Burgess-Limerick, R. (1997). A Walk Through a Laboratory. Ergonomics Australia On-Line, 11 (2). (http://www.uq.edu.au/eaol/Apr97/laboratory/laboratory.html)
The aim of this case study is to illustrate general principles of workstation design through examples taken from a walk through of a laboratory which provides on site quality control for a large minerals processing plant. The laboratory was undergoing extension and refurbishment and the walk through was conducted to identify areas deserving particular attention.
Musculoskeletal injuries occur when loads on anatomical structures (e.g., muscles, bones, ligaments, or tendons) are either instantly, or over time, greater than the structures can withstand. Work performed within the laboratory does not involve high force levels in general (with the exception of some manual handling), and consequently the predominant mechanism of injury will be the gradual accumulation of microdamage to musculoskeletal structures. The development of discomfort and fatigue provides a warning that cumulative damage may be occurring, as well as having the potential to impair performance. The incidence of discomfort, fatigue, and injury will be reduced by designing, and redesigning, workplaces in accordance with the following guidelines.
The most general principle is to design work and workplaces with the aim of promoting comfortable and varied working postures. Ideally the work should be dynamic (involve movement), and require moderate forces produced by large muscle groups.
This general principle can be expanded into the following more specific guidelines:
There is no one posture which is perfect. Any posture which is maintained for sustained periods will lead to discomfort and fatigue, particularly if significant muscle force is generated. Muscles rapidly fatigue in such situations because blood flow through the tissues is restricted.
Work within the laboratory is inherently varied, and this reduces the risk of musculoskeletal problems occurring due to static postures and isometric contractions. This variety should be enhanced whenever possible. The potential for problems increases whenever tasks are performed continuously for even relatively short periods of time. Tasks which are performed most frequently, and for the longest duration, should consequently receive most attention in the redesign process.
Work involving seated postures for long periods, should be interspersed with different tasks if possible to provide a variety of movements. Workstations which allow both sitting and standing will also promote greater postural variability. An example where this may be beneficial is the fume hoods where knee space underneath and an appropriate stool would allow both sitting and standing postures to be adopted while working at these locations.
Some tasks which required significant levels of isometric muscle activity were observed in the laboratory. The actuating mechanism for one device (illustrated below) requires the operator to maintain her ankle in a dorsi-flexed position (toes up) to raise the forefoot from the actuating mechanism while samples are removed and the next samples put in place. This sustained muscle contraction in the absence of movement is likely to cause fatigue, and possibly injury. (This is especially because the resting length of the ankle muscles is such that a neutral position is involving some degree of plantar-flexion (toes down) and thus the required toes up position involves large amounts of muscular effort to maintain). An alternate actuating mechanism was recommended.
Work should be designed so that joints remain in the middle third of their range of movement. Work should occur close to the body (within easy reach) and generally avoid awkward postures such as trunk rotation. Ulnar deviation of the wrist (toward the smallest fingers) greater than 10 degrees, neck extension (backward bending), or extreme neck flexion (forward bending) should particularly be avoided.
The height of work is particularly important in the laboratory setting. Equipment should be located such that controls can be operated with the hands at approximately waist height. The hands should be slightly lower if the task involves significant amounts of force, and higher if fine manipulation is required. The visual requirements of the task should be able to accommodated without requiring neck extension or extreme neck flexion. The provision of sloping work surfaces has the effect of reducing neck flexion (forward bending) and may be appropriate for some desk work.
A number of laboratory tasks were observed which involved undesireable postures.
In the task illustrated above left, the equipment is placed in such a position that the operator must lean and twist while applying a vertical force. Relocation of the equipment to allow operation directly in front of, and close to, the body would prevent this problem.
Operation of the saw (above middle) requires shoulder elevation beyond a comfortable range. Lowering, and moving the saw closer to the bench edgewould allow a more comfortable operating position.
Opening and closing the hood (above right) requires an extreme reach. Altering the catch mechanism so that it can be easily engaged and disengaged while the cage lid is closer to the operator's body would prevent this problem.
The prolonged use of the microscope (above left) can lead to fatigue because the visual requirements of the task mean that posture is highly constrained. Frequent breaks should taken, and a height adjustable seat provided at this workstation (see specifications for keyboard workstations below). The other tasks illustrated above (middle and right) illustrate poor design of equipment. In both cases the operator is prevented from getting sufficiently close to the work.
The duties of laboratory staff include monitoring equipment at various locations around the facility. The gauges to be read are commonly performed at low level. The consequence is that flexed postures requiring significant tension in back muscles are commonly adopted (left, middle). The alternative is to squat (right) which is unstable and uncomfortable for long periods. Provision of benches at each location adjacent to indicators, and the raising (or lowering) the height of indicators to waist height if possible was recommended.
In general the laboratory work does not involve maximum efforts, although some manual handling was observed.
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Not all maximum efforts are caused by large loads. Removing samples from an agitator (illustrated above) does not involve a heavy load, but the container requires significant force to remove. This is compounded by the necessity to grip the container using a very wide pinch grip between thumb and forefinger. The strength of the hand is reduced in this situation, and the task represents close to maximum effort, and hence a risk of injury to the wrist and forearm if performed frequently. The height of the agitator also means that the operator's shoulder is elevated beyond a comfortable range. Potential solutions involve lowering the equipment so that the removal task is occurring at waist level, and either reducing the force required to remove the samples by reducing the tightness of the fit, or providing a handle to allow the container to be removed using a more powerful grip which uses all fingers in a fist.
High frequency or long duration of work at any task increases the risk of discomfort, fatigue or injury, particularly if other risk factors are present. One way of reducing the effects of high frequency or long duration tasks is to provide rapid rotation between different tasks. One advantage of a multi-skilled workforce is that the exposure to a particular task can be spread over a larger number of employees thus reducing the risk of injury.
An example of where rational workplace layout is important in the laboratory is the storage of equipment and supplies. Frequently used, or heavy, equipment should be stored at waist height. Bulky, heavy, fragile, or unbalanced loads should not be stored above chest height. In general equipment and supplies should be stored with the aim of reducing as far as possible both the vertical distance loads are lifted, and the horizontal distance they are transported (as well as in accordance with the relevant standards relating to storage of hazardous substances).