Ergonomics Vol. 50, No. 2, February 2007, 192–207

Postural implications of obtaining line-of-sight for seated operators of underground mining load–haul–dump vehicles A. GODWIN*{{, T. EGER{, A. SALMONI{, S. GRENIER{ and P. DUNNx {School of Human Kinetics, Laurentian University, Sudburg, Ontario P3E 2C6, Canada {School of Kinesiology, University of Western Ontario, London, Ontario N6A 3K7, Canada xSchool of Engineering, Laurentian University, Sudburg, Ontario P3E 2C6, Canada {Queen’s University, Kingston, Ontario K7L 3N6, Canada

Operators of load–haul–dump (LHD) vehicles use awkward postures that may be held statically and at extreme ranges of motion for long shift periods to spot hazards in underground mining. This study examined postural variables associated with three amounts of seat rotation intended to maximize line-ofsight during forward driving. Three different models, representing the 1st, 50th and 99th percentile male for height and weight, were positioned with appropriate hand and foot constraints in the virtual LHD cab modelled in Classic JACK v4.0. A total of 15 virtual movement strategies were developed to model the postural behaviour of typical workers and each virtual subject was tested, first with the seat in a neutral 08 position and then with it rotated counterclockwise to 208 and 458. Results revealed that reductions in trunk rotation, trunk lateral bend and neck rotation were associated with the seat rotation intervention. The general relationship observed was that as seat rotation increased, view of critical visual attention locations and visible line-of-sight area increased while postural load variables decreased. For the most part, 208 of seat rotation was beneficial but 458 produced significantly greater changes to postural load and visible visual attention locations. Keywords: Seat rotation; Computer-aided design; Line-of-sight; Awkward posture; Jack

1. Introduction Most underground mining machine operators would agree that awkward neck and trunk postures have to be adopted to adequately view critical areas when operating load– haul–dump (LHD) vehicles. Occupational biomechanics and ergonomics practitioners *Corresponding author. Email: [email protected] Ergonomics ISSN 0014-0139 print/ISSN 1366-5847 online ª 2007 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/00140130600951970

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would argue that the mechanisms leading to low back pain and neck injury in LHD operators are not well understood (Eklund et al. 1994). Line-of-sight investigations performed by Godwin (2004) demonstrated that the left side and left front area around the LHD vehicles at the 2–3 m height offer the greatest visibility for operators. Consequently, operators frequently drive their bi-directional vehicles close to the nearside wall of the underground mining tunnel and adopt a posture that includes twisting of the trunk and neck accompanied by bending or extension of the trunk in an attempt to obtain a clear line-of-sight (Health and Safety Executive 1992, Boocock and Weyman 1994, Boocock et al. 1996). On vehicles without an enclosed cab, the operators may lean outside the protective structures of the vehicle in order to obtain a line-of-sight to important areas in the work environment. This leaves them at risk of injury from being pinned or struck against the wall or against other machine components (Sjoflot 1980, Boocock and Weyman 1994). The sideways-seated posture is of additional concern since it prevents operators from receiving proper support from the seat backrest and may affect the ability to grasp controls or depress foot pedals (Boocock and Weyman 1994). Apart from the postural implications, sustaining awkward postures of the neck, trunk and upper extremities may be responsible for additional difficulties that impact the successful operation of the LHD vehicle. These may include decreased attention to environmental cues, missing important visual cues, altered transmissibility of whole-body vibration and inability to properly access controls within the cab. The twisted posture most frequently adopted by LHD machine operators involves asymmetrical loading of the trunk musculature and neck rotation at the extreme range of motion (Kittusamy 2002). A study of construction equipment operators by Eklund et al. (1994) described how a sideways sitting operator must use frequent and long-term head rotations, which may be compounded by exposure to vibration and the frequent use of controls. Toren and Oberg (1999) concluded that preventing the twisting motion among farmers would minimize trunk and neck load and, subsequently, recommended that farm equipment should have a rotating chair. Prior to this, researchers in the agriculture industry investigated the beneficial effects of allowing body rotation of 308 (Sjoflot 1980) and seat rotation of 208 (Bottoms and Barber 1978). More recently, Taoda et al. (2002) found that swivelling a forklift operator’s seat by 458 was beneficial for reducing the physical load and muscular effort of the drivers. Rotating cabins, large windows, minimized cab frames and video driving aids have also been recommended to improve neck postures while driving heavy equipment (Eklund et al. 1994). Computer-aided design programs that use accurate anthropometric dimensions and specific human range of motion data have been found to be powerful tools to assess reach, vision and dynamic motion in order to prevent unnatural body positions (Das and Sengupta 1995). When applied to underground mobile mining equipment, the virtual environment of the JACK digital human modelling system has been valuable for assessing visibility issues. In particular, grid outputs and visibility analysis were found to be useful for identifying and testing potential design modifications (Jeffkins et al. 2004, Eger et al. 2005). This type of standardized testing was completed from a fixed point of reference and did not consider that an operator’s changing posture may influence the amount of view available. For this reason, human simulation programs such as Classic JACK are well-suited for human modelling in addition to the ability to evaluate structural and mechanical engineering-based problems (Das and Sengupta 1995). The program allows realistic human movement to be modelled in a virtual environment and provides an indirect method of assessing risk in specific work situations. In addition,

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testing ergonomic interventions with computer simulation tools is a cost-saving measure that ensures no risk for workers since the virtual manikin can be manipulated without risk of injury. Using a computer simulation approach, Classic Jack v4.0 (UGS Technomatix, Plano, TX, USA), this study examined the relationship between posture and line-of-sight during forward driving of an underground mining vehicle. Measures of visibility were evaluated for different operator manikins (1st, 50th and 99th percentile for height and weight) using the current vehicle design and a stationary seat. Subsequently, a seat rotation intervention designed to enhance forward driving view was introduced to the virtual environment. Two different amounts of seat rotation (208 and 458) were tested for their effect on view and posture for the virtual manikin operator. Given the sideways-seated design of the LHD vehicle (with operator sitting sideways in the cab), it is hypothesized that as seat rotation increases, there will be improvements in the lines-of-sight together with reductions in the extreme range-of-motion postures that operators must use to view locations with reportedly poor visibility. 2. Method The investigation of the relationship between line-of-sight and posture during operation of a LHD vehicle was accomplished with a computer simulation approach. The generation of the simulated mining environment, the LHD vehicle, with the seat design intervention, and the LHD operator movements is described below. 2.1. Computer simulation environment An underground mining environment, a LHD vehicle that is used to move rock in an underground mine, and the LHD operator position and seat rotation were modelled in the computer simulation program Classic JACK v4.0. A single tunnel (of 4.5 m width by 4.5 m height) was used to represent a small portion of a typical underground mining environment. The LHD model was created in Auto-CAD (AutoDesk Inc., San Rafael, CA, USA) (with an accuracy of less than a 5 mm deviation from the original manufacturer’s drawings) and imported as a VRML file into the Classic JACK simulation environment (as detailed in a previous paper by Jeffkins et al. (2004)). The virtual LHD operators were generated in Classic JACK. The 1st, 50th and 99th percentile manikins (for height and weight) were used in the simulations. The JACK manikins corresponding to these male percentile height and weight values are as follows: 1st percentile 160.27 cm, 55.27 kg; 50th percentile 175.49 cm, 77.69 kg; 99th percentile 190.87 cm, 107.71 kg. The JACK database calls upon the 1988 anthropometric survey of US army personnel (Gordon et al. 1989), which is widely used and was presumed to be applicable to the working mining population in Canada. Moreover, the JACK program also uses the Society of Automotive Engineers (SAE) J833 standard to scale small, medium and large manikins, which has been recommended for use with mining machinery (Society of Automotive Engineers 1989). The virtual human was positioned at the H-point of the cabin seat (representing the rearmost driving position) and JACK program constraints were imposed on the hands and feet (by attaching a site on the palm of each hand to the steering controls and a site on each foot to the operating pedals). The H-point is an SAE standard (defined according to the procedure in SAE J826) used in vehicle design to represent the hip-joint pivot reference point between an occupant’s thigh and torso (Schneider et al. 1999).

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A total of 15 different movement strategies were animated, using the 88 articulated joints and a 17-segment flexible torso of the Jack manikin, to represent the random variety of postures that would be present in a normal population. All movement strategies were created after observing a video of LHD operators working in an underground mine and from discussion with LHD operators. The virtual manikin began in a neutral position and was animated with various amounts of torso flexion, extension, axial rotation and lateral flexion along with neck rotation, bending and lateral movement. Each movement strategy has been given a general description in table 1 with the corresponding amount of neck and trunk postural deviation in the most extreme position. Each movement strategy was different in order to represent the variety of motions that would be expected when testing actual humans. The strategies were based on individual human joint movement limits that were imposed by the JACK program (Das and Sengupta 1995) and biomechanical principles suggesting that trunk rotation occurs primarily in the thoracic region and that trunk flexion occurs primarily in the lumbar region (McGill and Hoodless 1990, McGill 2002). 2.2. Line-of-sight variables Visual attention locations (VALs) and percentage of visible area at a 1 m height were used to evaluate line-of-sight from the LHD operator position. VALs have been defined as critical points that must be visible to the operator for safe operation of underground mining equipment (Sanders and Kelley 1981, National Institute for Occupational Safety and Health 2006). LHDs are required to manoeuvre forward, backward, around corners and up or down ramps. The literature defines separate VALs for backward and forward travel on underground mining machines. A total of 57 VALs were identified by Sanders and Kelley (1981) as a high priority for the safe operation of a LHD scoop in forward travel on flat ground. A detailed description of the 57 VALs used in this study can be found in appendix 1. A computer representation of a LHD and the 57 VALs located in the modelled environment is shown in figure 1. The total number of VALs visible to the modelled LHD operator during each simulation was recorded. Percentage of visible area at a 1 m height was chosen as a secondary measure of operator visibility and is defined by a 10 m610 m flat grid extending from the operator position into the forward direction of travel. A ruler line-ofsight function (a visibility plane in Classic JACK v4.0) was used to determine the amount of area on the grid that was visible to the seated operator and this was expressed as a percentage of the total grid area (100 m2). 2.3. Posture variables In order to explore the relationship between line-of-sight and postural loading, the following posture variables were estimated for each simulation: trunk flexion/extension (8); trunk axial rotation (8); trunk lateral bend (8); and neck rotation (8). Although the movement strategies were animated, these postural values were recorded at the most extreme range of motion. The movement animation was stopped at the point where an extreme VAL located on the same-side tunnel wall was visible to the operator. This VAL location was defined as the stopping point to evaluate posture since real operators are known to sight down the same-side tunnel wall and are likely to spend most of their operating time in a rotated position. The seat rotation intervention was evaluated on its ability to reduce the posture requirements necessary to view the extreme VAL.

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Table 1. General description of movement patterns (5 s duration) that were used to simulate load–haul–dump operator movement strategy and values of final neck rotation, trunk flexion/ extension, axial rotation and lateral bend. Movement pattern 1 2

3 4 5 6 7 8 9 10

11

12 13

14 15

Description Neck twist/thoracic twist (simultaneous) Neck twist/low thoracic twist/ upper lumbar twist (simultaneous) Neck twist for 3 s then upper thoracic twist and lateral bend Neck twist for 2.5 s then lumbar lateral bend Neck twist/thoracic extension (simultaneous) Neck twist/thoracic twist/lumbar lateral bend (simultaneous) Neck twist (minimal)/thoracic twist (simultaneous) Trunk twist and flexion for 3 s then neck twist Neck twist/thoracic twist/lumbar lateral bend (simultaneous) Neck twist for 2 s then upper thoracic twist/lumbar twist and lateral bend Neck twist (minimal)/thoracic twist and lateral bend/lumbar lateral bend (simultaneous) Neck twist/thoracic twist/lumbar lateral bend (simultaneous) Neck twist/lower thoracic twist/ lumbar flexion and twist (simultaneous) Neck twist for 2.5 s then thoracic lateral bend/lumbar lateral bend Neck twist/upper thoracic twist (minimal) (simultaneous)

Final neck rotation

Final trunk flexion (þ)

Final trunk rotation

Final trunk lateral bend

568

08

308

68

508

78

198

98

568

178

158

58

518

68

88

178

538

738

198

88

568

7108

228

118

398

258

268

78

488

68

308

88

398

138

328

188

408

58

298

78

388

78

418

168

458

108

388

238

538

268

338

88

558

58

218

158

568

58

68

38

2.4. Data collection in the simulation The following procedure was carried out for each simulation in Classic JACK v4.0. First, the LHD machine was accurately scaled and positioned in the model of the underground mining tunnel. Second, the locations of the VALs with regard to the LHD machine, as described in detail in appendix 1, were marked in the modelled environment and the 10 m610 m visibility grid was positioned at a 1 m height. Third, the modelled LHD operator was positioned in the cab of the modelled LHD machine (as described in section 2.1) and each movement strategy was randomly assigned to one of three operator percentiles (1st, 50th, 99th). Finally, postural load variables and line-of-sight variables were recorded for each virtual operator using three different amounts of seat rotation (08, 208 and 458, as depicted in figure 2).

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Figure 1. Computer representation of a load–haul–dump vehicle and the 57 visual attention locations (VALs) located in the modelled environment. # symbols and associated descriptions in the virtual environment represent priority 1 VALs (a). (b) illustrates a virtual operator (50th percentile) in the cab. A detailed description of the VALs (based on three coordinates fore-aft, side-to-side and vertical) is shown in appendix 1.

2.5. Data analysis Data were analysed using the SPSS (version 10.0; SPSS Inc., Chicago, IL, USA) statistical package. A repeated measures ANOVA was used to distinguish differences among the within-subject variable of counter-clockwise seat rotation (08, 208 and 458) and the between-subject variable of operator size (small ¼ 1st percentile, medium ¼ 50th percentile, large ¼ 99th percentile). The main effects and interactions were evaluated using the univariate Huynh-Feldt epsilon due to a violated sphericity assumption.

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Figure 2. Series of three screenshots showing the effect of increasing seat rotation: a) 08; b) 208; c) 458. Note that the orientation of the (50th percentile) operator remains the same although they are moving relative to the machine body. This is for demonstration and visual feedback purposes. It can be observed how the relative amount of neck rotation, trunk rotation and lateral bend decrease as seat rotation increases.

The Huynh-Feldt has a less conservative correction than the more frequently used Greenhouse-Geiser or Lower-Bound statistic but should be acceptable given the nature of this investigation. Each significant within-subject main effect was assessed with post-hoc paired t-tests using the Bonferroni approach to control for familywise error and an a level of 0.017 was required for significance. Each significant between-subject main effect was assessed with Tukey HSD post-hoc tests. The significant interactions were assessed with simple main effects for each seat rotation level and followed up with Tukey HSD post-hoc tests. 3. Results All means and standard deviations for the postural and line-of-sight variables for each level of seat rotation and operator size are displayed in table 2. The repeated measures ANOVA (table 3) yielded significant within-subject main effects for seat rotation on the following dependent variables: trunk rotation, trunk lateral bend and neck rotation at the extreme of the range of movement. Paired t-tests were used to evaluate what amount of seat rotation (208 or 458) was required to significantly reduce postural variables. In this instance, 208 seat rotation was found to be insufficient to significantly reduce postural variables when compared to the current, fixed-position seat. It was found that 458 of seat rotation was required to significantly reduce trunk rotation (p 5 0.001), trunk lateral bend (p 5 0.01) and neck rotation (p 5 0.001) when compared to either the current seat design (08) or an intervention of 208 seat rotation. In particular, the 458 seat rotation improved the posture required to view extreme same-side tunnel wall VAL locations by reducing mean trunk rotation from 228 to 138 and mean neck rotation from 468 to 338. There were no significant between-subject effects for any of the dependent posture variables, indicating that the movement strategies were distributed in a random manner to the three groups of operator sizes (small, medium, large or 1st, 50th, 99th percentile height and weight). Significant between-subject main effects for operator size were observed only for the visibility variables of VALs viewed (F(2, 12) ¼ 25.52, p 5 0.0001)

42 + 0.5 23.59 + 1.7

23.96 + 1.6

3.76 + 3.5 9.95 + 7.2 75.64 + 4.6 44.01 + 9.3

208

43 + 1.6

4.13 + 4.4 10.65 + 7.2 74.98 + 2.7 43.25 + 5.8

VAL ¼ visual attention location.

Visibility variables VALs viewed (number out of 57) Visible area (% out of 100 m2)

Posture variables Trunk flexion/extension (8) Trunk axial rotation (8) Trunk lateral bend (8) Neck rotation (8)

08

458

23.7 + 2.52

42 + 0.4

3.91 + 2.7 7.77 + 7.4 72.73 + 2.6 34.93 + 6.6

Small Operators

9.99 + 5.1

43 + 0.8

7.48 + 12.8 27.98 + 4.1 710.36 + 4.6 44.32 + 7.6

08

10.02 + 6.3

44 + 1.1

8.36 + 10.8 23.6 + 7.7 78.72 + 5.3 40.6 + 3.5

208

Medium Operators

11.13 + 5.5

44 + 1.3

7.60 + 8.3 16.86 + 11.7 76.26 + 4.7 31.30 + 4.0

458

29.89 + 1.7

44 + 0.89

10.38 + 8.3 26.98 + 14.6 712.7 + 7.5 49.42 + 7.8

08

32.55 + 2.0

45 + 1.0

9.32 + 6.7 23.36 + 10.9 711.3 + 6.0 45.34 + 10.4

208

Large Operators

Table 2. Mean (SD) of dependent variables for seat rotations (08, 208, 458) and three operator sizes.

35.34 + 2.1

46 + 0.5

8.34 + 5.1 14.38 + 11.6 76.26 + 5.6 31.5 + 6.3

458

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A. Godwin et al. Table 3. Repeated measures ANOVA results. Main effects Within-subject Seat rotation

Between-subject Operator size

Interaction Seat rotation by operator size

Posture variables Trunk flexion/extension (8) Trunk axial rotation (8) Trunk lateral bend (8) Neck rotation (8)

F ¼ 0.66 F ¼ 17.42** F ¼ 12.18** F ¼ 49.79**

F ¼ 0.68 F ¼ 3.34 F ¼ 1.95 F ¼ 0.34

F ¼ 0.71 F ¼ 2.04 F ¼ 1.05 F ¼ 2.13

Visibility variables VALs viewed (number out of 57) Visible area (% out of 100 m2)

F ¼ 2.325 F ¼ 11.41**

F ¼ 25.52** F ¼ 50.92**

F ¼ 2.89* F ¼ 7.47**

*Indicates significance at p 5 0.05. **Indicates significance at p 5 0.001. VAL ¼ visual attention location.

and the percentage area visible at 1 m height (F(2, 12) ¼ 50.92, p 5 0.0001). The Tukey HSD post-hoc comparisons demonstrated that large operators (99th percentile height and weight) saw significantly more VALs than smaller-sized operators. On average, large operators could see 45 VALs during the animated motion strategy while the medium and small operators could only see 44 or 42 VALs, respectively. When evaluating the percentage of the 100 m2 area located at 1 m height visible to the seated operator, large operators again had a visual advantage over both small and medium operators. However, small operators also had a significant visual advantage over the medium-sized operators – they were able to view 24% of the area as opposed to the 10% available to medium-sized operators. In the best case scenario, the largest operator could still only see 33% of the 100 m2 area around the front of the vehicle. Finally, the repeated measures ANOVA demonstrated a significant interaction effect between seat rotation and operator size on both line-of-sight variables (number of VALs viewed and percentage of area visible in the extreme posture). Simple main effects using separate one-way ANOVA for each visibility variable allowed operator size to be evaluated at each level of seat rotation (figures 3 and 4). A clear interaction was demonstrated for the number of VALs viewed by each operator size during animated motion strategies. Medium and large operators could observe significantly more VALs when the seat was rotated by 208 and 458. However, small operators actually viewed fewer VALs at 208 and 458 seat rotation compared to the current fixed (08) seat design. In terms of the amount of area visible on a 100 m2 grid located at 1 m height, the seat rotation intervention only benefited large operators, who could see 9% more area at 208 seat rotation and a further 6% at 458 seat rotation. The area visible on the 1 m grid stayed the same for small (24% visible area) and medium (10% visible area) operators regardless of the amount of seat rotation imposed (figure 4). 4. Discussion Following the lead of other industrial sectors, such as farming, a rotating LHD cab seat was suggested as a method to improve operator line-of-sight, which is a notable safety concern in underground mining. In general, when assessing the current seat layout, extreme range of motion postures for neck and trunk were associated with greater

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Figure 3. Medium and large-sized operators were able to view increasing numbers of visual attention locations (VALs) as seat rotation increased from 08 to 458 but small operators actually had reduced visibility as the seat rotated.

Figure 4. As much as 458 of seat rotation was required to demonstrate any increase in the percentage of visible area available to the large-sized operator (increased by 15%) while medium and small-sized operator did not benefit from a seat rotation.

numbers of VALs being visible to the operator. Deviations of arm and leg posture were not considered in this analysis but were expected to be affected by viewing requirements and the need to maintain contact with stationary hand and foot controls. Ideally, the ergonomic seat and console intervention would reduce the postural load variables of the neck, trunk and all limbs while maintaining or increasing the field of view. The main effect observed with increasing amounts of seat rotation in this virtual study was that, while the postural load variables improved, the line-of-sight variables tended to

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show increased view, indicating that operators were acquiring a better field of view in a less awkward posture. Generally, 208 of seat rotation was insufficient to significantly improve posture but 458 of seat rotation meant that, on average, the most extreme operator posture was 138 of trunk rotation, only 58 of trunk lateral bend and 338 of neck rotation. This represents reductions of trunk rotation by 40%, of trunk lateral bend by 46% and of neck rotation by 29%. It should, however, be noted that on average, even before the seat rotation intervention, trunk rotation was below the critical 208 suggested by researchers as the point at which passive resistance increases dramatically and muscular effort increases disproportionately (Boden and Oberg 1997, Toren 2001). Incorporating a seat rotation intervention of 458 further reduced the trunk rotation value to less than 158 for all sizes of operators tested. The real concern may actually be the amount of neck deviation that was still required in the simulated 458 rotated seated position. The average amount of neck rotation required in this condition was 338, which exceeded recommendations of the Swedish National Work Injury Criteria to keep neck rotation at less than 158 if the motion is required for greater than 80% of the work time (as cited by Eklund et al. 1994). The decrease in neck posture with seat rotation found in the present study was comparable to the improvement that was seen when 208 of seat rotation was introduced on tractors (Bottoms and Barber 1978). Similarly, Bottoms and Barber found that swivelling the tractor seat did not significantly improve neck twist but did reduce trunk twist. This proposed seat rotation intervention may not be enough to eliminate the cumulative loading risk for neck problems that is associated with sideways-seated drivers and prolonged awkward neck postures (Eklund et al. 1994). Additional interventions may need to be implemented if further research determines that neck rotation does not undergo sufficient excursions into neutral positions during typical LHD operating task demands. Further, Bottoms and Barber (1978) suggested that, due to the nature of changing and arduous field conditions, the actual muscle activity of tractor drivers would have been higher and the rotating seat might have provided more benefit than that observed in the stationary laboratory rig used in their study. There were similar limitations in the present study, which only evaluated the intervention using computer-assisted design environments and virtual human models, where it was not possible to simulate the effect of changing light conditions, light refraction or glare on visibility variables or to consider the effect that vibration, fatigue and operator cognitive awareness would have on a human operator and their ability to interact in an actual underground situation. It has previously been shown that operator size impacts on a driver’s ability to see clearly located obstacles in front of a vehicle (Loczi 2000). The impact of design changes will differ depending on operator size and this was confirmed with the present study. The interaction between seat rotation and operator size indicated that a seat rotation intervention does not appear to benefit the ability of small-sized operators to view critical locations around the LHD vehicle. On both measures of the field of view, the small operators saw no change as seat rotation increased from 08 to 458 but the large operators had significant increases in their view. For this reason, an intervention that raised the height of the seat would be of greater benefit to small operators. If their seats were raised to make their seated eye height equivalent to that of the larger operators, a seat rotation intervention may be of additional benefit. In other words, a seat that is capable of substantial upward/downward motion in addition to rotation may be required. Increasing seating height is a natural option; however, in most mining environments ceiling height is restricted, which might make machine design changes that raise the sitting height of the operator unfeasible.

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It should be noted that some consideration needs to be given as to how a seat rotates within the cab. Rotating about a point located in the middle of the seat actually reduced the visible area for the operator and, as such, the methodology was altered to consider seat rotation from a fixed point on the left rear side of the seat. Limitations exist with this implementation as well since this new rotation position brought the virtual operator closer to the front of the machine and may have been responsible for the reduced line-ofsight measured on the visibility plane extended to the front of the vehicle. Prototype testing with real machine components and humans would be needed to investigate the feasibility of rotating as well as translating the seat back into the current cabin space, so that the distance between operator and the front of the machine stayed the same. Another option may involve rotating the entire cabin space on a turntable type of device. Also, underground mine layouts typically require frequent reversals of direction and these results have considered only forward driving conditions. The bi-directional nature of the LHD vehicle would require a seat that is capable of dynamic changes rather than a permanently rotated seat at some fixed value. In addition, a forward driving situation involving a bucket loaded with broken rock presents a greater challenge to visibility than rearward travel when the engine blocks the operator’s line-of-sight. For this reason, it may be beneficial to have an infinitely adjustable seat rotation mechanism to allow the operator the appropriate amount of rotation for the particular driving circumstances. This modification would need to be associated with an operator-training period that incorporated information about less-visible scenarios with awareness about awkward neck and trunk postures. The question still remains as to which form of visibility assessment is essential for the safe operation of LHDs and whether specific points or a general visible area is more critical for the operator. At best, the large operators with the best visual advantage were still only able to view 79% of the critical VALs (45 out of 57). The VALs that were never visible to the operator were predominantly at ground level in the midline of the machine and to the right side. No amount of seat rotation would allow these VALs to be seen and a secondary intervention may be required to increase visibility. The addition of a camera monitoring system would be most beneficial if it could enhance those VALs not currently detected in the existing cabin design or with the proposed rotating seat design. Future work aims to evaluate which combination of camera locations could provide enhanced line-of-sight to forward and rearward travel with minimum impact on current operator work practices. Several limitations exist with this type of research that must be considered and improved upon for further data collection in a virtual environment. A motion capture system could feed more accurate operator movement strategies directly into the simulation environment and provide more meaningful human motion analysis. With only short simulated clips of operator movement strategies, it was difficult to evaluate the long-term effect of a seated, rotated posture. This remains a limitation in any static evaluation performed in Classic JACK. Factors contributing to cumulative loading have not been well-documented but repetitive or prolonged static movements and tasks that require asymmetric muscular tension (such as the rotated, sideways-seated posture observed in LHD driving) may move the tissue strain closer to the failure tolerance (McGill 1997). Finally, the simulation environment is not capable of including a cognitive component of human behaviour. Although a theoretical improved line-of-sight was available to the operator, this does not guarantee that a real human operator would actually recognize an underground hazard before the necessary stopping point of the vehicle. Issues of motivation, attention and perception will also change according to the type of worker (young vs. old), worker experience (new vs. experienced) and fatigue level.

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5. Conclusions Considering the significant reductions in postural variables accompanied by increases to visible area, the seat rotation intervention should be considered by manufacturers. Since LHD vehicle operation is a dynamic process with frequent changes in direction and varied terrain, the degree of cabin seat rotation should not be fixed. This study demonstrated that 208 of seat rotation was beneficial but as much as 458 of seat rotation significantly decreased postural angle variables and increased visibility. In operating circumstances that require frequent changes between forward and rearward driving, the operator may prefer to have less forward seat rotation to allow ease of movement between sighting forward and sighting backward. Additional simulation and prototype testing needs to be done to determine the specifics of the rotating device to ensure that visibility is maximized, postural load is minimized and safe operation is not compromised in the process. Acknowledgements Funding for this research was provided by the Workplace Safety and Insurance Board, Grant #01–018. Ongoing support from the Mining and Aggregates Safety and Health Association (MASHA) is also appreciated. References BODEN, A. and OBERG, K., 1997, Torque resistance of the passive tissues of the trunk at axial rotation. Applied Ergonomics, 29, 111–118. BOOCOCK, M.G. and WEYMAN, A.K., 1994, Task analysis applied to computer-aided design for evaluating driver visibility. In Proceedings of the 12th IEA Triennial Congress, Toronto, Ontario, Canada, 15–19 August 1995, 4, pp. 261–263. BOOCOCK, M.G., WEYMAN, A.K., CORLETT, T.C. and NAYLOR, J., 1996, The problems of restricted visibility from free-steered mining vehicles. In Vision in Vehicles – V, A.G. Gale, C.M. Haslegrave, S.P. Taylor and I.D. Brown (Eds.), pp. 355–362 (Amsterdam: Elsevier Science). BOTTOMS, D.J. and BARBER, T.S., 1978, A swivelling seat to improve tractor driver’s posture. Applied Ergonomics, 9, 77–84. DAS, B. and SENGUPTA, A.K., 1995, Computer-aided human modeling programs for workstation design. Ergonomics, 38, 1958–1972. EGER, T., JEFFKINS, A., DUNN, P., BHATTACHERYA, I. and DJIVRE, M., 2005, Benefits of assessing LHD vehicle visibility in a virtual environment. CIM Bulletin, 98, no. 1089. EKLUND, J., ODENRICK, P. and ZETTERGREN, S., 1994, Head posture measurements among work vehicle drivers and implications for work and workplace design. Ergonomics, 37, 623–639. GODWIN, A., 2004, Postural and line-of-sight investigation for load-haul-dump operators. Masters thesis, Laurentian University, Sudbury, Canada. GORDON, C.C., CHURCHILL, T., CLAUSER, C.E., BRADTMILLER, B., MCCONVILLE, J.T., TEBBETTS, I. and WALKER, R.A., 1989, 1988 Anthropometric Survey of U.S. Army Personnel: Summary Statistics Interim Report. Technical Report TR-89/027 (Natick, MA: U.S. Army Natick Research, Development and Engineering Center). HEALTH AND SAFETY EXECUTIVE, 1992, Improving Visibility on Underground Free Steered Vehicles. Health and Safety Executive Topic Report (London: Health and Safety Executive). JEFFKINS, A., EGER, T., SALMONI, A. and WHISSELL, R., 2004, Virtual JACK in a virtual machine: computer simulation is beneficial for investigating visibility during mobile mining equipment operation. Ergonomics in Design, 12, 12–17. KITTUSAMY, K.N., 2002, Ergonomic risk factors, A study of heavy earthmoving machinery operators. Professional Safety – Journal of ASSE, October, 38–45. LOCZI, J., 2000, Application of the 3-D CAD manikin RAMSIS to heavy truck design. In Proceedings of the IEA 2000/HFES 2000 Congress (Santa Monica, CA: Human Factors and Ergonomics Society), 6, pp. 832–835.

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MCGILL, S.M., 1997, The biomechanics of low back injury: implications on current practice in industry and the clinic. Journal of Biomechanics, 30, 465–475. MCGILL, S., 2002, Low Back Disorders: Evidence-Based Prevention and Rehabilitation (Champaign, IL: Human Kinetics Publishers). MCGILL, S.M. and HOODLESS, K., 1990, Measured and modeled static and dynamic axial trunk torsion during twisting in males and females. Journal of Biomechanical Engineering, 12, 403–409. NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH, 2006, Visibility. Available online at: http://www.cdc.gov/niosh/mining/topics/machinesafety/equipmentdsgn/visibility/visibility.htm (accessed May 2006). SANDERS, M.S. and KELLEY, G.R., 1981, Visual Attention Locations for Operating Continuous Miners, Shuttle Cars, and Scoops – Volume 1 (contract J0387213, Canyon Research Group, Inc.), Department of the Interior, U.S. Bureau of Mines, 29(1), 1–82. SCHNEIDER, L.W., REED, M.P., ROE, R.W., MANARY, M.A., FLANNAGAN, C.A.C., HUBBARD, R.P. and RUPP, G.L., 1999, ASPECT: The Next Generation H-point Machine and Related Vehicle and Seat Design and Measurement Tools. Paper no. 1999–01–0962, pp. 1–13 (Warrendale, PA: Society of Automotive Engineers). SJOFLOT, L., 1980, Means of improving a tractor driver’s working posture. Ergonomics, 23, 751–761. SOCIETY OF AUTOMOTIVE ENGINEERS, 1989, SAE J833 Human Physical Dimensions (Warrendale, PA: Society of Automotive Engineers). TAODA, K., TSUJIMURA, H., KITAHARA, T. and NISHIYAMA, K., 2002, Evaluation of a swiveling seat to reduce the physical load on forklift drivers (in Japanese). Sangyo Eiseigaku Zasshi, 44, 180–187. TOREN, A., 2001, Muscle activity and range of motion during active trunk rotation in a sitting posture. Applied Ergonomics, 32, 583–591. TOREN, A. and OBERG, K., 1999, Maximum isometric trunk muscle strength and activity at trunk axial rotation during sitting. Applied Ergonomics, 30, 515–525.

Appendix 1. Location of priority-1 visual attention locations (VALs) for forward operation of a load-haul-dump (LHD) vehicle. The reference points for the VALs are shown in figure 5. For more information, please see Sanders and Kelley (1981). Location VAL (number)

Visual feature

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

SS rib OS rib Crosscut corner Crosscut corner Crosscut corner Roof irregularities Centre line roof marks SS lead corner of machine OS lead corner of machine Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles Roadway obstacles

Fore–Aft

Side-side lateral

Up-Down height

OH þ ½ NSD FE þ ½ NSD FE þ 50.8 cm FE þ 50.8 cm FE FE þ ½ NSD FE þ ½ NSD FE FE FE þ 5 cm FE þ 5 cm FE þ ½ NSD FE þ ½ NSD FE þ NSD FE þ NSD FE þ NSD FE þ 5 cm FE þ 5 cm FE þ ½ NSD FE þ ½ NSD FE þ NSD

WMP (SS) þ 10.2 cm WMP (OS) þ 20.3 WMP (SS) þ 10.2 cm WMP (OS) þ 20.3 WMP (SS) þ 10.2 cm OCL MCL WMP (SS) WMP (OS) WMP (SS) þ 5 cm WMP (SS) þ ½ NSD WMP (SS) þ 5 cm WMP (SS) þ ½ NSD WMP (SS) WMP (SS) þ ½ NSD MCL WMP (OS) þ 5 cm WMP (OS) þ ½ NSD WMP (OS) þ 5 cm WMP (OS) þ ½ NSD WMP (OS)

OEH OEH OEH OEH OEH SH SH MMH MMH Floor Floor Floor Floor Floor Floor Floor Floor Floor Floor Floor Floor (continued)

206

A. Godwin et al. Appendix 1. (Continued). Location

VAL (number)

Visual feature

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

Roadway obstacles Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Rib obstructions Rib obstructions Rib obstructions Rib obstructions Rib obstructions Rib obstructions Roof obstructions Roof obstructions Roof obstructions Roof obstructions Rib obstructions Rib obstructions Roadway obstructions Roadway obstructions Roof bolts Edge of loading ramp Personnel Personnel Personnel Personnel Personnel Roof hazards

Fore–Aft

Side-side lateral

Up-Down height

FE þ NSD FE þ 5 cm FE þ 5 cm FE þ ½ NSD FE þ ½ NSD FE þ NSD FE þ NSD FE þ NSD FE þ 5 cm FE þ 5 cm FE þ ½ NSD FE þ ½ NSD FE þ NSD FE þ NSD FE þ 5 cm FE þ ½ NSD FE þ NSD FE þ 5 cm FE þ ½ NSD FE þ NSD FE FE FE FE FE FE FE FE OH þ 12.7 cm FE þ NSD FE þ NSD FE þ NSD FE þ NSD FE þ NSD FE þ NSD FE þ NSD

WMP (OS) þ ½ NSD WMP (SS) þ 5 cm WMP (SS) þ ½ NSD WMP (SS) þ 5 cm WMP (SS) þ ½ NSD WMP (SS) WMP (SS) þ ½ NSD MCL WMP (OS) þ 5 cm WMP (OS) þ ½ NSD WMP (OS) þ 5 cm WMP (OS) þ ½ NSD WMP (OS) WMP (OS) þ ½ NSD WMP (SS) þ 10.2 cm WMP (SS) þ 10.2 cm WMP (SS) þ 10.2 cm WMP (SS) þ 10.2 cm WMP (SS) þ 10.2 cm WMP (SS) þ 10.2 cm WMP (SS) WMP (OS) WMP (SS) þ 12.7 cm WMP (OS) þ 12.7 cm WMP (SS) þ 5 cm WMP (OS) þ 25.4 cm WMP (SS) þ 12.7 cm WMP (OS) þ 12.7 cm OCL WMP (SS) þ 5 cm WMP (SS) WMP (OS) WMP (SS) þ ½ NSD WMP (OS) þ ½ NSD MCL OCL

Floor HMP HMP HMP HMP HMP HMP HMP HMP HMP HMP HMP HMP HMP Floor Floor Floor HMP HMP HMP HMP HMP HMP HMP MMH MMH Floor Floor SH Floor OEH OEH OEH OEH OEH HMP

SS ¼ same side as driver; OS ¼ opposite side of driver; FE ¼ front edge of machine; HMP ¼ highest point of machine; MCL ¼ machine centre line; MMH ¼ median machine height; NSD ¼ necessary stopping distance; OCL ¼ operator centre line; OEH ¼ operator eye height; OH ¼ operator’s head; SH ¼ seam height; WMP ¼ widest machine point of machine.

Postural implications for operators of underground mining vehicles

207

Figure 5. Reference points for the visual attention locations. OS ¼ opposite side of driver; FE ¼ front edge of machine; MCL ¼ machine centre line; OCL ¼ operator centre line; WMP ¼ widest machine point of machine; SS ¼ same side as driver; MMH ¼ median machine height; HMP ¼ highest point of machine; OEH ¼ operator eye height.

Postural implications of obtaining line-of-sight for ...

Consequently, operators frequently drive their bi-directional vehicles close to the near- ... When applied to underground mobile mining equipment, the virtual.

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