Ergonomics

1. Ergonomics An ergonomics approach to designing for disabled workers

2. Agenda • Ergonomics & disability • Design implications • Consequences of adaptation • Reducing risk: Posture • Dimensional factors in work posture • Practical exercise • Force, repetition, vibration • RULA/REBA • Ergonomics Design Guide

3. Ergonomics • Ergo = work nomos = knowledge • Rational approach to optimizing work efficiency, minimizing health risk. • Based on: • Anatomy • Physiology • Psychology • Biomechanics • Work study/Task analysis • Epidemiology • Systems Design Engineering

4. What is ‘Disablement?’

5. Disablement “Disablement isthe loss or limitation of opportunities to take part in the normal life of the community [including employment] on an equal level with others, due to physical and socialbarriers."Disabled People's International 1981

6. Disability • Which is more rational for us to say; • “a disabled person” or “a person with a disability?”

7. Disability ‘Models’ ‘Disabled Person’ = Social Model • 20th/21st Century social/contextual approach. • Starts by looking at the capabilities of the person. • Defines 'impairment' and 'disability' as different things. • Suggests disabled people's disadvantage is due to institutional discrimination. • The focus is on independence. • The view is that the built environment should be made to suit all possible users. ‘Person With a Disability’ = Medical Model • 18th Century ‘scientific/rationalist’ approach. • Assesses impairment from the point of view of what a person cannot do, instead of what they can do. • Sees people as having to be adapted to fit the ‘normal’ world. • The emphasis is dependence; its focus is upon the impairment, rather than the needs of the person. • Attributes problems arising from the built environment to a lack of rehabilitation of people with disabilities.

8. Disability • It isthebuilt environmentthat is the source of the problem, not the person. • By falsely attributing ‘fault’ to the disabled person, equipment designers may not feel it necessary to accommodate their needs as a matter of course, only perhaps as ‘special cases.’

9. Ergonomics and Disablement • Ergonomics - recognizes that people are routinely disabled by barriers presented in a poorly designed built environment. • This environment includes tasks that do not take account of individual, natural, predictable variability. • Further recognizes that capacity and capability vary not only between, but also within individuals, due to accident, illness and age.

10. Inclusive Design Steps • Designing for a disabled worker logically requires the following steps. • Determine their needs now and (if feasible) in the future, based on: • task demands (task analysis, task measurement) • worker capacity (worker measurement, static and dynamic).

11. Inclusive Design Steps • Verify that meeting the disabled worker’s needs will not force others to adapt and suffer injury. • If others might have to adapt, design the task to meet the needs of these other users also. • Or specify removable adaptations • Or specify which users may and may not safely use the adapted equipment. • This will minimize risk of secondary and primary injuries and hence risk of personal injury litigation.

12. Primary and Secondary Injuries • Primary injuries (1): due to the poor fit of a task or ‘tool’ to the capacities or capabilities of the operator. • Primary injuries (2) Harm caused by poor fit of an adaptive aid to the capacities or capabilities of an unintended user. • Secondary injuries: Harm caused by the poor fit of an adaptive aid to the capacity or capability of an intended user.

13. Reducing Injury Risk Risk reduction begins with determining a user population’s variability in parameters related to adaptation suchas: Size (physical dimensions of body parts) Gender Age Weight Strength Handedness Mental capacity.

14. If we do not fit tasks to operators’ parameters, we force operators to adapt to their tasks. Hidden costs in terms of ill-health (latent injury). Reduces efficiency/productivity. Fit-Adaptation Worker - Job Match<<<<<>>>>>Worker - Job Mismatch Decreasing Adaptation<<<<<>>>>>> Increasing Adaptation Enabling, Safe Work<<<<<>>>>>Disabling, Injurious Work 14

15. Adaptation to Task: Health Consequences Pathological spine deformations in different occupations as determined by x-ray examination. Occupation % with Spine Deformations Average Age (years) Truck drivers 80.0 -- Tractor drivers 71.3 26 Miners 70.0 51 Bus drivers 43.6 40 Factory workers 43.0 45 Construction workers 37.0 51 Source: Rossegger, R., and S. Rossegger. 1960. Health effects of tractor driving. Journal of Agricultural Engineering Research 5(3): 241. 15

16. Reducing Risk (Example) • Back disorders are the most common debilitating musculoskeletal disorders affecting people who work in farming – adults and children. • Need rational risk assessment - important not to overlook risk factors. • Example: postural risk assessment for back injury.

17. Compressive loading at L5 disk: reference posture 100%

18. Compressive loading at L5 disk: Sitting & Reaching: C 180% B 175% A 125%

19. Biomechanical load (backrest angle) N 500 400 300 200 Height of backrest Giving lumbar support (cm) Disc Pressure 0 3 5 90 100 110 120 Backrest Inclination (Degrees) Intradiscal pressure - influence of backrest angle

20. The ability to adopt reclined postures is mainly affected by: • Reach demands of the task • Visual demands of the task • Now consider one of these factors • – reach - • in a short practical session.

21. Practical • Maximum Forward Grip Reach variability in this audience. • Based on the measurements we have taken, at what distance would we position a lever hand grip, assuming the lever might be operated by any of you as part of your job?

22. Calculating Percentiles • Find the mean (total measurements /number of measurements taken ‘n’ ) (so if n=10, with total of 250” then: 250/10 = mean is 25”) • Calculate the Standard Deviation: • Deduct the mean from each measurement (e.g. 26.5 – 25 = 1.5, 23 - 25 = -2) • Square each difference (all ‘-’ become ‘+’) e.g 1.5x1.5 = 2.25, -2x-2 = 4); • Add together all of the squares (2.25+4+,…,) • Divide this sum by n-1 • The figure you now have is the ‘standard deviation’ (shown as σ² or s²). Let’s assume σ² is 1.5 in this case.

23. Calculating Percentiles • Now consider your measurement…say 23 inches. Deduct the mean from this figure: 23 - 25 = -2 • Divide -2/σ² = -2/1.5 = -1.333 (This is known as a ‘z-score’) • Now look up -1.333 in a table of z-scores: • We see that -1.34 = p=9 and -1.28 = p=10 • These ‘p’s are percentiles. So, -1.33 is just over the 9th percentile. That means that in our sample of 10 measurements, we expect 9% to be 23 inches or shorter. • Therefore, we expect 91% to be longer than 23 inches.

25. Using %iles to Calculate Dimensions • We can also calculate this ‘backwards’ allowing us to find out the size we need to make something to fit a desired percentage of a user population. • This approach is essential when designing equipment or tools that unknown people (or changeable people, e.g. due to aging, loss of functionality etc) will possibly use. • Commonly use the 5th and 95th percentiles depending on which is critical.

26. Using %iles to Calculate Dimensions • Assume an anthropometric table is available: • Forward grip reach (mm…we’ll convert shortly) • Females 5th percentile = 655mm (25.79 inches) • Note that if you had made this for the 95th percentile US male the distance would have been 33.27 inches! • What would be the effect on posture and safety of a 5th percentile woman using a lever placed 7.48 inches beyond her maximum reach?

27. Percentiles in Design • 5th%le US female for: • Reach • Strength/Force requirement • But N.B. Consider correct %ile for guarding: e.g. to prevent slim or long fingers from being injured • 95th%le US male for: • Clearance • Weight bearing (plus adequate safety margin – e.g. could use 99.9th% and add 15-20%)

28. Source: Pheasant, S. and Haslegrave, C.M. (2006) “Bodyspace” 3rd Edition. Taylor and Francis

29. Limits of Usability • Designing for all possible users is ideal, but typically has practicability and affordability issues. Consider 5th-95th percentiles, extend either direction as dictated by the task or user group (e.g. 1st to 95th percentile). • If designing for one user, you must calculate and state what other users’ parameters must be. • Potential users - consider future changes in work force, addition of family members, gender, age, functional capacity, etc.

30. Static Anthropometry • Useful starting point for design of tasks and task environments. • Age, gender, racial factors. • Clearance generally >95th percentile male, plus clothing allowance; • Clearance in guarding components (e.g. to prevent access of body parts) may need to be <1st percentile. • Reach generally <5th percentile female.

31. Dynamic Anthropometry • The dimensions of the body in motion. • Range of motion (joints) • Age factors.

32. Force • Amount of safe force we can apply is influenced by: • Frequency • Posture • Maximum strength (for that movement) • Climatic factors • Health status • Fatigue • Always aim to minimize force (but not so much that a device will be activated unintentionally).

33. Repetition • High force, high repetition most dangerous • High force, low repetition dangerous • High repetition, moderate or low force can be dangerous also. • Figures differ for different tasks. • Always try to minimize repetition.

34. Vibration • Segmental: especially upper-limbs. Power tools, machinery etc. • Gloves with absorbing pads can help. Foam wrapping may also be useful in some cases. • Avoid gripping too firmly any hard surface or handle that is vibrating. Look at alternative methods of mounting the device. • Eliminate mechanical sources of vibration if possible – e.g. servicing equipment. • Whole body: driving off road

35. RULA-REBA • RULA (Rapid Upper Limb Assessment) • REBA (Rapid Entire Body Assessment) • Systematic tools to quickly assess risk from posture, force and repetition. • Reduce scores through task redesign and/or behavior guidance. • Re-assess after intervention.

36. Ergonomics Design Data • Extracts from Woodson (1981) are a useful field reference/guide. • However, anthropometric data are old and generally based on military personnel – • New civilian anthropometric data are available but expensive (c. $30,000). • Useful: Bodyspace (Pheasant, S. & Haslegrave, C.M. 2006).

37. Questions