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Interpretation: Making Sense of LCAs

Posted on August 12, 2013 by Eileen Ekstrom

According to the ISO 14040 standard on life cycle assessments, there are 4 stages of an LCA: (1) Goal and Scope, (2) Inventory Analysis, (3) Impact Assessment, and (4) Interpretation. We explored Inventory Analysis, which ISO 14040 defines as “the phase of life cycle assessment involving the compilation and quantification of inputs and outputs for a product throughout its life cycle”, in the previous posts on reference flows, assumptions behind reference flow calculations, and unit processes. Life Cycle Impact Assessment was also described and defined. We are now left to describe and interpret the results of our LCA. In this post, the principles of LCA interpretation will be described – those interested in exploring the results of Ecosystem Analytics Inc.’s LCA on cloth handkerchief versus paper facial tissue use should either read the executive summary or the full LCA report.

Interpretation, from ISO 14040, is the phase of LCA in which the findings from the inventory analysis and the impact assessment are considered together. We present the results of our LCA study and evaluate those results with respect to previously published studies. It is also important to describe the LCA study’s limitations and explore how the study limitations affect the conclusions that can be made. Interpretation must also include the evaluation of the results of the study in relation to the defined goal and scope. This harkens to the iterative nature of LCA, in which information of each step of the LCA informs and helps refine the overall assessment.

The astute reader might have noticed that we have not yet described the Goal and Scope of this LCA. We will conclude our LCA series by rounding back to a description of the Goal and Scope phase, and demonstrate how the concepts we have been discussing throughout this series feed into it.

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Sensitivity Analysis: Testing the Significance of Your Assumptions

Posted on July 9, 2013 by Eileen Ekstrom

A Life Cycle Assessment is only as good as the data and assumptions built in the LCA. As we described in the previous post on developing the function unit, many informed assumptions needed to be made about use patterns of handkerchiefs and facial tissues in the LCA completed by Ecosystem Analytics Inc. We tried to base as many of our assumptions on previously published studies, but still, a judgment had to be made by the LCA practitioner. Assumptions needed to be made on the time length of use considered, the geographic relevance of data used, and the choice of Life Cycle Impact Assessment (LCIA) model.

Luckily, the LCA field has built in the testing of key assumptions into the life cycle assessment process so that we can understand the robustness of the conclusions of any LCA. This process is called Sensitivity Analysis, and according to the ISO 14040 standard on LCAs, sensitivity analysis is the “systematic procedures for estimating the effects of the choices made regarding methods and data on the outcome of a study.”

For this LCA, we performed sensitivity analysis on 3 areas where key assumptions were made:

  1. Use Scenarios
  2. Country of Production/Electricity Mix Scenarios
  3. Impact Assessment Model Scenarios

Use Scenarios

As we described in the previous post on the design of the functional unit, we needed to make assumptions on the frequency of both facial tissue and handkerchief use over time. Two situations were constructed to model use – during respiratory illnesses (Cold) and during periods of wellness (Base Use). Three scenarios were designed to model use during a maximum illness (Max Cold), a minimum illness (Min Cold), and the absence of a respiratory illness (No Cold), based on published nose blow frequencies in a respiratory illness study. Two scenarios were constructed to cover the length of time that a handkerchief would be used before laundering it during the well, Base Use periods (Max Base Use = 1 day, Min Base Use = 7 days). All in all, six one-year use scenarios were created, with the functional unit (Max Cold & Max Base Use) one of them. The 5 other one-year use scenarios were tested as part of the sensitivity analysis, as well as two scenarios that covered the entire useful life of the handkerchief before disposal – Max Life Max Cold & Max Base Use and Max Life Max Cold & Min Base Use.

Country of Production/Electricity Mix Scenarios

As discussed in the previous post on geographic relevance, LCA practitioners often select data from a similar country or region instead of necessarily only using data from the country of production so to be able to use the most comprehensive and reliable LCA databases available. However, the electricity mix is selected in the unit processes to reflect the country of production since electricity often has a large impact on LCA results. For the sensitivity analysis, we flipped the electricity mix used in the model for the handkerchief and facial tissue functional unit. This resulted in scenarios that roughly modeled a case in which the location of manufacture had flipped – the facial tissues were manufactured in China and the handkerchiefs were manufactured in Canada.

Impact Assessment Model Scenarios

Every Life Cycle Impact Assessment (LCIA) model needs to make many informed assumptions to be able to transform a list of unit processes into numerical estimates of environmental impacts. Every LCIA model is constructed a little differently, reflecting new research in the LCA field. To test the importance of our choice of LCA model, we also ran our results through a newer LCIA model – ReCiPe 2008.

In the next post, we will discuss the role of interpretation in understanding LCAs and putting them in context while considering previous studies and the stated study limitations.

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Life Cycle Impact Assessment: Calculating Environmental Impacts

Posted on May 20, 2013 by Eileen Ekstrom

In previous posts, we described how to construct a model of the manufacture, transportation, use, and disposal of a product from unit processes and reference flows. This process is Life Cycle Inventory (LCI) analysis. According to the ISO 14040 standard on LCA, Life Cycle Inventory (LCI) is the “phase of life cycle assessment involving the compilation and quantification of inputs and outputs for a product throughout its life cycle.”

If one was trying to design a product, constructing a LCI would be the sole exercise needed. However, LCA practitioners need to calculate the environmental impacts of a product. So, we need a way to take our LCI model and transform it into a quantitative estimate of environmental impacts. Some environmental impacts can be calculated by hand. The amount of CO2 produced from the burning of natural gas can be calculated by hand. However, quantifying all the air emissions arising from the refining of oil to make plastic is something that would be very challenging without the help of computer technologies. Luckily, the LCA field is endowed with some good Life Cycle Impact Assessment (LCIA) models which take all unit processes and reference flows of the LCI and transform them to concrete environmental impacts. The Life Cycle Impact Assessment (LCIA) is a “phase of life cycle assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product,” according to the ISO 14040 standards. There are over 10 LCIA models used in the LCA field, and the European Commission Joint Research Center produced a good review of the different LCIA models.

For this LCA, the impacts of the production, transport, use, and disposal of cloth handkerchiefs and paper facial tissues were evaluated by calculating the Climate Change, Human Health, Ecosystem Quality, and Resources impact categories as defined by IMPACT 2002+. IMPACT 2002+ was selected as the LCIA given its wide use in the field and since it first calculates the environmental impacts of 15 more detailed categories (midpoint indicators), and then summarizes the midpoint categories into the 4 endpoint categories. This allows the details of environmental impacts to be assessed while still getting a comprehensive view of ecological impacts.

The 15 midpoint categories calculated by IMPACT 2002+ are: Human Toxicity, Respiratory Effects, Ionizing Radiation, Ozone Layer Depletion, Photochemical Oxidation, Aquatic Ecotoxicity, Terrestrial Ecotoxicity, Aquatic Acidification, Aquatic Eutrophication, Terrestrial Acidification/Nutrification, Land Occupation, Global Warming, Non-Renewable Energy, and Mineral Extraction. All the emissions that affect a midpoint category are summed and expressed as an amount of a key pollutant or energy quantity for that category. For the midpoint damage category of Global Warming, for example, all emissions of greenhouse gases such as carbon dioxide, methane, water vapor, nitrous oxide, and CFCs are converted to carbon dioxide equivalents (CO2-eq).

The midpoint categories are further grouped into the 4 endpoint categories. The Human Health endpoint category is a sum of the midpoint categories that address carcinogenic and non-carcinogenic toxicity to humans (Human Toxicity), respiratory effects in humans (Respiratory Effects and Photochemical Oxidation), Ionizing Radiation, and Ozone Layer Depletion. It is expressed in Disability Adjusted Life Years (DALY), which represents a measure of the loss of “healthy” years of life due to premature death or disability. Although climate change will likely have effects on human health, IMPACT 2002+ does not model them due to high uncertainty in estimating the effects at the time that the model was designed.

Ecosystem Quality sums the midpoint categories that quantify Aquatic and Terrestrial Ecotoxicity, Aquatic Acidification and Eutrophication, Terrestrial Acidification/Nitrification, and Land Occupation. It is expressed in the unit of Potentially Disappeared Fraction of species (PDF) per square meter per year (PDFx m^2 x yr) (Jolliet et al., 2003). PDF x m^2 x yr is the percentage of species that disappear from one square meter of earth surface during one year.

The Resources category sums the energy requirements (in megajoules, MJ) of Non-Renewable Energy and Mineral Extraction along with the extra energy it will take to extract those resources in the future since there will be less of them due to present consumption (Jolliet et al. 2003). The Climate Change endpoint category only sums the impacts of the Global Warming midpoint category, and therefore, provides a good summary of the carbon footprint.

In the next post, we will describe uncertainty analysis – how we vary the assumptions in our LCA to test whether our conclusions are robust.

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Stating the Assumptions: Geographic Relevance and LCAs

Posted on April 9, 2013 by Eileen Ekstrom

Last post, we described how LCA models are built from unit processes, and demonstrated how the end of life scenarios for facial tissues is constructed from the following 4 unit processes from the Ecoinvent database:

  • Disposal, paper, 11.2% water, to sanitary landfill/ CH U
  • Disposal, paper, 11.2% water, to municipal incineration/ CH U
  • Disposal, polyethylene, 0.4% water, to sanitary landfill/ CH U
  • Disposal, polyethylene, 0.4% water, to municipal incinerator/ CH U

Each of the unit processes has a CH at the end of them. That is the country abbreviation for Switzerland, the country where most of the Ecoinvent data was developed. Although the facial tissues we are modeling in this LCA were manufactured in Canada and used and disposed of in the U.S., the majority of the unit processes are from European (RER), Swiss (CH), and German (DE) data from the Ecoinvent database. Why not use Canadian or American unit processes? Most of the LCA research has been conducted in Europe, and still, some of the most comprehensive and reliable LCA databases are primarily based on European data. However, it is likely that Swiss landfills and incinerators are quite similar to American landfills and incinerators, making the lack of geographically relevant data less important. The description of the role of geographic relevance to this LCA can be found in Section 2.2.2 Assumption, in the full LCA.

Using European data to model manufacturing in the developing world is more likely to result in inaccuracies in the model. The handkerchief we modeled in this LCA was manufactured in China. Luckily, the textile manufacturing unit processes available in Ecoinvent were from global (GLO) data, with approximately 70% of the manufacturing unit processes from Chinese data and 30% from European or American data. This well represents the location of production (China), while also modeling for the possibility that some upstream manufacturing steps occurred elsewhere.

The other acronym used in the unit processes listed above is U – which stands for unit process in the Ecoinvent database.

The next post in this series will focus on the model used to transform all the input data into data on environmental effects and impacts – the Life Cycle Impact Assessment.

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Unit Processes: The Building Blocks of Life Cycle Assessments

Posted on March 28, 2013 by Eileen Ekstrom

In the last post, we explored how reference flows are calculated, by making careful, thought-out assumptions and well-applied research. In our exploration of the Ecosystem Analytics Inc. LCA on cloth handkerchief use versus disposable facial tissues, we demonstrated how reference flows for the end of life for facial tissues were calculated. We calculated the amount of paper facial tissues, cardboard box, and plastic box insert that need to be landfilled and incinerated to fulfill the functional unit for an average American living in New England. But what do we do with these amounts? We need a way to model the effects of landfilling and incineration, but it is highly unlikely that an LCA practitioner can go to a municipal landfill or incinerator to collect data on air, water, and land impacts and the energy produced or used. Even if a local landfill or incinerator was generous enough to allow access, the costs of conducting such an inventory for each project would be exorbitant. Luckily, publically-available, peer-reviewed, and well-researched databases of industrial processes and impacts exist for the LCA practitioner to use when conducting an LCA. One of the best LCA databases is the Ecoinvent database, developed by the Swiss Federal Institute of Technology Zürich (ETH Zurich) and Lausanne (EPF Lausanne), the Paul Scherrer Institute (PSI), the Swiss Federal Laboratories for Materials Testing and Research (Empa), and the Swiss Federal Research Station Agroscope Reckenholz-Tänikon (ART). Most of the data was acquired by studying Swiss and European manufacturing plants, energy production centers, and waste disposal locations, and quantifying the types of chemicals used and the emissions to the air, water, and land.

The Ecoinvent database is a database of unit processes. According to the ISO 14040 LCA standards, a unit process is the “smallest element considered in the life cycle inventory analysis for which input and output data are quantified.” So, for our example here, the amount of facial tissue, cardboard, and plastic packaging to be landfilled and incinerated is the smallest element we can calculate an input for. Therefore, they are the unit processes for the end of life for the facial tissues. We looked through the Ecoinvent database to find unit process listings that matched our needs and found these:

  • Disposal, paper, 11.2% water, to sanitary landfill/ CH U
  • Disposal, paper, 11.2% water, to municipal incineration/ CH U
  • Disposal, polyethylene, 0.4% water, to sanitary landfill/ CH U
  • Disposal, polyethylene, 0.4% water, to municipal incinerator/ CH U

We aggregated the reference flows for facial tissues and cardboard to fit the paper unit process. These reference flows and unit processes form the inputs to our LCA model.

  • Disposal, paper, 11.2% water, to sanitary landfill/ CH U, 551 g
  • Disposal, paper, 11.2% water, to municipal incineration/ CH U, 693 g
  • Disposal, polyethylene, 0.4% water, to sanitary landfill/ CH U, 3.48 g
  • Disposal, polyethylene, 0.4% water, to municipal incinerator/ CH U, 4.37 g

In the next post, we will discuss the assumptions made in picking unit processes for the LCA model – specifically how to simulate geographic relevance in the LCA.

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Reference Flows in a Complex World: Making Appropriate Assumptions

Posted on February 11, 2013 by Eileen Ekstrom

Last post, we introduced the concept of reference flows, which are a measure of the outputs from processes required to fulfill the function expressed by the functional unit of the LCA. We also illustrated how the reference flows are calculated for facial tissues and the facial tissue packaging. Those reference flows were very simple to calculate: they are just the weight of one facial tissue (or the proportion of the packaging for one facial tissue) times the total number of facial tissues used. But to calculate many of the reference flows needed to fully describe the product system as defined by the system boundaries, information from other studies and carefully considered assumptions need to be applied. We at, Ecosystem Analytics, believe that how reference flows are calculated should be fully transparent – all reference sources behind the calculations need to be cited and the assumptions made documented. In the full LCA on facial tissue versus handkerchief use, all reference flows are listed in the Appendix in Tables A1 and A2, and the references and assumptions behind each is listed in the tables or in the footnotes at the end of the tables. We will illustrate an example of how research and informed assumptions helped us calculate reference flows for the end-of-life for facial tissues.

End of Life – Facial Tissue & Packaging

Since this LCA is a cradle-to-grave study, we must quantify the reference flows for the disposal of the used facial tissues and tissue packaging. We have assumed that all used facial tissues and packaging are thrown away instead of being recycled or composted, since used facial tissues would not be accepted in most municipal recycling or composting programs. This LCA is based on the facial tissue or handkerchief use of an average adult American living in New England. Therefore, we used The State of Garbage in America report by Van Haaren et al. (2010) to determine the fraction of trash in New England that is either landfilled or incinerated. For New England, Van Haaren et al. (2010) found that 31% of municipal waste is landfilled, 39% is incinerated, 22% is recycled, and 8% is composted. Since recycling and composting were not considered viable waste options, we determined the relative % of waste that is landfilled and incinerated only:

  • Landfilling: 31% ÷ (31% + 39%) x 100% = 44.29% landfilled
  • Incineration: 39% ÷ (31% + 39%) x 100% = 55.71% incinerated

Then, the mass of the material was multiplied by the fraction intended for landfilling or incineration:

Facial Tissue:

  • Landfilling: 1013 g x 44.29% = 448.66 g
  • Incineration: 1013 g x 55.71% = 564.34 g

Cardboard Box:

  • Landfilling: 232 g x 44.29% = 102.75 g
  • Incineration: 232 g x 55.71% = 129.25 g

PE insert:

  • Landfilling: 7.85 g x 44.29% = 3.48 g
  • Incineration: 7.85 g x 55.71% = 4.37 g

In the next post, we will explore how unit processes are used to build up the model of how the products are manufactured, transported, and disposed.

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Reference Flows: The Work Horses of Life Cycle Assessments

Posted on January 18, 2013 by Eileen Ekstrom

In the previous post on quantifying the functional unit, I described the studies, assumptions, and calculations used to develop the reference amount used to compare two product alternatives. Since LCA is based on the function of the product, and since both products, the facial tissue and the handkerchief are used differently, great care needed to be taken in developing analogous amounts. 785 paper facial tissues or 30 cloth handkerchiefs washed 14.97 times were calculated to be the functional units, covering use by an average American’s yearly during respiratory illnesses and well times.

However, life cycle assessment covers all aspects of a product’s manufacture, transport, use, and disposal. We cannot only quantify the amount of product needed – we also need to determine the amount of packaging used, the amount of soap and water used during washing, and the energy needed for washing and drying. These are the reference flows. According to ISO standard 14044, reference flows are a “measure of the outputs from processes in a given product system required to fulfill the function expressed by the functional unit.” For either the facial tissue or handkerchief scenarios, these reference flows will need to be quantified, as specified by the system boundaries:

Paper Facial Tissue

  • paper facial tissue
  • packaging (cardboard box and LDPE packaging film)
  • transport to retail
  • disposal of facial tissue and packaging

Cloth Handkerchief

  • cotton handkerchief
  • handkerchief packaging (cardboard box, kraft paper, packaging film)
  • transportation to retail
  • machine washing and drying (water, detergent, detergent packaging, electricity & natural gas for heating/drying, sewage treatment of water, disposal of detergent packaging)
  • disposal of handkerchief packaging

To calculate the quantity of each reference flow, we need to determine the mass of the products used. For this LCA, disposable facial tissue use is based on a 200 count, 2-ply cardboard printed box of white facial tissues with a polyethylene (PE) plastic insert. The facial tissues are manufactured in Ontario, Canada. Reusable handkerchief use is based on a 6 pack of 100% cotton handkerchiefs in a printed cardboard box with a polyethylene sleeve, packed with kraft paper. The handkerchiefs are manufactured in China. Details of the mass and volume of the products can be found in Table 1 in the full LCA.

To facilitate calculating the reference flows, the mass of a single facial tissue or handkerchief and the proportional amount of packaging are determined:

  • Single Facial Tissue: 1.29 g facial tissue, 0.295 g cardboard box, 0.010 g PE insert
  • Single Handkerchief: 15.0 g handkerchief, 7 g cardboard box, 2.3 g PE sleeve, 1 g paper insert

To calculate the reference flow, the quantities for a single item need to be multiplied by the number used as dictated by the functional unit.

For example, for the facial tissue:

  • 1.29 g facial tissue x 785 = 1013 g
  • 0.295 g cardboard box x 785 = 232 g
  • 0.010 g PE insert x 785 = 7.85 g

Calculating the reference flows for the facial tissue or handkerchief and packaging is quite simple. In the next post, we will explore some of the assumptions that need to be made when calculating reference flows for transportation, use, and disposal.

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System Boundaries: Looking at the Whole Picture

Posted on December 14, 2012 by Eileen Ekstrom

Life Cycle Assessments aim to understand the impacts of products, services, and organizations over the entire life cycle, from manufacture and disposal. Still, even when a LCA does model impacts from cradle-to-grave, there still can be deviances from what is included from one study to the next. As part of the goal and scope of the LCA, the LCA practitioner outlines what will be included in the assessment and what will not. This description is the system boundary – all processes within the system boundary are modeled as part of the product’s impacts and all processes outside the system boundary are not included in the LCA model.

Ecosystem Analytics LCA on reusable handkerchiefs versus disposable facial tissues, like most LCAs, covers the production, transport to retail, use, and disposal of the products and retail packaging. Transportation between production steps, packaging used to assist shipping between production steps, and disposal of waste products and packaging used during production are included in the LCA as part of the product’s manufacturing.

Like most LCAs, there are some processes outside of the system boundary for this LCA. Transportation from retail to the user’s residence and transportation from the user’s residence to the location of final disposal was not included in the model, given the small size/weight fraction of the products relative to the overall shopping trip or garbage bag and that the transportation lengths can vary greatly. Likewise, the impacts of building capital equipment such as washing machines, drying machines, paper plants, textile production plants are not included in the LCA. Since the functional unit only covers 1 year of use, handkerchief disposal is not modeled as part of the functional unit due to the longer useful life of the handkerchief. In future posts, we will explore this as part of sensitivity analysis.

To explore what is included in one stage of the LCA, let’s looks at the use phase. Facial tissue use is fairly simple – only the paper facial tissues are used. Handkerchief use also involves the washing of the handkerchief, requiring the modeling of the impacts of use of tap water, detergent, detergent packaging, energy for the washer and dryer, wastewater treatment, and disposal of detergent packaging.

We have previously described how the functional unit is calculated, the reference unit for the study. In the next post, we will describe how each product used throughout the life cycle is included in LCA modeling.

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How Functional Units Are Developed and Quantified

Posted on November 20, 2012 by Eileen Ekstrom

As I described in the previous post, the functional unit serves as the reference unit for the study, normalizing all inputs and outputs to it, and enables comparisons between products with similar functions. It is generally expressed in qualitative terms, with sufficient detail to enable the LCA practitioner to convert it into a quantitative number. Oftentimes, life cycle assessments do not document how the functional unit was developed, as described in the presentation by Vee Subramanian and Eric Williams at the ACLCA LCAXII Conference in Tacoma, Washington. Life Cycle Assessments from Ecosystem Analytics Inc. include a thorough explanation on how the function unit was developed, which also provide detail on how the quantitative functional unit is calculated. This adds full transparency to the LCA and enables a thorough review of the basis for the functional unit.

For example, for the LCA Ecosystem Analytics recently completed comparing handkerchief use with facial tissue use, the functional unit was defined as: the number of nose blows per surface area for an average American adult over 1 calendar year, encompassing the use pattern during 4 respiratory illnesses (896 nose blows) and daily use during well periods (337 nose blows). But what is the use pattern over these periods, and how does that relate to the number of handkerchiefs and facial tissues used? This is described in Section 2.1.2.1- Functional Unit Creation, broken up into 3 sections: Nose Blow Frequency, Nose Blows per Facial Tissue or Handkerchief, and Handkerchief Reuse and Laundering.

Nose Blow Frequency

As described in ISO/TR 14049 Technical Report, defining and quantifying the function of a product is an essential part of developing the functional unit. For this LCA, the sole function of both handkerchiefs and facial tissues was to blow one’s nose. But how often does one blow his or her nose? Luckily, medical research on treating respiratory illnesses sheds light on this question. In a study on transmission of cold viruses, study participants blew their nose up to 24 times per person over 12 hours (2 nose blows/hour per person). According to Yale and Liu, the average length of a common cold is 7 days and the average adult has 2 to 4 colds a year. We assumed that the average person sleeps for 8 hours and is awake for 16 hours.

So for one average adult during respiratory colds: 2 nose blows/hour x 16 hours/day x 7 days/cold x 4 colds/year = 896 nose blows/year

But the colds in this scenario only last 28 days (7 day/year x 4 colds/year). What about the 337 other days of the year (365 days/year – 28 sick days/year)? Let’s assume that the average adult blows his or her nose once a day – 337 extra nose blows/year.

Nose Blows per Facial Tissue or Handkerchief

Standard sized paper facial tissue and cloth handkerchiefs differ in size. Handkerchiefs are 4 times as large in surface area. During respiratory illnesses, facial tissue and handkerchiefs are generally used intensively. We based the number of nose blows per tissue or handkerchief based on the relative surface area of the products: 2 nose blows/tissue and 8 nose blows/handkerchief.

  • Tissue use during cold: 896 nose blows/yr ÷ 2 nose blows/tissue = 448 tissues/yr
  • Handkerchiefs during cold: 896 nose blows/yr ÷ 8 nose blows/handkerchief = 112 handkerchiefs/yr

During everyday use, this LCA assumes that either facial tissue or handkerchiefs are used once.

  • Tissue, base use: 337 nose blows ÷ 1 nose blow/tissue = 337 tissues/yr
  • Handkerchief, base use: 337 nose blows ÷ 1 nose blow/handkerchief = 337 handkerchiefs/yr

In summary,

  • Total tissue use: 448 tissues/yr + 337 tissues/yr = 785 tissues/yr
  • Total handkerchief use: 112 handkerchiefs/yr + 337 handkerchiefs/yr = 449 handkerchiefs/yr

Handkerchief Reuse and Laundering

Although facial tissues are disposed after use, cloth handkerchiefs are reused. This LCA assumes that 30 handkerchiefs are in circulation and all 30 will be used and then washed as a fraction of the individual’s total laundry.

  • Handkerchief use: 449 handkerchiefs/yr ÷ 30 handkerchiefs in use = 14.97 times washed

In Summary:

Qualitative Functional Unit: the number of nose blows per surface area for an average American adult over 1 calendar year, encompassing the use pattern during 4 respiratory illnesses(896 nose blows) and daily use during well periods (337 nose blows).

Quantitative Functional Unit: 785 tissues/yr or 30 handkerchiefs washed 14.97 times/yr

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The Functional Unit: the Heart of all Life Cycle Assessments

Posted on October 25, 2012 by Eileen Ekstrom

At the American Center for Life Cycle Assessment LCAXII Conference recently held in Tacoma, Washington, Vee Subramanian and Eric Williams gave an interesting talk on “Uncertainty due to Inadequacy of Functional Units” in the Uncertainty 1 session. The functional unit, according to The Hitch Hiker’s Guide to LCA expresses “the function of studied products or service in quantitative terms and serves as basis of calculations. It serves as the reference unit for the study, normalizing all inputs and outputs to it, and enables comparisons between products with similar functions. In evaluating 8 different LCA standards and guidance protocols, Subramanian and Williams found that guidance on what should be included varied, but the majority of standards and protocols called for the functional unit to quantify the function of the product, magnitude of service, duration of service, and expected quality level. They noted the need for robust, unified guidelines and identified that current LCA standards do not require a description of how the functional unit was developed.

At Ecosystem Analytics, we believe a thorough and transparent description of the rationale behind the creation of the functional unit should be included in LCAs. In our recent LCA on handkerchief versus facial tissue use, we needed to define a functional unit to explore comparative use of the products, assuming that the products are only used to blow one’s nose.

The functional unit for the LCA was defined as: the number of nose blows per surface area for an average American adult over 1 calendar year, encompassing the use pattern during 4 respiratory illnesses(896 nose blows) and daily use during well periods (337 nose blows). This functional unit aimed to model use both during intensive use periods and light use periods over the year. Following the 4 quantities all functional units ought to incorporate…

  • Function: to blow noses
  • Magnitude of Service: Facial Tissue – respiratory illness: 2 nose blows/facial tissue; well periods: 1 nose blow/facial tissue. Handkerchief – respiratory illness: 8 nose blows/handkerchief; well periods: 1 nose blow/handkerchief
  • Duration of Service: 1 calendar year, encompassing the use pattern during 4 respiratory illnesses (896 nose blows) and daily use during well periods (337 nose blows). Facial Tissue — disposed after use. Handkerchief — 30 handkerchiefs in circulation, all handkerchiefs washed and dried as fraction of the individual’s regular laundry and reused.
  • Expected Quality Level: Facial Tissue — capable of containing 2 nose blows. Handkechief — capable of containing 8 nose blows and being washed 50 times prior to disposal.

In the next post, I will explore how functional units create the quantitative reference amount that serves as the basis for all LCA calculations.

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