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Safe Work Space Can Avert Injuries

June 22, 1989|Richard O'Reilly and Richard O'Reilly | RICHARD O'REILLY designs microcomputer applications for The Times

One of the first things you learn upon acquiring a personal computer is how difficult it is to fit on a desk. There are all those parts--the main computer box, a monitor, a keyboard, probably a printer and maybe an external disk drive or an external modem or even a CD-ROM drive.

But there is a lot more to setting up a computer properly than just finding a place to put everything and enough electrical outlets to plug the equipment in.

Your health and well-being may even be at stake. Federal, state and local officials across the nation have been looking into the growing number of computer-related repetitive motion injuries.

Experts suggest several precautions for avoiding such injuries. One of the most important considerations is placing the keyboard and the monitor at comfortable heights for typing and viewing. You also need to put the computer unit where it can be easily switched on and off, with its floppy disk drive conveniently at hand.

More often than not, what happens is that the monitor is placed on top of the computer unit, both are shoved to the back of the desk and the keyboard is set in front of them. The printer ends up wherever it will fit within stretching distance of the umbilical cable linking it to the computer.

Several things can be wrong with that scenario, according to recommendations adopted by the American National Standards Institute.

The basic ergonomic principles endorsed by ANSI are easy to describe: You should sit upright with your feet flat on the floor and your knees bent at about 90 degrees. Your lower back should be supported, and your arms should be at about a 90-degree angle when your fingers are on the keyboard.

(ANSI standards say any forearm angle between 70 and 135 degrees is acceptable for keyboard work. However, medical and ergonomics experts that I have worked with say 90 degrees is the optimum.)

Further, you should not have to look up at any part of your display screen. The top part of the screen (not the case) should be no higher than eye level.

Depending on your size, it may be difficult to achieve that optimum position.

You also need to have enough room under the desk or table for your knees and feet, preferably a space at least 24 inches wide and from 19 to 24 inches deep, depending on how long your legs are.

The foundation for a good computer work space is a good, adjustable chair. A secretarial style chair is better than an executive style chair with big arms that interfere with arm movement while you work at the keyboard.

"A well-designed chair will favorably affect posture, circulation, the amount of effort required to maintain posture and the amount of strain on the spine," according to ANSI standards.

The standards also specify that "reclined posturesare acceptable, (but) they require that the chair provide adequate support."

Well-designed chairs can be adjusted for seat height, back support and tilt angle. The minimum range of height adjustment should be from 16 to 20.5 inches, according to the ANSI standards. Seat width should be at least 18.2 inches, and the width of the lower back support should be at least 12 inches. The standards make no recommendation for height of the seat back.

Chairs that have pneumatic tubes for height adjustment are easier to use but may tend to lose pressure and sink while you are seated unless the quality is very good. Chairs that use screws for mechanical adjustments are more difficult to change but stay where you put them.

Chair adjustability is critical because that is how you assure that your hands and arms are at the proper height and angle for the keyboard height, if the keyboard surface is not adjustable. In addition, shorter people may find that when their chair is high enough, their feet can't rest flat on the floor. A variety of footrests are available to support your legs and feet in such cases.

With adjustable furniture, proper keyboard height for most persons falls in the range from 23 to 28 inches high, according to ANSI standards. Few manufacturers offer such furniture, however, so you'll probably have to compensate with chair height.

Most computer furniture has a single work surface to support keyboard, CPU and monitor. You should choose such furniture for proper typing height.

The important thing to remember about the monitor is to keep it low. Looking down as low as 60 degrees below horizontal is acceptable.

"People who wear bifocals or trifocals and who adopt a reclined posture may have a reduced range of acceptable viewing angles," the standards say. They also may have more problems with glare from ceiling lights.

If you have room on the desk top, you usually can get the monitor at an acceptable height by putting the CPU to one side so that the monitor rests directly on the work surface. The CPU can also be placed on its side behind the monitor or beside it or under the desk, as long as you can still conveniently reach the disk drives.

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