This phase involves the identification, collection, and quantification of the data necessary to meet the defined goal and scope of the study. The level of detail of the inventory depends on the objectives outlined in the study. This phase is usually the most time and resource consuming step of an LCA (International Organization for Standardization 14044 2007) . This analysis is guided by the goal and scope definition, and its core action is the collection and compilation of data on elementary flows from all processes in the studied product systems.
This step of the LCA is a technical, data-driven process to quantify energy and materials consumed, emissions to air and water, solid waste and any other discharged into the medium during the complete life cycle of a product, process, material, or activity. In a broad sense, inventory begins with raw materials and ends with the final management of product waste (International Organization for Standardization 14044 2007)(International Organization for Standardization 14044 2007).
According to (Fava, 1991) , the inventory analysis includes the following stages:
- Construction of the flow diagram according to the established system boundaries.
- Collection of data from all activities in the production system. It is necessary to establish the origin of these data: bibliographic and/or measurements in-situ.
- Calculation of environmental loads related to the functional unit.
- Normalization of the data in terms of units.
- Material balances, which allow the interrelation of inputs and outputs between the different subsystems.
- Quantification of the outflows from the system to nature or the Technosphere.
- Global inventory.
- Documentation of calculations.
Data acquisition can be divided into 4 main groups (Feijoo, et al., 2007)(Feijoo G., Hospido A., Gallego A., Rivela B. 2007):
- direct measures;
- published documents;
- electronic sources, and;
- personal communications.
Among all these information sources, databases have been and continue to be one of the fundamental ways to find the inventory data needed to perform an LCA. There are different systematizations in the expression of data, but one of the most used is defined by the Society for the Promotion of Life Cycle Assessment Development (SPOLD), which indicates the reference of input and output data from or to nature and from or to the Technosphere.
Linked to data management, one of the main issues affecting the application of an LCA lies in the reliability of data on raw materials and emissions in the life cycle inventory. Therefore, a data quality classification is shown in Table 4.1.1.
| Data specificity | Explanation |
|---|---|
| Very high | Measured directly at a specific site or scaled from measurements. |
| High | Derived from measurements at specific process site throughout the modeling. |
| Medium | Life cycle inventory data from database process, or data from literature specific to the actual process. |
| Low | Generic LCI database process, or data from literature (mixing of technologies in a country or region). |
| Very low | Judgment by experts or LCA practitioners. |
Some examples of process-based LCI available databases are available in (more 4.1.5).
Currently, the most comprehensive and widely used database is ecoinvent. The following link show an illustrative video related to the LCI data in LCA.