Ergonomics and Occupational Biomechanics Laboratory
Richard Wells

Work Assessment

MSD Hazard Identification
MSD Risk Assessment
Ontario Universities Low Back Pain Study (OUBPS)
Biomechanical Modelling: 4DWATBAK
Hand Demand
Predicting Hand Demand During Design
Determining the Acceptability of Manual Work
Assessing Work at Visual Display Terminals

MSD Hazard Identification


Definitions

Risk-Based Approach Based upon upstream indicators (hazards) rather than downstream (injuries) indicators. An approach based on a detailed evaluation of hazard and exposure potential at a particular site and risk when unacceptable levels are being exceeded
Hazard Identification Determines whether or not (Y/N) a particular task/situation could cause an adverse effect -MSD
Risk Assessment Incorporates number of steps, including hazard identification, to determine the probability that an adverse effect –MSD- could occur
Purpose: The purpose of the hazard identification and risk assessment step is to inform the prevention process
Hazard or Risk? Strictly speaking, hazard identification is not possible because the physical hazards (forces, postures and repetition) are ubiquitous. A two step hazard identification and risk assessment process is really two risk assessments at different levels
Specification of Thresholds: It is unreasonable to expect a simple checklist to accurately estimate the risk of developing MSDs because of multiple interacting risk factors, the difficulty of observing them, the large differences between workers and the relative lack of quantitative epidemiologic data on dose-response relationships. The physical hazards (forces, postures and repetition) are ubiquitous in workplaces and too sensitive (low) a threshold on a hazard identification tool will overwhelm a workplace with the requirement to perform further full risk assessments. While science cannot provide precise estimates of numeric thresholds for development of MSD’s, concrete benchmarks can be set that are informed by a variety of existing scientific evidence and may be justified to aid the OH&S system and workplaces in prevention activities.

An MSD Hazard Identification tool/ method/ checklist is a part of an MSD prevention program. The steps are shown below.

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Schematic of the Hazard Identification and Risk Evaluation Approach

In choosing or developing a Hazard Identification Tool for use as part of an MSD prevention program, the following are desirable:

1) Features

  • Inclusive of common MSDs and their risk factors
  • Inclusive with respect to sector/type of tasks
  • Presence of risk factors enough for hazard or are there cut-points and/or times/frequencies
  • Scoring method transparent and supportable (if scored)
  • If single score, does scoring system aggregate body regions or other non-additive effects
  • Clear description of how to interpret scores and resulting action
  • Includes reported MSD on job or other workers’ reports as criterion for further assessment

2) Measurement issues

    a. Designed as Hazard Identification, Screening” or Filter Instrument
  • b. Qualitative or semi-quantitative
  • c. Appropriate sensitivity
  • d. Inter and intra-observer variability known

3) Usability Issues

  • a. Use diagrams for observables
  • b. Are observables documented in tool or in training materials
  • c. Don’t ask observer about un-observables
  • d. Reasonable resource cost for administration (5-10 minutes/job for repetitive tasks in one place)
  • e. Reasonable amount of training required; Is usable by workplace parties (define as JHSC members

4) Overall Evaluation

  • a. Supported by best evidence
  • b. Proven effectiveness

The place of Hazard Identification in the prevention of MSDs can be seen in this presentation

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MSD Risk Assessment


The choice of a risk assessment approach depends on the situation being assessed and there is no one tool that is appropriate for all scenarios. While the outputs of some methods for MSD risk assessment have been shown to be related to MSD risk, they do not permit a clean separation of "safe" and "unsafe" jobs;

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Schematic of Recommended Actions for Risk Evaluation Approaches


Risk assement methods that are specific to the upper limb or include upper limb subsections include: ACGIH: HAL, BS EN, CTD RAM, ISO 11226, ISO/TS 20646-1, LUBA, ManTra, OCRA, OWAS, QEC, REBA, RULA, WSHA SNOOK, Strain Index, UAW-GM
The following documents give details of these risk assessment approaches.

Tools: Table 1
Tools: Table 2
Tools: Table 3

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Ontario Universities Low Back Pain Study (OUBPS)

This study was unique in deliberately using multiple exposure assessment approaches separatelly as part of a case-referenet epidemilogical study. The study is described in this poster

Wells, R., Norman, R., Neumann, P*., Andrews, D*., Frank, J., Shannon, H. and Kerr, M*. Assessment of Physical Work Load in Epidemiologic Studies: Common Measurement Metrics for Exposure. Ergonomics, 1997, 40(1): 51-62.

Posture Sampling

It is difficult to assess jobs that are not cyclic; that is if they don't repeat the same motions with a short cycle time.Industrial engineering has developed an approach call ed work sampling where the activities of workers or machnes are observed (sampled) every few minutes or hours. This gives the proportion of time a worker is performing a given activity.

By recording not just the activity (push pull or lift for example) we developed a method of recording the force magnitude, direction, trunk and arm posture. Using these values, loading on the spine could be calculated as the exposure measurement.

The use of this approach to document and assess complex occupational activities can be see in this presentation

Neumann, P*., Wells, R., Norman, R., Frank, J., Shannon, H. and the OUBPS Group., A posture and load sampling approach to determining low back injury risk in occupational settings: methods and results, International Journal of Industrial Ergonomics, 27:65-77, 2001.

Video Posture Assessment

In order to obtain trunk posture and load weight information, even in confined spaces and with minimum encumberance from equiment, a video based posture system was developed. Posture and load variables were obtained from video by a computer assisted tracking system. The video was replayed under computer control and the operator tracked trunk position in three planes using a “video game” joystick.

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Schematic of the approach to obtaining trunk kinematics from video

Neumann, P*., Wells, R., Norman, R., Kerr, M., Frank, J., Shannon, H. and the OUBPS Group, Trunk posture: reliability, accuracy and risk estimates for low back pain from a video based assessment, International Journal of Industrial Ergonomics, 28:355-365, 2001.

Neumann, W.P.* Wells, R.P., Norman, R.W., Kerr, M.S., Frank , J.S. Shannon, H.S., and the OUBPS Working Group. Trunk Posture: Reliability, Accuracy, and Risk Relationship of a Video Based Method for Physical Exposure Assessment from Trunk Posture. International Journal of Industrial Ergonomics, 28:355-365, 2001.

Questionnare

Andrews, D*., Norman, R., Wells, R. and Neumann, P. The Accuracy of Self Report and Expert Observer Methods for Obtaining Estimates of Peak Low Back Information During Industrial Work. International Journal of Industrial Ergonomics, 1997, 19:445-455.

34. Andrews*, D.M., Norman, R.W., Wells, R.P., and Neumann, P.* Comparison of self report and observer methods for repetitive posture and load assessment. Occupational Ergonomics, 1(3):211 222, 1998.

Electromyography


Mientjes, M*., Norman, R., McGill, S., and Wells, R. Assessment of An EMG based Method for Continuous Estimates of Low Back Compression During Three Dimensional Occupational Tasks and Jobs, Ergonomics 42(6): 868-879, 1999.

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Biomechanical Modelling: 4DWATBAK:

4DWATBAK is a unique combination of a biomechanical model and risk estimates obtained from epidemiological studies. The 3D mannequinn is coupled with the ability to assess risk over time; multiple task comprising a whole work shift. 3 spatial dimensions plus 1 time dimension equals 4D!


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Schematic of the 4DWATBAK Mannequinn

Its use can be seen in this poster and further details at this web site

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Hand Demand

The measurement of hand force in occupational settings is not well defined. How to account for the many ways in which the hand is used? Characterizing human hand capabilities or demand created by occupational tasks has been mainly accomplished by measuring the maximum force exerted on a handgrip dynamometer or similar transducer. If the occupational activity is not a power grip or a pinch but involves combinations of actions, such as moments and forces, how well do these measures characterize the demand on the tissues of the hand and forearm?

Using an approach from robotics, wrench, we defined a way of accounting for many prehensile activities, not just gripping.

The approach allows a complete description of the prehensile capabilities of the human hand. The force and moment wrench ( a 6 x 1 matrix, augmented by the internal grip force) is used to describe the external forces and moments exerted. The grip force is an interface measure necessary to transmit the wrench and is dependant on the particular grip geometry and object properties


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Schematic of the relationship between the internal loads and the external actions of the hand


The use of this approach to document and assess complex hand activities can be see in this poster and this presentation

Wells, R. and Greig, M. Characterising human hand prehensile capabilities by force and moment wrench, Ergonomics, 15;44(15):1392-402, 2001.

Greig, M. and Wells, R. (2004) Measurement of prehensile grasp capabilities by a force and moment wrench: Methodological development and assessment of manual workers, Ergonomics, 47(1); 41-58.

Morose, T., Greig, M., and Wells, R. (2004) Utility of using a force and moment wrench to describe hand demand, Occupational Ergonomics, 4:1-10.

Kopellar, E. and Wells, R. (2005) Comparison of measurement methods for quantifying hand force, Ergonomics, 48(8): 983-1007.

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Predicting Hand Demand During Design

The hand and fingers can grip an object in many ways and can exert (grip) forces on the object and transmit forces and moments to the environment. This approach that relates task requirements to distal arm demand. Graded contractions (forces, moments and combinations) between zero and maximum in five grips were applied by 40 adults (20M, 20F). Surface electromyography (EMG) from eight muscle of the forearm and hand and a rating of perceived exertion (RPE) were recorded. Artificial neural network modeling was used to describe the relationship between the forces and moments exerted and the EMG and RPE.

The use of this approach to predict the demand on the hand during design activities can be see in this presentation

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Determining the Acceptability of Manual Work

Moore, A.E. and Wells, R. (2005) Psychophysically determined acceptable torques for in-line screw running: Effect of cycle time and duty cycle. Ergonomics, 48(7):859-874.

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Assessing Work at Visual Display Terminals

An increasing number of people work at VDTs or Visual Display Terminals. Although the work appears easy with no possibility for injury, it has been found that the very "easy" nature of the work can overload the musculoskeltal system. VDT work is characterised by relatively low loads but long durations when the muscle cannot turn off. The shoulder muscles are particularly at risk for this problem. We have been developing a range of measures to help assess VDT work. A short presentation of assessment options can be seen here

Assessment of individual pieces of equipment can be performed in the laboratory or actually in the office. The first example illustrates how office equipment can be evaluated in the laboratory.

A number of recommendations for support of the mouse arm have appeared in the computer and RSI-related literature. These include supporting the wrist on the work surface and moving the mouse from the wrist, planting the elbow on the chair’s arm rest and moving the mouse from the elbow joint, resting the forearm on the work surface and moving the mouse from the shoulder and moving the mouse from the shoulder joint with the arm unsupported. Which is better?

Based upon the study:

  • The elbow support condition appeared to minimize the static load on the shoulder muscles sampled (trapezius and infraspinatus) and the forearm muscles
  • The shoulder support condition appeared to require the highest muscle activity in the shoulder muscles
  • The wrist support condition appeared to require the highest muscle activity in the muscles of the arm

The presentation can be seen here


R. Wells, I.H. Lee, and S. Bao, 1996 Investigations of the optimal upper limb support conditions for mouse use, in: Proceeding of Human Factors Association of Canada, pp 1-6.


It is much more complicated to assess office work in the field. Exposure to musculoskeletal loading at work depends on many factors including tasks performed, workload, workstation, equipment, technique, task-time and organization. It is difficult to separate out the effects of each factor from overall level of musculoskeletal loading. Combining EMG and task identification using video has shown promising results in industry.

Separating EMG by task in the workplace was found to allow the examination of the effects of specific tasks on musculoskeletal load during work on VDT in an office setting.It was found that:
  • Use of a mouse is a constrained task that has high static muscle activity and low peak muscle activity in mouse hand
  • The period of time while keyboarding was marked by significantly higher static loading in both the forearms and shoulders

The presentation can be seen here

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Copyright © 2005 Richard Wells,
Ergonomics and Occupational Biomechanics Laboratory
This page last updated June 2008