Heavy physical work
Heavy and continuous manual work increases the rate of breathing and the heart beat. Therefore, if the worker is not in good physical shape, he will tire easily. There are risks involved in working at maximum capacity. The use of mechanical power to replace heavy work helps reduce these risks. Mechanical power also helps increase the work opportunities for people with less muscle power.
It is important that the workload is not too heavy and changes during the day. Effective rest periods must be included in the day’s work.
Working rhythmically is the most natural way to work. This “dynamic” load enables the muscles to alternate between contraction and relaxation. If an object is lifted up and held in a position, this puts the muscles under a uniform “static” load. Muscles under static load become tired because they are continually contracted. After a short time the muscles feel painful. A static load on the muscles over a long period of time will also increase pressure on the heart. The pulse increases because the blood remains in the muscles.
Static loads, such as high hand positions or bending, are common. They are often combined with repetitive operations visual loads and work pressure. It is necessary to have a new look at the way work is done.
Another problem is lifting, which has to be dealt with carefully. Lifting and carrying heavy loads manually should be avoided. This should be performed by mechanical devices as much as possible; else several people should do the work. It is important that everybody work together and use the correct lifting methods.
Correct way of lifting
It is the legs and not the back that should be used to lift loads. Throw your shoulders backwards, arch your back and bend at the knees. Keep the load as close to your chest as possible and then straighten your legs to lift the load while keeping your back straight.
It can be done as follows
Design of controls and tools
- Load close to your body (starting position).
- Feet apart and body correctly balanced.
- Bend at the knees.
- Neck and back in an almost straight line Li straighten the legs while keeping the back straight.
- Where possible the load should be held in both hands.
It is important that control switches, levers knobs of different kinds are within easy reach of the operator in a normal standing or sitting posture. Frequently many of the controls of a lathe or similar machines are below waist height and at more than arm’s reach from the operator position. The location is of the primary importance for frequently used controls.
Requirements of controls include
Selection of adequate types of controls (e.g. hand controls for precision of high-speed operation and foot controls such as pedals for larger force operation, though two or more pedals should not be used per operator).
Distinction between emergency controls and those which are used in normal operations (by separation, colour coding, clear labelling or guarding).
Prevention of accidental activation of controls by proper spacing, adequate resistance, recesses or shields.
Adequate resistance in operation, with a clear indication of activation of the controls.
Operating procedures based on common sense are very important. In a hurried situation or an emergency, people tend to operate important controls as they would normally react. Common sense reactions may differ among countries. Sometimes, “on” and “off” switch positions can even be reversed. It is important to ensure that operation directions are compatible with common sense and do not entail any danger by mistaken operations. If a piece of equipment is purchased that violates the local custom for movement, it should be very clearly labelled to indicate “on” and “off” actions.
Hand tool selection
The design of hand tools can affect the productivity and health of an operator if it does not fit the individual or task. In most instances the tools are bought from an outside vendor. Poor quality ones must be avoided.
The following considerations are important in selecting hand tools
- Avoid static load at the shoulder or arm due to continuous holding of a tool at a raised position or gripping of a heavy tool.
- Proper arm position and adequate weight.
- Avoid awkward wrist angles.
Reduce uncomfortable pressure on the palm or joints.
- Avoid pinch points.
- Make handles easy to grasp, with good electrical insulation and without sharp edges or corners.
- Consider special-purpose tools for repeated actions, e.g. a soldering iron with a bent tip, a tool holder in using a chisel, etc.
Easy and dynamic handling is important for controls and tools. They are usually small and may seem unimportant. But the selection of good controls and tools are as important as that of costly machines. Ask opinions of the operators who use them.