54 Life Cycle Assessment

Learning Objectives

By the end of this section, you should be able to:

Understand the steps involved in life cycle assessment (LCA)

Interpret LCA results critically

Life Cycle Assessment


  • Cradle-to-grave: this scope includes all aspects of a product, starting from raw material extraction to the product’s end of life (use and disposal)
  • Cradle-to-gate: this scope includes all aspects of a product from raw material extraction to production, but does not include the product’s use or disposal
  • Gate-to-gate: this scope includes the manufacturing/production and processing aspects of a product only

Life Cycle Assessment (LCA) is a technique used to quantify the environmental impact of a product from raw material acquisition through end of life disposition (cradle-to-grave)

Product assembly image from Sammutawe / CC BY-SA

There are four stages of a life cycle assessment:

  1. Step 1: Goal Definition and Scoping: Identify the LCA’s purpose, the products of the study, and determine the study boundaries. This can include things like what is included and what is not included in the study
  2. Step 2: Life-cycle Inventory: Quantify the energy and raw material inputs and environmental releases associated with each life cycle phase.
  3. Step 3: Impact Analysis: Assess the impacts on human health and the environment.
  4. Step 4: Interpret Results: Evaluate opportunities to reduce energy, material inputs, or environmental impacts at each stage of the product life-cycle.

Life Cycle Assessments are based on international standards set by the International Organization for Standardization (ISO 14040).

Each of the steps are set by different ISOs:

  • Step 1: ISO 14041
  • Step 2: ISO 14041
  • Step 3: ISO 14042
  • Step 4: ISO 14043

Exercise: Biofuels Product Scope

Consider the following system boundary diagram for the production of biofuels. Which scope does this representation cover (cradle-to-grave, cradle-to-gate, or gate-to-gate)?


This diagram represents a cradle-to-gate scope because it shows the raw materials used for the production of biofuels, the transportation of raw materials, as well as initial processing.

Step 1: Goal Definition and Scoping

Define the goal:

  • What is the intended application of the study?
  • Who is the intended audience?

Define the scope:

  • What is the product system to be studied?
  • What is the functional unit?*
  • What are the boundaries of the product system?
  • What are the assumptions and limitations of the study?
  • What impact categories need to be included in the study?

*Functional Units: a measure of the function of the studied system. It provides a reference to which the inputs and outputs can be related and enables a comparison of two essentially different systems.

Examples of functional units:

  • For a paint system (the paint as well as layers of coating materials applied to a surface), the functional unit may be defined as the unit surface protected for 10 years
  • For a printer, the funcional unit may be defined as the number of printed pages of an acceptable print quality
  • For a power generation system, the functional unit may be defined as 1kWh of electricity

Example: Reusable Shopping Bags

Let’s say you own a local grocery store in Kitsilano. Your customers start requesting that you sell reusable shopping bags to minimize waste. You think its a great idea, but want to make sure that the reusable shopping bags you sell have the lowest environmental impact. Since you are an engineer and learned about LCA in CHBE 220, you decide to perform a streamlined LCA.

What is your goal?

Determine which shopping bag has the lowest environmental impact

After doing a search of what is available on the market, you determine that your options for shopping bags are as follows:

  • Single use paper
  • Single use plasic
  • Reusable plastic
  • Reusable cotton

What are your system boundaries and process?

To simplify your LCA, you make the following assumptions:

  • All bags are manufactured 100km from the customer
  • All bags travel 10km from the customer to the end of life
  • Half of paper bags are recycled at end of life and the other half go to a landfill
  • Plastic and cotton bags go to landfill at the end of life

What is the functional unit for this system?

Let’s take our functional unit to be the amount of shopping bags consumed by a household to carry 70 grocery items (~7 items per bag per trip) home from the supermarket each week for 52 weeks. Note you’ll see that each bag type in the table below has relative capacities, and this is used to account for some bags having the ability to carry more or fewer items than others while comparing to single-use plastic bags as a basis.

Bag Type Single-Use Plastic Single-Use Paper Reusable Plastic Reusable Cotton
Material HDPE Unbleached Kraft paper Polypropylene Cotton
Mass per bag 7g 42.6g 95g 85g
Relative Capacity 1 0.9 1.1 1.1
Bags per year 520 578 4.55 4.55
Mass bags per year 3640g 24622.8g 432.25g 386.75g



Step 2: Life Cycle Inventory

The life cycle inventory step is a highly data-intensive step that is based on detailed material and energy balance analyses over the life cycle of a product. The aim of this step is to account quantitatively for the components which make up the life cycle for our products.


  • Quantifiable data for each product to assess impacts (although these can be highly dependent on the assumptions we make in step 1)


  • Assumptions made when data unavailable
  • Can be very time-intensive to account for all materials, energy, and steps to create a product

A life-cycle inventory can be summarized by block flow diagrams. The following diagram is one example for a typical manufacturing process for lithium-ion battery cells.[1]

Example: Reusable Shopping Bags Life-Cycle Inventory

Once again, you’d like to continue your LCA on the four options of shopping bags that you can offer in your grocery store. You gather the following information for quantities involved in each step of the lifecycle of these bags. Note most of these are measured in terms of a mass (eg grams, g) or mass per distance for travel (eg. tonne-kilometers, tkm).

Single-Use Plastic Bag
Polyethylene, HDPE, granulate 3640g
Stretch blow moulding 3640g
Transport, 100km manufacturing to customer 0.364tkm
Transport, municipal waste collection, 10km customer to landfill 0.0364tkm
Disposal, polyethylene, 0.4% water, to sanitary landfill 3640g
Single-Use Paper Bag
Kraft paper, unbleached, at plant 24622.8g
Production of paper bags 24622.8g
Transport, 100km manufacturing to customer 2.4623tkm
Transport, municipal waste collection, 10km customer to landfill/recycling 0.24623tkm
Disposal, packaging paper, to sanitary landfill 12311g
Recycling paper 12311g
Reusable Plastic Bag
Polyethylene, granulate 432.25g
Extrusion, plastic film 432.25g
Transport, 100km manufacturing to customer 0.043225tkm
Transport, municipal waste collection, 10km customer to landfill 0.0043225tkm
Disposal, polyethylene, to sanitary landfill 432.25g
Reusable Cotton Bag
Textile, woven cotton, at plant 386.75
Transport, 100km manufacturing to customer 0.03867tkm
Transport, municipal waste collection, 10km customer to landfill 0.003867tkm
Disposal, inert material, to sanitary landfill 386.75g



Step 3: Impact Assessment

Impact Assessment Results: impact assessment converts the inventory into impact categories or endpoints, detailing human health and environmental impact.

  • Converts the inventory into impact categories or mid/endpoints that characterize the environmental effects
  • Impact categories may include: carcinogens, climate change, respiratory organics, and inorganics, radiation, ozone layer, ecotoxicity, acidification/eutrophication, land use, minerals, fossil fuels
  • We can add weights to impact categories to indicate if we want to weight them more or less significantly in overall analysis (this is again where some assumptions may come in and so we have to be careful when setting up and interpreting LCAs)

The following figure shows an example of life-cycle assessment results for EV batteries from a study conducted by the United States Environmental Protection Agency (US EPA).[1]

*ADP: abiotic depletion potential – depletion of non-living resources such as minerals, clay, fossil fuels, etc.

*AP: acidification potential – the potential of the battery releasing harmful acids into the environment

*EcoTP: ecological toxicity potential – the potential of the battery being toxic to surrounding ecology

*EP: eutrophication potential – nutrient addition that leads to the (over)growth of aquatic plant species; can lead to things like algal blooms and food chain disruptions

*GWP: global warming potential – the potential of warming caused by the release of greenhouse gases as caused by the battery

*HTP: human toxicity potential – the potential the battery process has for releasing chemicals that are toxic (dosage is taken into account) into the environmental

*OCH: occupational cancer hazard – the potential the battery process has for exposing people that work on this battery to carcinogens

*ODP: ozone depletion potential – the potential the battery process has for releasing chemicals that degrade the ozone layer

*OnCH: occupational non-cancer hazard – the potential the battery process has for exposing people that work on this battery to other diseases, injuries, or other health problems

*POP: photochemical oxidation potential – the potential the battery process has for releasing chemicals that react in the sunlight and release harmful products into the environment

*EOL: end-of-life; note that the negative values for the EOL bar signify recovery of the material at the end of battery’s life, which reduced the life-cycle impact.

Step 4: Report Results

Life cycle interpretation: findings of the inventory analysis or impact assessment are evaluated in relation to the goal and scope of the study to reach conclusions and recommendations.

In this stage we aim to:

  1. Identify significant issues
  2. Evaluate results for completeness, consistency, and sensitivity of the data
  3. Draw conclusions and make recommendations consistent with the goal and scope of the study

Example: Reusable Shopping Bags LCA Results

Consider the following chart that you put together after conducting an impact assessment on the 4 options for shopping bags. Note in this case that a lower score will mean less environmental impact (ie. lower score is better).

After contacting suppliers, you find that the cost per year for each of the shopping bags is as follows:

  • Singe-Use Plastic: 10.40 dollars/year
  • Singe-Use Paper: 40.46 dollars/year
  • Reusable Plastic: 4.55 dollars/year
  • Reusable Cotton: 27.30 dollars/year

Some questions you might ask:

  • Which bag would you promote given the impact information?
  • Which bag would you promote given the cost information?
  • Which bag would customers most likely lean towards given the cost?
  • Are there any assumptions you would change?
  • Did your final result differ from your initial guess?

Given both the cost information and the environmental assessment, you might decide to go with the reusable plastic shopping bags, or offer these alongside re-useable cotton bags with some information to customers.


Exercise: LCA Results on Different Lithium-Ion Batteries

A life-cycle assessment is conducted on two different types of vehicle batteries: electric vehicle (EV) batteries and plug-in hybrid electric vehicle (PHEV) batteries. Each of these has different lithium-ion chemistries. The EV batteries have 3 different chemistries ([latex]LiMnO_{2}[/latex], [latex]Li-NCM[/latex], and [latex]LiFePO_{4}[/latex]), while the PHEV batteries have 2 different chemistries ([latex]LiMnO_{2}[/latex] and [latex]LiFePO_{4}[/latex]).[1]

Legend for the charts:

*ADP: abiotic depletion potential
*AP: acidification potential
*EcoTP: ecological toxicity potential
*EP: eutrophication potential
*GWP: global warming potential
*HTP: human toxicity potential
*OCH: occupational cancer hazard
*ODP: ozone depletion potential
*OnCH: occupational non-cancer hazard
*POP: photochemical oxidation potential

EV Batteries:

PHEV Batteries:

Your client is asking you to make a recommendation on which vehicle type (EV or PHEV) they should manufacture based solely on human toxicity potential through product use for batteries. Which vehicle type do you recommend based on the information you have and why?


Step 1: Determine where the human toxicity potential (HTP) is located on the graph.

Step 2: Compare the data of both EV and PHEV batteries side by side. Note that the ‘product use’ factor is the light blue/teal bar



Step 3: Determine the approximate percentages for ‘product use’ for each of the factors and the batteries.


Health Factor [latex]LiMn_{2}[/latex] [latex]LiFePO_{4}[/latex] [latex]Li-NCM[/latex]
HTP 80% 80% 80%


Health Factor [latex]LiMn_{2}[/latex] [latex]LiFePO_{4}[/latex]
HTP 90% 90%


Step 4: Determine which battery type is the best choice based on your client’s specifications.

Since the percentages are consistent among battery chemistries, our choice will be between the EV battery and the PHEV battery. The EV has a smaller impact on human toxicity potential through product use when compared to PHEV. Therefore, we recommend an EV battery.




[1]”Application of LifeCycle Assessment to Nanoscale Technology: Lithium-ion Batteries for Electric Vehicles”, United States Environmental Protection Agency, 2013.



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Foundations of Chemical and Biological Engineering I Copyright © 2020 by Jonathan Verrett is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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