Practical method of assessing local and global impacts for risk-based decision making: a case study of metal degreasing processes.

For risk-based decision making, local and global impacts should be considered simultaneously. In metal degreasing processes, various cleansing agents are used and a significant amount of such cleansing agents is released into the environment. An appropriate measure of reducing chemical risk associated with industrial cleaning processes should be implemented on the basis of evaluation results representing the local and global impacts. In this study, we assessed metal degreasing processes using a chlorinated solvent with an open-top washing machine and four alternative scenarios, namely, improving the settings of the machine (two cases), changing the local ventilation system, and installing a recovery system using activated carbon. The applied methods are plant-specific risk and life cycle assessments. Specifically in the risk assessment, detailed process data available for decision makers are utilized to evaluate occupational and neighborhood risks. The results of this case study indicate a tradeoff relationship between the local and global impacts in metal degreasing. Through the discussions on the practicability of the integration of the local and global impacts into actual decision making, we conclude that the way to use, select, or integrate risk and life cycle assessments should be analyzed systematically as the situation demands at decision making.