Ergonomics and Organization of Work, vol 4; No.3, December 1997Some Research Findings in Ergonomics - A Review,by S.K. Sensarma, India |
Introduction
Ergonomics is defined as the study of the relationship between man and his work environment. This word is based on the Greek terms ergon', which means work', and nomos', which means law'. This science thus studies the many-sided factors anatomical, physiological and psychological which determine how well human beings interact with machines and their work environment. The aim is to achieve an optimal situation, and the benefits are measured in terms of the efficiency, comfort, and well-being of an individual doing a particular job.
The science of industrial physiology plays a very important role in research and development programmes in the field of ergonomics. Through the application of this applied branch of human physiology, one can evaluate the different stress factors work load, bad working posture, environmental heat load, etc. encountered by workers on the shop floor in terms of physiological parameters, such as energy expenditure, heart rate, and body temperature. By measuring one or more of these physiological variables during work, it is possible to determine to what degree the value during work differs from that prevailing in the resting state.
Such measurements provide an estimate of the physiological stress experienced in performing a given task. They thus indicate how physically demanding a job is highlighting, for example, the effect of environmental heat loads and also play a vital role in determining how conditions can be improved in order to make work more human and comfortable and to increase the efficiency of workers. This paper deals with some Central Labour Institute research findings relating to (i) the effect of bad working posture, (ii) the strain involved in some physical tasks and (iii) the effect of high ambient temperature and intense thermal radiation on workers.
Methodology
a) Evaluation of environmental heat stress
In order to evaluate heat stress in the work environment, the following measurements were made, using standard equipment and procedures: (i) dry and wet bulb temperature; (ii) air movement; and (iii) black globe temperature.
From these measurements, a single index referred to as the Corrected Effective Temperature (CET) was worked out, relating to a condition with cent percent humidity and still air. The difference between the 'Black Globe Thermometer Reading' and the 'Dry Bulb Reading' indicates the extent of radiant heat.
b) Evaluation of stresses through physiological responses
An individual on the shop floor encounters a variety of stresses. The most important of these are caused by: (i) work load; (ii) bad working posture; and (iii) environmental heat load.
The following physiological measurements were considered: (i) energy expenditure; (ii) heart rate during work and recovery period; and (iii) oral temperature.
Whereas energy expenditure indicates the level of physical effort involved in a task, heart rate and oral temperature give the combined effect of both work load and environmental heat load. The severity of the physical strain involved in a task is reflected by the increase in heart rate and oral temperature.
c) Radiological examinations
X-ray pictures are taken in order to study some of the changes occurring in a particular part of the body.
Ergonomic evaluation of some typical jobs in a petrochemical plant
The investigation was carried out in two areas 'PVC bagging' and 'PVC compounding' of a petrochemical plant, in order both to study the effects of posture and work stress on workers' physiological functions and to suggest some appropriate remedial measures for reducing strain and fatigue by means of improved work posture.
A group of ten workers was selected from each area. In PVC bagging, the jobs were: (i) filling bags with PVC resin; (ii) stitching filled bags; and (iii) carrying filled bags (25 kg) and loading them on to the wooden pallets. In PVC compounding, the operations were: (i) pre-mixing (semi- manual); and (ii) pre-mixing (manual) and scooping. The workers had to assume awkward postures in order to perform these tasks.
The findings show that of the three operations in PVC bagging, loading on to the wooden pallets exacted the highest energy cost (4.0 kcal min-1), whereas in PVC compounding, the hardest task was scooping (3.6 kcal min-1). The physiological expenditure in terms of working heart rates show that loading and scooping were strenuous (130 and 136 beats min-l, respectively), and it also appeared that the stress on the cardiovascular system was disproportionate to the metabolic demand. As thermal conditions at the various work sites were well within the 'prescriptive zone', the additional circulatory stress detected among the workers seemed to be attributable to poor working posture only, and not to the superimposed effect of environmental temperature.
The study calls for the improvement of working conditions by means of appropriate work design, with the aim of eliminating awkward postures and thus minimising the stresses involved in various tasks.
Study of dock workers
Dock workers are exposed to a very high degree of physical stress caused by lifting and carrying of heavy loads (weighing around 100 kg). In view of this hazard, an endeavour was made to study the impact of prolonged lifting and carrying of such loads on workers' spines, other bones, joints, etc.
Two groups of healthy workers aged 40 56 years one consisting of 'loaders' and the other of 'controls' were studied. It was observed from the X-ray findings that the most vulnerable part of the body was the vertebral column; the cervical and lumbar regions also showed significantly greater damage among the loaders than among the control group members. This appeared to be due to the way heavy loads were lifted and carried by the dock workers. The subjective complaints of the loaders also supported the radiological findings. The incidence of 'back pain', 'pain in joints and bones' etc., was greater among loaders than among the control groups.
Factors contributing to the various degenerative changes in the spine and vertebrae were: (i) awkward posture; (ii) prolonged lifting and carrying of heavy loads; and (iii) age. In this particular study, both the experimental and the control group belonged to the same age group, and hence it was possible to eliminate age as a factor.
If one compares the mild and severe cases of spondylosis, it can be observed that in all the regions of inter-vertebral column, the degree of severity was greater among loaders than among the control group. There was a markedly greater frequency of cases with spondylolisthesis and reduced disc space among the loaders.
These findings strongly support the conclusion that the lifting and carrying of loads have a greater impact on the vertebral column than do other activities in dock work.
Study on thermal stress in forging plants and its impact on workers
In the forge shop, a considerable number of workers perform their duties in the proximity of furnaces. While the operations connected with the loading and unloading of the furnaces are being performed, workers have to remain very close to the furnace for a considerable length of time at a stretch. In the course of forging work, they very often also have to handle heavy raw materials and to use a forging hammer. In view of this, it is obvious that the workers in this trade are exposed not only to high thermal stress from furnaces (900 1,200 C) but also to a certain amount of physical strain resulting from various tasks. When it was realised that such adverse working conditions might be imposing excessive strain on these workers, an attempt was made to identify different types of stress and to evaluate them scientifically, the aim being to quantify the level of thermal stress at the work sites and to study the physiological effects of exposure to such stress.
The investigation was carried out on two groups of workers in three forging plants in the western part of the country. A total of 43 workers in two groups 25 furnacemen and 18 hammermen were studied from the physiological point of view.
Forge shop conditions and forging work
The findings indicate that the thermal conditions near the furnaces in the forge shop were adversely hot, with a large amount of thermal radiation a fact revealed by the difference between the air temperature and globe thermometer recordings. The average CET values for the furnace areas were 31.6 to 32.6 C, with a recorded maximum of 37.2 C. This was beyond the upper permissible limit (29.5 C) for continuous work. Except for one plant, the average CET values for hammermen were, however, within this prescribed limit. Nevertheless, the maximum values for hammer areas recorded in all three plants were also quite high and sometimes exceeded the limit. The findings indicated that intense radiant heat was prevalent in the forge shop in the proximity of furnaces, as reflected in the difference between globe thermometer and air temperature records, which ranged from 12 to 20 C. However, the extent of the radiant heat as shown in mean values near the hammer was not so high as compared to that for furnacemen unless the hammer was located very near to the furnace, as was observed in one of the plants.
The findings show that though the duration of work-spell was of longer period, the maximum effective working time in the shift was within 60% for furnacemen, while for hammermen, this was around 45%.
The findings also indicate that though workers in the two groups did not generally handle very heavy weights, they did sometimes have to work with loads of as much as 100 kg.
Physiological responses
The heart rate during work and recovery, and the oral temperature response were recorded in order to assess the physiological strain experienced by the workers while they were on the job. It can be seen from the findings that while the mean working heart rate for furnacemen ranged from 145 to 152 beats per minute, the maximum value recorded was 222 beats per minute. The mean working heart rate values for hammermen were from 132 to 139 beats per minute, with a recorded maximum of 188. The recovery heart rate pattern in both groups was also found to be unsatisfactory.
The maximum rise in oral temperature in the case of furnacemen was 1.0 to 1.3 C. A similar trend was also observed for hammermen. This rise could be attributed to heat gain caused by work under adverse conditions. However, the degree of heat storage was comparatively less in hammermen.
The working heart rate response and its recovery pattern, as well as the rise in body temperature, were all indicative of excessive physiological strain resulting from unfavourable working conditions in the forging plants; they were beyond the permissible limit for continuous work and would finally cause fatigue among workers.
Discussion
The findings of the study reveal that working conditions in the forge shop were quite stressful and not at all conducive to effective functioning. Such conditions should cause great concern, and appropriate measures should be taken. An attempt should be made to humanise the work, keeping in mind all the factors involved in the forge shop. The study revealed that forging work includes a large amount of manual work which should be eliminated as far as this is possible by partial mechanization. An attempt should be made to introduce a conveyor-type arrangement to feed the hammer directly from the furnace after the jobs are properly heated up and ready to be forged in the hammer. Reorganization of the work-rest period should be regarded as a measure of the last resort. As the temperature in the furnace cannot be decreased in order to improve the working conditions, effort should be made to shield the furnace walls and charging walls by means of some thermal insulator, and provision should also be made for water circulation through furnace doors. In addition, workers directly exposed to high thermal radiation should be provided with protective clothing. In order to minimize excessive physiological strain, workers should also be encouraged to drink water frequently; at the minimum, after each work spell.
Studies on the aluminised fabric suit
During the forge shop study involving different categories of workers, it was noticed that the furnacemen had to work near the furnace in order to discharge their duties and were directly exposed to high radiant heat. This resulted in excessive physiological strain. Owing to technical difficulties, the furnace temperature cannot be reduced in order to improve the work environment in the forge shop; nor can any thermal barrier be used to protect the workers from the intense thermal radiation. In view of this, an attempt was made to utilize some protective clothing to shield the furnacemen from the direct radiant heat in the proximity of the furnace.
An aluminised fabric suit was used in an effort to provide some relief to the furnacemen engaged in the unloading of a furnace in a forging plant; this was followed by an attempt to quantify the reduction, if any, in physiological strain provided by the protective clothing and wire mesh face shield.
Two sets of experiments were conducted for each worker, one with the worker dressed in conventional clothing, i.e., a cotton outfit (the usual working attire); and the other one with the worker dressed in an outfit made of aluminised fabric. The experiments were conducted under almost identical conditions (CET values and rate of work) for the same people.
The results showed a considerable reduction of circulatory stress. The mean working heart rate recorded with the conventional clothing was 152 beats per minute (max. value 214 beats min-l), whereas the result was 118 (max. value 167 beats min-1) when the work was performed while wearing an aluminised outfit. The reduction in physiological strain was found to be 22.4 percent (max. 37.2%) as compared to the value recorded with the conventional outfit'. The subjective reports of the test persons also corroborated the above results.
The recovery heart rate responses, too, showed a definite change as a result of using the protective clothing. The early recovery also indicates reduction of stress on the circulatory system, and thus physiological relief for the workers.
Conclusion
The findings of the studies indicate that workers employed in the tasks observed are subjected to a fair amount of stress. Such stress results either from an unfavourable work environment or from heavy physical work or an inappropriate work posture. This situation calls for the creation of conditions under which fatigue is not accumulated and in which work can be performed with optimal efficiency through the maintenance of a physiologically stable state.
This paper focuses on the level of stress conditions in specific industries. There is good reason to believe that similar situations may also prevail in other industries in which employees are working under identical conditions. This highlights the need for a comprehensive investigation of the various factors which may affect the efficiency and comfort of workers.
The paper mentions some measures which can be employed in order to eliminate causes of stress. Cooperation between workers and management can help in overcoming such problems and creating a congenial work environment.
S.K. Sensarma
Director (Industrial Physiology)
Central Labour Institute
Sion, Mumbai 400 022
INDIA