Office Ergonomics - Equipment
Chair
The chair is your foundation for comfortable computer work. It must fit you
and be appropriate for your tasks. What to consider when selecting a chair:
Stability. Select a chair that has a five-point base.
Seat pan. The ideal seat pan allows two to three fingers’ width (3-3.5 inches)
from the front edge of the seat pan to the back of your lower leg at the knee
when your back touches the backrest. The seat pan should allow your lower
back to contact the backrest.
Seat-pan padding and fabric. Hard, unpadded seat
pans are uncomfortable to sit on for more than
an hour. Soft, deeply padded seat pans cause
you to sink in too far, shifting pressure
from the buttocks to surrounding
tissues. The result is tension in the hip
muscles.
The front edge of the seat pan should
have a softly padded, rounded front
edge (called a waterfall edge). Straight,
unpadded edges compress thigh tissues and
restrict blood circulation which can cause pain and
numbness in the legs. Seat-cover fabric should be porous and breathable. A
slippery seat pan will cause you to slide away from the
backrest and provide little back support.
Seat-pan angle. The seat pan should adjust to
reclining, flat, or forward angles – the three basic
angles for seated work – so that you can achieve
a comfortable posture.
Backrest. The backrest should be large
enough to support your entire back,
including the lumbar (lower back) region,
but not so large that it interferes with your
arms: 15 to 20 inches high and 13 inches wide
is preferable. It should be adjustable for
height and tilt and contour to the curve
of your lower back. Most computer users
tend to sit in an upright or slightly
forward posture. Adjust the tilt angle
so that the backrest touches your back.
Armrests. Armrests should be adjustable and should not interfere with the
work surface. You should be able to move in close to your work without losing
support from the backrest. Your forearms should rest comfortably on the
armrests, with your shoulders relaxed. If the armrests are too high they will
elevate your shoulders and cause stiffness or pain in the shoulders and neck; if
they’re too low they promote slumping and leaning to one side. Remove armrests
if you don’t use them, if they interfere with your tasks, or if they can’t be
properly adjusted.
Chair height. You should be able to adjust the height of the seat pan so that
your legs are at right angles and your feet rest flat on the floor. Your forearms
should be horizontal and at right angles to your upper arms and your elbows
should just clear the top of the work surface
Work area
How you organize the materials that you use to do computer work can affect
your productivity and comfort. Your work area should be large enough to
accommodate materials that you use often and to permit a full range of motions
for tasks — about 16 inches in front of you or to your side. Place materials
that you use occasionally farther away. Use storage areas such as overhead
shelves, filing cabinets, and desk drawers for items that you use infrequently.
Avoid storing items under your desk, which can take up leg space or strain
your back when you retrieve them. Take the time to organize materials that you use to do computer work. You’ll be more efficient and reduce the number of times that you have to reach for them
Desk or work surface
Select a stable, adjustable-height work surface that has a separate, adjustable
keyboard platform or keyboard and mouse platform. Adjustable-height work
surfaces and keyboard platforms accommodate different users and tasks.
If you can’t adjust the height of your work surface, you should have a keyboard
platform with adjustable height and angle; one that isn’t adjustable may
position you too far from the work surface. The platform must be wide enough
for the keyboard and for a mouse or other pointing device; the height adjustment
control should not interfere with your legs.
The work surface should have a matte finish to reduce glare. Beneath the
surface there should be ample room for your legs — nothing to obstruct knees,
legs, shins, or thighs. Minimum work-surface depth, including space for a keyboard
if it is not on a platform:
- 24 inches, flat-panel display
- 30 inches, 13-inch monitor
- 40 inches, 17-inch monitor
Keyboard
The keyboard should be thin to help keep
your wrists straight while you’re typing.
If you use a keyboard platform, choose
one with adjustable height and angle.
Wrists and forearms should be relatively
straight, slightly above the keyboard:
your hands should be at or just below
elbow height. Shoulders should be
relaxed, elbows close to your body.
Matte-finished keyboard surfaces reduce
reflection and eyestrain.
Keyboards can be fitted with palm rests
that support your hands, minimize
contact with table edges, and help keep
your wrists straight. Make sure the palm
rest supports your palms, not your
wrists. The top of the palm rest should
not be higher than the first row of keys
on the keyboard.
Alternative keyboard designs are also
available, including split and angled
keyboards and keyboards with different
key arrangements. Some computer users
feel that these alternative keyboards
reduce typing fatigue; they’re not successful
for all users, however. Proper
chair height and work surface adjustments
are more important than an
alternative keyboard.
Mice and other pointing devices
Your mouse or pointing device should be at the same height as the keyboard, to
either side of it. Your arm should be close to your body for support. Your hand,
wrist, and forearm should be reasonably straight and slightly above the mouse.
(A palm rest can help support your hands and keep your wrists straight.)
Other types of pointing devices include touch pads, mouse pens, glide points,
mice that reorient the hand and wrist, and mice designed for either hand
Monitor
The topmost active line of the monitor screen should be at or slightly below
eye level. The topmost active line is the first line that you typically look at, not
the top line of the status bar. The area of the screen that you look at most often
should be about 15 degrees below eye level. The distance between your eyes
and the screen should be about an arm’s length (16-29 inches) when your neck
is straight.
If you wear bifocal, trifocal, or progressive lenses, you may want to position
the monitor lower to avoid tilting your head back to read through the bottom
portion of the lens. Monitors that swivel horizontally and tilt vertically enable
you to achieve the best viewing angle. If you need more workstation space or
if others will use the workstation, consider mounting the monitor on an adjustable
arm.
The monitor should have brightness and contrast controls that are easy to
adjust. Text characters should be easy to see, distinct, and not have a perceptible
flicker or waiver. Regular screen cleaning also helps keep text and images
clear.
Flat-panel displays
Flat-panel displays are becoming increasingly common. Most practices that
apply to traditional monitors also apply to flat panel displays; however, there
are significant differences:
Flat panels free up work surface space and tend to offer more screen area,
consume less power, and generate less heat than traditional monitors. Flatpanel
displays also have a sharper image but are slower to respond to quickly
moving images than traditional monitors. Flat-panel displays generally have
lower screen contrast ratios than traditional monitors so they may be more
prone to glare. Colors also may appear somewhat differently on flat panels;
choose displays that offer the widest contrast ranges and color adjustments.
Laptop computers
Laptop computers are not designed for prolonged use. The display, keyboard,
and pointing device are close together which creates awkward wrist, arm,
shoulder, and neck postures. If you use a laptop for prolonged periods, make
yourself comfortable by doing the following:
- Plug a standard-size keyboard and mouse into the laptop.
- Place the keyboard and mouse at a comfortable height on a desk or work surface. (Your hands should be at or just below elbow height; wrists and forearms relatively straight, slightly above the keyboard.)
- Place the laptop on a platform or riser so that the display is at a comfortable height (the area of the screen that you look at most often should be about 15 degrees below eye level).
Telephones
If you use a phone frequently, place it close to you so you don’t have to reach
across the work surface for it. Try using a headset or a speaker phone if you
have a tendency to cradle the phone between your ear and shoulder. Headsets
also make it easier to refer to files or to use the computer while you’re on the
phone.
Document holders
A document holder should be stable and adjustable for height and angle of
view. Place the document holder close to your screen and at the same height
and viewing distance to reduce head, neck, or back strain as you look from
screen to document. If a document is too heavy or won’t fit a document holder,
you can prop it up at an angle between the keyboard and screen if space is
available.
Footrests
When you sit in a properly adjusted chair your feet should be flat on the floor.
If not, support them with an angled (no more than 30 degrees) footrest that
doesn’t restrict leg movement. Don’t use your chair base as a footrest.
What to look for when selecting a footrest:
- Stable, portable, incline-adjustable.
- Large enough to support the soles of both feet.
- Covered with nonslip material.
Lighting and glare
A brightly-illuminated work area will wash out the images on a computer
screen because the monitor produces its own illumination and contrast. Computer
workstations should have lower light levels than typical office areas.
Illumination should be 20-50 foot-candles for screen viewing and 50-70 footcandles
for reading printed documents. Foot-candle? Lighting intensity is
commonly measured in foot candles. A foot candle is the illumination produced
by one candle at a distance of one foot. The most practical way to measure
illumination is with a light meter.
Your workstation should be located away from and at right angles to windows;
windows should have adjustable blinds or drapes to reduce glare and eye
fatigue. (Vertical blinds reduce glare more effectively than horizontal blinds.)
Walls, furniture, and equipment near a monitor or display screen should have
nonreflective, subdued colors to minimize glare.
Light fixtures near computers should have diffusers, cube louvers, or parabolic
louvers. Recessed or indirect lighting systems can eliminate glare and reflections
but are not suitable for all computer work areas. Workstations should be
spaced between rows of overhead lights to reduce glare and reflection.
If glare is still a problem, attach a visor hood to the monitor. Use anti-glare
screens as a last resort because they can blur screen images and reduce contrast.
Most newer monitors have tinted screens to control glare.
Temperature, humidity, and static electricity
Avoid overcrowding computer work areas. Set thermostats to maintain
temperature levels between 68 and 72 degrees. Relative humidity should
be 40-60 percent. Use antistatic floor mats or other static dissipaters in
low-humidity workplaces.
Source: OR-OSHA
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Disclaimer: This material is for training purposes only. Its purpose is to inform employers of best practices in occupational safety and health and general OSHA compliance requirements. This material is not, in any way, a substitute for any provision of the Occupational Safety and Health Act of 1970 or any standards issued by OSHA.
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