Critical analysis of the mathematical relationships and comprehensiveness of life cycle impact assessment approaches.
The impact assessment phase of Life Cycle Assessment (LCA) has received much criticism due to lack of consistency. While the ISO standards for LCA did make great strides in advancing the consensus in this area, ISO is not prescriptive, but has left much room for innovation and therefore inconsistency. To address this lack of consistency, there is currently an effort underway to provide a conceptual framework for Life Cycle Impact Assessment (LCIA) and a recommended practice to include a list of impact categories, category indicators, and underlying methodologies. This is an enormous undertaking, especially in light of the current fundamental lack of consensus of the basic elements to be included in a LCIA (e.g., impact categories, impacts, and areas of protection). ISO 14042 requires selection of impact categories that "reflect a comprehensive set of environmental issues" related to the system being studied, especially for "comparative assertions" that involve public marketing claims. To be comprehensive, it is necessary to have a listing of impacts that "could" be included within the LCIA before entering into discussions of impacts that "should" be included. In addition to providing a critical analysis of existing and emerging impact assessment approaches, this paper will formulate a structured representation that allows more informed selection of approaches. The definitions and relationships between midpoint, endpoint, damage, and areas of protection will be presented in greater detail, along with the equations that are common to many of the approaches. Finally, a discussion of the advantages and disadvantages of displaying results at various stages in the environmental models will be presented in great detail.