From a methodological point of view, the definition of LCA is as follows (SETAC, 1993): "Objective procedure for assessing the environmental and energy loads related to a process or activity, carried out by identifying the energy and materials used and the waste released into the environment. The assessment includes the entire life cycle of the process or activity, including the extraction and processing of raw materials, manufacturing, transport, distribution, use, reuse, recycling, and final disposal."
The definition stated in the UNI EN ISO 14040 standard identifies LCA as a "compilation and evaluation throughout the life cycle of the input and output flows, as well as the potential environmental impacts, of a product system."
The main difference between the two definitions lies in the substantially different perspective of those who view LCA as a process analysis and those who view it as a product analysis. To better clarify the difference, it is important to remember that by industrial system, we mean a set of procedures whose main function is the production of useful goods; it is separated from the environment by well-defined physical boundaries and is connected to it through the exchange of inputs and outputs. From this perspective, the environment is not the natural one defined by ecology, but rather everything outside the industrial system being considered. According to this approach, it is clear that the inputs of the system are parameters that affect the "resource conservation" issues, while the outputs are related to "pollution" problems.
From this initial description, it is understood how the definition of the function of the industrial system and its boundaries represent two of the key operations for the successful completion of an LCA study. It is therefore logical to assert that, rather than describing the product, an LCA describes the system that generates it; only in cases where the industrial system has a single internal product flow does the study of the system's behavior coincide with that of the product.
ISO standards refer to a "product system" to indicate "the elementary set of process units connected in terms of matter and energy, pursuing one or more defined functions." The analogical model of the system under investigation in an LCA is always a simplification of reality, as, like all models of this kind, it does not include a complete representation of interactions with the environment.
The structure of an LCA, as proposed by the ISO 14040 standard, can be summarized into 4 main phases:
1. Goal Definition and Scoping : Preliminary phase where the study's objectives, functional unit, system boundaries, data requirements, assumptions, and limitations are defined;
2. Life Cycle Inventory (LCI) Analysis : This part of the study is dedicated to collecting and processing data to build an analog model of the real system being studied.
3. Life Cycle Impact Assessment (LCIA) : It is the study of the environmental impact caused by the process or activity. This phase involves the transition from the objective data calculated during the inventory phase to the environmental hazard assessment.
4. Life Cycle Interpretation and Improvement : Conclusive part of the study, which aims to propose the necessary changes to reduce the environmental impact of processes or activities, evaluating them iteratively with the same LCA methodology so as not to take actions that worsen the current state.
