Life Cycle Impact Assessment

Life cycle impact assessment (LCIA) is among the last steps of LCA. The purpose of a LCIA “is to provide additional information to assess life cycle inventory (LCI) results and help users better understand the environmental significance of natural resource use and environmental releases”. The LCIA helps provide significance and results for easier decision making; however, it is important to understand it does not directly measure the impacts of chemical releases to the environment as an environmental risk assessment does. The third step of LCIA follows sequentially after the LCI using the many flows to and from the environment developed in the LCI. These LCI flows, without an impact assessment step, are not easily interpreted and understanding the significance of emissions is impossible. The LCIA is different from a risk assessment measuring absolute values of environmental impacts in that the LCIA helps determine the significance of emissions and impacts in relation to the study scope. The absolute value of the impacts cannot be determined by the LCIA due to (Margni and Curran 2012):

• The relative expression of potential environmental impacts to a reference unit 
• The integration of environmental data over space and time
• The inherent uncertainty in modeling environmental impact
• The fat that some possible environmental impact occurs in the future

Even though the LCIA has limitations, it is useful in determining what impacts matter, what unit processes are contributing the most through hot spot analysis and identify best scenario options when environmental tradeoffs occur.

Figure 1.1  Life cycle assessment stages

Figure 1.2  Impact assessment ISO mandatory and optional steps