Guidelines for computer workstation adjustments
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Adjusting a VDT workstation is neither complicated nor technical. Begin
with the chair and, after adjusting the chair to the most comfortable
position, proceed to other workstation components. Refer to the following
guidelines for adjustment tips and ideas.
A chair should fit the person using it and the task for which it is
intended. Here are the key factors in selecting and adjusting a chair:
- Stability – Use a chair that has good stability (five-point base).
- Seat – The preferred seat-pan length allows for space between the
front edge of the seat and the back of the lower leg, at the knee, while
the users back is contacting the backrest.
- Seat-pan angle – Preferably, the seat back should be moveable independently from the seat pan. The user should be able to lean back slightly to modify the pelvic angle at random.
- Seat-pan height adjustment – The height of the seat pan should
be easily adjustable by the user when seated.
Ideally, the chair height should be adjusted first, followed by
adjustment of other workstation components. If the work surface is too high,
the chair height will need to be adjusted upward until the hand, wrist, and
forearm are parallel to the keyboard and slightly above the keys. A footrest
can be added as needed to compensate for the increased chair seat height.
Seat-Pan Shape and Padding
The front edge of the seat should preferably have a rounded profile.
A straight seat pan front edge tends to compress nerves and blood vessels
behind the knee, sometimes causing discomfort and tingling in the lower
extremities. The seat-covering material should be porous and breathable.
Slippery seat pans may cause the user to slide away from the backrest,
producing a loss of lumbar support.
Hard, unpadded seat pans are uncomfortable to use. In contrast, soft, deeply
padded seat pans may cause the user to sink too far into the seat. A seat should
be selected with padding somewhere between these two extremes.
Backrests should have a 15-20-inch-high support surface, a width
ranging between 14-16 inches, and be vertically adjustable above the seat pan. The backrest should also be moveable independently from the seat pan to allow the user to lean back slightly at their discretion. A good backrest will support the lumbar region of the back, but not be so large that it interferes with use of the arms while performing tasks.
Armrests should be optional. When properly used, armrests reduce muscle loads on the neck, shoulders, and arms; reduce pressures in the spine, assist rising and sitting in the chair, and support task-related movement. If chairs have armrests, they should be adjustable to the user's width and height, and they should allow the chair to fit under the work surface without interference. Avoid adjusting armrests too high; in that position, they may cause shoulder discomfort. Overall, evidence shows that armrests are beneficial when they are adjustable and follow task-related postures and arm positions.
The display screen should be adjusted so that the topmost line of viewable
text on the screen is at or slightly below the user’s line of vision.
The display should also be located as far away from the user as possible while
still allowing for comfortable viewing. Bifocal users may need to locate
their monitors lower on the work surface to minimize tilting their heads back
while reading through the bottom portion of their lenses. Screens that swivel
horizontally and tilt or elevate vertically enable the operator to adjust the
screen for the best viewing angle. Sometimes, a display screen may need to be
mounted on an adjustable arm to allow for comfortable positioning.
The mouse or pointing device should be located directly alongside the
keyboard and to either side of it. Once the mouse or pointing device is
properly placed, the user should be able to use it comfortably while
maintaining the upper arm parallel to the torso. Also, the hand, wrist,
and forearm should be held in a reasonably straight, horizontal position
when using the input device. A wide variety of input devices are currently
available. One should be chosen meeting user preference, and it should be
used according to these general principles.
Most of the currently available keyboards are suitable for occasional
or routine computer use. If you can, choose one with a thin profile.
It should be positioned in a manner which minimizes bending of the wrist
during use. For best results, the user should arrange the workstation so
that the keyboard can be reached comfortably and without over-reaching.
Although not a requirement, some users may wish to place a wrist rest in
front of the keyboard, in order to help maintain a ‘'neutral" wrist posture.
If used, the document holder should be stable and adjustable for height,
distance, and angle of view. It should fully support the source material
and can be placed by user preference on either side of the monitor.
In some situations, the document holder may need to be placed between
the keyboard and the monitor. In all cases, placement of the document holder
should aid the user in viewing source material without uncomfortably
twisting the neck on a prolonged, repeated basis.
For intensive computer work without interruptions, use of a worktable
with a height adjustable surface and a separate, adjustable keyboard shelf
is recommended. The adjustable keyboard shelf should accommodate both the
keyboard and the mouse on the same level. Adequate clearance should also
exist underneath the workstation.
If a fixed-height worktable is used, an adjustable-height keyboard tray
should be available. The keyboard tray should be wide enough to accommodate
both the keyboard and the mouse, and the height adjustment mechanism
shouldn’t interfere with clearance underneath the workstation.
An adjustable-height keyboard tray also allows the worksurface to be used
for tasks such as writing, answering the telephone, and staging reference
If an operator’s feet do not rest flatly on the floor once the
chair height has been properly adjusted, a foot rest may be needed. Many
different types and styles of footrests are available. One should be selected
suiting user preference, and it should be easily moveable in order to avoid
becoming a tripping hazard. A footrest should only be considered after all
other workstation adjustment options have been exhausted.
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