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6105
Appendix T1 Guidelines
for Office Ergonomics |
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1.0
Introduction
Ergonomics is
the matching of the work environment, tools, and the people who use them. Good ergonomics promotes productivity,
minimizes physical distractions, and reduces the risk of injury and
illness. Unlike many occupational safety
and health issues, ergonomic considerations vary highly with the person, his or
her physical characteristics and preferred working style.
It is important
to understand that the body’s response to cumulative trauma makes no
distinction between on-the-job, at-home, or recreational activities. Prolonged, repetitive motion – especially
when it is forceful and requires unnatural joint deflection – will likely cause
strain injury. Similarly, prolonged
sitting in an incorrectly sized or adjusted chair or one with poor support is
likely to cause leg, back, and upper torso pain. A computer screen with glare and poor image
resolution causes eyestrain and corrective lenses need to be compatible with
all of our activities – including home and office computer use.
2.0
Computer & Workstation
Equipment
The computer’s
role as an essential office (and home) resource has developed faster than has
general public understanding of potential problems from poor body alignment and
effects from long hours in front of a keyboard and screen. Moreover, since these conditions typically do
not cause acute pain or other immediate warning signs, many people are slow to
connect their initial discomfort to their computer use and associated poor
ergonomics. A stiff neck or low-grade
headache at the end of the day caused by hours in front of a poorly located
computer monitor feels like any other bout of headache or stiff neck.
Variety in
motion is an important strategy in preventing all repetitive strain injuries,
including those associated with computer use.
Break up long sessions of keyboarding with other tasks. Take stretch breaks regularly; get up and
walk around even if you have no particular need to do so.
This appendix discusses some universally applicable recommendations that will be helpful to you – at work and at home. Use them to choose and use your computer and related equipment to align your physiology with your tasks. If you are a supervisor making purchase choices about a staff member’s workstation, be alert to the penalty exacted by poor ergonomics. Even a small impairment to productivity because of eyestrain or physical misalignment will cost more than the proper equipment. An ergonomics-related injury will likely cost many times over what the proper equipment would.
Consult with
your Environmental, Safety, Health, and Quality (ESH&Q) staff and/or
Occupational Medicine about ergonomic problems and solutions.
3.0
Chairs
The single most
important piece of office workstation equipment is your chair. Various studies have shown that 25 to 50
percent of workers who habitually sit in incorrectly fitted or mis-adjusted
chairs suffer from back problems. A
poorly designed, improperly selected, or worn-out chair will defy all of your
attempts to achieve proper posture.
Height
If you need to purchase a chair, and you are not the “average 5’7”
person,” an actual measurement is important to determine proper seat
height. Find a chair that allows you to
sit with both feet flat on the floor and with thighs and shins exactly
perpendicular. Measure the distance from
the hollow of your knees to the floor and subtract two inches. This is the correct height for the chair seat
from the floor. Your new chair should
have a range of height adjustments on either side of this measurement.
If the chair height is less than this optimum, the knees will be
elevated, preventing the thighs from supporting the proper amount of torso
weight. This places stress on the
buttocks and lower back. (Note than an
average adult has over 100 pounds of torso weight; the greater the load-bearing
surface, the better.)
If, on the other hand, the chair is too high, excessive pressure is placed on the thighs at the front edge of the seat, possibly causing loss of circulation to the lower legs. Chairs with worn-out cushions can cause this also, even at the correct height. A downward-turned front edge on the seat is a good design feature, reducing pressure on your thigh.
The depth of the seat is important too. If you are taller than average, select a
chair that supports your thighs to within 2-3 inches of your inner knee
surface. If you’re shorter than average,
avoid a chair seat that pushes into the back of your knee or that prevents your
lower leg from extending straight down.
Adjustability
Most people will use whatever chair they are
given. If it is not adjustable or can
only be adjusted with great difficulty, they will use it as found. Loss of productivity is almost guaranteed due
to back, leg, and foot discomfort.
If more than one person uses a computer workstation, the chair
should be easily adjustable, with pneumatic-type adjustments. Obviously, the range of adjustment should
accommodate all of the chair users. Any
minimally suitable chair will have adjustments for seat and back height,
armrest height, tilt tension, and back angle.
Better quality chairs will also have adjustments for lumbar-support-area
height, armrest angle, seat tilt, and the distance from seat edge to chair
back.
Chair Back
The lower curve of the back (the lumbar area) should be well
supported by the chair back. The chair
should maintain the spine's normal, erect curvature. Since people are proportioned differently,
the chair-back elevation and/or the lumbar-support feature should also be adjustable. Some chairs have the additional capability to
allow the chair back to be adjusted horizontally relative to the seat.
Arm Rests
Armrests are somewhat misnamed.
They actually benefit the upper body by supporting the arms. Though they are generally advantageous, many
people who do lots of keyboarding do not care for arm rests. Their objections often are related to
experiences with full-length “executive chair” armrests that prevent chairs
from being positioned close enough to the keyboard. Your arm should be supported slightly while
typing in the position described under “Keyboard Height.”
Proper armrests need not be very long horizontally, but their
height should be adjustable if more than one person uses the chair. Some chairs allow the armrests to be swiveled
outward when they are not needed. Some
chairs have provisions to remove the armrests, and this may be appropriate to
do if they’re not needed.
Stability
Older office chairs usually were equipped with four legs and
casters. These are potentially unstable
and may tip if you lean forward between two legs. Newer chairs have at least five legs. Avoid any chair that is designed so that the
leading edge of the seat extends farther than the radius of the legs; they are
inherently unstable and can tip suddenly.
Casters should be selected for the type of floor surface. Wide carpet casters on a hard floor make for
an “elusive chair” which may roll away from you as you sit. Narrow hard-surface casters dig into carpet,
making the chair hard to roll. Chair
mats are needed for carpeted floors to prevent carpet wear and to make chair
movement easier while seated – preventing possible backache from the exertion
required to move a chair that is directly on the carpet.
4.0
Keyboard
Height
A keyboard at correct height allows your upper and lower arms to
be at a ninety-degree angle while typing.
A prolonged period of work with angles more than 15-percent either way
from this optimum position can cause pain in the shoulders, back, neck, arms
and wrist. Note that positioning the
keyboard in your lap may well provide optimum alignment, and there are keyboard
trays made for this purpose.
Angulation
The keyboard should be sloped in a manner that places your wrist
in a straight or “neutral” position, or with only a slight tilt up or
down. Keyboards trays or drawers should
be selected to accommodate tilt in either direction from “neutral.” Some users find it beneficial to alter the keyboard angle
through the day.
Position
The keyboard should be squarely to your front. Even a slight misalignment causes torsional
stress on the upper body that results in fatigue and
pain in the neck, shoulders and back.
Wrist Support
The wrists should be supported while typing. If the workstation is well designed, the keyboard
support surface may offer proper wrist support.
Most keyboards, however, cannot be properly angled without a need for
supplementary wrist support. Ideally,
the support should be soft and allows skin to “breathe.” There
are a number of stand-alone wrist support devices on the market. Most keyboard tray systems include this
feature.
Keyboard Use
Typing force has an effect on the overall strain to your wrists
and hands. Most people type with
excessive force, and people with chronic wrist/hand strain injuries often type
with the greatest force. Use a light
touch, and be conscious of the angle of your wrists as you type. There are ergonomic keyboard designs that
attempt to match the plane of the keys to a more natural wrist and hand
alignment. Because the keys are angled
outward and more difficult to see, these keyboard designs are of greatest
benefit to touch typists.
5.0
Video Display Terminal (VDT) or Monitors
Height
The top of the screen should be at or slightly below eye level,
with your head in a normal, erect position.
This is a very important parameter.
If you are forced to look downwards or upwards for prolonged periods,
neck, back, and shoulder strain are likely.
There are a number of platforms or stands available to alter height and
provide storage space for the keyboard or other items. There are also pivoting support brackets that
hold the VDT off the work surface altogether.
Note that an incorrect VDT height is almost certain to contribute to
other posture problems as you unconsciously compensates for your position.
Tilt
Ideally, the screen surface should be perfectly
vertical or a slight downward tilt (~10°).
This offers the best compromise between glare prevention and elimination
of optical distortion. Upward tilt
invites reflections from overhead lighting.
Extreme tilt in either direction can cause image distortion, and it
requires the eyes to change focus as they scan up and down the screen.
Position
As with the keyboard, the screen should be directly in front of
you. Twisting or turning motions during
typing contribute to neck, shoulder and back discomfort. Materials that are being read during typing
should also be directly to the front.
This usually necessitates the use of a document holder. It should hold the document as close as
possible to the screen and at the same distance from the eye as the screen
image.
Distance
The screen surface (which is not necessarily the front edge of the
VDT) should be within 18 to 24 inches of your face. In reality, the size of the screen and the
display’s character size influence this measurement, and large VDTs can be
positioned farther away. In any event,
you should not position the screen to compensate for vision problems; wear
corrective lenses if you need them, and position the screen at the proper
distance.
Brightness,
Contrast, and Color
Most VDTs and monitors have both brightness and
contrast adjustment controls. The screen
should be sufficiently bright to overcome incidental glare from lighting and
windows, but excessive brightness can cause blurred screen characters and
eyestrain. Experiment with different
contrast settings for different software to make best use of the background
formats you use most often. Likewise,
experiment with color settings – especially for page backgrounds. Stark-white page backgrounds may not be the
best choice for long-term viewing. Try
an off-white or parchment-color page background. Certain color combinations are obviously
distracting and will cause eyestrain: adjacent red and green, for example. Good contrast and image resolution are
important no matter what colors are used.
Image
All cathode-ray-tube devices – televisions, VDTs, etc. –
eventually lose image quality. This
usually takes years of normal use, but in time the phosphor coating on the
screen deteriorates, causing loss of character resolution and color
purity. Also, prolonged display of
unchanged images may cause these to be “burned” into the screen, although
current monitor design makes this less of a problem than it once was. In any event, screen-saver features help
prevent these problems. A VDT or monitor
with a deteriorated image should be replaced.
Proper screen refresh rate prevents flicker. Select a rate at the upper end of the range
recommended by the monitor manufacturer.
Screen Maintenance
Cleanliness of the screen is important. Smudges, dust, scratches and so forth, can
blur the image and can cause the eye to attempt to focus in two planes
simultaneously, causing strain. This is
particularly noticeable if a glare filter is used over the front of the screen
and it is blemished. These should be
virtually undetectable to the eye when in use.
Document Holders
Documents that are being read during typing should not be flat on
the desk. They should be in a near
vertical position, in the same focal plane as the VDT screen. Avoid any need to turn the head or change eye
focus while typing. There is a wide
selection of devices to hold paper and/or books in proper position, and price
is not a good predictor of their suitability.
Corrective Lenses and
VDT Use
Many visual problems associated with the use of VDTs can be traced
directly to poor eye care. Uncorrected
or improperly corrected vision problems are more likely to cause or exacerbate
visual fatigue, which affects how well you can see. Your comfort, concentration, and your
productivity are all negatively affected.
The purpose of corrective lenses is to bring your vision back into an acceptable range. The use of corrective lenses should have no effect on your ability to use a VDT so long as the lens prescription factors in your computer use. Near-vision correction (reading glasses) typically is selected for a reading distance of 12 to 18 inches, while computer monitors are often 24 inches or more from the eyes. Be sure to tell your eye-care professional how much time you spend in front of a computer, and the height and distance of the monitor from your eyes.
Lenses recommended for VDT use, in usual order of preference, include:
·
the monofocal: single-prescription eyewear selected specifically for
your type of computer use
·
the full-width or flat-top bifocal:
different corrections for near and distance vision Bifocals can be a problem
for VDT use. Conventional reading-type
bifocals may not be appropriate. If you
must tilt your head back or into an uncomfortable position to see the screen,
you need a different type of lens.
·
and the progressive lens:
the “no-line” lens that corrects vision in a gradual manner from near to
distance. Progressive lenses may not
provide a sufficiently large zone of correction for the field of view required
for the width and height of your monitor and your document holder. Having to move your head back and forth or up
and down to get proper focus on the entire screen indicates a problem.
6.0
Foot Support
Most people who
must sit for prolonged periods find it more comfortable to have their feet in a
slightly upward tilted position. This
can be accomplished with a makeshift footrest, but there are commercial
products that offer adjustable angle and heights. Using some type of foot support helps many
people cope with chronic lower back problems.
7.0
Desk/Workstation
Height
Your desk height should allow proper arm alignment for keyboard
use. Most conventional desks are made
with work surfaces higher than this optimum keyboard height, and although they
may be ideal for writing and other functions, they will put a keyboard much
higher than it should be. Computer
workstations usually provide a lower surface for a keyboard. There are retrofit,
roll-out shelves or trays available for conventional desks that put the
keyboard at the proper height. And
remember the option of using the keyboard in your lap.
Work Area
At a minimum, the available surface area should accommodate the
computer enclosure, the VDT or monitor, the document holder and the keyboard –
observing good position parameters.
Matte-finish or non-glare surface colors help reduce reflected glare and
associated eyestrain.
Leg Room
Most people are comfortable if they have about 25 to 28 inches vertical
distance from the underside of the work surface to the floor. Very tall individuals will need more
distance. There should be sufficient
space for some lateral leg movement, and the front-to-back space beneath the
desk should allow for periodic stretching of legs. Avoid storing materials beneath your desk; it
can interfere with proper leg extension and alignment.
8.0
Office Environments
Noise
Noise is an unavoidable feature of most offices. It does have a serious penalty, however. Stress, loss of concentration, and reduced
productivity are all associated with noise.
It is important to remember, too, that one person's music can be
another's noise.
In general, every effort should be made to keep nuisance noise to
a minimum: phone ringing volume, office machinery, door slamming, etc. Impact and ink jet-type computer printers
generate considerable noise. Resilient
padding underneath the printer and printer enclosures can help make them
quieter. Office partitions often can
help isolate or attenuate noise.
Carpeting, drapery and upholstery all absorb considerable noise energy.
Traffic
Traffic (as in people) in the work area is a powerful
distraction. Visual barriers are often
needed to screen people with high-concentration tasks from passersby. Some workstations have integral
partitions. Arrangement of the office
can reduce traffic in the vicinity of desks and workstations.
Wall
Finish & Coverings
Wall paint or covering is a very effective means of
controlling VDT screen glare. Basic
white is a poor choice for an office where computers are in frequent use; light
grays, tans, blues and greens are usually better choices. Reflectivity can be specified in paint
selection. Textured wall coverings may
be preferable to paint in some settings.
Lighting
Lighting can enhance or hinder office operations. VDT screen glare is known to cause eyestrain,
headaches, and loss of concentration and productivity. Unfortunately, computers are often in
environments where other tasks are performed and where high illumination levels
are needed.
Unless the VDT is in its own room, it will likely be subject to
excessive ambient light levels and glare.
Windows are especially troublesome.
Evaluate glare with the VDT turned off; a black screen offers the best
test surface for glare potential.
Occasionally, a glare filter or hood will be needed on a VDT to reduce
stray light and glare on the screen.
Lighting measurement is not always a straightforward process
either. The most up-to-date guidelines
for light levels address a number of variables such as reflectivity of the work
surface, task performed, and so on. If
you suspect a problem, ask your ESH&Q staff to
evaluate the lighting in your work area.
Room lighting for computer-only operations can be much lower than
for general offices: 20 to 50 foot-candles as opposed to 80 or more. Be aware, however, that many people feel
uncomfortable at first in environments with this lower level of illumination.
Task lighting is often the best solution. Whole room or ambient light level is kept to
a safe (for walking) minimum, while desk lamps
illuminate individual work areas to the necessary levels. This usually offers considerable energy
savings as well. New, modular office
workstation systems carry this concept to an advanced degree with integrated
lighting systems.
Additional
considerations when evaluating office lighting:
Fluorescent Lighting
Usually, general-purpose fluorescent lighting is not the best
choice for computer environments. It is
often installed with excessive illumination levels, and its light is highly
diffused (omni-directional), which promotes screen glare. This does not mean that all fluorescent
lighting is unsuitable. It will likely
benefit from some “fine tuning,” however.
Tube Color
There are several choices of light hue in fluorescent
tubes: cool white, warm white and full spectrum. There is some evidence that full spectrum
causes less glare and is more pleasing to the average eye.
Diffusers
The grid or lens in a fluorescent fixture has a great deal of
influence on glare production. Egg-crate-types, which direct light downward, are often more
suitable than prismatic types which tend to diffuse light in all directions. Parabolic diffusers—a special type of
grid—are perhaps optimal for computer areas.
Although they are more expensive, they do the best job of minimizing
lateral glare.
Windows
Nearly everyone wants a window near his or her desk. Natural light diffusing through a window is a
powerful glare source, however. Try to
locate the VDT to minimize glare.
Windows near VDTs should have opaque blinds, and screens should be
turned away from the window.
Direction of Light
Glare is produced when light reflects from the screen. Although its original source may have been
overhead lights or a window, walls and other reflective surfaces can contribute
to glare problems.
Another related problem occurs when there is an illumination
source within your field of vision while you attempts to focus on the screen or
document. The pupils adjust their
dilation for the eyes' total light field, and that may not be consistent with
the illumination in the primary focus field: the screen and document. Eyestrain and headaches are possible
outcomes. Light-blocking partitions or
repositioning the VDT are potential solutions.
Temperature
and Humidity
The ideal office temperature is in the range of 72 to
75 degrees, with a relative humidity of 40 to 60 percent. Unfortunately, there are many possible
reasons why these conditions cannot always be maintained. There are also biological differences in
individuals' comfort levels, and majority rule is sometimes the only
resolution.
Humidity is more important than many people realize – both for
comfort and health. Excessive humidity,
especially in warm weather, causes discomfort.
It also has undesirable effects on office paper. Very low humidity, on the other hand, can
cause irritation of mucous membranes, even to the extent of nosebleeds. Low humidity also promotes static electricity
that can damage electronic devices.
Ventilation
All offices need fresh air to prevent normal indoor pollutants
from reaching objectionable concentrations and to replenish oxygen used in
respiration. Fresh air is usually
introduced into larger buildings by mechanical means: fan and damper systems
that blend outside air with heating or cooling supply air, and by exhaust fans
which draw air out of the building – often with their intakes near sources of
potential contamination.
Fan systems are designed for a certain number of occupants. If changes occur to space use and occupancy,
the original ventilation design may become inadequate. It is important to coordinate space-use
decisions with Facilities Management to prevent problems later with poor air
quality.
Persistent or recurring odors may be an indication that an area is
not getting sufficient fresh air. Mold
and mildew growth is also a warning sign, and it should be taken
seriously. Call Facilities Management,
your ESH&Q staff,
and/or Occupational Medicine if you suspect there is a problem with your
ventilation.
Radiation
In recent years, there has been a great deal of speculation and
publicity about possible human health effects from radiation emitted from
computer VDTs. Early cathode-ray tubes,
including those used in televisions, could emit X-rays – a type of ionizing
radiation. For many years, however,
product manufacturing safety standards have made this problem negligible.
All electrical equipment can produce electromagnetic fields: non-ionizing radiation. Even though VDTs have internal shielding, there can be detectable electromagnetic fields close by. The energy of these fields diminishes quickly with distance, however, so that an operator sitting at the typical distance from the VDT gets an extremely low exposure. Research to date suggests there are few if any health effects associated with this type of radiation in doses experienced by computer users.
In short, radiation from computer equipment is not a problem unless the shielding or case has been damaged or removed. Even in that instance, electrical shock is a much greater concern. Never use a piece of electronic equipment that you suspect is damaged, and never attempt to repair equipment unless you are trained and equipped to do so safely.
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ISSUING
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APPENDIX
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APPROVAL
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EFFECTIVE
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EXPIRATION
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ESH&Q Division |
02/06/06 |
02/06/06 |
02/06/09 |
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