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Ergonomic Chair Features
People vary widely in their shapes and sizes, and the chairs they use should reflect these characteristics. Workers should be able to select from a variety of different chair models.
A "poorly fitting" chair may introduce musculoskeletal problems or aggravate existing conditions. Compressive forces on the spine are greater when sitting than when standing. Fatigue and discomfort result when muscles and joints are forced into awkward postures, especially after prolonged sitting.
The chair is the most intimate piece of equipment the office worker has, yet it is often overlooked in the design of a workstation. Whether in a conference room, at a computer workstation, or at a drafting stand, the chair must be designed with function in mind. For example, a cozy, stylish conference chair may present problems for the office worker who types for a long period of time each day.
Currently there are no restrictions on using the term "ergonomically designed" to describe chain or any other type of office furniture. Pay attention to the claims made by chair manufacturers.
Fitting the Population
The chair must adjust to the size and comfort of each worker. Not only should the chair raise and lower to accommodate varying heights, but the seat depth should adjust as well. If the seat depth of the chair is too great, the back support cannot be used.
An adjustable seat angle is beneficial for the office worker. A forward sloping seat, or "waterfall front", is helpful to relieve pressure on the backs of the legs while the worker is typing or writing. A 5-degree backward slope promotes use of the backrest and prevents the worker from sliding forward. The backrest should support the lumbar spine but not restrict its movement.
The armrest should be adjustable for height, width between armrests, and distance to the seat front. These adjustments are important for reducing the pressure on the seat surface and the load on the spine. The length and width of the armrests must also be considered. Armrests can become obstacles when they are too wide or too high (e.g., armrests that prevent a chair from sliding under a table). When awkwardly positioned, armrests may hinder a worker getting out of the chair. Five casters are necessary to prevent the chair from tipping. The casters must roll over carpeted surfaces easily.
The following chair evaluation checklist, will help guide you in selecting a chair that can be adapted to your individual needs.
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Chair Evaluation Checklist
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| The Seat: |
| | If the seat height is a fixed height, the seat pan should be 18 to 19 inches above the floor. |
| | If the seat height is adjustable, the seat pan should be 16 to 20.5 inches above the floor. |
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The seat pan should adjust from an angle of 5 to 15 degrees forward tilt to 5 degrees backward tilt and should lock in place. |
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The seat should be 15 to 17 inches deep. Check to see that the seat back can be moved in over the seat pan. |
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The seat pan should be at least 18 inches wide. |
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The seat should have a rounded, waterfall front edge. |
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The seat should be contoured to support postures, distribute pressures, and provide freedom of movement. |
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The seat cushion thickness should range from 1.5 to 2.0 inches. |
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The seat covering should "give" and "breathe".
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| The Seat Back: |
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The seat back should be 15 to 20 inches high. |
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The seat back angle to the seat should be a minimum of 90 to 105 degrees (preferably up to 120 degrees), and lock in position. |
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The seat back width in the lumbar region should be at least 12 inches. |
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The seat must have lumbar support. The lumbar support should be 6 to 9 inches long and 12 inches wide. |
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The lumbar support should be positioned 6 to 10 inches above the seat and should be adjustable. |
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The lumbar support should protrude forward about 2 inches from the back of the seat. |
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As the seat back reclines, the lumbar support should move upward relative to the spine.
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| The Arm Rests: |
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The chair should have adjustable armrests. |
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The armrests should be 9 to 12 inches long and 8 to 9 inches above the seat.
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| The Chair Base and Adjustment Controls: |
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The chair should have a stable five-point base with casters to avoid tipping over. |
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The chair positions (armrests, lumbar support, seat back, seat height) should be easily adjustable. |
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The controls should be easily reached and adjusted from the standard seated work position. |
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The adjustment controls should provide immediate feedback. |
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The direction of operation of the adjustment controls should be logical and consistent. |
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Chair adjustments should only require the use of only one hand. |
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The chair should pivot 360 degrees, allowing easy ingress/egress and access to various work surfaces. |
Back to Creating an Ideal Computer Workstation
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References: |
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Chaff-in, D.B. and Andersson, G.B., Occupational Biomechanics, 2d ed. New York: John Wiley & Sons, Inc. 1991. |
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Dainoff, M.J., "Design of Sitting Machine Crucial to Office Efficiency," Contract 27:6, June 1985. |
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Eastman Kodak Company, Ergonomics Group. Ergonomic Design for People at Work, New York: Van Nostrand Reinhold, 1986. |
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Grandjean, E., Ergonomics in Computerized Offices, Bristol; Taylor & Francis, 1987. |
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Lueder, R.K., "Why Your Employees Can't Sit Still," Office Ergonomics Review, October 1984. |
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