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Over-reaction to ELF and VLF radiation can also compromise ergonomics. In a campus computer lab, for example, all displays and keyboards were angled thirty degrees from the front of desktops to reduce the radiation exposure of students behind the machines. The risks of poor working posture in this case appear to be greater than the radiation risks.
A final form of radiation, static electric, can cause discomfort by bombarding the user with ions that attract dust particles, leading to eye and skin irritations. Anti-static pads, increasing humidity, and grounded glare screens are effective remedies for these symptoms.
A continuing process
Massive computerization of offices, laboratories, dormitories, and homes represents a fundamental change in the way many of us work and communicate. It would be surprising if there were no adverse effects from such profound changes. It would also be surprising if all policy debates were based on sound scientific evidence, rather than parochial politics and media exposes. But, as University of Pennsylvania bioengineering professor Kenneth Foster has written, "One difficulty is that 'safety,' if considered to be the absence of increased risk, can never be demonstrated. A hazard can be shown to exist; absence of hazard cannot."
To monitor research and develop institutional guidelines, the University of Pennsylvania has created a Task Force on Computing in the Workplace, with representatives from the Offices of Environmental Health and Safety, Fire and Occupational Safety, Information Systems and Computing, Radiation Safety, Purchasing, University Life as well as staff and faculty from the Wharton School and Schools of Engineering, Medicine and Nursing. Interested readers are welcome to contact the authors for information on the Task Force and its work.
Until more conclusive research becomes available, individuals, departments, and institutions will have to weigh the evidence and make their own decisions about protective measures to minimize the risks of computing. And, in our opinion, the information technology managers and their vendor partners who provided the leadership to computerize our campuses, now owe it to their colleagues to work with epidemiology and ergonomics experts to create computer-intensive environments that are both productive and healthful.
Avoiding carpal tunnel syndrome: A guide for computer keyboard users
Carpal tunnel syndrome (CTS) is a painful, debilitating condition. It involves the median nerve and the flexor tendons that extend from the forearm into the hand through a "tunnel" made up of the wrist bones, or carpals, and the transverse carpal ligament. As you move your hand and fingers, the flexor tendons rub against the sides of the tunnel. This rubbing can cause irritation of the tendons, causing them to swell. When the tendons swell they apply pressure to the median nerve. The result can be tingling, numbness, and eventually debilitating pain.
CTS affects workers in many fields. It is common among draftsmen, meatcutters, secretaries, musicians, assembly-line workers, computer users, automotive repair workers, and many others. CTS can be treated with steroids, anti-inflammatories, or physical therapy, or with surgery to loosen the transverse carpal ligament. Recovery of wrist and hand function is often, but not always, complete.
Causes
Like many skeletomuscular disorders, CTS has a variety of causes. It is most often the result of a combination of factors. Among these are:
Genetic predisposition. Certain people are more likely than others to get CTS. The amount of natural lubrication of the flexor tendons varies from person to person. The less lubrication, the more likely is CTS. One study has related the cross-sectional shape of the wrist, and the associated geometry of the carpal tunnel, to CTS. Certain tunnel geometries are more susceptible to tendon irritation.
Health and lifestyle. People with diabetes, gout, and rheumatoid arthritis are more prone than others to develop CTS, as are those experiencing the hormonal changes related to pregnancy, menopause, and the use of birth control pills. Job stress has also been linked to an increased likelihood of CTS. And CTS seems to be more frequent among alcoholics.
Repetitive motion. The most common cause of CTS that's been attributed to the workplace is repetitive motion. When you flex your hand or fingers the flexor tendons rub against the walls of the carpal tunnel. If you allow your hand time to recover, this rubbing is not likely to lead to irritation. The amount of recovery time you need varies from fractions of a second to minutes, depending on many circumstances, including the genetic and health factors mentioned above, as well as the intensity of the flexing, the weight of any objects in your hand, and the extent to which you bend your wrist during flexing.
Trauma. A blow to the wrist or forearm can make the tendons swell and cause or encourage the onset of CTS.
Prevention
Computer keyboard users can take several steps to lower their chances of developing CTS. Some of these center around the configuration of the workplace, or "ergonomics." Others have to do with human factors.
Ergonomics. Proper seating is crucial to good ergonomics. The height of your seat and the position of your backrest should be adjustable. The chair should be on wheels so you can move it easily. Arm rests on the chair, though optional, are often helpful.
Table height. To adjust the chair properly, look first at the height of the table or desk surface on which your keyboard rests. On the average, a height of 27-29 inches above the floor is recommended. Taller people will prefer slightly higher tables than do shorter people. If you can adjust your table, set your waist angle at 90 degree, then adjust your table so that your elbow makes a 90 degree angle when your hands are on the keyboard.
Wrist angle. If your keyboard is positioned properly your wrists should be able to rest comfortably on the table in front of it. Some keyboards are so "thick" that they require you to bend your hands uncomfortably upward to reach the keys. If so, it will help to place a raised wrist rest on the table in front of the keyboard. A keyboard that requires you to bend your wrists is a common cause of CTS among computer users.
Elbow angle. With your hands resting comfortably at the keyboard and your upper arms vertical, measure the angle between your forearm and your upper arm (the elbow angle). If it is less than 90 degree, raise the seat of your chair. If the angle is greater than 90 degree, lower the seat. Try to hold your elbows close to your sides to help minimize "ulnar displacement" - the sideways bending of the wrist (as when reaching for the "Z" key).
Waist angle. With your elbow angle at 90 degree, measure the angle between your upper legs and your spine (the waist angle). This too should be about 90 degree. If it is less than 90 degree, your chair may be too low (and your knees too high). Otherwise, you may need to alter the position of the backrest or adjust your own posture (nothing provides better support than sitting up straight). (Note: If making your waist angle 90 degree changes your elbow angle, you may need to readjust the height of your chair or table.)
Feet. With your elbows and waist at 90 degree angles, your feet should rest comfortably flat on the floor. If they don't, adjust your chair and table height and repeat the steps above. If your table isn't adjustable and your feet don't comfortably
reach the floor, a raised footrest can help. Otherwise, you may need a different table.
Work routine
You need very little recovery time between keystrokes to cool and lubricate the flexor tendons. If you type constantly, however, the need for recovery builds. Further, working with your hands bent upward at the wrists or frequently bending your wrists sideways heightens the friction within the carpal tunnel. It takes longer to recover from these motions. Working under stress (deadline pressure, anger, or other anxiety) can make matters even worse.
Many studies recommend a 10-15 minute break each hour to give yourself the recovery time you need. This needn't be a break from productive activities - just a break from your keyboard. Exercises can help, too. Try the following:
a) Make tight fists, hold for one second, then stretch your fingers out wide and hold for five seconds. Repeat several times.
b) With arms outstretched in front of you, raise and lower your hands several times. Rotate your hands ten times (make circles in the air with the fingertips).
Variety is the key. CTS occurs most frequently in workers whose motions are not only repetitious but are kept up for hours at a time. If you use a keyboard, structure your workdays to include a mix of activities each hour. For example, instead of typing all morning and filing all afternoon, mix typing and filing throughout the day.
Early detection
The most painful cases of CTS are those that have gone undetected or untreated over a long time. CTS can be caught easily in its early stages, however, and much of the pain and all of the disability avoided.
Early symptoms include a tingling in the fingers, often beginning several hours after work activity has stopped. Because of this delay in the appearance of symptoms, many CTS sufferers don't make the connection between their work activities and the pain they feel until it's too late. The tingling can lead, over time, to stiffness and numbness in the fingers and hand, and then to severe wrist and hand pain.
Реферат опубликован: 4/04/2005 (8326 прочтено)