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Manufacturing kitchen cabinets is a complex process that consist of many operations and require many skills. Among the various operations we selected three as the most representative:
The shaping operation consists of modelling pieces of wood with a shaper according to the style of kitchen cabinet being made (Figure 1).
To complete a task a worker has to:
The task lasts approximately three seconds. The task is done while standing on a concrete floor.
Highly repetitious movements, excessive force while pressing wood objects on the shaper, and exposure to vibration put the workers at risk for repetitive motion injuries (RMIs). The wrists, neck and shoulders are at the highest risk. In addition, prolonged standing in a stooped position and repetitious side motions can contribute to low back injuries. The Ergonomics section of OSH Answers has more information on musculoskeletal disorder risk factors.
Prolonged standing on a concrete floor can contribute to lower leg and back discomfort that, over time, can develop into injuries.
All of these factors have a compounding effect. In other words, each of them increases the effects of the others.
The sanding operation consists of smoothing the surface of wooden sheets by using a hand-operated power sander (Figure 2). The worker uses both hands to carry out this task. The dominant hand is used to operate the sander while the other hand is used to hold the sheet of wood (Figure 3). To complete a task a worker has to:
Sanding requires excessive movements such as bending and reaching while keeping the elbow above the shoulder level. Forceful movements are used to hold both the sander and the sheet of wood. Sanding is done in a standing position.
Sanding exposes workers to a high risk for repetitive motion injuries. Hands, neck and shoulders are at the highest risk for RMIs. The high mechanical stress due to repetitive and forceful movements while operating the sander and the sustained muscular effort to hold work objects are responsible for such a high risk.
Repetitive and forceful movements, and exposure to vibration also put the elbow and wrist of the operating hand at a high risk for RMIs. The prolonged stooped standing position and excessive and forceful bending create a risk for low back injury.
Assembling all the components that will form a kitchen cabinet involves the use of various tools such as staplers, screwdrivers and hammers. Assembling kitchen cabinets is a manual operation requiring many steps and many skills. While assembling, workers use a variety of body positions such as bending, twisting and reaching (Figure 4, 5, 6, 7, 8). They also have to stoop and crouch while working (Figure 9).
The assembly tasks at a kitchen cabinet manufacturing plant create the conditions that favour the development of RMI, as well as low back problems. Operating heavy tools in very awkward body positions (Figure 9, 10, 11), and exerting forces in an off line direction are extremely hazardous for RMIs of the upper limbs.
The neck and shoulders are also at risk for RMIs. Whole body motions and lifting, while handling assembled cabinets, put workers at risk for back injuries.
Continuous standing on a concrete floor can cause lower leg and back discomfort that, over time, can develop into injuries.
All these factors have a compounding effect. In other words, each of them increases the effects of the others.
The three tasks that were selected for examination in the kitchen cabinet manufacturing plant pose similar risks for repetitive motion injuries. However, these three tasks require different approaches for controlling the risk for RMIs.
The working position is the major hazard for RMIs while shaping. This can be improved by providing:
Implementation of a full-scale rotation of tasks would improve the working conditions even more.
Awkward body positions and forceful movements are the major risk factors for RMI. Prolonged standing creates lower leg and back discomfort. These conditions can be improved by making these changes:
The physical effort required while sanding can be rather strenuous and repetitive. It seems that improvements can be achieved by re-designing the task and by introducing task rotation, or enrichment and enlargement of the task.
In the assembly operation, awkward postures and forceful movements are the major risk factors for RMIs. Vibration and stress due to prolonged standing also contribute to the development of RMIs.
To reduce awkward body positions, use jigs and fixtures to hold the work object (Figure 15). A fixture that allows the worker to rotate the kitchen cabinet, for example, reduces over-reaching and also reduces the handling of the kitchen cabinet.
It is also important to select the proper tool for the task. Matching the tool to the task reduces awkward postures of the wrist, elbow and shoulder (Figure 16).
Using tool balancers reduces the amount of force necessary to hold and operate the tool (Figure 17).
To reduce stress on the legs and back from prolonged standing, workers should use anti-fatigue matting.
The Canadian Centre for Occupational Health and Safety in co-operation with the Government of Newfoundland and Labrador, Department of Employment and Labour Relations, Occupational Health and Safety Branch would like to acknowledge the participation of Mother Hubbard's Kitchen Cabinets Ltd. who so freely gave their time and resources to assist us in the development of this case study.
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