ERGONOMICS BULLETIN

SUBJECT: DESIGN AND OPERATING GUIDELINES FOR COMPUTER WORKSTATIONS

I. ENVIRONMENT

  1. LIGHTING
  • Light should be adequate for operator to clearly see text and screen, but not bright enough to cause direct or reflected glare.
  • Light diffusers for fluorescent light fixtures should be considered for the area.
  • Task lighting should be considered for more demanding visual tasks such as proof reading and working with poor quality photocopies.
  1. GLARE
  • Position computer screens at right angles to windows to minimize reflection and glare.
  • Provide non-reflective screens (e.g., anti-glare filter) and keyboards (e.g., matte finish).
  • Work surfaces around the screen should be non-reflective.
  • Consider using blinds or curtains if sunlight is to bright or hot.
  • High gloss and brightly colored paints should be minimized on office walls and ceiling.
  • Position screen so that artificial lighting does not reflect from the screen.
  • If you are having trouble identifying the source of the glare hold a mirror in front of the computer screen.
  1. NOISE
  • Noise may increase operator stress and thus fatigue. Take steps to limit excessive or annoying noise from operation of equipment or machinery. Contact the campus Environmental Health, Safety and Risk Management Office for noise control assistance.
  1. VENTILATION
  • Ventilation should be provided to all work area's to maintain personal comfort and acceptable indoor air quality.

Contact the Environmental Health, Safety and Risk Management Office to assist with analysis of indoor air quality concerns. Contact Facilities staff for analysis and repair of ventilation systems.

II. WORKSTATION DESIGN

  1. CHAIRS

Chairs should be adjusted to fit the user. Below are recommendations for ergonomic chairs, but it is important to understand that numerical values may fluctuate depending on the person. Comfort is the key factor in determining if a chair is fitted properly.

  • Chair should easily adjust - preferably a pneumatic lift to allow easy adjustment of the entire chair to suit the task at hand.
  • Seat height
    • The seat adjustment range can be determined by measuring the work level from the floor and subtracting 12 inches. That number should be the midpoint in seat adjustment range.
    • For a standard desk chair 15.5-20 inches is recommended.
    • Upper legs should be almost parallel with the floor (90 degree angle at the hip joint).
  • Seat pan
    • Width should be at least one inch wider than your hips and thighs on either side (17 to 19 inches is the average recommendation).
    • Depth should be no less than 17 inches and should be adjustable either by a backrest with in-out adjustability or sliding seat pan to allow good stability and proper use of the backrest.
    • Slope should be within a range of adjustability from 0 to 7 degrees.
    • The seat should be contoured so to allow weight distribution through buttocks and upper part of thighs only.
    • There should be 1-5 inches from the front edge of the chair to the back of the knee so that there is no pressure on back of knees or underside of thighs
    • The seat should have a rounded front edge to reduce pinching and improve blood flow to lower leg.
    • The seat should have 1-2 inches of padding with breathable upholstery.
  • Backrest
    • Width of 13 to 14 inches
    • Height of 6 to 20 inches.
    • Lumbar support is done through gentle curves in the backrest shape and should be 4 to 10 inches to affect the size and firmness of the lumbar support and accommodate for different preferences and body shapes.
    • Height adjustability should allow individuals to change how the lumbar support curve contacts the back and should move up and down within a 7 to 10 inch range.
    • In and out (forward) adjustability of 12 to 17 inches
    • Tilt angle of 5 to 30 degrees
  • Armrests
    Armrests should only be used periodically because they can lead to arm, wrist and shoulder problems. Armrests can interfere with you getting close to your work, so adjustability is essential.
    • Height should be 7 to 11 inches
    • Length should be 6 to 10 inches
    • Width should be a minimum of 2 inches

If arm rests are being used shoulders should be relaxed not elevated.

  • Chair should swivel if twisting is necessary.
  • Any chair with mobility should have at least 5 castors for increased support.
  1. FOOTRESTS
  • Ensure person is positioned correctly with proper chair height and back support in the small of the back then check whether person is able to comfortably place both feet on the ground.
  • Footrests should have adjustable height and surface area large enough to comfortably accommodate both feet.
  • Footrests should be 12 x 16 inches with an angle of 25 to 30 degrees. A non-skid surface is recommended.
  1. KEYBOARD
  • Keyboards should be separate from the computer screen to allow for independent adjustment - powerbooks and laptops are not designed for long term keyboarding.
  • Upper arms should be at the operator's side with a 90 degree angle at the elbow (keyboard home row height 23-28 inches - a standard desk is 30 inches off the ground which is too high for typing for extended periods of time.)
  • Keyboard slope should be adjustable from 0-25 degrees.
  • Wrist pads should be considered for the edge of the keyboard support surface and should be used only during typing breaks, hands should float above keys during typing with the wrists kept straight.
  • Keyboard should be replaced if keying requires excessive force.
  • Key tops should be dished to minimize slipping of the fingers.
  • Keyboard and keys should have matte finish to minimize glare.
  1. SCREEN
  • The top of the computer screen should be just below eye level (mid-screen height 37-43 inches). The viewing angle should be 5-20 degrees. Individuals who wear bifocals should pay attention to monitor placement and lower computer monitor or purchase glasses designed for computer work to avoid tiliting their head back to read the screen through the lower part of the bifocals.
  • The screen should be tilted back slightly (maximum 15 degrees).
  • Viewing distance (eye to screen) should be approximately arms length (between 20-30) inches.
  • Adjust screen brightness, contrast, etc. for comfortable viewing.
  • Screen display should be free from flicker.
  • Screen should have a minimally reflective surface.
  • Character display should be a size (3/16 inch), color and quality that ensures legibility.
  1. WORKSTATION
  • Use a footrest if the chair or table is to high.
  • Use a document holder that is located just to the left or right of the screen. The copy holder should be adjusted to maintain the document at the same height as the screen and the same distance from the operator's vision.
  • Keyboard and screen should be directly in front of the operator. The screen viewing angle should be between 0-15 degrees.
  • Writing surface should be provided (minimum dimensions 12 by 16 inches, optimum 30 by 30 inches).
  • L-shaped workstations should be considered for operators who perform varied tasks (e.g., writing, typing, attending to a printer, etc).
  • The work surface should be at about elbow height and there should be a 90 degree angle at the elbow joint.
  • The work space should allow sufficient leg space. Minimum width of 31 inches, minimum depth of 25 inches and minimum height of 26 - 28 inches.
  • When typing the wrists should be in line with the forearms and not bent forward or backward or side to side.
  • A matte finish should be used to minimize reflection.
  • Rounded corners on workstations are recommended so that arms and wrists do not come in contact with any sharp or square edges.
  • Frequently used items should be kept with 10 inches of the individual to minimize reaching and occasionally used items within 20 inches.
  • Enough work surface should be available for all computer accessories.
  • Use a headset if a large portion of time involves using the phone.
  1. MOUSE
  • Arm should be supported, at the side, and close to the body, with elbow at about work surface height. Upper arm and forearm should be at about 90 degrees. Position should allow the forearm to move, not the wrist (avoid ulnar or radial deviation). The wrist should be in line with the forearm (avoiding extension and flexion of the wrist).
  • The mouse should be kept at the same level as the keyboard and as close to the centerline of the body as possible.

III. TASK CONSIDERATIONS

  • Maintain the body in a position that is neutral or comfortable.
  • Do not hold a telephone between your neck and shoulder.
  • Your chair must be adjusted properly to be effective. No single position is appropriate for extended periods of time. Be sure to stand, stretch and take frequent breaks.
  • Operations that require one hand on the keyboard with the other thumbing through a document may require the keyboard to one side and document in front.
  • Eye strain is often caused by eye muscles holding a particular focal distance and so may be alleviated by changing your focal distance. A wall hanging or poster, which allows the operator to focus on a distant object (preferably something at least 20 feet away)will offer visual relief and help reduce eye strain.

IV. ADMINISTRATIVE CONTROLS

  1. EXERCISES
  • Exercise is one of the most effective steps in avoiding the effects of excessive force, awkward position and repetitive motion.
  • Take several brief stretch breaks throughout the day. Stretching improves blood flow and rejuvenates working muscles.
  • Implement a voluntary daily exercise/stretching program in your work area.
  • Periodically exercise your eyes to reduce visual fatigue. One simple exercise is to focus your eyes on objects at variable distances. In addition, use corrective lenses if needed
  1. BREAKS
  • Take periodic breaks to stretch working muscles and reduce eye strain - one 15 minute break at least every two hours.
  • Rotate jobs to avoid constant keyboard work.
  • Change positions frequently.

V. LIFTING

  1. OBJECT CHARACTERISTICS
  • Keep the size and weight of the object being lifted as small as possible.
  • Lift balanced loads so you do not have to apply forces to control a moving center of gravity.
  • Lifting is not recommended above shoulder height or below knee height. Store light objects up higher.
  1. TECHNIQUES
  • Keep the load as close to the body as possible.
  • Avoid forward leaning or bending and lateral bending when lifting.
  • Avoid twisting while lifting.
  • Maintain good balance and footing.
  • Keep the back straight when lifting.

VI. GENERAL OFFICE SAFETY

  • Use elevators to carry loads up stairs.
  • Good housekeeping is important.
  • Floor surfaces should offer good traction.
  • Aisles should be wide enough and remain clear of tripping hazards.
  • Use the correct tool for the job. Do not stand on chairs, properly use ladders or step stools.