Life Cycle Assessment: Principles and Applications

Posted on Sep 27, 2025 in Industrial Process Engineering

1. Life Cycle Assessment Definition

Life Cycle Assessment (LCA) is a decision-making tool for assessing environmental impacts associated with all stages of the life cycle of a commercial product, process, or service.

Product Lifetime is the time interval from when a product is sold until it is discarded.

Cradle-to-gate refers to the environmental impact of a product from its production to the moment it enters the store. Cradle-to-grave also takes into account the usage and disposal of the product.

2. Main Phases of LCA

The main phases of LCA include:

  • Goal and Scope Definition: Identifying the purpose of the LCA, the study’s boundaries, assumptions, and expected output.
  • Life Cycle Inventory (LCI): Quantifying energy use, raw material inputs, and environmental releases associated with each life cycle stage.
  • Life Cycle Impact Assessment (LCIA): Assessing the impacts on human health and the environment based on LCI results.
  • Interpretation: Analyzing LCI and LCIA results to present conclusions.

LCA applications can be internal or external, such as comparing environmental performances of different products, improving product environmental performance, developing new environmentally friendly products, adapting product performance to standards, or understanding a product’s environmental impact throughout its life cycle.

3. Goal and Scope of the Study

The goal of the study sets up the tasks for the research. Its basic elements are the intended application, the reason for carrying out the study, and the intended audience.

The scope of the study defines the exact boundaries, depth, and limitations to ensure the purpose can be fulfilled.

Key elements of the scope include:

  • Function: The main purpose of the product system (e.g., cigarette ignition for matches and lighters). To compare products, they must have the same function.
  • Functional Unit: A quantification of the function, providing a reference for inputs and outputs.
  • Reference Flow: A measure of the outputs from processes required to fulfill the function expressed by the functional unit.

4. Product System, Product Flow, and Elementary Flows

  • Product System: A collection of unit processes with elementary and product flows that perform one or more defined functions, modeling the product’s life cycle.
  • Product Flow: Products entering or leaving another product system.
  • Elementary Flow: Material or energy entering or leaving the system that is drawn from or released into the environment without prior or subsequent human transformation.

Inputs can come from nature (resources) or the technosphere (products). Outputs can be released to nature (emissions) or go to the technosphere (products).

5. Process-Based Inventory Analysis Procedure

  1. Start with reference flows corresponding to the functional unit and design the flowchart.
  2. For each unit process, identify its inputs and direct emissions.
  3. Document data on the flowchart or in a table, citing data sources.
  4. Calculate emissions for each unit process by multiplying the amount per functional unit by its emission and extraction factors.
  5. Calculate total aggregated emissions and extractions by summing all elementary flows from all unit processes.

6. Allocation in LCA

Allocation addresses how to divide emissions and resource usage among multiple products or processes within multiproduct systems. According to ISO 14044, the main steps are:

  1. Avoid Allocation: Wherever possible, allocation should be avoided by:
    • Dividing the unit process into sub-processes and collecting related input/output data.
    • Expanding the product system to include additional functions related to co-products.
  2. Physical Relationship Partitioning: Where allocation cannot be avoided, partition inputs and outputs based on physical relationships between products or functions.
  3. Other Relationship Allocation: Where physical relationships are insufficient, allocate based on other relevant relationships between products and functions.

7. Ways to Avoid Allocation

  • Process Subdivision: Exclude subprocesses not directly applicable to the main product from the system boundary.
  • System Expansion: Eliminate by-products as activity outputs by including them as negative inputs. This involves modeling changes (substitutions) by including the reduction in supply of the same product from the marginal supplier to the market for the by-product. For example, allocating co-products proportionally to their economic value.

8. Physical Allocation Methods

When allocation is necessary, emissions and resource use can be attributed to co-products based on physical causal relationships:

  1. Marginal Variation: Applicable when co-product ratios can be varied. Impacts are determined for a baseline situation and a situation with varied product quantities. The change in impacts divided by the change in co-product quantity estimates the impact per unit co-product.
  2. Representative Parameter for Common Function: Used when co-products provide an identical function. Allocation is based on a quantity or parameter representative of this function, provided it aligns with study objectives and is effectively used for that function.
  3. Property Reflecting Causal Physical Relation: Applicable when a physical indicator captures a cause-and-effect relationship between co-products and associated emissions or resources used. This indicator must strongly link all co-products and represent the cause of emissions.

9. Economic Allocation

When no clear physical relationship exists for allocating by-products, economic causality is considered. Emissions and resource use are allocated according to the respective values of the co-products, reflecting their mercantile value and the financial incentive driving production.

10. Selection of Impact Categories

In LCA, impact categories are selected to represent environmental issues of concern. These include:

  • Impact Category: A class representing environmental issues (e.g., climate change, toxicity, depletion of fossil carriers).
  • Category Indicator: A quantifiable representation of an impact category.

Inventory results are grouped into midpoint categories (e.g., global warming), each with a midpoint indicator. Inventory flows are multiplied by characterization factors to contribute to these categories. Midpoint categories can then be allocated to damage categories (e.g., human health, ecosystems), represented by endpoint indicators.

11. Classification and Characterization in Impact Assessment

  • Classification: Assigning LCI results to relevant midpoint environmental impact categories. For example, CO2, CH4, and N2O are classified under global warming. A substance can contribute to multiple categories.
  • Characterization: Converting LCI results into common units within each impact category using characterization factors (or equivalence factors). These factors indicate a substance’s relative contribution to a specific environmental problem compared to a reference substance.

12. Main Midpoint Impact Categories

  • Non-renewable Resource Depletion Potential: Models the depletion of non-renewable resources.
  • Global Warming: Assesses the contribution of greenhouse gases to the man-made greenhouse effect.
  • Stratospheric Ozone Depletion: Evaluates the impact of substances like halocarbons on the ozone layer.
  • Human Toxicity: Assesses potential harm to human health from chemical emissions.
  • Eco-toxicity: Evaluates toxic effects on ecosystems.
  • Photo-oxidant Formation (Summer Smog): Assesses the formation of photo-oxidant substances in the troposphere.
  • Acidification: Measures the impact of acidic emissions (e.g., NOx, SO2) on terrestrial and aquatic ecosystems.
  • Eutrophication: Assesses the impact of nutrient enrichment in aquatic systems, leading to algal blooms.

13. Midpoint or Problem-Oriented Approach

In the midpoint approach, emissions and extractions are weighted using midpoint characterization factors to represent their contribution to specific midpoint categories. These factors are scientifically modeled. Inventory flows are multiplied by these factors and summed to provide a midpoint score, often expressed in equivalent mass of a reference substance (e.g., CO2 equivalents for greenhouse gases).

*EXAMPLE

14. Endpoint or Damage Approach

The damage approach assesses the contribution of each midpoint category to broader damage categories (areas of protection like human health and ecosystems). Midpoint impact scores are multiplied by midpoint-to-damage characterization factors to quantify these contributions.

15. Cultural Theory in LCA

Cultural theory considers seriousness from three perspectives:

  • Egalitarian: Uses the precautionary principle and a long-term view, assuming maximum possible impact.
  • Individualist: Uses only proven effects of an impact.
  • Hierarchist: Uses impacts substantiated by scientific facts but not necessarily demonstrated in actual cases, typically falling between the other two.

16. Normalization in LCA

Normalization expresses an impact per functional unit relative to the total impact in that category. It compares the contribution of a product or service to the total global, continental, or regional impact for a given category. This is done by multiplying inventory flows by characterization factors, summing them, and dividing by the population to get a normalized score per person.

17. Weighting Principles

Weighting combines scores from different impact or damage categories into a single score, based on social, political, and ethical values. Principles include:

  • Panel of Experts: Qualitative analysis by experts, often lacking reproducibility and having a narrow viewpoint.
  • Social Evaluation (e.g., EPS system): Expresses environmental damage in financial terms.
  • Prevention Costs: Assesses impact seriousness based on the costs of preventing or combating environmental changes.
  • Energy Consumption: Links impact seriousness to energy consumption, sometimes seen as an indicator of total environmental pollution.
  • Distance-to-Target Principle: Relates impact seriousness to the difference between current and target values.
  • Avoiding Weighting (e.g., using only energy consumption): Simplifies by focusing on one indicator, but may omit serious impacts.
  • Weighting Triangle (Eco-indicator 99): Shows analysis dependency on weighting factors for three damage categories.

18. Result Interpretation Phase Elements

  1. Identification of Significant Issues: Structuring LCI and LCIA results to identify key environmental issues based on the goal and scope.
  2. Evaluation: Considering completeness, sensitivity, and consistency checks in accordance with the study’s goal and scope. Techniques include completeness, sensitivity, and consistency checks.
  3. Conclusions, Recommendations, Reporting, and Critical Review: Drawing conclusions and making recommendations for the intended audience, interactively with other interpretation elements.

19. Quantitative LCA Methods

  • Dutch Handbook on LCA (CML): Classifies and characterizes impacts into groups A, B, and C; includes normalization and evaluation.
  • Eco-indicator 99: Measures damage to resources, human health, and ecosystem quality.
  • Ecological Scarcity Method: Assesses impacts based on the “distance to target” principle.
  • TRACI (U.S. EPA Method): Characterizes potential environmental effects under U.S. conditions.
  • Impact 2002+: Combines midpoint and damage approaches.
  • Impact World+: A regionalized impact assessment method for global application.
  • Recipe 2008: Merges midpoint and damage approaches.
  • New European Method – Life Cycle Data System (ILCD): Developed under the ILCD framework.
  • Usetox: A consensus model for characterizing human and ecotoxicological impacts of chemicals.
  • The Ecological Footprint Method: Reduces ecological impacts to necessary surface area.
  • EPS System: Assesses the impact of emissions from each life stage of a product.
  • MIPS Concept: Measures the quantity of materials consumed to provide a service.

20. Waste Management Planning Model (WAMPS)

WAMPS is a screening tool for finding alternatives in waste management systems. It presents environmental and economic consequences of different scenarios from a life cycle perspective, based on the ORWARE LCA model. WAMPS provides decision-makers with information for comparing waste management alternatives, acknowledging that systems depend on local parameters.

21. Waste Management Planning Model (Easewaste)

Easewaste compares different waste management strategies, treatment methods, and process technologies. Users define data for waste composition, collection, treatment, recovery, and disposal, along with LCI data. The functional unit is a given amount of solid waste generated for an area. The model calculates resource consumption, emissions, and waste generation.

22. Environmental Product Declaration (EPD)

An EPD is a certified declaration reporting environmental data over a product’s life cycle, following ISO 14025. Main steps include:

  1. Perform LCA study based on PCR (Product Category Rules): Comply with ISO 14040 and ISO 14044.
  2. Compile Information in EPD Format: Align with ISO 14020 guidelines.
  3. Verification: Undergo EPD verification or EPD process certification.
  4. Registration and Publication: Submit documentation for publication.

23. Life Cycle Stages According to EPD

The product life cycle is divided into:

  • Upstream Processes (Cradle to Gate): Production of material inputs (e.g., raw material acquisition, intermediate component production).
  • Core Processes (Gate to Gate): Processes managed by the EPD owner and other related processes.
  • Downstream Processes (Gate to Grave): Further processing, distribution, retail, product use, and end-of-life management.

24. Carbon Footprint and Water Footprint

  • Carbon Footprint (CFP): The sum of greenhouse gas emissions and removals in a product system, expressed as CO2 equivalents, based on LCA focusing on climate change.
  • Water Footprint Assessment: Compilation and evaluation of water inputs, outputs, and potential environmental impacts related to water use. It involves four stages: Goal and scope definition, inventory analysis, impact assessment, and interpretation.