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Within the past two years, substantial media attention has been directed at potential adverse health effects of long-term computer use. Renewed concerns about radiation, combined with reports of newly-recognized "repetitive stress injuries" such as carpal tunnel syndrome, have led some to call for regulation in the workplace and others to rearrange their offices and computer labs. There is little evidence that computer use is on the decline, however. On the contrary, more people are spending more time doing more tasks with computers -- and faculty, students and staff at colleges and universities have some of the most computer-intensive work styles in the world.
If, as is widely suspected, health effects are cumulative, then many of us are at risk in our offices, labs, dormitories, and homes. Unfortunately, many years will be required before epidemiological studies can provide definitive guidelines for computer users, managers, furniture suppliers, and office designers. In the interim, individuals and institutions must educate themselves about these issues and protective measures.
One set of issues concerns workstation design, setup, and illumination, together with users' work habits. The City of San Francisco, which recently enacted worker safety legislation, cited research by the National Institute of Occupational Safety and Health (NIOSH) into VDT operator complaints of eyestrain, headaches, general malaise, and other visual and musculoskeletal problems as the rationale for imposing workplace standards, to be phased in over the next four years.
A second set of issues relates to suspected radiation hazards, including miscarriage and cancer. A special concern with radiation is that nearby colleagues could be affected as well, since radiation is emitted from the backs and sides of some terminals. The most recent NIOSH study is reassuring, but some caution still seems prudent.
Ergonomics and work habits
Most people can ride any bicycle on flat ground for a short distance with no problems. On a fifty mile ride over hilly terrain, however, minor adjustments in seat height, handlebar angle, and the like can mean the difference between top performance and severe pain. Similarly, occasional computer users may notice no ill effects from poorly designed or badly adjusted workstations, whereas those who spend several hours a day for many years should pay careful attention to ergonomics, the study
of man-machine interfaces.
The key to most workstation comfort guidelines is adjustability--to accommodate different body dimensions, personal workstyle preferences, and the need to change positions to avoid fatigue. A recommended working posture shows the body directly facing the keyboard and terminal, back straight, feet flat on the floor, eyes aligned at or slightly below the top of the screen, and thighs, forearms, wrists, and hands roughly parallel to the floor. Achieving this posture may require:
A chair with a seat pan that adjusts both vertically and fore-and-aft, an adjustable height backrest, and adjustable tilting tension
An adjustable height work surface or separate keyboard/mouse tray (note that many keyboard trays are too narrow to accommodate a mouse pad, leaving the mouse at an awkward height or reach on the desktop)
A height adjustment for the video display (a good use for those manuals you'll never read!)
An adjustable document holder to minimize head movement and eyestrain
Adjustable foot rests, arms rests, and/or wrist rests.
Studies show that many people are unaware of the range of adjustments possible in their chairs and workstations. Although the best chairs permit adjustment while seated, you may have to turn the chair upside down to read the instructions. (Be careful not to strain your back while upending and righting the chair!) If your posture deviates substantially from that in the diagram--or if you are experiencing discomfort--experiment with adjustments or try exchanging chairs or workstations
with colleagues. A posture cushion, which maintains the natural curvature of the spine and pelvis while supporting the lumbar region, may also prove helpful. It should be noted that any adjustment may feel uncomfortable for a week or so while your body readjusts itself.
(Some people have been advised by their physicians to use a backless "Balans" chair, which minimizes compression of the spine and shifts the body weight forward with the aid of a shin rest. This posture may be uncomfortable, however, since it requires stronger abdominal and leg muscles than conventional sitting positions. The Balans chair is not recommended for overweight or exceptionally tall persons)
Light and glare
Eyestrain, headaches, and impaired vision are often a product of improper illumination resulting in glare, which is light within the field of vision that is brighter than other objects to which the eyes are adapted. Both direct glare from sunlight and lighting fixtures directed at the user's eyes and indirect glare due to reflections from
video screens or glossy surfaces are common problems for VDT users.
Many offices are too bright for computer use, which may be a carryover from the days when paperwork required such brightness or the result of many office workers' preferences for sunlight and open windows. A NIOSH study recommends 200-500 lux for general office work; other sources suggest 500-700 lux for light characters on dark monitors and somewhat more for dark-on-light. If documents are not sufficiently illuminated, desk lights are recommended in preference to ceiling lights, which
increase reflections from video screens. Reducing overhead lighting could also result in substantial energy savings.
VDT workstation placement is also important. Terminal screens should be positioned at right angles to windows, so sunlight is neither directly behind the monitor nor behind the operator, where it will reflect off the screen. If this is infeasible, blinds or drapes should be installed. Screens should also be positioned between rows of overhead fixtures, which can be fitted with baffles or parabolic louvers to project light downward rather than horizontally into the eyes or terminal screens.
Some users have found filters placed in front of the screen to be effective in reducing reflections, however some dimming or blurring of the display may result. Experts 1advise trial and error, since the best solution appears to depend upon specific conditions and user preferences. Finally, if you wear glasses or contact lenses, be sure your physician is aware of the amount of terminal work you do; special lenses are sometimes necessary. Bifocals, in particular, are not recommended for extensive terminal work, since the unnatural neck position compresses the cervical vertebrae..
Breaks and exercises
Working in the same position for too long causes tension buildup and is thought to increase the risk of repetitive motion injuries, such as carpal tunnel syndrome. Remedies include changing postures frequently, performing other work interspersed with computing (some studies recommend a 10-15 minute break from the keyboard every hour), and doing exercises such as tightening and releasing fists and rotating arms and hands to increase circulation. Be aware, also, that the extra stress created by deadline pressure exacerbates the effects of long hours at the computer.
Radiation hazards
For at least a decade, concerns have been raised about possible effects of radiation from video display terminals, including cancer and miscarriages. Earlier fears about ionizing radiation, such as X rays,
have been laid to rest, since these rays are blocked by modern glass screens. Also well below exposure standards are ultraviolet, infrared, and ultrasound radiation.
More recent controversy surrounds very low frequency (VLF) and extremely low frequency (ELF) electromagnetic radiation produced by video displays' horizontal and vertical deflection circuits, respectively. Researchers have reported a number of ways that electromagnetic fields can affect biological functions, including changes in hormone levels, alterations in binding of ions to cell membranes, and modification of
biochemical processes inside the cell. It is not clear, however, whether these biological effects translate into health effects.
Several epidemiological studies have found a correlation between VDT use and adverse pregnancy outcomes, whereas other studies found no effect. The most recent analysis, published this year by NIOSH, found no increased risk of spontaneous abortions associated with VDT use and exposure to electromagnetic fields in a survey of 2,430 telephone operators. This study, which measured actual electromagnetic field strength rather than relying on retrospective estimates, seems the most trustworthy to date. The authors note, however, that they surveyed only women between 18 and 33 years of age and did not address physical or psychological stress factors.
A 1990 Macworld article by noted industry critic, Paul Brodeur, proposed that users maintain the following distances to minimize VLF and ELF exposure:
28 inches or more from the video screen
48 inches or more from the sides and backs of any VDTs.
Although these guidelines seem overly cautious, a fundamental principle is that magnetic field strength diminishes rapidly with distance. Users could, for example, select fonts with larger point sizes to permit working farther from the screen. Remember that magnetic fields penetrate walls.
Реферат опубликован: 4/04/2005 (8147 прочтено)