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Cost assessment for ergonomic risk (CAFER)
Internat~ona[lou~na!e[
la strial Ergonomics
!4.'m ELSEVIER
International Journal of Industrial Ergonomics 20 (1997) 307-315
Cost assessment for ergonomic risk (CAFER) Isaac Barsky a, S.P. Dutta b,, a Workplace Basics, La Salle, Ontario, Canada b Department oflndustrial and Manufacturing Systems Engineering, University of Windsor, Windsor, Ontario, Canada
Received 10 February 1996; revised 13 August 1996
Abstract Consumer safety in the use of a product is always given the highest priority by product designers. However, little or no consideration, it seems, is afforded the production workers who must produce and assemble these products. Given the conservative bent of governments, industry will have less incentive to invest in equipment which will reduce the risk of work-related injuries, or to give maximum consideration to designing the products and processes in such a manner that the risk of worker injury is minimized. One possible approach to make industries more accountable in this regard, is to utilize ISO 9000 as a vehicle for incorporating FMEA-like analysis techniques for occupational health issues and to audit every customer/supplier to assure that actions are being taken to solve any problems which have been identified. The authors suggest some strategies for implementing and controlling this type of system. Relevance to industry The concepts and methods presented here will allow product designers and process planners to not only assess the injury risk of their proposed design on the workers who must manufacture the product, but also determine the costs associated with such risks. © 1997 Elsevier Science B.V. Keywords: Cost assessment; Injury risk factors; F.M.E.A.; Work standard; ISO 9000
1. I n t r o d u c t i o n In the 1960's and 1970's, industries in developed countries all over the world became increasingly aware that its workplace were being exposed to soft tissue injuries at an alarming rate. Coincidentally, unions were beginning to demand better and safer working conditions for their members, and exerting pressure on both management and governments to address these problems. Thus was passed the Occu-
* Corresponding author.
pational Safety and Health ( O S H A ) legislation in the USA, along with the creation of a number of ' w a t c h d o g ' and support agencies, including the National Institute of Occupational Safety and Health (NIOSH). A new era o f worker's rights was about to begin! Simultaneously, the industrial workplace and Frederick T a y l o r ' s 'classical' definition of a 'fair d a y ' s work' were also undergoing dramatic changes. Over the last ten to fifteen years, worker empowerment, group decisions, just-in-time deliveries and I S O / Q S 9000 quality systems are just a few of the new terms which have been added to our management vocabulary and, in quite a few instances, have
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actually been instituted in the workplace. Work standards or time standards, one of the original Taylor concepts, have, however, remained relatively untouched - until now, that is. Suddenly, faced with astronomical workplace injury costs and legislation broadening and protecting worker's rights, revisions are being contemplated to the way work standards are established and used. This is partly because current practices in this regard is perceived as a significant contributor to injuries at the workplace, particularly musculo-skeletal disorders (MSDs). Special mention is made of incentive pay practices derived from such standards, which have been identified as potential risk factors for MSDS. The so-called 'quality revolution' brought about by Dr. Deming has, in fact, gone so far as to advocate the elimination of the emphasis placed on work standards entirely. During the 1980's researchers began the process of developing ergonomic standards for industrial work, obviously visualizing a set of legislated standards, similar to those available for environmental control of workplaces. At least four such programs have been reported: the OSHA ergonomics regulation in the USA, the ISO ergonomics standardization project and the Canadian projects in British Columbia and in Quebec. These four projects share common goals of influencing risk factors by changing the work system. However, the recent trend towards a conservative agenda by governments (with the tacit approval of industry, at least in North America) makes legislated ergonomic standards only a remote dream. Under these conditions, the future of work standards, and the role that ergonomic 'criteria' will play therein, needs to be evaluated. The paper proposes an alternative strategy which will define injury risk factors on the job, and thereby will assess a nonvalue-added cost or 'tax' against a poorly designed product or process which could lead to the possibility of worker injury (whether long or short term)
2. Problems and issues
The authors wish to provide a brief background of the classical work standard and highlight the original purpose of this yardstick.
The purpose of the work standard is: 1. To develop a standard time for performing all the task elements required to produce a part or product, or to provide a service. The standard time is multiplied by the labor rate to determine a standard labor cost. Adding material cost, overhead and profit will then establish the selling price for the product or service. 2. Once this price has been established a n d / o r a contract has been made, all engineering, management and labor efforts are coordinated to try and meet or even better this work standard. 3. In today's work environment, with the introduction of ISO/QS 9000 quality systems, 'Continuous Improvement' is an important element in the system and work standards play an important role in establishing a benchmark and providing information about the detailed work methods currently being used at various operations. In summary, therefore the definition of the work standard is the time required to perform a series of discrete work elements plus added allowances for operator fatigue and personal needs; allowances for changing tools and maintaining the equipment plus other non-cyclic elements such as material handling and inspection. The usual methodology for establishing the work standard is: 1. Develop the most efficient, non-hazardous workplace design. 2. Establish the most efficient, injury-risk-free method of handling moving and storing materials and tools, handling chemicals, etc. 3. Establish the discrete work elements required by the operator to perform the operation or task. 4. Establish the average time required to perform each element and the total average to perform the complete task. 5. Add all allowances necessary to the total time to establish the total standard time. Given this, the issues arising from such a definition can be summarized as: (i) The classical (Taylor) work standard is one which is well defined and can be easily developed, even by persons who do not have high technical backgrounds. (ii) Because this standard commits a supplier to a firm, fixed labor cost, it should not include any
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variables which cannot be easily controlled so that they can be maintained at the level at which they were included in the work standard. (iii) Since a work standard is a target easily understood and accepted by both workers and management, and to which they then direct their energies, it also has the following disadvantages: (a) It is difficult to revise, even when the workplace design and work methods have been altered. (People don't easily accept changes in their workplace, nor do they easily adapt to these changes.) (b) It does not reflect differences in the way people work nor the physical and personality differences in people. (c) It inhibits the 'work smarter' concept opting, rather, in favor of the 'work harder', 'achieve your target', then, 'forget it' concept. (iv) The most troublesome aspect of a work standard is the 'Ergonomic Class' allowances (such as fatigue, standing, walking, personal, etc.). The issues here are: (a) Should these allowances be included in the work standard or would it better reflect the nonvalue-added costs of these elements, by creating a new cost category or by treating them similar to the overhead allowance? Will treating them as non-value-added costs give management the incentive to take some action with respect to ergonomic issues? (b) Do we really have sufficient knowledge regarding the amount of allowance each of these elements deserves? Management has always viewed these allowances with a great deal of reservation, mainly because of the lack of good quantitative data, which not only reflects the amount of allowance made for fatigue, for example, but also factors in differences between operators, workplaces, etc. (c) Again, once an allowance is added to the work standard, it is very difficult to remove it, even though conditions have changed. (d) Ergonomics is not yet an exact science and in that regard we are still trying to identify the factors which affect the worker and his/her ability to perform their work safely and efficiently. Take stress, for example. Modern machinery often tends to surround the worker, isolating him/her from audible or visual contact with any other workers.
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The development of stress is evidenced in these workers with a coincidental drop in productivity. How can allowances be quantified in this case? Does stress develop equally among all workers or do some handle this stress better than others. (i.e. Is it necessary to develop regression relationships?)
3. Current industrial practice Some illustrations of the issues outlined earlier are provided in the following paragraphs.
(i) Setting standards: It was discovered that shop floor IEs at all plants in the study still held traditional roles in production teams. Using productivity improvement techniques such as MTM, the IE filled out work process specification forms describing detailed assembly procedures for each operator to follow. Although IEs encouraged operators to suggest ways to improve their work-environment layout, ergonomics, storage or waste disposal they did not solicit input regarding the methods or time standards involved in the assembly process. This Tayloristic approach to methods and time standards was contradictory to the plant's teamwork and worker empowerment philosophies. On the one hand, the workers were entrusted with full responsibility for their work area; on the other hand, they were not given a chance to set the motion and time standards related to the assembly of parts they handled hundreds of times each day. It became clear that this policy was a detriment to plant-wide employee morale and even productivity. First, workers registered frequent complaints that they were not given enough time to complete their operations. Second, they often did not follow the prescribed assembly methods. Third, they seldom volunteered suggestions to reduce their cycle time. In summary, the traditional IE practices observed did little to encourage worker-generated continuous improvement (Anonymous, 1995).
(ii) On applying allowances: Although allowances are an important part of time standards, they have not received much attention. Allowances such as by the ILO are logical and systematic but do not seem to have an underlying scientific basis... (Konz, 1995).
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(iii) Ergonomic work analysis: Ergonomic work analysis, the specific description of real activity, shows that the operator and the user are not always reliable performers of the work prescribed but, more often than not, have to take into account a lot of variables owing to the work itself, it's environment and the personal state of the actor(s). In many cases, the work is the subject of a construction or reconstruction in terms of the situation where the activity takes place. The aim of ergonomics is then to modify this situation in a favourable way. When the technical system is transferred from one country to another, the sources of variation are multiplied and have an even greater impact on the work (Wisner, 1995).
(iv) New occupational skills and their maintenance: In the automated factory, jobs are changing from direct performance to monitoring; that means from manual to mental skills. One of the increasing problems is: how to maintain the skills? Dr. Lisanne Bainbridge formulated her "Paradox of Automation: that extensive automation leads to the paradoxical situation that, because they seldom occur, breakdowns are becoming less easy to handle." This is what end users and designers nowadays face in the process industry... In this context, the term 'brute force automation' is sometimes used. To conclude this point, the selection, education and training of future production personnel is more than ever a challenge! (Kragt, 1995).
(v) Repetitive work: There is no doubt that repetitive work encompasses multiple risks to health and well-being of workers. On the other hand, it seems that general opinion and also that of ergonomists has clung to anachronistic images of industrial repetitive work. Maybe the image of dull work without intellectual content has made ergonomists recommend that repetitive work be abandoned and prevented them from exploring possibilities to improve the situation. It is inevitable that repetitive work will remain with us for a long time. It may decrease in some sectors, but may remain or increase in others. Repetitive work may become, and already probably is, an important asset for increasing organizational flexibility and productivity, which may be difficult to achieve through automation. This cannot be achieved if
repetitive work retains its image as the low-value, low esteem work of the unqualified workforce... It is an important challenge to ergonomists to understand the real value of repetitive work, to improve and develop it and to convince companies of the need for a new vision (Kuorinka, 1995).
(vi) Limits to validity of standards: The direct result of gross estimation of risk is the relative validity of normative limits to workload. These limits, established from a knowledge base which is often questionable, are generally overestimated, and do not include a proper margin of error, leading to grave consequences for operator health and safety. The norms or limits are generally conceived on an experimental basis (which is more often than not, theoretically correct) but are then presented as 'relatively precise'; this is not only false but also dangerous, because it encourages misinterpretation of the results of job analysis. Moreover, the users often lack the skills either to assess the applicability of a norm to a specific situation they have to deal with, or to interpret the deviation between the recommended values obtained from the reference norms, and the values actually noted at the workplace. This is the direct result of the inability of the user to comprehend the significance of the theoretical basis of such norms including the purpose of numerous equations and correction coefficients which form the basis for its development (Monod and Kapitaniak, 1996). All this presents a very confusing picture about the role of ergonomics (and ergonomists) in work design. It is, however, recognized that ergonomic problems can, in general, be traced back to improper process and product design. These are reflected in either lowered human performance or excessive stress leading to occupationally related illness or injury or both (Rodgers, 1996). Such effects can be measured through 'injury risk factors,' arising from excessive forces, sustained awkward postures, excessive workloads and extreme environments. Obviously, these are translated into costs, both overt and covert, which are added on to the overall cost of manufacturing a part or component. It is this consideration which allows for a different approach to the setting of ergonomic standards. Industry already recognizes the impact of other hidden costs in its preparation of
L Barsky, S.P. Dutta/International Journal oflndustrial Ergonomics 20 (1997) 307-315
standards, e.g., fatigue. Why then should this cost also not be considered? The authors are, therefore, proposing an altemative strategy which deals with a new method of performing pro-active analyses to reflect workplace injury risks as a 'stand-alone' cost or added to work standards as an allowance to reflect the risks involved in poor design. Making the costs more visible might create incentives for eliminating their root cause.
4. Assumptions
According to Imai (1986), " a problem in business or industry is anything that inconveniences people downstream, either people in the next process or the ultimate consumer. Unfortunately, the people who create the problem are not directly inconvenienced by it". Appropriately, this quote describes designers of our products and processes and by inference, the business or industry which employs them. The dilemma facing management, designers and ergonomists is what Juran and Gryna (1988) call "Speak with data (and facts)". Although making good decisions without data is highly questionable, to say the least, yet we must be ever vigilant about the information we collect and use. According to Evans and Lindsay (1993) the current attitude among Pacific Rim industries is: "When you see data, doubt them! When you see a measuring instrument, doubt it!" Thus, given the natural suspicion of managers and engineers, what assurances are there that they will accept workplace standards proposed by ergonomists, especially since the current political environment is highly conservative and ergonomic theories are yet to be proven. These are unpredictable times, however, and possibly the solution lies in total quality system called I S O / Q S 9000, which industries around the world are being forced to adopt, with the environment and ergonomic standards slated for future adoption. The ISO/QS-9000 system specifies what companies and design teams 'shall' and 'should' do to evaluate and 'continually' improve their product and process designs in order to assure that the best quality product is produced. Once registered as a participant in the system, they are also stringently audited to ensure conformance with the system. The
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authors, therefore, must make the following assumptions: 1. The proposed model or an adaptation of the model be included in the 'should' section of QS-9000 Design and Development Planning (Section 4.4), the Continuous Improvement Section (C.I.) and eventually in Occupational Health and Safety Management Systems Standardization (Ergonomics, Safety and Health). 2. The cost or tax assessed for improper product and workplace design or any other potential ergonomic problem must be highlighted in some way and that the auditors exert some pressures on the company to eliminate the causes of the problems; or 3. The cost be added to the time standard as an allowance which can be removed once the cause has been eliminated, or be highlighted as a separate cost in the quotes, rather than hidden in overhead/burden cost.
5. The CAFER model
The cost assessment for ergonomic risk (CAFER) model attempts to determine a cost (in dollars or minutes) of injury expense suffered by a worker and, attributable directly to a product or process which has been designed in such a manner that the risk of injury is present. Fig. 1 presents a flowchart of the steps which product design or process planning teams would use to analyze a proposed product/process risk design and to evaluate the potential of worker injury, attributed directly to the design characteristics and, to calculate a cost equivalent to that risk.
6. Case study # 1 - Product design
Table 1 presents data which the authors had collected over the 1987-1989 period for previous research work (Dutta and Barsky, 1992) and which has been used here as a sample of data which can be collected to support this model. Not yet available, but with the assistance of industry, data will be gathered which will not only identify the number of injuries of a certain type being sustained, but the severity of each injury according to Fault Tree cate-
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L Barsky, S.P. Dutta / International Journal of Industrial Ergonomics 20 (1997) 307-315 PRODUCT
PROCF.,SS
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Finally~ROJECT~'--~. ~,~..ffONTRO._L...._.,.~'I
Fig. l. Flow chart of steps in CAFER model.
Table 1 Sample injury statistics for evaluating cost by anatomical regions for industries in E s s e x - K e n t region Year injury
Injured worker
Shift on which injury occurred
occurred
Sex
Age
1
1988 1987-1989 1987-1989 1987-1989 1987-1989 1987-1989 1987 1987-1989 1987-1989 1987-1989 1987-1989 1987-1989 1989 1987-1989 1987-1989
M F M F F F F M M F F F M F M
18 19 19 20 20 20 20 20 21 21 21 21 21 21 21
2
x x x
x x x x × x x x x
3
Part of anatomy injured
Lost time (hours)
Lost time ($)
Head Back Wrist Shoulder Finger Shoulder Wrist Hand Finger Chin Leg Knee Ankle Back Knee
15 2 48 6 8 6 412 3 8 2 1 54 15 43 1
$450.00 $60.00 $1,440.00 $180.00 $240.00 $180.00 $12,321.00 $100.00 $240.00 $75.00 $37.00 $1,620.00 $416.00 $1,290.00 $37.00
1. Barsky, S.P. Dutta / International Journal of Industrial Ergonomics 20 (1997) 307-315
gorization, and the probability that a certain injury will occur given the work design criteria. The following is an example of the procedure that a product design team would follow in determining the ergonomic risk and the associated cost: 1. A design team is redesigning a product consisting of a number of sub-assemblies. One sub-assembly will consist of a steel U-shaped formed bracket to which wire harness will be attached, and covered by a plastic molded cover. The wire harness will be attached to the bracket using plastic fasteners which must be first inserted into holes in the bracket. The wire harness will then be laid into the fasteners and held in place when a plastic cover is snapped around the wire and into grooves in the fastener. 2. The team in developing the design has used a number of analytical techniques including FMEA, in which they considered the possible effect of vibration on the fastener and the possibility of the fastener breaking and allowing the wire harness to fall and eventually present a safety hazard. Using Failure Modes and Effects Analysis (FMEA), Quality Function Deployment (QFD), Value Engineering etc., the leg diameter of the fastener was increased.
TASK
313
3. A similar analysis using a matrix as shown in Fig. 2, would be used to determine what probable ergonomic hazards exist if the harness be attached in the manner being proposed. From this analysis, it has been determined that: (a) The method of assembling the fasteners would probably be done manually, requiring that an operator press the leg of the fastener through a hole in the metal bracket and using a large amount of force. (b) Since 8 to 10 fasteners would be required to hold the harness; the operation would be repeated with a high frequency with little time for rest and recuperation of the hand area involved. (c) There would probably also be twisting of wrist/arm/and shoulders involved in inserting the fastener. 4. After determining the anatomical areas at risk in the assembly of the harness, a cost would be assessed using the data from Table 1 and the probability of the injury occurring. (Note: The probability data has not yet been accumulated by the authors. It is however, readily available in most industries by analyzing historical data and/or from compensation boards,) The Risk Assessment Cost would therefore be
ANATOMICAL
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Switch 1. Insert High risk control/ plastic of C.T.D. fasteners into punched -Carpal *Fingers Bracket 240.00 Sub-Ass holes, Tunnel *Thumb -Inflamed *Wrist 6,880.50 90.00 -get (8) plastic Tendons *Hand fasteners. -Upper -pos. (1)fastene Thorasic *Shoulder 180.00 to hole. Push area *Trapesius into hole with problem twisting motion. -repeat for (7) Causes fasteners. *Pinch grip 2. Lay wire *Force *Hand harness into *Freq. *Wrist fastener and clip cap. TOTAL
73.00%
1
80.00% 11.00%
1 1
65.00%
1
*Use contact cement to attach harness 175.20 to bracket. (J. Dunn) 5,504.40 (96-10-22) 9.90
117.00
$8,806.50
Fig. 2. Analysis of injury risk and associated cost for case study #1.
L Barsky, S.P. Dutta / International Journal of lndustrial Ergonomics 20 (1997) 307-315
314
calculated by multiplying the cost selected from Table 1 (for the anatomical area in question) by the probability of the injury occurring, by the estimated number of persons who would perform this operation. 5. The design team could then decide what strategies should be implemented to eliminate this cost. 6. The design team would eventually have to demonstrate to 'external ISO 9000 auditors', that they are performing these kinds of analysis.
difficulties in mounting the bearing ring assembly to the cam. . A Continuous Improvement team decided to examine this operation using the CAFER model. The results of this investigation are shown in Fig. 3. . The analysis of this investigation indicated that: (a) The production requirement for this operation was 300 assemblies per hour. Thus an operator was allowed only 10 seconds to get the parts, assemble the unit and dispose of the finished assembly. (b) The assembly required a 'pressed-fit' operation where the operator placed the I.D. of the bearing ring sub-assembly over the O.D. of the cam, and with downward pressure, forced the ring onto the cam surface. Due to the snug fit between the mating parts, a number of adjusting turns of the ring was necessary, followed by the downward force application. (c) The operator needed a wide pinch grip and a great deal of force to hold and control the 12 cm
7. Case study # 2 Assemble reverse clutchassembly for auto transmission -
l. An Annular Bearing assembly consisting of an outer ring, 12 ball bearings and a retainer ring, with an O.D. of 12 cm, is mounted over a 7 cm Cam weighing approximately 2 kg. 2. A time study using ERGOMOST, did not identify any specific problems for this operation, but once production started, workers had some apparent
ANATOMICAL
AVERAGE
PROBABILITY
NO. OF
DESCRIPTION I
TASK POSEIBLE
AREA
COST OF
OF
PERSONS
INJURY
ACTIONS t
ITEM I
PHYSICAL
INJURY
AT
INJURY
PERFORMING
COST
PERSON I
STATION
DEMAND5
RISKS
RISK
ITARCE1~
OP~EAnON
Ifi
"ArE
OCCURRENCE
~
POTENTIAL
RECOMMENDED
*Redesign product so sea~ng Bearing Assy., is easier
Assembly Assemble Station #4 Annular Bearing Aesemb/y to Cam, -Pos. bearing *Carpal to Cam Tunnel -Rotate Bearing (Twisting Assy clockwise with high then counterforce clockwise. Find applied) best seating posWon. "Tendonitis -Apply force (Wrist & to seat aesy., elbow) twisting to find best alignment. *Headache and Stress (Freq.=300/hr.) (Visual concentration)
-Wrist
6,880.50
90.00%
2
-Elbow
820.00
75.00%
2
-Shoulder
180.00
5000%
2
-Eyes
400.00
20.00%
2
12,384.90 *Add 2 seconds to Work Std. 1,230.00 timeof 10.3 sec (See Reference 180.00 S. Rodgers) 160.00
*Large Force with Pinch Grip (Would require 2 - 3 sec. rest time) TOTAL
$13,614.90
Fig. 3. Analysis of injury risk and associated cost for case study # 2 .
Note: Impossible to automate job.
L Barsky, S.P. Dutta/International Journal oflndustrial Ergonomics 20 (1997) 307-315
O.D. ring while locating it during the assembly operation. (d) A high degree of visual concentration and sensory-motor feed back is required for this job. (e) The high production rate presents little time for the operator to rest, thus increasing the risk of injury. 5. Using tables developed by Rodgers (1987), the recommendations of the C.I.G. was to add 2.2 seconds onto the cycle time, and to rotate workers every hour. Further considerations were to request the design team to investigate some alternative designs for this product, which would reduce the injury risk for the assembly operator. The addition of 2.2 seconds would represent a fairly large (20.4%) increase in assembly time for the company and would, hopefully, provide them with some incentive to find an adequate solution to this problem.
8. Conclusions The procedure outlined above should also be applied to the planning and design or redesign of manufacturing and service processes where work standards are being developed. It would require little additional effort to conduct a 'physical demands analysis' to identify what potential ergonomic risks mig~ht be encountered by an operator performing the operations being proposed. The 'risk-cost' would be calculated as indicated above but in this instance it is recommended that the cost be translated into minutes or hours which would be added to the work standard as an 'ergonomic risk allowance'. This allowance would be removed from the work standard when the process is redesigned to eliminate or reduce the risk of injury. The design injury risk cost, as discussed in the example above, should be weighted more heavily than costs in the process planning stage because the product design and specifications tend to greatly influence the manufacturing process design. Therefore, anticipating ergonomic risks at the design stage would go a long way towards reducing the injury costs at the production stages. Although ergonomic issues are being dealt with by more and more industries, today, the approach to
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solving worker injury risk problems is still mostly 'laissez-faire'. An organized approach, similar to the one being presented here, must be developed where the ergonomic risks and associated costs are highlighted rather than hidden as an operating expense, and continuous improvement efforts be documented to demonstrate the activities being undertaken to correct the conditions causing these risks. The authors are presenting this model as a concept or approach that might be used in conjunction with (or instead of) ergonomic standards. The cost data is available and will be updated in the near future. Efforts are also underway to collect meaningful probability data.
References Anonymous, 1995. Setting work standards. Industrial Engineering Solutions, May, 42-44. Dutta, S.P., Barsky, I., 1992. Age, shiftwork and industrial accidents - A longitudinal study. In: Kumar, S. (Ed.), Advances in Industrial Ergonomics and Safety IV. Taylor and Francis, London, pp. 113-120. Evans, J.R., Lindsay, W., 1993. The Management and Control of Quality, 2nd ed. West Publishing. lmai, M., Kaizen, 1986. The Key to Japan's Competitive Success. Random House, London, pp. 163-165. Juran, J.M., Gryna, F.M., 1988. Juran's Quality Control Handbook, 4th ed. ASQC Quality Press. Konz, S., 1995. Environmental fatigue allowances. International Journal of Industrial Engineering 2 (1), 5-13. Kragt, H., 1995. Enhancing human performance. Ergonomics 38 (8), 1674-1685. Kuorinka, 1., 1995. Repetitive work in perspective. Ergonomics 38 (8), 1686-1690. Monod, H., Kapitaniak, B., 1996. Theory versus practice of ergonomics guidelines. In: Mital, A., Krueger, H., Kumar, S., Menozzi, M., Fernandez, J.E. (Eds.), Advances in Occupational Ergonomics and Safety I, Vol 2. International Society for Occupational Ergonomics and Safety, Cincinnati, OH, pp. 909-912. Rodgers, S.H., 1987. Recovery time needs for repetitive work. Seminars in Occupational Medicine 2 (1), 19-24. Rodgers, S.H., 1996. Measuring and setting ergonomic standards - Issues and perspectives. In: Mital, A., Krueger, H., Kumar, S., Menozzi, M., Fernandez, J.E. (Eds,), Advances in Occupational Ergonomics and Safety I, Vol 2. International Society for Occupational Ergonomics and Safety, Cincinnati, OH, pp. 884-890. Wisner, A., 1995~ The Etienne Grandjean memorial lecture. Ergonomics 38 (8), 1542-1557.
la strial Ergonomics
!4.'m ELSEVIER
International Journal of Industrial Ergonomics 20 (1997) 307-315
Cost assessment for ergonomic risk (CAFER) Isaac Barsky a, S.P. Dutta b,, a Workplace Basics, La Salle, Ontario, Canada b Department oflndustrial and Manufacturing Systems Engineering, University of Windsor, Windsor, Ontario, Canada
Received 10 February 1996; revised 13 August 1996
Abstract Consumer safety in the use of a product is always given the highest priority by product designers. However, little or no consideration, it seems, is afforded the production workers who must produce and assemble these products. Given the conservative bent of governments, industry will have less incentive to invest in equipment which will reduce the risk of work-related injuries, or to give maximum consideration to designing the products and processes in such a manner that the risk of worker injury is minimized. One possible approach to make industries more accountable in this regard, is to utilize ISO 9000 as a vehicle for incorporating FMEA-like analysis techniques for occupational health issues and to audit every customer/supplier to assure that actions are being taken to solve any problems which have been identified. The authors suggest some strategies for implementing and controlling this type of system. Relevance to industry The concepts and methods presented here will allow product designers and process planners to not only assess the injury risk of their proposed design on the workers who must manufacture the product, but also determine the costs associated with such risks. © 1997 Elsevier Science B.V. Keywords: Cost assessment; Injury risk factors; F.M.E.A.; Work standard; ISO 9000
1. I n t r o d u c t i o n In the 1960's and 1970's, industries in developed countries all over the world became increasingly aware that its workplace were being exposed to soft tissue injuries at an alarming rate. Coincidentally, unions were beginning to demand better and safer working conditions for their members, and exerting pressure on both management and governments to address these problems. Thus was passed the Occu-
* Corresponding author.
pational Safety and Health ( O S H A ) legislation in the USA, along with the creation of a number of ' w a t c h d o g ' and support agencies, including the National Institute of Occupational Safety and Health (NIOSH). A new era o f worker's rights was about to begin! Simultaneously, the industrial workplace and Frederick T a y l o r ' s 'classical' definition of a 'fair d a y ' s work' were also undergoing dramatic changes. Over the last ten to fifteen years, worker empowerment, group decisions, just-in-time deliveries and I S O / Q S 9000 quality systems are just a few of the new terms which have been added to our management vocabulary and, in quite a few instances, have
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actually been instituted in the workplace. Work standards or time standards, one of the original Taylor concepts, have, however, remained relatively untouched - until now, that is. Suddenly, faced with astronomical workplace injury costs and legislation broadening and protecting worker's rights, revisions are being contemplated to the way work standards are established and used. This is partly because current practices in this regard is perceived as a significant contributor to injuries at the workplace, particularly musculo-skeletal disorders (MSDs). Special mention is made of incentive pay practices derived from such standards, which have been identified as potential risk factors for MSDS. The so-called 'quality revolution' brought about by Dr. Deming has, in fact, gone so far as to advocate the elimination of the emphasis placed on work standards entirely. During the 1980's researchers began the process of developing ergonomic standards for industrial work, obviously visualizing a set of legislated standards, similar to those available for environmental control of workplaces. At least four such programs have been reported: the OSHA ergonomics regulation in the USA, the ISO ergonomics standardization project and the Canadian projects in British Columbia and in Quebec. These four projects share common goals of influencing risk factors by changing the work system. However, the recent trend towards a conservative agenda by governments (with the tacit approval of industry, at least in North America) makes legislated ergonomic standards only a remote dream. Under these conditions, the future of work standards, and the role that ergonomic 'criteria' will play therein, needs to be evaluated. The paper proposes an alternative strategy which will define injury risk factors on the job, and thereby will assess a nonvalue-added cost or 'tax' against a poorly designed product or process which could lead to the possibility of worker injury (whether long or short term)
2. Problems and issues
The authors wish to provide a brief background of the classical work standard and highlight the original purpose of this yardstick.
The purpose of the work standard is: 1. To develop a standard time for performing all the task elements required to produce a part or product, or to provide a service. The standard time is multiplied by the labor rate to determine a standard labor cost. Adding material cost, overhead and profit will then establish the selling price for the product or service. 2. Once this price has been established a n d / o r a contract has been made, all engineering, management and labor efforts are coordinated to try and meet or even better this work standard. 3. In today's work environment, with the introduction of ISO/QS 9000 quality systems, 'Continuous Improvement' is an important element in the system and work standards play an important role in establishing a benchmark and providing information about the detailed work methods currently being used at various operations. In summary, therefore the definition of the work standard is the time required to perform a series of discrete work elements plus added allowances for operator fatigue and personal needs; allowances for changing tools and maintaining the equipment plus other non-cyclic elements such as material handling and inspection. The usual methodology for establishing the work standard is: 1. Develop the most efficient, non-hazardous workplace design. 2. Establish the most efficient, injury-risk-free method of handling moving and storing materials and tools, handling chemicals, etc. 3. Establish the discrete work elements required by the operator to perform the operation or task. 4. Establish the average time required to perform each element and the total average to perform the complete task. 5. Add all allowances necessary to the total time to establish the total standard time. Given this, the issues arising from such a definition can be summarized as: (i) The classical (Taylor) work standard is one which is well defined and can be easily developed, even by persons who do not have high technical backgrounds. (ii) Because this standard commits a supplier to a firm, fixed labor cost, it should not include any
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variables which cannot be easily controlled so that they can be maintained at the level at which they were included in the work standard. (iii) Since a work standard is a target easily understood and accepted by both workers and management, and to which they then direct their energies, it also has the following disadvantages: (a) It is difficult to revise, even when the workplace design and work methods have been altered. (People don't easily accept changes in their workplace, nor do they easily adapt to these changes.) (b) It does not reflect differences in the way people work nor the physical and personality differences in people. (c) It inhibits the 'work smarter' concept opting, rather, in favor of the 'work harder', 'achieve your target', then, 'forget it' concept. (iv) The most troublesome aspect of a work standard is the 'Ergonomic Class' allowances (such as fatigue, standing, walking, personal, etc.). The issues here are: (a) Should these allowances be included in the work standard or would it better reflect the nonvalue-added costs of these elements, by creating a new cost category or by treating them similar to the overhead allowance? Will treating them as non-value-added costs give management the incentive to take some action with respect to ergonomic issues? (b) Do we really have sufficient knowledge regarding the amount of allowance each of these elements deserves? Management has always viewed these allowances with a great deal of reservation, mainly because of the lack of good quantitative data, which not only reflects the amount of allowance made for fatigue, for example, but also factors in differences between operators, workplaces, etc. (c) Again, once an allowance is added to the work standard, it is very difficult to remove it, even though conditions have changed. (d) Ergonomics is not yet an exact science and in that regard we are still trying to identify the factors which affect the worker and his/her ability to perform their work safely and efficiently. Take stress, for example. Modern machinery often tends to surround the worker, isolating him/her from audible or visual contact with any other workers.
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The development of stress is evidenced in these workers with a coincidental drop in productivity. How can allowances be quantified in this case? Does stress develop equally among all workers or do some handle this stress better than others. (i.e. Is it necessary to develop regression relationships?)
3. Current industrial practice Some illustrations of the issues outlined earlier are provided in the following paragraphs.
(i) Setting standards: It was discovered that shop floor IEs at all plants in the study still held traditional roles in production teams. Using productivity improvement techniques such as MTM, the IE filled out work process specification forms describing detailed assembly procedures for each operator to follow. Although IEs encouraged operators to suggest ways to improve their work-environment layout, ergonomics, storage or waste disposal they did not solicit input regarding the methods or time standards involved in the assembly process. This Tayloristic approach to methods and time standards was contradictory to the plant's teamwork and worker empowerment philosophies. On the one hand, the workers were entrusted with full responsibility for their work area; on the other hand, they were not given a chance to set the motion and time standards related to the assembly of parts they handled hundreds of times each day. It became clear that this policy was a detriment to plant-wide employee morale and even productivity. First, workers registered frequent complaints that they were not given enough time to complete their operations. Second, they often did not follow the prescribed assembly methods. Third, they seldom volunteered suggestions to reduce their cycle time. In summary, the traditional IE practices observed did little to encourage worker-generated continuous improvement (Anonymous, 1995).
(ii) On applying allowances: Although allowances are an important part of time standards, they have not received much attention. Allowances such as by the ILO are logical and systematic but do not seem to have an underlying scientific basis... (Konz, 1995).
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(iii) Ergonomic work analysis: Ergonomic work analysis, the specific description of real activity, shows that the operator and the user are not always reliable performers of the work prescribed but, more often than not, have to take into account a lot of variables owing to the work itself, it's environment and the personal state of the actor(s). In many cases, the work is the subject of a construction or reconstruction in terms of the situation where the activity takes place. The aim of ergonomics is then to modify this situation in a favourable way. When the technical system is transferred from one country to another, the sources of variation are multiplied and have an even greater impact on the work (Wisner, 1995).
(iv) New occupational skills and their maintenance: In the automated factory, jobs are changing from direct performance to monitoring; that means from manual to mental skills. One of the increasing problems is: how to maintain the skills? Dr. Lisanne Bainbridge formulated her "Paradox of Automation: that extensive automation leads to the paradoxical situation that, because they seldom occur, breakdowns are becoming less easy to handle." This is what end users and designers nowadays face in the process industry... In this context, the term 'brute force automation' is sometimes used. To conclude this point, the selection, education and training of future production personnel is more than ever a challenge! (Kragt, 1995).
(v) Repetitive work: There is no doubt that repetitive work encompasses multiple risks to health and well-being of workers. On the other hand, it seems that general opinion and also that of ergonomists has clung to anachronistic images of industrial repetitive work. Maybe the image of dull work without intellectual content has made ergonomists recommend that repetitive work be abandoned and prevented them from exploring possibilities to improve the situation. It is inevitable that repetitive work will remain with us for a long time. It may decrease in some sectors, but may remain or increase in others. Repetitive work may become, and already probably is, an important asset for increasing organizational flexibility and productivity, which may be difficult to achieve through automation. This cannot be achieved if
repetitive work retains its image as the low-value, low esteem work of the unqualified workforce... It is an important challenge to ergonomists to understand the real value of repetitive work, to improve and develop it and to convince companies of the need for a new vision (Kuorinka, 1995).
(vi) Limits to validity of standards: The direct result of gross estimation of risk is the relative validity of normative limits to workload. These limits, established from a knowledge base which is often questionable, are generally overestimated, and do not include a proper margin of error, leading to grave consequences for operator health and safety. The norms or limits are generally conceived on an experimental basis (which is more often than not, theoretically correct) but are then presented as 'relatively precise'; this is not only false but also dangerous, because it encourages misinterpretation of the results of job analysis. Moreover, the users often lack the skills either to assess the applicability of a norm to a specific situation they have to deal with, or to interpret the deviation between the recommended values obtained from the reference norms, and the values actually noted at the workplace. This is the direct result of the inability of the user to comprehend the significance of the theoretical basis of such norms including the purpose of numerous equations and correction coefficients which form the basis for its development (Monod and Kapitaniak, 1996). All this presents a very confusing picture about the role of ergonomics (and ergonomists) in work design. It is, however, recognized that ergonomic problems can, in general, be traced back to improper process and product design. These are reflected in either lowered human performance or excessive stress leading to occupationally related illness or injury or both (Rodgers, 1996). Such effects can be measured through 'injury risk factors,' arising from excessive forces, sustained awkward postures, excessive workloads and extreme environments. Obviously, these are translated into costs, both overt and covert, which are added on to the overall cost of manufacturing a part or component. It is this consideration which allows for a different approach to the setting of ergonomic standards. Industry already recognizes the impact of other hidden costs in its preparation of
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standards, e.g., fatigue. Why then should this cost also not be considered? The authors are, therefore, proposing an altemative strategy which deals with a new method of performing pro-active analyses to reflect workplace injury risks as a 'stand-alone' cost or added to work standards as an allowance to reflect the risks involved in poor design. Making the costs more visible might create incentives for eliminating their root cause.
4. Assumptions
According to Imai (1986), " a problem in business or industry is anything that inconveniences people downstream, either people in the next process or the ultimate consumer. Unfortunately, the people who create the problem are not directly inconvenienced by it". Appropriately, this quote describes designers of our products and processes and by inference, the business or industry which employs them. The dilemma facing management, designers and ergonomists is what Juran and Gryna (1988) call "Speak with data (and facts)". Although making good decisions without data is highly questionable, to say the least, yet we must be ever vigilant about the information we collect and use. According to Evans and Lindsay (1993) the current attitude among Pacific Rim industries is: "When you see data, doubt them! When you see a measuring instrument, doubt it!" Thus, given the natural suspicion of managers and engineers, what assurances are there that they will accept workplace standards proposed by ergonomists, especially since the current political environment is highly conservative and ergonomic theories are yet to be proven. These are unpredictable times, however, and possibly the solution lies in total quality system called I S O / Q S 9000, which industries around the world are being forced to adopt, with the environment and ergonomic standards slated for future adoption. The ISO/QS-9000 system specifies what companies and design teams 'shall' and 'should' do to evaluate and 'continually' improve their product and process designs in order to assure that the best quality product is produced. Once registered as a participant in the system, they are also stringently audited to ensure conformance with the system. The
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authors, therefore, must make the following assumptions: 1. The proposed model or an adaptation of the model be included in the 'should' section of QS-9000 Design and Development Planning (Section 4.4), the Continuous Improvement Section (C.I.) and eventually in Occupational Health and Safety Management Systems Standardization (Ergonomics, Safety and Health). 2. The cost or tax assessed for improper product and workplace design or any other potential ergonomic problem must be highlighted in some way and that the auditors exert some pressures on the company to eliminate the causes of the problems; or 3. The cost be added to the time standard as an allowance which can be removed once the cause has been eliminated, or be highlighted as a separate cost in the quotes, rather than hidden in overhead/burden cost.
5. The CAFER model
The cost assessment for ergonomic risk (CAFER) model attempts to determine a cost (in dollars or minutes) of injury expense suffered by a worker and, attributable directly to a product or process which has been designed in such a manner that the risk of injury is present. Fig. 1 presents a flowchart of the steps which product design or process planning teams would use to analyze a proposed product/process risk design and to evaluate the potential of worker injury, attributed directly to the design characteristics and, to calculate a cost equivalent to that risk.
6. Case study # 1 - Product design
Table 1 presents data which the authors had collected over the 1987-1989 period for previous research work (Dutta and Barsky, 1992) and which has been used here as a sample of data which can be collected to support this model. Not yet available, but with the assistance of industry, data will be gathered which will not only identify the number of injuries of a certain type being sustained, but the severity of each injury according to Fault Tree cate-
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L Barsky, S.P. Dutta / International Journal of Industrial Ergonomics 20 (1997) 307-315 PRODUCT
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Finally~ROJECT~'--~. ~,~..ffONTRO._L...._.,.~'I
Fig. l. Flow chart of steps in CAFER model.
Table 1 Sample injury statistics for evaluating cost by anatomical regions for industries in E s s e x - K e n t region Year injury
Injured worker
Shift on which injury occurred
occurred
Sex
Age
1
1988 1987-1989 1987-1989 1987-1989 1987-1989 1987-1989 1987 1987-1989 1987-1989 1987-1989 1987-1989 1987-1989 1989 1987-1989 1987-1989
M F M F F F F M M F F F M F M
18 19 19 20 20 20 20 20 21 21 21 21 21 21 21
2
x x x
x x x x × x x x x
3
Part of anatomy injured
Lost time (hours)
Lost time ($)
Head Back Wrist Shoulder Finger Shoulder Wrist Hand Finger Chin Leg Knee Ankle Back Knee
15 2 48 6 8 6 412 3 8 2 1 54 15 43 1
$450.00 $60.00 $1,440.00 $180.00 $240.00 $180.00 $12,321.00 $100.00 $240.00 $75.00 $37.00 $1,620.00 $416.00 $1,290.00 $37.00
1. Barsky, S.P. Dutta / International Journal of Industrial Ergonomics 20 (1997) 307-315
gorization, and the probability that a certain injury will occur given the work design criteria. The following is an example of the procedure that a product design team would follow in determining the ergonomic risk and the associated cost: 1. A design team is redesigning a product consisting of a number of sub-assemblies. One sub-assembly will consist of a steel U-shaped formed bracket to which wire harness will be attached, and covered by a plastic molded cover. The wire harness will be attached to the bracket using plastic fasteners which must be first inserted into holes in the bracket. The wire harness will then be laid into the fasteners and held in place when a plastic cover is snapped around the wire and into grooves in the fastener. 2. The team in developing the design has used a number of analytical techniques including FMEA, in which they considered the possible effect of vibration on the fastener and the possibility of the fastener breaking and allowing the wire harness to fall and eventually present a safety hazard. Using Failure Modes and Effects Analysis (FMEA), Quality Function Deployment (QFD), Value Engineering etc., the leg diameter of the fastener was increased.
TASK
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3. A similar analysis using a matrix as shown in Fig. 2, would be used to determine what probable ergonomic hazards exist if the harness be attached in the manner being proposed. From this analysis, it has been determined that: (a) The method of assembling the fasteners would probably be done manually, requiring that an operator press the leg of the fastener through a hole in the metal bracket and using a large amount of force. (b) Since 8 to 10 fasteners would be required to hold the harness; the operation would be repeated with a high frequency with little time for rest and recuperation of the hand area involved. (c) There would probably also be twisting of wrist/arm/and shoulders involved in inserting the fastener. 4. After determining the anatomical areas at risk in the assembly of the harness, a cost would be assessed using the data from Table 1 and the probability of the injury occurring. (Note: The probability data has not yet been accumulated by the authors. It is however, readily available in most industries by analyzing historical data and/or from compensation boards,) The Risk Assessment Cost would therefore be
ANATOMICAL
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AT
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Switch 1. Insert High risk control/ plastic of C.T.D. fasteners into punched -Carpal *Fingers Bracket 240.00 Sub-Ass holes, Tunnel *Thumb -Inflamed *Wrist 6,880.50 90.00 -get (8) plastic Tendons *Hand fasteners. -Upper -pos. (1)fastene Thorasic *Shoulder 180.00 to hole. Push area *Trapesius into hole with problem twisting motion. -repeat for (7) Causes fasteners. *Pinch grip 2. Lay wire *Force *Hand harness into *Freq. *Wrist fastener and clip cap. TOTAL
73.00%
1
80.00% 11.00%
1 1
65.00%
1
*Use contact cement to attach harness 175.20 to bracket. (J. Dunn) 5,504.40 (96-10-22) 9.90
117.00
$8,806.50
Fig. 2. Analysis of injury risk and associated cost for case study #1.
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calculated by multiplying the cost selected from Table 1 (for the anatomical area in question) by the probability of the injury occurring, by the estimated number of persons who would perform this operation. 5. The design team could then decide what strategies should be implemented to eliminate this cost. 6. The design team would eventually have to demonstrate to 'external ISO 9000 auditors', that they are performing these kinds of analysis.
difficulties in mounting the bearing ring assembly to the cam. . A Continuous Improvement team decided to examine this operation using the CAFER model. The results of this investigation are shown in Fig. 3. . The analysis of this investigation indicated that: (a) The production requirement for this operation was 300 assemblies per hour. Thus an operator was allowed only 10 seconds to get the parts, assemble the unit and dispose of the finished assembly. (b) The assembly required a 'pressed-fit' operation where the operator placed the I.D. of the bearing ring sub-assembly over the O.D. of the cam, and with downward pressure, forced the ring onto the cam surface. Due to the snug fit between the mating parts, a number of adjusting turns of the ring was necessary, followed by the downward force application. (c) The operator needed a wide pinch grip and a great deal of force to hold and control the 12 cm
7. Case study # 2 Assemble reverse clutchassembly for auto transmission -
l. An Annular Bearing assembly consisting of an outer ring, 12 ball bearings and a retainer ring, with an O.D. of 12 cm, is mounted over a 7 cm Cam weighing approximately 2 kg. 2. A time study using ERGOMOST, did not identify any specific problems for this operation, but once production started, workers had some apparent
ANATOMICAL
AVERAGE
PROBABILITY
NO. OF
DESCRIPTION I
TASK POSEIBLE
AREA
COST OF
OF
PERSONS
INJURY
ACTIONS t
ITEM I
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AT
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ITARCE1~
OP~EAnON
Ifi
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*Redesign product so sea~ng Bearing Assy., is easier
Assembly Assemble Station #4 Annular Bearing Aesemb/y to Cam, -Pos. bearing *Carpal to Cam Tunnel -Rotate Bearing (Twisting Assy clockwise with high then counterforce clockwise. Find applied) best seating posWon. "Tendonitis -Apply force (Wrist & to seat aesy., elbow) twisting to find best alignment. *Headache and Stress (Freq.=300/hr.) (Visual concentration)
-Wrist
6,880.50
90.00%
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5000%
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2
12,384.90 *Add 2 seconds to Work Std. 1,230.00 timeof 10.3 sec (See Reference 180.00 S. Rodgers) 160.00
*Large Force with Pinch Grip (Would require 2 - 3 sec. rest time) TOTAL
$13,614.90
Fig. 3. Analysis of injury risk and associated cost for case study # 2 .
Note: Impossible to automate job.
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O.D. ring while locating it during the assembly operation. (d) A high degree of visual concentration and sensory-motor feed back is required for this job. (e) The high production rate presents little time for the operator to rest, thus increasing the risk of injury. 5. Using tables developed by Rodgers (1987), the recommendations of the C.I.G. was to add 2.2 seconds onto the cycle time, and to rotate workers every hour. Further considerations were to request the design team to investigate some alternative designs for this product, which would reduce the injury risk for the assembly operator. The addition of 2.2 seconds would represent a fairly large (20.4%) increase in assembly time for the company and would, hopefully, provide them with some incentive to find an adequate solution to this problem.
8. Conclusions The procedure outlined above should also be applied to the planning and design or redesign of manufacturing and service processes where work standards are being developed. It would require little additional effort to conduct a 'physical demands analysis' to identify what potential ergonomic risks mig~ht be encountered by an operator performing the operations being proposed. The 'risk-cost' would be calculated as indicated above but in this instance it is recommended that the cost be translated into minutes or hours which would be added to the work standard as an 'ergonomic risk allowance'. This allowance would be removed from the work standard when the process is redesigned to eliminate or reduce the risk of injury. The design injury risk cost, as discussed in the example above, should be weighted more heavily than costs in the process planning stage because the product design and specifications tend to greatly influence the manufacturing process design. Therefore, anticipating ergonomic risks at the design stage would go a long way towards reducing the injury costs at the production stages. Although ergonomic issues are being dealt with by more and more industries, today, the approach to
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solving worker injury risk problems is still mostly 'laissez-faire'. An organized approach, similar to the one being presented here, must be developed where the ergonomic risks and associated costs are highlighted rather than hidden as an operating expense, and continuous improvement efforts be documented to demonstrate the activities being undertaken to correct the conditions causing these risks. The authors are presenting this model as a concept or approach that might be used in conjunction with (or instead of) ergonomic standards. The cost data is available and will be updated in the near future. Efforts are also underway to collect meaningful probability data.
References Anonymous, 1995. Setting work standards. Industrial Engineering Solutions, May, 42-44. Dutta, S.P., Barsky, I., 1992. Age, shiftwork and industrial accidents - A longitudinal study. In: Kumar, S. (Ed.), Advances in Industrial Ergonomics and Safety IV. Taylor and Francis, London, pp. 113-120. Evans, J.R., Lindsay, W., 1993. The Management and Control of Quality, 2nd ed. West Publishing. lmai, M., Kaizen, 1986. The Key to Japan's Competitive Success. Random House, London, pp. 163-165. Juran, J.M., Gryna, F.M., 1988. Juran's Quality Control Handbook, 4th ed. ASQC Quality Press. Konz, S., 1995. Environmental fatigue allowances. International Journal of Industrial Engineering 2 (1), 5-13. Kragt, H., 1995. Enhancing human performance. Ergonomics 38 (8), 1674-1685. Kuorinka, 1., 1995. Repetitive work in perspective. Ergonomics 38 (8), 1686-1690. Monod, H., Kapitaniak, B., 1996. Theory versus practice of ergonomics guidelines. In: Mital, A., Krueger, H., Kumar, S., Menozzi, M., Fernandez, J.E. (Eds.), Advances in Occupational Ergonomics and Safety I, Vol 2. International Society for Occupational Ergonomics and Safety, Cincinnati, OH, pp. 909-912. Rodgers, S.H., 1987. Recovery time needs for repetitive work. Seminars in Occupational Medicine 2 (1), 19-24. Rodgers, S.H., 1996. Measuring and setting ergonomic standards - Issues and perspectives. In: Mital, A., Krueger, H., Kumar, S., Menozzi, M., Fernandez, J.E. (Eds,), Advances in Occupational Ergonomics and Safety I, Vol 2. International Society for Occupational Ergonomics and Safety, Cincinnati, OH, pp. 884-890. Wisner, A., 1995~ The Etienne Grandjean memorial lecture. Ergonomics 38 (8), 1542-1557.