Book extract

New edition: Ergonomics in action: a practical guide to the workplace

by Céline McKeown
£30 softback 256 pages
ISBN 978 0 901357 47 2

Design features

Hand or arm injuries following the use of tools may indicate inappropriate tool design or improper use. Such injuries can range from something as simple as a callus or blister, to something more severe such as a ULD. In most instances, injuries can be avoided by ensuring that tools are properly designed, taking both the user and the task into account.

Handle design
One of the most common complaints made by workers is that they have to bend their wrist when using tools. For some reason, designers have until recently designed most tools with straight handles and heads. As a result, when the tool user works on or against a flat surface, they will usually have to bend their wrist.

The user experiences a loss of grip strength from working with a bent wrist. To overcome this problem, and to control the tool fully, the pressure of the grip may be increased. Increasing the grip pressure will speed up the rate at which the muscles fatigue. Therefore, to avoid the reduction of grip strength and subsequent acceleration of muscle fatigue, maintaining a straight wrist should be a primary design and selection consideration. This can be achieved easily in many work situations by bending the handle (see below).

In some situations, bending of the wrist can be eliminated by providing a pistol grip tool where the handle is bent by 70–90º. However, this design is only acceptable if used in an appropriate orientation. In general, pistol grip tools should only be used when the tool axis is horizontal. If the tool axis is vertical or the force is applied perpendicularly to the work plane, a straight grip should be used. Examples of wrist posture, tool design and orientation of use are shown below.

Handle construction
If users have to work with a tool which has a smooth, hard handle constructed of a material such as flat metal or plastic, they may experience difficulty in stopping their hand from sliding across the handle as they apply force. To prevent the hand from moving, the user will increase the pressure of the grip – this situation is made worse if their hands are hot and sweaty.

Care should be taken if the handle is designed with flutes or ridges (eg a screwdriver). If these flutes or ridges are too deep or have sharp edges, they may increase the pressure placed on the soft tissue of the hand when the user grips the handle and this may result in discomfort and pain. Soft oval indents on a handle are preferable – they allow improved purchase without causing pressure points.

If handles are made of metal, they may remain cold throughout the course of the shift. Exposure to colder temperatures may increase the possibility of a user developing a ULD, so the use of metals in handle design should be avoided.

It is recommended that soft, compliant and textured materials are used on handles so that they are easier to grip, although care needs to be taken that these cannot be damaged easily, subsequently presenting sharp edges.

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