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Ergonomics & Aging
Many characteristics of a handtool contribute to the amount of force necessary to hold and operate it.In addition, over time, repeated or prolonged mechanical stress can injure the skin, damage underlying tendons, or impair the functioning of nerves. Body parts that are sensitive to mechanical stress are:
Stressful hand and wrist postures or positions are often a function of tool shape and handle design. They are also a result of improperly positioning work. Injuries may be avoided if you are aware of potentially dangerous postures and positions, learn proper handling techniques, and heed your intuitions about dangerous situations.
HANDTOOL DESIGN, SELECTION, AND SETUP
Support: Equip tools with some means of mechanical support so you don't need to hold a heavy tool continuously while working. If mechanical support cannot be provided, the workstation should be designed so you can put the tool down or rest it in a holster when it is not in use. Balance: Additional force is required to use a badly balanced tool. The tool's center of gravity should be close to the body, close to the handles, and in line with the center of the hand holding the tool. Also, the weight of an unsupported hose can unbalance a tool. Torque control: High torque requires a lot of force to keep the tool from rotating out of your hand. Torque settings should be set to the minimum required by job specifications, especially for in-line and pistol-shaped tools. Weight: Use the lightest weight tool possible to avoid injury. Excessively heavy tools should be equipped with a means of mechanical support and attached hoses should be supported. Grip: Tool handles should allow stable and efficient grip. The handle should be cylindrical or oval in shape, with a diameter of between 1.25 and 1.75 inches. Tool handles should contact as much of the hand and fingers as possible. Grips should be made of non-slip compressible and non-conductive material. However, if the task requires fine manipulations, a small handle and a precision grip are preferred.
Handles should not press on the base of the palm. Use tools with long handles or handles which are large and rounded enough to distribute the force over a large area of the palm. Avoid form-fitting handles (handles with finger grooves), since they may not fit the hand size of every user.
Handles should be kept clean of slippery grease, oil, or sweat.
Span: On two-handled manual tools, like scissors, the open span should be about 4 inches and the closed span should be about 1.5 inches. Spring-loaded handles: A spring-loaded mechanism saves muscular effort and reduces mechanical stress on the backs and sides of fingers for such tools as scissors, pliers, and other manual cutting and gripping tools which have to be opened and closed repeatedly during use. Trigger design: Only a light touch should be required to operate a trigger control. The trigger should have rounded edges and be free of pinch points. The handle should also be designed to allow the user to grip the tool firmly with or without activating the trigger.
POSTURES & POSITIONS
Bend the tool, not the wrist Choose the right tool shape. Pistol-shaped tools should be used on a vertical surface or on a horizontal surface below waist height. Avoid bending over your work. Reduce the need for outstretched arms. Avoid overhead work. Use a ladder. Keep the elbows close to the body. Tilt the work surface instead of the wrist. Stand with weight evenly distributed between feet. When standing for long periods of time, rest one foot on a sturdy object above floor height and switch legs periodically. Sit up straight so the chair offers good back support. Adjust the chair back so it comfortably supports the natural curve of the lower back. Adjust the seat height to allow thighs to be parallel to the floor.
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