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Local risks and global impacts considering plant-specific functions and constraints: a case study of metal parts cleaning

Research paper by Yasunori Kikuchi, Masahiko Hirao

Indexed on: 24 Nov '09Published on: 24 Nov '09Published in: The International Journal of Life Cycle Assessment



Abstract

To achieve sustainable development in industrial processes, attributed chemical risks as well as environmental impacts should be managed. Such non-monetary issues have been analyzed by scientific assessment methodologies such as various risk assessment (RA) and life cycle assessment (LCA) procedures. Local risks to be addressed in RA are microenvironments, including the workplace and neighborhood. Although a comprehensive interpretation of such risks is necessitated in industrial decision making, no practical method has been developed to interpret various types of risk with sufficient understandings of plant-specific functions and constraints. Because elaborate model-based approaches are inevitable for practical process development, actual case studies on chemical risks and detailed plant-specific functions and constraints should be performed. Manufacturing processes require that metal parts must be cleaned in preparation for surface treatments or the completion of metal processing. The significant amount of cleansing agents utilized in cleaning processes has become an issue in Japan. Almost all cleaning processes in Japan are carried out by small- and medium-sized enterprises (SMEs). Machinery processes have not been systematically analyzed in terms of chemical risks and, in addition, the environmental management skills of SMEs are generally far behind those of large enterprises. The objective of this study is to reveal the relationships between chemical risks and plant-specific conditions for a practical risk reduction carried out by industrial decision makers. For this purpose, we aimed at the analysis of such relationships in metal-cleaning processes. Through this analysis, the correlation between local risks and global impacts were discussed in terms of plant-specific conditions.Through several investigations on cleaning processes, plant-specific functions and constraints were determined with process data required for plant-specific RA and LCA. By plant-specific RA, workers' and neighbors' health risks of inhalational exposure to the utilized cleansing agents were evaluated as unit exposure amount [mg·kg−1·day−1] and total exposure amount [mg·day−1] in the workplace and neighborhood. As global environmental impacts, human health impacts were evaluated by LCA using disability-adjusted life years through the life cycle of process chemicals including cleansing agents and utilities. On the basis of evaluation results, the relationships among plant-specific conditions and the results were analyzed and discussed by using the results of regression analyses and the Akaike information criterion (AIC).The impacts due to the use of cleansing agents contributed largely to total human health in the LCA results. The results of the functional unit “Cleaning of unit weight of products” demonstrated that the magnitudes of total impacts were not considerably different. In plant-specific RA results, the neighborhood concentrations in some cases were higher than the average concentration in Japan. The neighbors' total exposure amounts were highly connected with the emission amount of cleansing agents and population densities. Because workplace concentrations were different from site-to-site and do not have a simple relationship to the emission amount of cleansing agents, the exposure amounts of workers indicated complicated trends. According to detailed interpretation of all the results, a relationship between occupational exposure and agent emission was revealed. Some devices that enhance the process functions became emission factors, such as the local ventilation device installed to keep the workplace safe. Additionally, the shapes of metal parts to be cleaned and cleaning requirements increased the emission of cleansing agents to indoors and outdoors directly. Additionally, some regression analyses and AIC comparisons showed that these plant-specific conditions can be regarded as factors having non-negligible effects on local risks and global impacts.In cleaning processes, utilizing various agents to meet cleanliness requirements, plant-specific conditions should be taken into account in their assessments to reduce the chemical risks practically. Constraints from decision makers in the other stages of a product life cycle are unchangeable for on-site engineers in a given process. In this regard, however, the process functions for complying with the requirements originating from the constraints can be managed by on-site engineers. To deal with the risks originating from such factors, operations and devices should be appropriately designed. To achieve such designs, statistical approaches and process understandings should be used in a collaboration to reveal the practical relationship among local risks, global impacts, and process conditions.Local risks and global impacts attributable to metal parts cleaning processes were evaluated in terms of workers' and neighbors' health risks and global human health impacts. A careful interpretation of evaluation results revealed that local risks have features different from those of global impacts. In this paper, we demonstrate that local risks are highly connected with plant-specific conditions. For an appropriate practical implementation of local impacts, as well as plant specification, the characteristics of industrial sectors, including related laws and regulations, should be taken into account to address them from the viewpoint of agent emissions, which can be obtained in ordinary LCA. Otherwise, the data collected in life cycle inventory should be sufficiently expanded to estimate the requirements or to specify an appropriate model.The approach to analyze and relate the plant-specific functions and constraints with local risk and global impact can be useful and effective for revealing their factors, which can be supporting information of generating alternatives for reducing them. The application of such an approach can also clarify the plant-specific risk and LCA performance in general. Additionally, the clarified relationship might lead to the increase of the attention of global issues within the decision making including industrial process design and policy making. Several models should be developed for model-based decision making considering plant-specific conditions.