Protection Agency (EPA). Those studies yielded mixed results. Another early series of LCA studies was conducted on the impacts of cloth versus disposable diapers, again yielding mixed results. According to Heller, the mixed results from these early studies were partly a reflection of the variable methodologies being used. At that time, investigators were only just beginning to explore LCA. There was no common theoretical framework upon which to build. The field experienced slow growth in the 1980s, but it did not really “jump forward” into something that “everyone could grab onto” until the 1990s. Since then, the methodology has experienced very rapid growth, with a number of organizations helping to coordinate the harmonization of different theoretical frameworks and to standardize methods and procedures. The EPA, the Society of Environmental Toxicology and Chemistry, and International Organization of Standards (ISO) have all been involved. ISO issued two international standards for LCA, both of which were renewed in 2006: ISO 14040 and ISO 14044. For example, ISO 14040 defines LCA as the “compilation and evaluation of the inputs and outputs and the potential environmental impacts of a product system throughout its life cycle.”

Importantly, Heller said, even though ISO has provided good standardization, LCA is still very much an “accommodating methodology.” It is used to study a broad range of systems and address a broad range of questions, with many methodological decisions being made along the way. Sometimes, as investigators become familiar with the system under study, decisions made earlier during the LCA may need to be reconsidered. He said, “Appreciating these methodological decisions is pretty important in understanding what the results are really telling us—what we can really draw from those outcomes.”

The Three Stages of LCA

Standard LCA has three main stages: (1) goal and scope definition; (2) inventory analysis; and (3) impact assessment. Heller described each in turn.

Goal and Scope Definition

The first stage of LCA involves deciding the purpose of the study, the questions being addressed, and the knowledge being sought. These decisions inform which of two major LCA approaches to take. The typical, or traditional, LCA approach is known as “attributional LCA.” Its goal is to describe a system as it is, using data averages. (A “system” includes all the environmentally relevant physical flows in and out of the life cycle and its subsystems.) The second approach is known as “consequential LCA.” Its

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