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Restrictions to posture in working environments
Applied Ergonomics 1984, 15.2, 109-110 Posture
Restrictions to posture in working environments A.G. Clark and J.E. Ridd Materials Handling ResearchUnit, Robens Institute, University of Surrey, Guildford, UK This paper reviews some typical industrial work postures which have to be adopted as a result of either poorly designed machinery or workplace layout. Brief case studies of investigations carried out by the Materials Handling Research Unit (MHRU) are described. They illustrate the dangers associated with the postures and work environments which have been found to contribute to hi.qh incidences of industrial back injury. The handling problems considered by this paper will include those associated with cable drums, 200 litre drums, sacks and workstation desiqn. Keywords: Environment (working), workplace layout, back Work environments which impose restrictions on free movement are common (Lawrence, 1955; Davis and Troup, 1966; Robins and Jones, 1966; Stephenson, 1971), presenting increased hazards to workers and possibly causing loss of efficiency. These problems are often brought about by poor workplace or machine design, but for many situations designers' guidelines are available (Rigby et al, 1961; Renault, 1974; British Standards Institution, 1975). These are usually based on anthropometric studies and give access requirements, dimensions and load weights for various work environments and activities. However, not every workplace can be easily related to what must inevitably be generalised guidelines and it is for these situations that sDecific ergonomic evaluation is required. From past investigations by the Materials Handlin~ Research Unit (MHRU) a number of workplace deficiencies have become apparent. The most frequently encountered and often the most difficult to remedy have been those involvin~ restrictions imposed on operators by the shape and position of machine controls, by physical barriers, and by workstation layout and task design. The introduction of new machines and new technology may eradicate particular manual handling problems, but often this also results in the appearance of new and unforeseen difficulties. The followinz five case studies illustrate these points with emphasis being placed particularly on postural restrictions. The first examples demonstrate the need for: (i)
good housekeeping;
(ii)
careful consideration of shop-floor layout during the design stage.
At a cable manufacturing firm a system was recommended for rationalising the cable drum storage yard. The rearrangement suggested allowed for easy access by forklift trucks and, as a result, reduced the distance drums had to be rolled manually into their path. Investigation of the manual handling of drums showed that store workers tended to push with outstretched arms. When using intra-abdominal
pressure (IAP) as an indirect comparative measure of back strain it was shown that leaning the buttocks against the drum and walkin~ it backwards reduced the IAP by an average of 50%. This demonstrates how a simple postural chan~e can considerably reduce the associated stress. The second example highlights the importance of careful ergonomic consideration of plant design. The MHRU was approached to make an appraisal during the planning stage of the shoo-floor design of a diced foods mix and packing factory. The company requested an evaluation of a pick car and conveyor system to access racks three bays high, compared with floor level or table level pallets with an extended conveyor. Plant operators expressed a preference for the latter, considering it to be as efficient as the pick car, and less expensive. A laboratory simulation was carried out using heart rate and lAP as physiological measures of strain and back stress. It showed that the pick car was favourable, provided that the operator was not required to lean out of the cab further than 7 0 - 8 0 cm into the rack bays. The storage pallets, however, measured 1'2 m 2 and hence required a greater reach than could be achieved safely. There proved to be other inherent problems which necessitated modification of the standard pick car design to make the task less stressful and less hazardous to the operator. Amongst these were the need for changes of the drive control positions to improve the driver's posture, inclusion of a hook to pull products from the back of the pallets, and an increase in lighting levels. These numerous modifications of the pick car which were required to improve operator safety resulted in a recommendation that the alternative system be installed: namely, the floor and table level pallets and extended conveyor. Workplace/worker height mismatch is exemplified in the following case study. It involves the transfer of petrol from a petrol tanker to storage tanks at service stations. Protective bars near the valve cocks demonstrate physical restrictions on the operation. The outlet cocks on the road tankers observed were sited 0"75 m above the ground and 0.75 m in
0003-6870/84/02 0109-02 $03.00 Q 1984 Butterworth & Co (Publishers) Ltd
Applied Ergonomics
June 1984
109
Posture from the vehicle side as measured from the outside edge of the hose rack. Drivers were forced to stoop and lean over the protective bar to reach the valve cocks for connection and disconnection of hoses. This represents one of several restricted postures that drivers assumed during a shift. Although the loads were not excessive, as many as 100 force applications were made per shift in restricted postures, thus increasing risk of cumulative musculo-skeletal damaRe. Other tankers exist with outlet valves 0-95 m high and 0'2 m from the vehicle edge which enabled handling at about elbow height. A change to this design was suggested. Connection of hoses to the storage tanks involved problems of lifting and handling during removal of manhole covers below ground level. Recommendations were made that a secure locker above ground should be produced as a common site for all fill pipe ~alves. The final two examples illustrate the widespread problem in industry of machine/operator mismatch. The design of a crane cab is a problem for which few solutions have yet been found. F~g. 1 shows the posture adopted by crane drivers at the coal unloading dock of a power station. Drivers spent half of their 8 h shift in this posture in two 2 h sessions separated by 2 h spent on other duties. For one 45 s pick up and dump manoeuvre of the crane grab, the driver made 20 movements of each hand, operating four levers. A ten point scale to rate pain and a body chart to locate discomfort were used to assess this activity after a 2 h work period. It was shown that the three subiects monitored each suffered pain in the biceps, abdominal musculature, lumbar spine and neck and shoulder regions. In another instance, a new crane had been installed on a dockside and the cab was fitted with a TV monitor and adjustable seat to alleviate forward leaning during operation. The inability of the TV to ~ive an overall view of the ship's hold, and poor positioning of the cab, meant that the working posture - in the opinion of the drivers was more uncomfortable than in the older cabs.
In the final example the proposed introduction of new technolok,y to improve throughput of workpieces at a camshaft manufacturing firm promised to reduce risks of tenosynovitis. The study showed, however, that there was an increased risk of back strain to the operator due to the change in emphasis of the task. Camshaft straightening had been shown to result in high incidences of tenosynovitis. The job involved continual twisting of the wrist to turn the shaft. which lay horizontally on the machine in front of the operator. The postural constraints came from three sources: the static nature of the task, the wrist movement and the handling of camshafts, both into and out of the storage racks. The new automatic straightener which was under trial during the study alleviated the problem of tenosynovitis by removing the large number of fine hand movements, but the loading task remained. Due to the speed of the automatic machine (eight times that of the manual operator), the work involved mainly loading and unloading at this higher rate.
Conclusion Wherever man and machine are in close association there are inevitably problems of bodily discomfort during operation. It is often a simple task to identify causes from a brief study and to take remedial action. However, some cases, for instance crane cab design, seem to defy improvement despite technological assistance. Similarly, new technology introduced to streamline production by semi-automation may remove certain tedious operations but the manual involvement, although reduced per item, may become more intense. Many of the problems encountered are easily remedied by simple postural changes provided the activity is considered in total, but often the most dramatic effect can be achieved by ensuring good housekeeping and by applying ergonomic theory to the design of work environments.
References
British Standards Institution 1975 Safeguarding of Machinery, BS 5304.
Davis, P.R., and Troup, J.D.G. 1966 Ergonomics, 9, 475-484. Effects on the trunk of erecting pit props at different working heights.
Lawrence, J.S. 1955 Brit J Indust Med, 12, 249-261. Rheumatism in coal miners. Part III: Occupational factors.
R~gie Nationale des Usines Renault 1974 Les profiles de poste, m6thode d'analyse des conditions de travail. (Workplace profiles, a method for the analysis of working conditions.) Masson-Sirtes, ed, Paris.
Rigby, L.V., Cooper, J.I., and Spickard, W.A. 1961 Guide to integrated system design for maintainability. USAF, ASD Technical Report 61-424.
Robins, W.J., and Jones, J.C. 1966 Ergonomics, 9, 366. The effects of restricting the spaces between walls, chairs and tables.
Stephenson, E.E. Fig. 1
Cranedriver's working posture
110
Applied Ergonomics
June 1984
1971 Machinery space arrangement. Marine Engineering. R.L. Harrington, ed, The Society of Naval Architects and Marine Engineers, New York. pp 670--676.
Restrictions to posture in working environments A.G. Clark and J.E. Ridd Materials Handling ResearchUnit, Robens Institute, University of Surrey, Guildford, UK This paper reviews some typical industrial work postures which have to be adopted as a result of either poorly designed machinery or workplace layout. Brief case studies of investigations carried out by the Materials Handling Research Unit (MHRU) are described. They illustrate the dangers associated with the postures and work environments which have been found to contribute to hi.qh incidences of industrial back injury. The handling problems considered by this paper will include those associated with cable drums, 200 litre drums, sacks and workstation desiqn. Keywords: Environment (working), workplace layout, back Work environments which impose restrictions on free movement are common (Lawrence, 1955; Davis and Troup, 1966; Robins and Jones, 1966; Stephenson, 1971), presenting increased hazards to workers and possibly causing loss of efficiency. These problems are often brought about by poor workplace or machine design, but for many situations designers' guidelines are available (Rigby et al, 1961; Renault, 1974; British Standards Institution, 1975). These are usually based on anthropometric studies and give access requirements, dimensions and load weights for various work environments and activities. However, not every workplace can be easily related to what must inevitably be generalised guidelines and it is for these situations that sDecific ergonomic evaluation is required. From past investigations by the Materials Handlin~ Research Unit (MHRU) a number of workplace deficiencies have become apparent. The most frequently encountered and often the most difficult to remedy have been those involvin~ restrictions imposed on operators by the shape and position of machine controls, by physical barriers, and by workstation layout and task design. The introduction of new machines and new technology may eradicate particular manual handling problems, but often this also results in the appearance of new and unforeseen difficulties. The followinz five case studies illustrate these points with emphasis being placed particularly on postural restrictions. The first examples demonstrate the need for: (i)
good housekeeping;
(ii)
careful consideration of shop-floor layout during the design stage.
At a cable manufacturing firm a system was recommended for rationalising the cable drum storage yard. The rearrangement suggested allowed for easy access by forklift trucks and, as a result, reduced the distance drums had to be rolled manually into their path. Investigation of the manual handling of drums showed that store workers tended to push with outstretched arms. When using intra-abdominal
pressure (IAP) as an indirect comparative measure of back strain it was shown that leaning the buttocks against the drum and walkin~ it backwards reduced the IAP by an average of 50%. This demonstrates how a simple postural chan~e can considerably reduce the associated stress. The second example highlights the importance of careful ergonomic consideration of plant design. The MHRU was approached to make an appraisal during the planning stage of the shoo-floor design of a diced foods mix and packing factory. The company requested an evaluation of a pick car and conveyor system to access racks three bays high, compared with floor level or table level pallets with an extended conveyor. Plant operators expressed a preference for the latter, considering it to be as efficient as the pick car, and less expensive. A laboratory simulation was carried out using heart rate and lAP as physiological measures of strain and back stress. It showed that the pick car was favourable, provided that the operator was not required to lean out of the cab further than 7 0 - 8 0 cm into the rack bays. The storage pallets, however, measured 1'2 m 2 and hence required a greater reach than could be achieved safely. There proved to be other inherent problems which necessitated modification of the standard pick car design to make the task less stressful and less hazardous to the operator. Amongst these were the need for changes of the drive control positions to improve the driver's posture, inclusion of a hook to pull products from the back of the pallets, and an increase in lighting levels. These numerous modifications of the pick car which were required to improve operator safety resulted in a recommendation that the alternative system be installed: namely, the floor and table level pallets and extended conveyor. Workplace/worker height mismatch is exemplified in the following case study. It involves the transfer of petrol from a petrol tanker to storage tanks at service stations. Protective bars near the valve cocks demonstrate physical restrictions on the operation. The outlet cocks on the road tankers observed were sited 0"75 m above the ground and 0.75 m in
0003-6870/84/02 0109-02 $03.00 Q 1984 Butterworth & Co (Publishers) Ltd
Applied Ergonomics
June 1984
109
Posture from the vehicle side as measured from the outside edge of the hose rack. Drivers were forced to stoop and lean over the protective bar to reach the valve cocks for connection and disconnection of hoses. This represents one of several restricted postures that drivers assumed during a shift. Although the loads were not excessive, as many as 100 force applications were made per shift in restricted postures, thus increasing risk of cumulative musculo-skeletal damaRe. Other tankers exist with outlet valves 0-95 m high and 0'2 m from the vehicle edge which enabled handling at about elbow height. A change to this design was suggested. Connection of hoses to the storage tanks involved problems of lifting and handling during removal of manhole covers below ground level. Recommendations were made that a secure locker above ground should be produced as a common site for all fill pipe ~alves. The final two examples illustrate the widespread problem in industry of machine/operator mismatch. The design of a crane cab is a problem for which few solutions have yet been found. F~g. 1 shows the posture adopted by crane drivers at the coal unloading dock of a power station. Drivers spent half of their 8 h shift in this posture in two 2 h sessions separated by 2 h spent on other duties. For one 45 s pick up and dump manoeuvre of the crane grab, the driver made 20 movements of each hand, operating four levers. A ten point scale to rate pain and a body chart to locate discomfort were used to assess this activity after a 2 h work period. It was shown that the three subiects monitored each suffered pain in the biceps, abdominal musculature, lumbar spine and neck and shoulder regions. In another instance, a new crane had been installed on a dockside and the cab was fitted with a TV monitor and adjustable seat to alleviate forward leaning during operation. The inability of the TV to ~ive an overall view of the ship's hold, and poor positioning of the cab, meant that the working posture - in the opinion of the drivers was more uncomfortable than in the older cabs.
In the final example the proposed introduction of new technolok,y to improve throughput of workpieces at a camshaft manufacturing firm promised to reduce risks of tenosynovitis. The study showed, however, that there was an increased risk of back strain to the operator due to the change in emphasis of the task. Camshaft straightening had been shown to result in high incidences of tenosynovitis. The job involved continual twisting of the wrist to turn the shaft. which lay horizontally on the machine in front of the operator. The postural constraints came from three sources: the static nature of the task, the wrist movement and the handling of camshafts, both into and out of the storage racks. The new automatic straightener which was under trial during the study alleviated the problem of tenosynovitis by removing the large number of fine hand movements, but the loading task remained. Due to the speed of the automatic machine (eight times that of the manual operator), the work involved mainly loading and unloading at this higher rate.
Conclusion Wherever man and machine are in close association there are inevitably problems of bodily discomfort during operation. It is often a simple task to identify causes from a brief study and to take remedial action. However, some cases, for instance crane cab design, seem to defy improvement despite technological assistance. Similarly, new technology introduced to streamline production by semi-automation may remove certain tedious operations but the manual involvement, although reduced per item, may become more intense. Many of the problems encountered are easily remedied by simple postural changes provided the activity is considered in total, but often the most dramatic effect can be achieved by ensuring good housekeeping and by applying ergonomic theory to the design of work environments.
References
British Standards Institution 1975 Safeguarding of Machinery, BS 5304.
Davis, P.R., and Troup, J.D.G. 1966 Ergonomics, 9, 475-484. Effects on the trunk of erecting pit props at different working heights.
Lawrence, J.S. 1955 Brit J Indust Med, 12, 249-261. Rheumatism in coal miners. Part III: Occupational factors.
R~gie Nationale des Usines Renault 1974 Les profiles de poste, m6thode d'analyse des conditions de travail. (Workplace profiles, a method for the analysis of working conditions.) Masson-Sirtes, ed, Paris.
Rigby, L.V., Cooper, J.I., and Spickard, W.A. 1961 Guide to integrated system design for maintainability. USAF, ASD Technical Report 61-424.
Robins, W.J., and Jones, J.C. 1966 Ergonomics, 9, 366. The effects of restricting the spaces between walls, chairs and tables.
Stephenson, E.E. Fig. 1
Cranedriver's working posture
110
Applied Ergonomics
June 1984
1971 Machinery space arrangement. Marine Engineering. R.L. Harrington, ed, The Society of Naval Architects and Marine Engineers, New York. pp 670--676.