Production optimisation systems and consequences for workers health and safety: Lean production and effects on stress and musculoskeletal disorders
thesisposted on 03.09.2014, 08:29 by Theoni Koukoulaki
This thesis investigates production optimisation systems such as lean production and their consequences for the health and safety of workers. In particular it examines potential positive effects and adverse effects on stress and musculoskeletal disorders (MSDs). The thesis com-prises an extended literature survey and a field study in the manufacturing and the services sector applying lean production. It provides an extensive review of studies carried out in lean production environments in the last 20 years that aims to identify the effects of lean production (negative or positive) on occupational health and related risk factors. Thirty-six studies of lean effects were accepted from the literature search and sorted by sector and type of outcome. Lean production was found to have a negative effect on health and risk factors; the most negative outcomes being found in the earliest studies in the automotive industry. However, examples of mixed and positive effects were also found in the literature. The strongest correlations of lean production with stress were found for characteristics found in Just-In-Time production that related to reduced cycle time and reduction of resources. In-creased musculoskeletal risk symptoms were related to increases of work pace and lack of recovery time also found in Just-In-Time systems. An interaction model is developed to pro-pose a pathway from lean production characteristics to musculoskeletal and psychosocial risk factors and also positive outcomes. An examination is also made of the changing focus of studies investigating the consequences of lean production over a 20-year period. Theories about the effects of lean production have evolved from a conceptualization that it is an inherently harmful management system, to a view that it can have mixed effects depending on the management style of the organization and the specific way it is implemented. The field study was carried out in lean environments in the manufacturing and services sec-tors, namely in the electronics, beverage, and metal industry and call centres in Greece and UK. For the psychosocial factors and recording of MSD symptoms; self reported questionnaires were administrated to the workers. In total 353 workers responded to the questionnaires. Additionally qualitative data were collected through semi-structured interviews with managers and lean officials, safety officers and workers in the sample. Finally, observation visits in the companies completed the data collection process. The lean implementation level of the companies was estimated on a five-point scale, according to a validated model (Conti et al, 2006). A follow up study to collect qualitative data was possible in one company in the sample. The research hypotheses of the field study tested the relationship between job stress and MSDs with quantitative job demands, job control, performance monitoring, and the level of lean implementation. The hypotheses were partly supported in both sectors: In the service sector findings confirm that quantitative job demands are predictors of job stress, consistent with similar studies in call centres. Stress is strongly asso-ciated with MSD development. In the manufacturing sector, quantitative job demands were not predictors of job stress, neither of MSDs. Positive challenges were a mediator of job stress. Stress was not a predictor for MSDs symptoms. Mechanical exposure increased after lean implementation in manufacturing although the opposite was aimed at. Consultation of workers on lean characteristics was another mediator to MSD development. A comparison was made between manufacturing and the services sectors. Differences be-tween sectors in job demands -with the exception of learning demands that are higher in manufacturing- were not significant. Predictability on the other hand was higher in call centres. Employees in the call centres reported statistically significant more frequent MSD symptoms compared to workers in manufacturing. Stress differences were not significant among sectors whereas job satisfaction was significantly higher in manufacturing. This can partly be explained by the positive social context, job security and management commitment to have no lay offs due to lean application; that workers enjoyed in the manufacturing companies of the sample. This was not the case in the call centres. In conclusion it was not the stressors that were higher in the call centres sample but a significant number of job support and control characteristics that were reported as being higher in the manufacturing sample of the study. Analysis of the relationship between job characteristics, stress and leanness revealed a high degree of non-linearity. The best fit was achieved with quadratic curves. At low levels of lean implementation stress was increasing. At a middle level of implementation stress reached a peak after which, with advanced implementation, it decreased. This is consistent with earlier study findings. The study demonstrates that it is not so much the level of lean implementation that is important for the health & safety effects but the lean characteristics that are employed. Characteristics linked to JIT can be critical and can be associated with increased job demands and for some cases increased stress and MSD symptoms. Moreover it is the social context (management mentality and actual workers participation) in lean application that is crucial for the implications of lean work to health. Further research is needed to compare lean effects between sectors including also other services. Finally, more research is needed on alternatives to intensive systems that would have better consequences for the health & safety of workers. Ergonomics has an obligation to pro-pose work redesign that aims at sustainability for all parties.