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(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.
Реферат опубликован: 27/01/2008