SM5002 Chap.1 Goal, Scope and the Functional Unit
Goal, Scope and the Functional Unit
Why the first phase decides the rest
A process-based life cycle assessment follows the four phases set out in ISO 14040:2006: goal and scope, life cycle inventory, life cycle impact assessment, and interpretation. The sequence is iterative rather than linear, so a study regularly loops back to refine earlier choices once data arrives. Even so, goal and scope come first for a reason.
Every number later produced by openLCA answers only the question framed at this stage, and a vague or shifting frame produces results that cannot be compared, defended or reused.
Lecture 1 sets two learning outcomes for this phase: being able to identify a suitable functional unit, and developing skill in defining a system boundary.
Both recur through the rest of the module, in the openLCA workshops, in the critical appraisal of published healthcare studies for the group presentation, and in the individual written assignment.
Writing the goal
ISO 14044:2006 asks that the goal outline who, what, when, where, why and how.
In practice that means stating the intended application, the reasons for carrying out the study including its aims and objectives, the intended audience, and whether the results will be used in comparative assertions disclosed to the public. That last item matters because public comparisons carry heavier obligations for review and transparency.
The lecture groups academic research goals into four purposes.
A study may evaluate a baseline and monitor progress over time, identify carbon hotspots in a system, use a consistent method to compare alternative products, or model ways to optimise a process through reduction or substitution.
Business goals and potential audiences are drawn from the GHG Protocol standard for product life cycle accounting, which frames the same question from a company perspective.
Defining the scope
The scope must be defined well enough that the breadth, depth and detail of the study are compatible with and sufficient for the stated goal.
ISO 14044 lists what it should include: the product system studied and its functions, the functional unit and reference flows, the system boundaries, allocation procedures, the impact categories and impact assessment method, data requirements, assumptions, limitations, initial data quality requirements, any critical review, and the type and format of the report.
The lecture groups these into four bundles: the system assessed, the methods applied, the data and assumptions, and reporting and review.
Function, functional unit and reference flow
A function is what the product does for its user, described in terms of what it does rather than what it is. The functional unit quantifies that service.
A reference flow is the amount of product needed to deliver the functional unit. The lecture’s lighting example runs through all three: providing 800 lumens of light to a room; lighting a room with 800 lumens for one year at 12 hours a day, which is 4,380 hours; and the number of lamps required to supply those hours.
Comparative studies depend on this structure.
Two or more products can only be compared if they deliver the same key function in terms of physical performance, which assumes exact equivalence or substitution. Once that holds, very different systems become comparable: with 100 kcal of food as the functional unit, the reference flows might be 200 g of dragon fruit or 77 g of rice.
In healthcare, a comparison of spinal fusion instrument sets uses the instruments needed for one patient’s operation as the functional unit, with one single-use set on one side and one use of a reusable set, such as one fiftieth of its lifetime use, on the other.
Drawing the system boundary
ISO 14040 defines the system boundary as the set of criteria specifying which unit processes form part of a product system.
The candidates include raw material acquisition, the main manufacturing sequence, distribution and transport, the production and use of fuels, electricity and heat, use and maintenance, disposal of wastes and products, recovery through reuse, recycling or energy recovery, ancillary materials, capital equipment, and supporting operations such as lighting and heating.
Where the line is drawn changes the result, and comparative studies should apply the same boundary criteria to every option.
The vocabulary around the boundary is precise. A unit process is the smallest element whose inputs and outputs are quantified. Elementary flows enter from or leave to the environment without human transformation, such as crude oil from the ground or emissions to air.
Product flows cross into or out of another product system, while intermediate flows pass between unit processes inside the system being studied.
The boundary type follows from the product. Under the GHG Protocol product standard, final products take a functional unit as their unit of analysis and a cradle-to-grave boundary.
Intermediate products whose eventual function is unknown take the reference flow as the unit of analysis and may use a cradle-to-gate boundary, which must leave out use and end of life and must be disclosed and justified.
The written assignment for this module asks for a cradle-to-grave model of a single-use healthcare product, with a figure showing the stages included.
Cut-off criteria and allocation
Exclusions from the boundary must be clearly stated and justified.
ISO cut-off criteria specify the amount of material or energy flow, or the level of environmental significance, below which a process is excluded, for example a nominal share of total mass or energy, or a likely contribution of less than 1% to the carbon footprint. The GHG Protocol uses the related idea of a materiality threshold.
Allocation arises when one process yields two or more products.
The GHG Protocol prefers to avoid it by subdividing the process, redefining the unit of analysis to include the co-products, or expanding the system. Where it cannot be avoided, emissions are partitioned by a physical relationship such as weight or size, by economic value, or by another relationship such as time in use, and the same method is applied to similar inputs and outputs across the life cycle.
What this chapter covers
- 01
The four ISO 14040 phases and why they iterate
- 02
What a goal statement must contain under ISO 14044
- 03
The scope checklist from product system to report format
- 04
Function, functional unit and reference flow in comparisons
- 05
System boundaries, cradle to gate and cradle to grave
- 06
Cut-off criteria, materiality and allocation of shared processes
Worked example · free
Defining the system for single-use and reusable scissors
- 1State the function as a service, not as an object.
- 2Quantify it as a functional unit matched to the reusable service life.
- 2Give the reference flow for each option.
- 1Name the boundary type and the rule for comparisons.
Key terms
- Functional Unit
- The quantified performance of a product system, used as the basis on which alternatives are compared.
- Reference Flow
- The amount of product needed to fulfil the function expressed by the functional unit.
- System Boundary
- The set of criteria specifying which unit processes are part of a product system.
- Unit Process
- The smallest element in an inventory for which input and output data are quantified.
- Elementary Flow
- Material or energy taken from or released to the environment without human transformation.
- Cut-off Criteria
- Thresholds of mass, energy or environmental significance below which a flow is excluded from a study.
- Allocation
- Partitioning the emissions of a shared process between the studied product and its co-products.
Goal, Scope and the Functional Unit FAQ
Can a study of a single-use medical device stop at the factory gate?
Not if the device is a final product. The GHG Protocol standard requires final products to be assessed cradle to grave, and a cradle-to-gate boundary is reserved for intermediate products whose use is unknown, with the choice disclosed and justified in the report.
Why do two options in a comparison need the same functional unit?
Results are only comparable when both options deliver identical service. Matching the functional unit assumes exact substitution, so differences in the totals reflect the products themselves rather than different amounts of work being done by each.
How small does a flow have to be before it can be left out?
There is no single figure. Cut-off criteria are set in the scope, often as a share of mass, energy or environmental relevance such as under 1% of the footprint, and every exclusion has to be named and defended in the write-up.
Does the choice of allocation basis really change results?
Yes. Splitting a 1,500 g CO2e decontamination burden by weight gives about 107 g per pair of scissors, while splitting it by share of tray space gives 75 g, so the basis must be stated and applied consistently.
Assessment move
Before opening openLCA, write one sentence each for the function, functional unit and reference flows of your product and test them against the 40-use scissors case. Then sketch the five life cycle stages, mark what is excluded and why, and keep that sketch as the draft system boundary figure for the written assignment.
