Sudden force – jerky or unexpected movements while handling an item or load are particularly hazardous because the body must suddenly adapt to the changing force. Tasks where force is applied suddenly and with speed also generates high force. Examples of sudden force include: impact recoil of a large nail gun throwing or catching objects cutting reinforcement steel with large bolt cutters carrying an unbalanced or unstable load such as bagged stock feed pellets that suddenly moves (Figure 5) handling frightened or resistant animals handling patients who suddenly resist or no longer assist during the handling procedure. Figure 5 Movement Repetitive movement – using the same parts of the body to repeat similar movements over a period of time. Examples of repetitive movement include: painting lifting goods from a conveyor belt and packing them in a carton typing and other keyboard tasks(Figure 6) repeatedly reaching for and assembling components in electronics manufacturing using a socket and ratchet or spanner to unscrew long bolts. Figure 6 Posture An ideal posture is one where the trunk and head are upright and forward facing, the arms are by the side of the body, the forearms are either hanging straight or at right angles to the upper arm, and the hand is in the handshake position. Postures that are both awkward and sustained are particularly hazardous.
Wrapping machines on process lines Strain on the lower back when handling heavy rolls of plastic wrapping in awkward and twisted postures, often above shoulder height. This is caused by inappropriate design and positioning of the roll spindle and by restricted access. Design the spindle to be adjustable. This allows the rolls to be loaded at a suitable height and orientation, and eliminates the need to lift them. Design equipment to help worker load rolls. Locate the spindle in an accessible place on the plant. Provide information about how to install the plant in a way that allows adequate access. Power drills Prolonged use of the forearm muscles and wrist caused by a heavy or poorly balanced drill. Exposure to vibration or impact shock recoil from hammer drills. Excessive force needed to grip and control the tool to counter the effect of vibration and impact shocks. Design drills to be as light as possible. Design drills with the handle under the drill’s centre of gravity. Design plant to reduce shock and vibration. Provide a suitable way of holding the tool with both hands. Pliers Pressure to the palm of the hand caused by handles that are too short. Prolonged use of the forearm muscles and compression of the wrist caused by using pliers with straight handles. Design pliers with handles that extend beyond the palm. Design pliers with bent handles so that the user can maintain a straight wrist. Crimping, clamping and cutting tools Excessive force with outstretched fingers required to grip handles that are too wide apart. Design handles with a grip span of 10 cm or less. Chainsaws Excessive vibration. High force required to handle the chainsaw. Design to reduce vibration. Design the chainsaw to be as light as possible, and provide well-placed handles. Chairs Poorly designed chairs that cannot be adjusted provide little back support and cause workers to adopt poor postures and movements. Follow existing design guidelines for chairs, and consider how the chair will be used in the workplace. workstations and other work surfaces Workstations that cannot be adjusted result in unnecessary reaching, bending and exertion of force. Design workstations to be adjustable. Alternatively, dimensions should suit as many workers as possible.