Virtual reality based ergonomic risk evaluation of welding

Proceedings 19th Triennial Congress of the IEA, Melbourne 9-14 August 2015

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Virtual reality based ergonomic risk evaluation of welding tasks

Azizur Rahmana, Ekambaram Palaneeswaranb , Ambarish Kulkarnic

a ,b ,c Faculty of Science Engineering and Technology, Swinburne University of Technology, John Street, Hawthorn, Victoria 3122, AUSTRALIA

Work related musculoskeletal disorders (WMSDs) are significant among workers engaged in manual handling tasks, e.g. structural steel welding trades. Several research studies and industry reports revealed that such risks are mostly preventable e.g. through relevant ergonomic assessments, facilitating arrangements and job/ workplace redesigns. Common approaches for ergonomic risk evaluations of manual handling tasks in workplaces are: (i) perceptions based information and (ii) field observations, both have certain limitations and challenges. Therefore, applying virtual reality (VR) technique with kinematic motion captures and simulation studies in virtual environment have been additionally considered in our research. This hybrid approach has conveniently enabled more advanced and reliable data for the MSD risk evaluations. This paper presents key details of our VR simulation studies employed for ergonomic evaluation of structural steel welding tasks, especially back pain related musculoskeletal disorders from the metal joining tasks in construction and manufacturing industries. This study results will be useful for further developing WMSDs related decision support system. Practitioner Summary: Ergonomic risk evaluation of manual handling tasks is crucial as these have strong relation with work related musculoskeletal disorders. Through a hybrid research approach including field observations and virtual reality simulation studies, advanced risk assessments can be conveniently consolidated for rational arrangements and decision support – even for challenging occupations such as structural steel welding trade. Moreover, jobs/tasks can be suitably designed/ redesigned without employing risky or expensive field observations or unreliable perceptions. Keywords: Ergonomics, risk assessment, manual handling, musculoskeletal disorder, virtual reality

1. Introduction

Work related musculoskeletal disorders (WMSDs) are significant among workers engaged in manual handling (MH) tasks, especially in challenging trades such as structural steel welding. For example, 43% of manual handling related injuries in the workplace are sprains and strains of joints/ adjacent muscles and another 33% of injuries are due to muscular stress arise from lifting/ handling objects (Safe Work Australia, 2012). In general, common forms of WMSDs such as back pain and joint injuries are associated with muscular stress from MH tasks, fatigue and other effects from repetitions, risks of awkward postures, adverse impacts of force and frequency of tasks (Rahman et al, 2015). For example, Table 1 portrays a summary of injury mechanisms and MH related WMSD claims of labourers and technicians/ trade workers in Australia.

Conventional methods of ergonomic evaluations and MSD risk assessments require risky and expensive physical mock-up observations or basic details from video/ historic data analyses and perceptions. For example, RULA- Rapid Upper Limb Assessment and REBA- Rapid Entire Body Assessment are useful frameworks (Shoaf et al, 2000). Our ongoing research synergistically employed a contemporary hybrid approach including motion captures, postural analyses, biomechanical modelling and VR simulation studies as well as qualitative research from focused literature reviews, field observations, brainstorming discussions and expert consultations. In this paper, a set of key findings and discussions as well as basic details of our VR model for assessing MSD are presented. The risk of injury is also related to the activity duration, frequency, or a combined exposure to risk factors. Although psychological factors, whole body vibration, and environmental factor would also be contributing to the assessment of Welding related MSD risks, such causes are not covered in our current research.


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Table 1. MSD claims from certain manual handling occupations in Australia in 2012-13 Injury mechanisms Labourers Technician and

Trades Workers Muscular stress while handling objects other than lifting, carrying or putting

1325 740

Muscular stress while lifting, carrying, or putting down objects

1495 940

Repetitive movement 525 300 Stepping, kneeling or sitting 115 120 Total 3095 2100 2. Key tasks and MSD risks in structural steel welding works

Ergonomic risks of WMSDs can arise from workplace elements (conditions) and actions, or a combination of both, which might yield significant physical stresses and adverse impacts. Examples include forceful exertions, awkward postures, repetitive exertions, and environmental factors. In structural steel and welding trade works, common tasks are: (i) cutting marked-out metal sections and shapes using hand tools, flame cutting torches or metal cutting machines; (ii) shaping and bending metal sections and pipes using hand and machine tools or by heating and hammering; (iii) joining metal sections; and (iv) cleaning and smoothing welds by filing, chiselling and grinding. Rahman et al. 2015 discussed regarding a set of MH related factors for WMSDs. Table 2 portrays specific aspects and factors of structural steel welding tasks covered in the research paper. Table 2. MH related WMSD factors in welding tasks Aspect Main factors Example sub-factors

Load Mass Object Physical characteristics Size, shape, etc. Action and posture Shared/ unshared e.g. between hands, with others (i.e. teamwork);

Holding away from trunk; Reaching above shoulder height; Bending and/ or twisting the back and/ or neck

Movement Range e.g. limited, extreme; Angle Frequency Number of repeated/ similar works in a shift/ unit time; Rest between

repetitions Duration Period e.g. short, medium, long

Task

3. Methods

3.1 Field observations

Our field observations in some structural steel welding facilities revealed a list of tasks and the object particulars. Furthermore, basic visual observations indicate certain cases/ circumstances of postural discomforts. A series of brainstorming discussions and expert consultations revealed specific details regarding ergonomic risks. This paper covers key ergonomic risks in the task of ‘joining metal sections’, especially related to back related WMSDs 3.2 VR simulations

The filed observations of structural steel and welding tradespersons work cycle enabled design of virtual simulation studies and posture analyses in the virtual reality laboratory at the Swinburne University of Technology. Using motion capture facilities, simulations of actual working cycles were studied in virtual


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environment. Representative mimics were recorded through advanced motion capture system connected with virtual environment. A 20 infrared Optitrack high resolution camera system with high-speed marker tracking (100 frames per second) was used to capture motions. Software such as C-motion and Motive were used in this research. Furthermore, ergonomic evaluations of postures were conducted in accordance with the guidelines in ISO 11226:2000. For example, trunk inclinations of more than 60 degrees are not acceptable in static postures.

Figures 1 to 4 portray observations and details of postures 1 to 4 respectively. Posture 1 in the welding working cycle is basically slight bending for positioning the welding devices, gas cylinder. From the field observation of workplace, it has been noted that moving gas cylinder is one of the risky tasks for the structural steel welding trade persons, i.e. with respect to posture and task requirements. In our sample study, the weight of welding gas cylinders is 37.2kg, which is manually lifted and placed on the two wheeled trolley, mostly by a single person. According to ISO 11226:2000, trunk inclinations between 20 to 60 degrees should be with full trunk support and otherwise the holding duration should be controlled within limits.

Figure 1. Posture 1 in actual and virtual environments

Posture 2 represents the welding cycle action of picking the welding gun and parent material, which is frequent bending and reaching, e.g. around 35 times per hour and repetitive in a workday (i.e. 8 hours shift) to accomplish welding task requirements. In these actions, welders often bend their back severely and mostly without any support. Picking loads for this purpose varies from 1 to 15 kg. Every time, the welding trade person has to bend and grab the work piece or welding gun and aim to hit the welding spot. Ergonomically awkward postures have been detected in these operations, especially higher WMSD risks (e.g. back pain).


Task Requirements: Trunk inclination = 900

Holding time = 30 seconds Frequency = 35 times per hour Weight handled = 1 to 15 kg


Holding time = 6 minutes Frequency = 2 times per hour Gas cylinder weight = 37.2kg


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Posture 3 portrays the common kneeling position of a welder. This posture is required in certain welding circumstances when joining of structural steel sections are large and complex or difficult to lift up. This position is very common in most of the structural steel and welding works. The welders may rely on knee support on the floor and yet the back and neck are in awkward positions. Also extended durations or repetitions might add additional MSD risks to knee and joints as well.


Posture 4 is the reaching and forward bending pose common in the structural steel and welding trade. Welders often grab welding guns and target to hit inclined work pieces by bending and reaching their back. This posture is mostly repetitive in daily routines of the trade, i.e. 35 to 40 times per minute. In many cases, this position has to be held for 1 minute for welding purpose followed by approximately 15 seconds of rest.

Figure 4. Posture 4 in actual and virtual environments 4. Risk assessment and discussions

4.1 Risk assessment

Data and information have been consolidated from field observations and virtual reality simulation studies including motion captures, posture analyses, ergonomic evaluations and biomechanical modelling. Ergonomic risk assessments for selected tasks and postures have been systematically conducted. Table 3 presents the 5 x 5 risk matrix applied for assessment and rating of WMSD risks. 6 domain experts have been consulted for finalising the risk assessments. Table 4 portray WMSD risk ratings for 4 identified key tasks of structural steel welding trade. For example, joining tasks of welders is the major concern for WMSDs from body stressing effects. Table 5 presents a consolidated summary of risk assessments for above-mentioned 4 most common postures in structural steel welding. For example, posture 4 is highly hazardous.


Holding time = 2 minutes Frequency = 25 to 35 times per hour Weight handled = 1.2 kg


Holding time = 1 minutes Frequency = 35 to 45 times per hour Weight handled = 1.2 kg


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Table 3. Risk rating matrix

Risk rating Consequence Likelihood Minor, 1

(No injury)

Disruptive, 2 (Minor injury-no loss time)

Significant, 3 (Loss time injury)

Critical, 4 (Serious injury)

Catastrophic, 5 (Death/serious injury)

Almost certain, 5 (Is almost certain to occur)

High High Very high Very high Very high

likely, 4 (Is likely to occur) Major Major High Very high Very high

Possible, 3 (May occur) Moderate Major Major High Very high

Unlikely, 2 (Is not likely to occur) Low Moderate Moderate Major High

Rare, 1 (May occur in exceptional circumstances)

Low Low Moderate Moderate Major

Table 4. Body stressing related WMSD risk assessments for structural steel and welding tasks MH mechanism: Body stressing Task

Likelihood Consequences Risk rating

Task 1: Cutting marked-out metal sections and shapes using hand tools, flame cutting torches or metal cutting machines

Likely Catastrophic Very high

Task 2: Shaping and bending metal sections and pipes using hand and machine tools or by heating and hammering

Likely Critical Very high

Task 3: Joining metal sections by using various welding techniques, bolting or riveting

Almost certain

Significant Very high

Task 4: Cleaning and smoothing welds by filing, chiselling and grinding

Possible Catastrophic Very high

Table 5. WMSD risk assessment for common postures in welding task – joining sections

Task requirements Risk assessment Postures Weight

(kg) Frequency (per hour)

Duration (hr)

Likelihood Consequence Risk rating

Notes

Posture 1 37.2 2 7.5 Likely Significant High Back pain is likely and consequence is loss time injury

Posture 2 15 35 7.5 Almost certain

significant Very high

Almost certain to get back pain and consequence is loss time injury

Posture 3 1.2 30 7.5 Possible Disruptive Major Back pain may occur and minor consequence, no-loss time

Posture 4 1.2 40 7.5 Likely critical Very high

Likely to occur back pain and consequence is critical


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4.2 Discussions

After assessment of task requirements and risks, jobs and workplaces can be suitably designed or redesigned (Rahman et al, 2015). Basically, the design requirements of structural steel and welding tradesperson work and workplace are derived from (a) job content including details of object(s) to be handled and particulars of tasks to be performed and (b) action and posture and (c) individual capacities/ conditions. In general, an individual performing a welding job basically uses his/ her physical capacity along with available facilitative mechanisms to get the job done safely. If a person’s current physical capacity is lower than the postural demand requirement, health and safety cannot be ensured without suitable changes or facilitative mechanisms. For example, adverse exposures on back due excessive exertions can eventually cause serious effects on an individual’s musculoskeletal health.

5. Summary and conclusion

Musculoskeletal disorders from welding tasks in different industries are serious concerns and also among the leading causes for claims. Ergonomic risk evaluation of welding tasks is crucial as these have strong connectivity with WMSDs. Through our field observations, VR simulation studies including posture analyses and biomechanical modelling, we have consolidated systematic risk assessments for structural steel welding trade. With such contemporary and rational arrangements, jobs/tasks can be suitably designed/ redesigned for improved safety and health outcomes – even for highly risky and challenging trades.

Acknowledgements

Authors express their acknowledgement for (a) significant contributions in simulation studies by the postgraduate student Mr Panha Kruoch, (b) valuable support from the Faculty of Science, Engineering and Technology in Swinburne University of Technology, Australia; and (c) useful information/ knowledge-based contributions from various industry practitioners and academic researchers References ISO 11226:2000(E). 2000. Ergonomics – Evaluation of Static Working Posture. Switzerland: International Standard

Organization. Pontonnier, C., A. Samani, M. Badawi, P. Madeleine, and G. Dumont. 2014. Assessing the Ability of a VR-Based

Assembly Task Simulation to Evaluate PhysicalRisk Factors', Visualization and Computer Graphics. IEEE Transactions 20 (5): 664-674.

Rahman, A., E. Palaneeswaran, and A. Kulkarni. 2015. Musculoskeletal Health and Safety of Aged Workers in Manual Handling Works. In Proceedings of the International Conference on Industrial Engineering and Operations Management, United Arab Emirates, Dubai.

Robertson, D. G. E., G. E. Caldwell, J. Hamill, G. Kamen, and S. N. Whittlesey. 2004. Research Methods in Biomechanics. United States of America: Edwards Brothers.

Safe Work Australia. 2012. Compendium of Workers' Compensation Statistics. Australia. ISBN 978-0-642-33331-5. Shoaf, C., A. Genaidy, J. Haartz, W. Karwowski, R. Shell, P. Hancock, and R. Huston. 2000. “An adaptive control model

for assessment of work-related musculoskeletal hazards and risks.” Theoretical Issues in Ergonomics Science 1 (1): 34-61.

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Virtual reality based ergonomic risk evaluation of welding