What are the Four Phases of Life Cycle Assessment?

ISO 14040 defines four phases that structure every LCA: goal and scope definition, life cycle inventory, life cycle impact assessment, and interpretation. Each phase builds on the previous one.

Goal and Scope Definition#

This phase establishes what you’re measuring and why. The goal states the intended application, reasons for conducting the study, and target audience. The scope defines boundaries and level of detail.

Functional unit creates the reference point. Instead of comparing “one car” to “one bicycle”, you might compare “transporting one person 10 kilometres”. This makes different systems comparable.

System boundaries determine what’s included. Cradle-to-grave covers extraction through disposal. Cradle-to-gate stops at factory gate. The choice depends on your goal and affects results.

Data requirements specify the quality and sources you’ll use. Primary data comes from actual measurements. Secondary data comes from databases. The mix affects reliability.

Life Cycle Inventory (LCI)#

LCI collects data on inputs and outputs for every process. You need quantities of materials, energy, transport, and waste across the product system.

Data collection takes most project time. For a manufactured product, you track raw material extraction, refining, component production, assembly, packaging, distribution, use, and disposal. Each stage generates emissions and consumes resources.

Process mapping creates a flow diagram showing all activities. Each process box needs input and output data. Missing processes create gaps in your assessment.

Allocation splits impacts when processes generate multiple products. A refinery produces petrol, diesel, and heating oil. You need rules for dividing emissions across outputs.

Life Cycle Impact Assessment (LCIA)#

LCIA converts inventory data into environmental impacts. Emissions don’t mean much as raw numbers. Impact assessment translates them into comparable effects.

Classification assigns inventory flows to impact categories. CO₂ contributes to climate change. Nitrogen oxides contribute to acidification and eutrophication. Some substances affect multiple categories.

Characterisation quantifies contributions within each category. Different greenhouse gases get converted to CO₂ equivalents based on warming potential. Acidifying substances become H⁺ equivalents.

Optional elements include normalisation (comparing to reference values) and weighting (combining categories). These steps involve value judgements. ISO standards allow but don’t require them.

Impact categories cover:

• Climate change
• Ozone depletion
• Acidification
• Eutrophication
• Photochemical ozone formation
• Resource depletion
• Water scarcity
• Toxicity (human and ecological)

Interpretation#

Interpretation analyses results and checks reliability. You identify significant issues, evaluate completeness and consistency, and draw conclusions.

Hotspot analysis shows where impacts concentrate. Perhaps raw material extraction dominates climate change impacts while manufacturing dominates water use. This directs improvement efforts.

Sensitivity analysis tests how methodological choices affect results. Change allocation rules or impact assessment methods and see what happens. Robust conclusions survive these changes.

Uncertainty analysis quantifies data quality effects. Primary measured data carries less uncertainty than estimated values. Results with wide uncertainty ranges need careful interpretation.

Iterative Process#

These phases aren’t strictly sequential. Interpretation might reveal that your initial scope needs refinement. Data availability might force boundary adjustments. ISO 14040 recognises this through iterative loops between phases.

A complete LCA cycles through these phases multiple times, refining scope, improving data quality, and strengthening interpretation. The first pass identifies gaps, subsequent iterations fill them.