Page 133 - Materials Chemistry, Second Edition

118 A. Bjørn et al.

9.1 Introduction

During the life cycle inventory (LCI) analysis phase of an LCA the collection of
data and the modelling of the flows to, from and within the product system(s) is
done. This must be in line with the goal definition (see Chap. 7) and (to the extent
possible) meet the requirements derived in the scope definition (see Chap. 8). The
LCI result is a list of quantified elementary flows crossing the system boundary of
the studied life cycle and it is used as input to the subsequent LCIA phase (see
Chap. 10). Insights that the LCA practitioner gains when conducting the LCI
analysis are also commonly used to adjust the requirements of the scope definition,
e.g. when unforeseen data limitations lead to the need for a modification of the
completeness requirements (see Sect. 8.6.3). Typically, the LCI analysis is the
phase that requires the most efforts and resources from the LCA practitioner, and it
is rarely practically possible to collect the highest quality of data for all processes of
the LCI due to the unreasonable high cost that would be involved. Fortunately, it is
also rarely needed in order to meet the goal and support the intended applications of
the LCA. Therefore, the inventory analysis requires a structured approach to ensure
that time is being spent on collection of data for those parts of the product’s life
cycle that are most important for the overall impacts from the product system.
Several iterations between the LCI and LCIA phase are normally needed to meet
the goal of the study, with each iteration providing insight into which inventory data
are the most important for the LCA results (see Chap. 6).
In this chapter, we provide practical guidance on how to perform an LCI analysis
using an iterative approach to LCA. We will focus on providing detailed guidance
for the four decision contexts (A, B, C1 and C2) in line with the ILCD guideline.
The chapter is structured around six steps of an LCI analysis:
1. Identifying processes for the LCI model
2. Planning and collecting data
3. Constructing and quality checking unit processes
4. Constructing LCI model and calculating LCI results
5. Preparing the basis for uncertainty management and sensitivity analysis
6. Reporting.

Before digging into the details, we note that this chapter teaches how to construct
an LCI using knowledge about the industrial processes taking part in a life cycle
and the physical flows connecting them. This is called a process-based (or
bottom-up) approach to inventory modelling. A complementary approach to con-
structing an LCI is to model the life cycle inventory for the product from a mac-
roscale perspective by drawing on a combination of (1) information on elementary
flows associated with one unit of economic activity in different sectors and
(2) national statistics on the trade of products and services between sectors. This is
called environmentally extended input–output analysis (EEIO) and in contrast to
the process-based approach it can be seen as a top-down approach to inventory
modelling. The strength of EEIO is that a completeness of 100%, in theory, can be