تاثیر تولید ناب در خطرات اسکلتی عضلانی و روانی: بررسی روند تکنیک اجتماعی بیش از 20 سال

This paper provides an extensive review of studies carried out in lean production environments in the last 20 years. It 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. Increased 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 propose 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.

Sociotechnical systems theory (STS) as developed by the Tavistock Institute of Human Relations in the 1950s was strongly rooted in the mechanised production systems of the day; see, for example, the study of weaving mills in India (Rice, 1958). Sociotechnical system design in manufacturing was developed as an alternative to Tayloristic production systems and led to a design approach, particularly popular in Scandinavian countries (Weisbord, 1990), that, did away with paced assembly lines in favour of production cells in which multi-skilled semi-autonomous work groups had considerable discretion over working practices. However, it is lean production methods that have been the dominant force in manufacturing around the world and these are now spreading to many sectors beyond manufacturing. “Lean production was born in Japan and developed to cope with a capital shortage caused by the devastation of World War Two”, (Price, 1995 in Babson ed.). It was founded on a belief that the key to improving profit was to reduce cost. Taiichi Ohno implemented the lean system in Toyota in the 1970s (Ohno, 1998). Lean production was also introduced as a successor to Tayloristic production systems but is often criticised as neo-taylorism. Niepce and Molleman (1998), evaluated lean systems against the principles of SocioTechnical Systems theory. Some similarities were identified mainly regarding the introduction of work groups. The main differences concerned the value bases and assumptions about workers and the way control at work is exercised in the two approaches. A sustainable synthesis of these systems keeping the best of each system was investigated. Other researchers have proposed a sociotechnical framework for lean production implementation (Paez et al., 2004). However, the question remains; are there characteristics of lean production that mean it cannot lead to the good quality jobs that are central tenets in sociotechnical systems theory? Although STS in manufacturing is associated with a particular kind of design solution the theory, as Eason (1988) has pointed out, can be used to investigate the effectiveness of any work system. The theory suggests that, because of their tight interdependencies, technical and social system sub-systems must be co-optimised to produce an effective work system. Eason (1996, 2007) has shown that on many occasions what happens is that a technical system is implemented that leads to unwanted, negative effects in the social system with implications for the performance of the whole system. The purpose of the literature review reported here, was to examine the consequences of lean production for the health and safety of workers, i.e. to examine the implications of this kind of technical system for some aspects of the social system. Lean production has been evolving and spreading over the past 20 years and there have been many studies of its impact on health and safety and this review will, in particular, examine emergent trends during this period. There were many studies of lean production in the 1990s primarily in automotive manufacturing (e.g. Adler et al., 1997; Babson, 1993; Berggren et al., 1991; Lewchuck and Robertson, 1996). However, in the last decade new studies have focused on lean effects in other manufacturing sectors and in the service sector (e.g. Conti et al., 2006; Jackson and Mullarkey, 2000; Sprigg and Jackson, 2006). Some researchers have reconsidered the belief that lean is inherently ‘mean’ particularly in other than automotive industries where lean production is not fully implemented. Specific lean practices have been examined for their correlation with stress and musculoskeletal disorders. Therefore, there is an evidence base that can be used to understand the mechanisms underpinning the health effects of lean production. This review will investigate, whether specific characteristics of lean production lead to specific risk factors and health effects. Internal work organisation and work patterns are constantly changing around the world in response to macro trends like globalisation and the resulting fierce market competition. In the last three decades new organisational systems have been introduced. Flexibility has been achieved through new production systems but improvements in productivity have not been sufficient for enterprises to be competitive. New strategies have been adopted that attach importance to quality and the satisfaction of clients. Lean production is perceived as a strategy that can achieve internal flexibility attuned to customer requests and the need to minimise waste. The European Commission Green Paper ‘Partnership for a new organisation of work’ (1997) stresses that the challenge is how to develop or adopt policies that support rather than hinder organisational renewal and to strike a productive balance between the interests of business and the interests of workers (Koukoulaki, 2010). This paper reviews studies that were carried out the last 20 years and identifies the lean characteristics that lead to positive or negative effects on health and safety (psychosocial and musculoskeletal effects). Both effects are examined in this paper since there is potentially a correlation. Psychosocial exposure apart from stress and mental disorders can also lead to musculoskeletal disorders. Moreover lean production can create time pressure that affects all parameters of physical and mental workload. A comparison between lean effects in different manufacturing sectors and services is made. An interaction model of the effects of lean production on job characteristics and their relation to musculoskeletal and psychosocial risks is proposed.

The current paper made a literature review across the last 20 years (1990–2013) and has included several studies on lean production effects in automotive manufacturing and other sectors (Conti et al., 2006; Leroyer et al., 2006; Lloyd and James, 2008; Mehri, 2005; Parker, 2003; Saurin and Ferreira, 2009; Schouteten and Benders, 2004; Seppala and Klemola, 2004; Sprigg and Jackson, 2006; Womack et al., 2009; etc.). Overall the findings of the surveys and literature reviewed indicate that the effects of lean production on working conditions are more evident in the automotive industry (increased stress and symptoms of MSDs) and less evident in other manufacturing sectors. In manufacturing an increase in workload was observed for half of the studies but not always linked to increased strain. Other studies demonstrated either no change (Mullarkey et al., 1995) or both negative and positive effects of lean production on workers (Conti et al., 2006; Jackson and Mullarkey, 2000; Saurin and Ferreira, 2009; Schouteten and Benders, 2004, etc). In services and other sectors the outcomes seem to be more balanced. It is in this section that all the positive outcomes have been reported. These positive outcome studies describe self-managed teams and empowerment of workers. Parker (2003) has attributed these inconsistencies in the findings to the problem of what constitutes lean production and how it is implemented because this varies considerably among studies. Lean production was originated in Toyota in Japan and then transferred to US automotive plants. So it is logical that in the automotive industry the lean implementation is full and its effect on working conditions may be expected to be more evident. Moreover some organisations introduce hybrid forms that include aspects of lean and other production systems. Such forms are more prevalent in manufacturing and other sectors. Parker (2003) concluded that lean production is likely to have different consequences for work characteristics depending on the different elements of lean production that are introduced. In particular in her study the installation of a moving assembly line was associated with severe negative effects on work characteristics and employee outcomes (increased job depression) compared to lean teams and workflow formalisation and standardisation (inventory reduction and processes simplification and standardisation) that had negative but not so extreme effects. Conti et al. (2006) identified eleven particular work practices significantly related to job stress. Those were work pace/intensity, resource removal, working longer than desired hours, cycle time, doing work of absent workers, feeling blame of defects and ergonomics difficulty. The characteristics of lean production that seem to have overall the strongest association with negative effects on workers in this study are Just-I-Time practices such as removal of waste and non-value activities. It appears that these practices are causing intensification of work that is linked to increased levels of strain and stress. Parker and Conti are part of a new school of thought in lean production research, advocating that lean production is not by definition harmful. Specific lean characteristics can have adverse effects on work characteristics and workers' health. Moreover what are of great importance are the choices companies make in lean implementation. For instance a company could choose to apply one lean characteristic to its extreme, (e.g. removal of ‘waste activities’), that has a direct effect on work intensification, while minimising other characteristics that could act as a buffer to stress (e.g. autonomy and group support in teams). This dangerous combination could only bring about the unfavourable effects of lean production. In their review Westgaard and Winkel (2011) investigated potential ‘conditions of work’ mentioned as modifiers (described here as buffers) that could alleviate lean effects. The most important ones were group autonomy, social support at work and worker participation when a lean system is introduced and in improvement programs. The analysis of studies made in different periods of time showed the changing trends in both the application of lean practices and the effects on workers over a 20 year period. Theories of the effects of lean production effects have evolved from a view that it is an inherently harmful management system to a system that can have mixed effects depending on management style and the way it is implemented. However, there are specific lean practices that lead to negative effects that are fundamental to lean production and cannot be omitted if lean methods are claimed to be adopted. The underlying mechanism of lean production, as illustrated in Fig. 4; is intensification of work. Just-in-Time practices are causing intensification of work and they are the practices that trigger health effects. In conclusion, recent research on lean production reported that negative effects on workers are strongly associated with some lean practices. Specific lean practices such as Just-in-Time and standardised work cause intensification of work and are strongly associated with both mechanical and psychosocial exposure. However, this cannot lead to the conclusion that lean production is not by definition harmful. Waste reduction practices are considered to be the core of lean production and without them a production system can hardly identify itself as lean. Not all lean characteristics are harmful but the core ones can be harmful if no buffers (such as job control and social support) are applied. In conclusion it is not only the level of lean implementation that correlates to risk factors but also the type of lean characteristics that are applied. The main underlying mechanism for the health effects of lean production is the intensification of work and that in some cases is unavoidable. Finally we can examine how the evolving story of lean production relates to concepts in sociotechnical systems theory (STS). A central concept in STS is the interdependencies that exist between the technical and social sub-systems that, in some instances can produce very tight couplings (Thompson, 1967; Perrow, 1999) in which, for example, the characteristics of the technical system have direct effects on the social system. Eason and Waterson (2013) have, for example, shown how tight coupling caused by everybody using the same electronic patient record can have adverse effects on the autonomy of different groups of healthcare workers. In the present context some of the core components of lean production such as JIT have such direct effects and have adverse implications for the health of the workforce. There are two other features of this analysis that relate to enduring themes in STS. The first is that there are ways in which the social system can mitigate adverse effects of the technical system. The book that described one of the original STS studies in British coal mines was called ‘Organisational Choice’ (Trist et al., 1962) because the effects of a new mechanised technical system were different in two coal mining areas because of local organisational arrangements. In the case of lean production the use of buffering mechanisms has been shown to mitigate the adverse effects. However, what the lean production case also shows is that there is also technical choice: it is not one integrated technical system but an array of components that can be implemented fully or partially. Assessing the risk associated with a broad approach such as lean production depends therefore on an understanding of the systemic interdependencies created by each of the components. Niepce and Molleman (1998) and Paez et al. (2004) raised the question of whether lean production and sociotechnical systems design are compatible. It is increasingly apparent that in both cases there is flexibility in the choice of the technical and social components that makeup the overall system in each case. By selecting appropriate components it may be theoretical possible to construct an overall system that meets the objectives of lean production and of sociotechnical design. However, this review strongly suggests that there are core practices in lean production that have direct and adverse affects on workers and it remains difficult to see how these practices can be reconciled with core sociotechnical systems design principles that emphasise local autonomy and discretion in relation to task performance.