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:
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:
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:
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:
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
Copyright ©2000-2019 Geigle Safety Group, Inc. All rights reserved. Federal copyright prohibits unauthorized reproduction by any means without permission. Disclaimer: This material is for training purposes only to inform the reader of occupational safety and health best practices and general compliance requirement and is not a substitute for provisions of the OSH Act of 1970 or any governmental regulatory agency. CertiSafety is a division of Geigle Safety Group, Inc., and is not connected or affiliated with the U.S. Department of Labor (DOL), or the Occupational Safety and Health Administration (OSHA).
