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ERGONOMICS
AT WORK!
The science
of ergonomy aims to balance work productivity with the physical
and mental wellbeing of the worker. There are three key elements
to attaining this delicate balance: the worker, the work site,
and the work itself. For the purposes of length, mainly issues
relating to the work site will be discussed below.
To maintain a healthy and productive work site, the following
elements must be optimized:
CHAIR
Because not all people have the same shape and size, all workchairs
should be adjustible for the following parameters.
HEIGHT:
The height of the chair should be adjusted so that the elbows are
bent between 90° and 110° when the hands are on the keyboard.
This position imposes the least amount of strain on the worker's
muscles, therefore diminishing fatigue and increasing performance.
SEAT:
The seat should be flat or slightly rounded. This design encourages
an equal distribution of weight through the buttocks. The seat should
also be long enough to support the upper thigh. The edges of the
seat should be rounded, so as to minimize pressure on the back of
the leg. The optimal dimensions for the seat are approximately 45
cm wide and 43 cm long. According to "The American Society of Safety
Engineers" (1985), the seat's angle should be inclined backwards
only 2° to 5°.
BACKREST:
A backrest with lumbar support is ideal. Lumbar support helps the
back to maintain a neutral position and diminishes muscle fatigue.
The support should be positioned in sitting by doing a full flexion
of the back, and installing the support where the buttocks meet
the backrest. The ideal angle for the backrest is between 90°
and 110° relative to the seat. There should be space between
the backrest and the seat to accommodate the buttocks. Normally,
the recommended dimensions for the backrest are from 35 to 48 cm
wide and 38 and 53 cm high.
ARMRESTS:
Armrests are strongly recommended for those who work with computers.
The minimal distance between armrests should be 45 cm. Even with
armrests, it is important that the chair be permitted to slide beneath
the work surface.
BASE:
A chair's base determines its mobility and stability. Chairs with
pivoting bases are preferable because they optimize mobility. A
base with 5 feet ensures maximal stability.
WORK SURFACE
The height of the worksurface for the average size person should
be between 55 and 75 cm.
LEGROOM
The space underneath the work surface should be enough to enable
the worker to cross his/her legs. This space should be free of all
objects (e.g., wastepaper baskets).
POSITION OF COMPUTER SCREEN & ACCESSORIES
COMPUTER
SCREEN:
It is recommended that the computer monitor be no more than 20°
beneath the worker's horizontal line of sight, and no less than
10° . The recommended distance between the worker and the screen
should be between 45 and 50 cm, depending on the worker's age and
the size of the objects on the screen. The centre of the screen
should be aligned with the worker's chin, unless the worker wears
bifocals. If the worker's attention is mainly placed squarely on
the screen, the monitor should be placed directly in front of the
worker. If, however, the worker's focus is placed on a document
on the work surface, then the screen should be placed just to the
side of the document, with the document aligned centrally.
KEYBOARD:
The optimal angle for a keyboard is between 5° and 10°.
To prevent unnecessary rotation of the trunk, the keyboard should
be positioned directly in front of the worker.
DESKTOP ORGANIZATION
The workspace should be organized so that all objects (e.g., telephone,
agenda, stapler, calculator, etc.) are within 45 to 50 cm of the
worker. This arrangement minimizes excessive movements, avoiding
unnecessary strain.
WRIST REST
A wrist rest provides the worker with a comfortable location to
place his/her wrists while writing, typing, or simply resting. Specifically,
by enabling the wrists to remain in a neutral position, these devices
diminish the static strain placed on the upper extremities and on
the neck while working.
FOOTREST
A footrest is often necessary for smaller individuals or those whose
feet cannot touch the ground when seated. The footrest helps reduce
pressure on the nerves and blood vessels in the rear thigh.. The
ideal height of the footrest is the height needed to obtain a 90°
angle at the knee.
References:
Obright K, Hartsell HD : Office ergonomics. Orthopeadics Division
Review: 12-16, 1993. Walmsley A: Posture perfect. Report on Business
Magazine. September, 1992.
Vander Doelen J: Sit on it! Human Factors Association of Canada,
(14)1: 1-3, 1984.
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