workstation design guidelines -...

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Islamic University of Gaza - Palestine

Workstation Design Guidelines

Department of Industrial Engineering

Dr. Abed Schokry


Workstation Design Guidelines

• There are 14 guidelines that must be taken into considerations by ergonomists when considering the design of a workstation.

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Workstation design guidelines

1. Avoid static loads and fixed work postures,

2. Reduce Musculoskeletal Disorders,

3. Set the work height at 50 mm below the elbow,

4. Furnish every worker with an adjustable chair,

5. Use the feet as well as the hands,

6. Use gravity, don’t oppose it,

7. Conserve momentum,


8. Use two-hand motions rather than one hand motion,

9. Use parallel motions for eye control of two-hand motions,

10. Use rowing motions about the elbow,

11. Pivot motions about the elbow,

12. Use the preferred hand,

13. Keep arm motions in the normal work area,

14. Let the small woman reach and fit the large man.

Workstation design guidelines (cont.)


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GL 1: Avoid Static Loads and Fixed Work Postures

• Static load increases systolic and diastolic blood pressure.

• Metabolic wastes accumulate in the muscles.

• Consider increasing recovery time.


Avoid Static Postures

• Employees should be encouraged to wear proper shoes for work requires lots of standing.

• Workstations should be equipped with mats.

• Have hips parallel to the floor.

• Provide bar rail to vary work posture.


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Falls

• Slips and falls are a major cause of injury deaths and have annual direct cost/capita of $50–400.

• Causes of falls:

– Slips: unexpected horizontal foot movement

– Trips: restriction of foot movement

– Stepping-on-air: unexpected vertical foot movement


Solutions for Falls

• Prevent the fall:– Use well-designed ladders, scaffolds, and ramps properly.

– Provide safe steps.

– Use the three-contact rule.

– Provide good friction and reduce lubricants.

• Reduce the consequences of the fall:– Interrupt the fall.

– Soften the impact.


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Head Weight

• The head weighs about the same as a bowling ball.

• Keep the line of sight below the horizontal.

• Maintain forward head tilt of 10º-15º

• Avoid backward and sideward tilts.


Hands/Arms

• An arm weighs about 4.4 kg.

• Avoid using the hand to hold up a tool or work piece.

• Avoid working with elevated hands.

• Support the arms on the work surface or chair arms.


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GL 2: Reduce Musculoskeletal Disorders

• Don’t bend your wrist.

• Don’t lift your elbow.

• Don’t reach behind your back.

• Follow guidelines for hand and arm motions.


GL 3: Set the Work Height at 50 mm Below the Elbow

• Work height is defined in terms of elbow height.

• Optimum height is slightly below the elbow.

• Optimum height from the elbow is the same for sitting and standing.

• Work height is not table height.


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Solutions for Work Height

• Change machine height.

• Adjust elbow height.

• Adjust work height on machine.


Video Display Terminal Workstations

• Key items: screen, keyboard, document, eyes, hands

• Workstation furniture must be adjustable.

• Locate the primary visual element first: ahead of the eye, perpendicular to the line of sight.

• Train the operator in adjusting the equipment.

• Provide a wrist rest.


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GL 4: Furnish Every Employee with an Adjustable Chair

• The cost of an adjustable chair is very low compared tolabor cost.

• Allow users to try chairs in their specific jobs.

• Buy chairs that are easily adjustable.

• Train people in proper adjustment.


Chair Design

• Seats – Seat Height from Floor– Seat Length– Seat Width– Slope of Seat– Seat Shape

• Backrests– Position of Backrest– Molded Chair Back Position & Curvature

• Armrests• Legs/pedestals

– Clearance of feet and calves under chair


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GL 6: Use Gravity; Don’t Oppose It

• Make movements horizontal or downward; avoid lifting.

• Consider using the weight of the body to increase mechanical force.

• Use gravity to move material to the work.

• Use gravity as a fixture.

• Use gravity in feeding and disposal.


GL 7: Conserve Momentum

• Avoid unnecessary acceleration and deceleration.

• Use circular motion for moving and polishing.

• Eliminate grasping motions by providing edges, rolled edges, and holes.

• Avoid transporting weight in the hand.


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GL 8: Use 2-Hand Motions Rather Than 1-Hand Motions

• Cranking with 2 arms is 25% more efficient than with one.

• Using 2 hands is more productive despite taking more time and effort.

• Don’t use the hand as a fixture.


GL 9: Use Parallel Motions for Eye Control of 2-Hand Motions

• Minimize the degree of spread rather than worry about symmetry.

• Estimate the cost of eye control with predetermined time systems.


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Parallel vs. Symmetrical motions

BC DD

B C C C

A D B B

A D A A

Parallel motions• Shoulder moves• Easy eye travel

Symmetrical motions• Shoulder steady• Difficult eye control


GL 10: Use Rowing Motions for 2-Hand Motions

• Alternation causes movement of the shoulder and twisting of the torso.

• Alternation causes higher heart rates.

• Rowing motions are more efficient and provide greater power.


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GL 11: Pivot Motions About the Elbow

• Motion time is minimized with motion about the elbow.

• Cross-body movements are more accurate than those about the elbow.

• Physiological cost is lower for movements about the elbow.


• The dominant hand is:

– 10% faster for reach-type motions

– More accurate than the non-dominant

– More exposed to cumulative trauma

– 5% to 10% stronger

• Work should arrive from the operator’s preferred side and leave from the non-preferred side.

GL 12: Use the Preferred Hand


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• Avoid long benches.

• Use swing arms.

• For high use, keep it close.

• Remember the arm pivots on the shoulder, not the nose.

• The shoulder is very sensitive to small changes in workplace layout.

GL 13: Keep Arm Motions in the Normal Work Area


GL 14: Let the Small Person Reach; Let the Large Person Fit

• Design so most of the user population can use the design.

• Jobs must be designed for both sexes: Small or Large -Weld

• Multi-person use of equipment and stations is becomingmore common.

• The proportion to exclude depends on the seriousness ofdesigning people out and the cost of including morepeople.


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Ergonomic Prevention Approach

• Engineering approach – Analyze the job it detail.

• Video tape the job, various posture evaluation schemes (MANTRA, RULA, REBA, OWAS, JSI)* can be used for rough estimation of joint deviation, repetition/duration, and forces involved.

• They provide a scores for action limit and maximum limits, by which jobs can be selected for improvement.

• *: Those are software programs.


Posture targeting and recording tools

• Most of these tools are developed to quickly identify tasks that have high risk of MSD. These tools are easy to learn and can be used in participative ergonomics approach.

– RULA (Rapid Upper Limb Assessment)

– REBA (Rapid Entire Body Assessment)

– Job Strain Index (JSI)

– Quick Exposure Checklist (QEC)

– Manual Task Risk Assessment Index (MANTRA)

– OWOAS (Nordik tool for whole body posture assessment)


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Ergonomic Prevention Approach (2)

• Internal joint forces can be evaluated by EMG, biomechanical models

• Solution approaches are:– automation, – mechanization, – job enlargement, – redesign the workstation for adjustability and better working

posture, – better method to do the work to reduce force, – Duration and repetition.

• Administrative approach – Job rotation, use of part time workers, exercises, stress reduction


Examples of engineering solutions

• Counter balance and suspend hand tools - reduce static load of holding the tool,

• Tilt the work surface, tilt fixture - facilitate better posture, viewing, reach,

• Replace keying in by barcode, provide scanners, provide portable scanners – reduce repetitive motions

• Provide hand tools with correct grip style/diameter/texture – reduce gripping force, improve wrist posture,

• Maintain sharpness of the knives – reduce force required to cut Hand tools are properly maintained - reduce vibration,


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More of engineering solutions

• Use correct work height – better upper body and hand-arm posture

• Limit reaching motions to minimum - better upper body and hand-arm posture

• Lower the work area if shoulders needed to be lifted -better hand-arm posture

• Provide arm rest if elbows are needed to be raised –reduce static load at shoulder


More of engineering solutions

• Consider sitting/standing/sit-stand work posture – reduce static load in lower back, promote change of torso (upper body) posture,

• Arrange workplace to minimize twisting, forward or lateral bending – reduce harmful posture of torso,

• Correct viewing angle - minimize static load on neck muscles, eye strain,


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