride control on; maintained roads) the resulting A(8) level would likely decrease to approximately 0.46 m/s 2 (Table VII; i.e. 20 % reduction since the non-optimized seat amplified vibration in the z-axis 20% on average). This value is below the EU 2002/44 daily exposure action value and just slightly above the ISO HGCZ. Furthermore, if a seat was installed in the LHDs that was optimized to attenuated vibration, exposure would decrease further likely Vol. 30 No

12 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC resulting in an A(8) value below both the ISO HGCZ and the EU 2002/44 directive daily action value. This is certainly possible given the current work that is being done to develop active response seats that are able to adapt to driving conditions leading to vibration attenuation [28] and improved comfort and performance, suggested to be % over a traditional suspension seat [29]. 5. CONCLUSION The estimated A(8) values were lower when calculated under ideal operating conditions (ride control on; lower operating speeds; maintained roadway; optimized seat). The changes did not result in operator exposure below the ISO HGCZ; however, a large reduction in exposure was shown to be possible with these interventions. In particular, LHD operators need to be aware of the effects of driving speed on their WBV exposure. Mining industry leaders need to support reasonable driving speeds for safe production, and they need to mandate comprehensive road maintenance programs to ensure rough roadbeds are repaired in a timely fashion. This study also supports the use of a feature, ride-control, designed to reduce the transmission of vibration to the operator and illustrates the importance of installing a seat in the vehicle that does not amplify vibration at the operator/seat interface. 302 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

13 Tammy R. Eger., Michael S. Contratto, and James P. Dickey Appendix 1a LHDa - Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). The A(8) value was calculated for driving scenario one (ride control on; using gears 1, 2, 3 & AS; over mixed terrain; loaded and unloaded bucket) and driving scenario two (ride control off; using gears 1, 2, 3 & AS; over mixed terrain; loaded and unloaded bucket) and compared to ISO Health Guidance Caution Zone values and European Union Directive 2002/44/EC daily exposure action value and daily exposure limit values. Driving Scenario Trial Description Gear Load Ride Control Travel (1;2;3;AS) (Empty;Ore) (on/off) forward;backward 2 2 *Drivers daily exposure duration is based on Eger et al., (2008) ** According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. ***According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) Vol. 30 No

14 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Appendix 1b LHDa - Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). The A(8) value was calculated for driving scenario three (ride control on; using gears 1, 2 & 3; over mixed terrain; loaded and unloaded bucket) and driving scenario four (ride control off; using gears 1, 2 & 3; over mixed terrain; loaded and unloaded bucket) and compared to ISO Health Guidance Caution Zone values and European Union Directive 2002/44/EC daily exposure action value and daily exposure limit value. *Drivers daily exposure duration is based on Eger et al., (2008) ** According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. ***According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) 304 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

15 Tammy R. Eger., Michael S. Contratto, and James P. Dickey Appendix 1c LHDa- Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). A(8) value is calculated based on vibration exposure values under recommended conditions (maintained roads; lower operating speeds; ride control feature on). * According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. **According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) Vol. 30 No

16 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Appendix 1d LHDa- Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). Difference in predicted risk is shown for A(8) calculations with the current seat and A(8) calculated with vibration values measured at the floor (i.e. to illustrate no amplification at the seat). *Drivers daily exposure duration is based on Eger et al., (2008) ** According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. ***According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) 306 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

17 Tammy R. Eger., Michael S. Contratto, and James P. Dickey Appendix 2a LHDb- Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). The A(8) value was calculated for driving scenario one (ride control on; using gears 1, 2, 3 & AS; over mixed terrain; loaded and unloaded bucket) and driving scenario two (ride control off; using gears 1, 2, 3 & AS; over mixed terrain; loaded and unloaded bucket) and compared to ISO Health Guidance Caution Zone values and European Union Directive 2002/44/EC daily exposure action value and daily exposure limit values. *Drivers daily exposure duration is based on Eger et al., (2008) ** According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. ***According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) Vol. 30 No

18 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Appendix 2b LHDb- Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). The A(8) value was calculated for driving scenario three (ride control on; using gears 1, 2 & 3; over mixed terrain; loaded and unloaded bucket) and driving scenario four (ride control off; using gears 1, 2 & 3; over mixed terrain; loaded and unloaded bucket) and compared to ISO Health Guidance Caution Zone values and European Union Directive 2002/44/EC daily exposure action value and daily exposure limit value. *Drivers daily exposure duration is based on Eger et al., (2008) ** According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. ***According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) 308 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

19 Tammy R. Eger., Michael S. Contratto, and James P. Dickey Appendix 2c LHDb- Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). A(8) value is calculated based on vibration exposure values under recommended conditions (maintained roads; lower operating speeds; ride control feature on). * According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. **According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) Vol. 30 No

20 Influence of Driving Speed, Terrain, Seat Performance and Ride Control on Predicted Health Risk Based on ISO and EU Directive 2002/44/EC Appendix 2d LHDb- Predicted health risks based on the estimated 8-hour equivalent frequency-weighted r.m.s. acceleration value, A(8). Difference in predicted risk is shown for A(8) calculations with the current seat and A(8) calculated with vibration values measured at the floor. *Drivers daily exposure duration is based on Eger et al., (2008) ** According to IS the frequency weighted acceleration values corresponding to the lower and upper limits of the HGCZ (for 8 hrs of exposure) are 0.45 and 0.90 m/s2 respectively. ***According to the EU directive a daily exposure action value of 0.5 m/s2 and a daily exposure limit value of 1.15 m/s2 (frequency-weighted acceleration) 310 JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL

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