EPA/600/R-06/060

May 2006 

LIFE CYCLE ASSESSMENT: 

PRINCIPLES AND PRACTICE

by 

Scientific Applications International Corporation (SAIC) 

11251 Roger Bacon Drive 

Reston, VA 20190 

Contract No. 68-C02-067 

Work Assignment 3-15 

Work Assignment Manager 

Mary Ann Curran 

Systems Analysis Branch 

National Risk Management Research Laboratory 

Cincinnati, Ohio 45268 

NATIONAL RISK MANAGEMENT RESEARCH LABORATORY 

OFFICE OF RESEARCH AND DEVELOPMENT 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

CINCINNATI, OHIO 45268
Notice 

The U.S. Environmental Protection Agency through its Office of Research and Development funded and 

managed the research described here under contract no. 68-C02-067 to Scientific Applications 

International Corporation (SAIC). It has been subjected to the Agency’s review and has been approved 

for publication as an EPA document. Mention of trade names or commercial products does not constitute 

endorsement or recommendation for use. Use of this methodology does not imply EPA approval of the 

conclusions of any specific life cycle assessment. 

ii
Foreword 

The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation's 

land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to 

formulate and implement actions leading to a compatible balance between human activities and the ability

of natural systems to support and nurture life. To meet this mandate, EPA's research program is providing 

data and technical support for solving environmental problems today and building a science knowledge 

base necessary to manage our ecological resources wisely, understand how pollutants affect our health, 

and prevent or reduce environmental risks in the future. 

The National Risk Management Research Laboratory (NRMRL) is the Agency's center for investigation 

of technological and management approaches for preventing and reducing risks from pollution that 

threaten human health and the environment. The focus of the Laboratory's research program is on 

methods and their cost-effectiveness for prevention and control of pollution to air, land, water, and 

subsurface resources; protection of water quality in public water systems; remediation of contaminated 

sites, sediments and ground water; prevention and control of indoor air pollution; and restoration of 

ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies that 

reduce the cost of compliance and to anticipate emerging problems. NRMRL's research provides 

solutions to environmental problems by: developing and promoting technologies that protect and improve 

the environment; advancing scientific and engineering information to support regulatory and policy

decisions; and providing the technical support and information transfer to ensure implementation of 

environmental regulations and strategies at the national, state, and community levels. 

This publication has been produced as part of the Laboratory's strategic long-term research plan. It is 

published and made available by EPA's Office of Research and Development to assist the user

community and to link researchers with their clients. 

 

Sally Gutierrez, Director

National Risk Management Research Laboratory 

iii
Abstract 

The following document provides an introductory overview of Life Cycle Assessment (LCA) and 

describes the general uses and major components of LCA. This document is an update and merger of two 

previous EPA documents on LCA (“Life Cycle Assessment: Inventory Guidelines and Principles,” 

EPA/600/R-92/245, and “LCA101” from the LCAccess, website, 

http://www.epa.gov/ORD/NRMRL/lcaccess). It presents the four basic stages of conducting an LCA: 

goal and scope definition, inventory analysis, impact assessment, and improvement analysis. The major 

stages in an LCA study are raw material acquisition, materials manufacture, production,

use/reuse/maintenance, and waste management. The system boundaries, assumptions, and conventions to 

be addressed in each stage are presented. This document is designed to be an educational tool for 

someone who wants to learn the basics of LCA, how to conduct an LCA, or how to manage someone 

conducting an LCA. Companies, federal facilities, industry organizations, or academia can benefit from

learning how to incorporate environmental performance based on the life cycle concept into their 

decision-making processes. This report was submitted in fulfillment of contract 68-C02-067 by Scientific 

Applications International Corporation (SAIC) under the sponsorship of the United States Environmental 

Protection Agency. This report covers a period from December 2005 to May 2006, and work was 

completed as of May 30, 2006. 

iv
Contents

Notice.................................................................................................................................. ii 

Foreword............................................................................................................................ iii 

Abstract.............................................................................................................................. iv 

Exhibits............................................................................................................................. vii 

Tables................................................................................................................................ vii 

Abbreviations................................................................................................................... viii 

Chapter 1 - Life Cycle Assessment......................................................................................1 

What is Life Cycle Assessment (LCA)?..........................................................................1 

What Are the Benefits of Conducting an LCA? ..............................................................3 

Limitations of Conducting an LCA .................................................................................5 

Chapter 2 - Goal Definition and Scoping ............................................................................7 

What is Goal Definition and Scoping? ............................................................................7 

How Does Goal Definition and Scoping Affect the LCA Process? ................................7 

Getting Started .................................................................................................................7 

Define the Goal(s) of the Project .................................................................................7 

Determine What Type of Information Is Needed to Inform the Decision-Makers......8 

Determine the Required Specificity.............................................................................9 

Determine How the Data Should Be Organized and the Results Displayed .............11 

Define the Scope of the Study ...................................................................................11 

Raw Materials Acquisition ....................................................................................11 

Manufacturing........................................................................................................12 

Use/Reuse/Maintenance.........................................................................................12 

Recycle/Waste Management..................................................................................12 

Determine the Ground Rules for Performing the Work.............................................18 

Chapter 3 - Life Cycle Inventory.......................................................................................19 

What is a Life Cycle Inventory (LCI)? ..........................................................................19 

Why Conduct an LCI? ...................................................................................................19 

What Do the Results of the LCI Mean?.........................................................................19 

Key Steps of a Life Cycle Inventory..............................................................................19 

Step 1: Develop a Flow Diagram...............................................................................19 

Step 2: Develop an LCI Data Collection Plan ...........................................................22 

Step 3: Collect Data ...................................................................................................28 

Inputs in the Product Life-Cycle Inventory Analysis.............................................29 

Outputs of the Product Life-Cycle Inventory Analysis ..........................................34 

Step 4: Evaluate and Document the LCI Results.......................................................44 

Chapter 4 - Life Cycle Impact Assessment........................................................................46 

What is a Life Cycle Impact Assessment (LCIA)?........................................................46 

Why Conduct an LCIA? ................................................................................................46 

What Do the Results of an LCIA Mean? .......................................................................47 

Key Steps of a Life Cycle Impact Assessment ..............................................................47 

Step 1: Select and Define Impact Categories.............................................................48 

Step 2: Classification .................................................................................................48 

Step 3: Characterization.............................................................................................50 

Step 4: Normalization ................................................................................................51 

Step 5: Grouping........................................................................................................52 

v
Step 6: Weighting ......................................................................................................52 

Step 7: Evaluate and Document the LCIA Results....................................................53 

Chapter 5 - Life Cycle Interpretation.................................................................................54 

What is Life Cycle Interpretation?.................................................................................54 

Comparing Alternatives Using Life Cycle Interpretation..............................................54 

Can I Select an Alternative Based Only on the Results of the LCA?............................54 

Key Steps to Interpreting the Results of the LCA .........................................................54 

Step 1: Identify Significant Issues .............................................................................55 

Step 2: Evaluate the Completeness, Sensitivity, and Consistency of the Data..........56 

Step 3: Draw Conclusions and Recommendations....................................................58 

Reporting the Results.....................................................................................................59 

Critical Review ..............................................................................................................59

Conclusion .....................................................................................................................60 

Appendix A - Sample Inventory Spreadsheet....................................................................63 

Appendix B - LCA and LCI Software Tools.....................................................................74 

Glossary .............................................................................................................................78

vi
Exhibits 

 Page

Exhibit 1-1. Life Cycle Stages 1 

Exhibit 1-2. Phases of an LCA 2 

Exhibit 2-1. Sample Life Cycle Stages for a Treatment Project 13 

Exhibit 2-2. Example Flow Diagram of a Hypothetical Bar Soap System 15 

Exhibit 3-1. Generic Unit Process 20 

Exhibit 3-2. Detailed System Flow Diagram for Bar Soap 21 

Exhibit 3-3. Allocating Resources and Environmental Burdens on a Mass Basis for a Product and 

Co-Product 38 

Exhibit 4-1. Commonly Used Life Cycle Impact Categories 49 

Exhibit 5-1. Relationship of Interpretation Steps with other Phases of LCA 55 

Exhibit 5-2. Examples of Checklist Categories and Potential Inconsistencies 58 

Tables 

 Page

Table 3-1. U.S. National Electrical Grid Fuel Mix for 2004 33 

vii
Abbreviations 

BOD biological oxygen demand

Btu British thermal unit 

CO carbon monoxide 

COD chemical oxygen demand 

CO2 carbon dioxide 

DQIs data quality indicators 

EPA United States Environmental Protection Agency

GWh gigawatt-hour 

ISO International Standards Organization (International Organization of Standardization) 

kWh kilowatt-hour

LCA life cycle assessment 

LCI life cycle inventory

LCIA life cycle impact assessment 

LCM life cycle management 

MJ megajoule 

NO2 nitrogen dioxide 

NRMRL National Risk Management Research Laboratory

REPA Resource and Environmental Profile Analysis 

SETAC Society of Environmental Toxicology and Chemistry

SO2 sulfur dioxide

TRACI Tool for the Reduction and Assessment of Chemical and other environmental Impacts 

TRI Toxics Release Inventory

VOCs volatile organic compounds

viii
Chapter 1 

Life Cycle Assessment 

What is Life Cycle Assessment (LCA)? 

As environmental awareness increases, industries and businesses are assessing how their activities affect 

the environment. Society has become concerned about the issues of natural resource depletion and 

environmental degradation. Many businesses have responded to this awareness by providing “greener” 

products and using “greener” processes. The environmental performance of products and processes has 

become a key issue, which is why some companies are investigating ways to minimize their effects on the 

environment. Many companies have found it advantageous to explore ways of moving beyond

compliance using pollution prevention strategies and environmental management systems to improve 

their environmental performance. One such tool is LCA. This concept considers the entire life cycle of a 

product (Curran 1996). 

Life cycle assessment is a “cradle-to-grave” approach for assessing industrial systems. “Cradle-to-grave” 

begins with the gathering of raw materials from the earth to create the product and ends at the point when

all materials are returned to the earth. LCA evaluates all stages of a product’s life from the perspective 

that they are interdependent, meaning that one operation leads to the next. LCA enables the estimation of 

the cumulative environmental impacts resulting from all stages in the product life cycle, often including

impacts not considered in more traditional analyses (e.g., raw material extraction, material transportation, 

ultimate product disposal, etc.). By including the impacts throughout the product life cycle, LCA 

provides a comprehensive view of the environmental aspects of the product or process and a more 

accurate picture of the true environmental trade-offs in product and process selection. 

The term “life cycle” refers to the major activities in the course of the product’s life-span from its 

manufacture, use, and maintenance, to its final disposal, including the raw material acquisition required to 

manufacture the product. Exhibit 1-1 illustrates the possible life cycle stages that can be considered in an 

LCA and the typical inputs/outputs measured. 

Exhibit 1-1. Life C ycle Stages (Source: EP A,1993)

Recycle / W aste M anagement

U se / Reuse / M aintenance

M anufacturing

Raw M aterials Acquisition

System Boundary

Inputs Ou tp uts

Raw

M aterials

Energy

A tm os pheric

Em is sions

Waterborne

Wastes

Solid

Wastes

Coproducts

O ther

Releases

1
Specifically, LCA is a technique to assess the environmental aspects and potential impacts associated 

with a product, process, or service, by: 

• Compiling an inventory of relevant energy and material inputs and environmental releases 

• Evaluating the potential environmental impacts associated with identified inputs and releases 

• Interpreting the results to help decision-makers make a more informed decision. 

The LCA process is a systematic, phased approach and consists of four components: goal definition and 

scoping, inventory analysis, impact assessment, and interpretation as illustrated in Exhibit 1-2:

1. Goal Definition and Scoping - Define and describe the product, process or activity. 

Establish the context in which the assessment is to be made and identify the boundaries 

and environmental effects to be reviewed for the assessment. 

2. Inventory Analysis - Identify and quantify energy, water and materials usage and 

environmental releases (e.g., air emissions, solid waste disposal, waste water discharges). 

3. Impact Assessment - Assess the potential human and ecological effects of energy, water, 

and material usage and the environmental releases identified in the inventory analysis. 

4. Interpretation - Evaluate the results of the inventory analysis and impact assessment to 

select the preferred product, process or service with a clear understanding of the 

uncertainty and the assumptions used to generate the results. 

Life Cycle A ssessm en t Fram ew or k

Goal

D efinitio n an d

Scope

In ven tory

A na ly sis

Impact

A ssessment

In terpretation

Exhibit 1-2 . Pha ses of a n LC A (So ur ce: IS O, 199 7 )

2
Life cycle assessment is unique because it encompasses all processes and environmental releases 

beginning with the extraction of raw materials and the production of energy used to create the product 

through the use and final disposition of the product. When deciding between two or more alternatives, 

LCA can help decision-makers compare all major environmental impacts caused by products, processes, 

or services. 

What Are the Benefits of Conducting an LCA? 

An LCA can help decision-makers select the product or process that results in the least impact to the 

environment. This information can be used with other factors, such as cost and performance data to select 

a product or process. LCA data identifies the transfer of environmental impacts from one media to 

another (e.g., eliminating air emissions by creating a wastewater effluent instead) and/or from one life 

cycle stage to another (e.g., from use and reuse of the product to the raw material acquisition phase). If an 

LCA were not performed, the transfer might not be recognized and properly included in the analysis 

because it is outside of the typical scope or focus of product selection processes.

LCA Helps to Avoid Shifting Environmental Problems from One Place to Another 

An LCA allows a decision maker to study an entire product system hence avoiding the suboptimization that could result if only a single process were the focus of the study. For example, when 

selecting between two rival products, it may appear that Option 1 is better for the environment 

because it generates less solid waste than Option 2. However, after performing an LCA it might be 

determined that the first option actually creates larger cradle-to-grave environmental impacts when 

measured across all three media (air, water, land) (e.g., it may cause more chemical emissions during 

the manufacturing stage). Therefore, the second product (that produces solid waste) may be viewed 

as producing less cradle-to-grave environmental harm or impact than the first technology because of 

its lower chemical emissions. 

This ability to track and document shifts in environmental impacts can help decision makers and 

managers fully characterize the environmental trade-offs associated with product or process alternatives. 

By performing an LCA, analysts can: 

• Develop a systematic evaluation of the environmental consequences associated with a given 

product. 

• Analyze the environmental trade-offs associated with one or more specific products/processes 

to help gain stakeholder (state, community, etc.) acceptance for a planned action. 

• Quantify environmental releases to air, water, and land in relation to each life cycle stage 

and/or major contributing process. 

• Assist in identifying significant shifts in environmental impacts between life cycle stages and 

environmental media. 

• Assess the human and ecological effects of material consumption and environmental releases to 

the local community, region, and world. 

• Compare the health and ecological impacts between two or more rival products/processes or 

identify the impacts of a specific product or process. 

• Identify impacts to one or more specific environmental areas of concern. 

3
4

A Brief History of Life-Cycle Assessment 

Life Cycle Assessment (LCA) had its beginnings in the 1960’s. Concerns over the limitations of raw 

materials and energy resources sparked interest in finding ways to cumulatively account for energy

use and to project future resource supplies and use. In one of the first publications of its kind, Harold 

Smith reported his calculation of cumulative energy requirements for the production of chemical 

intermediates and products at the World Energy Conference in 1963. 

Later in the 1960’s, global modeling studies published in The Limits to Growth (Meadows et al 1972) 

and A Blueprint for Survival (Goldsmith et al 1972) resulted in predictions of the effects of the 

world’s changing populations on the demand for finite raw materials and energy resources. The 

predictions for rapid depletion of fossil fuels and climatological changes resulting from excess waste 

heat stimulated more detailed calculations of energy use and output in industrial processes. During 

this period, about a dozen studies were performed to estimate costs and environmental implications of 

alternative sources of energy. 

In 1969, researchers initiated an internal study for The Coca-Cola Company that laid the foundation 

for the current methods of life cycle inventory analysis in the United States. In a comparison of 

different beverage containers to determine which container had the lowest releases to the 

environment and least affected the supply of natural resources, this study quantified the raw materials 

and fuels used and the environmental loadings from the manufacturing processes for each container. 

Other companies in both the United States and Europe performed similar comparative life cycle 

inventory analyses in the early 1970’s. At that time, many of the available sources were derived from

publicly-available sources such as government documents or technical papers, as specific industrial 

data were not available. 

The process of quantifying the resource use and environmental releases of products became known as 

a Resource and Environmental Profile Analysis (REPA), as practiced in the United States. In Europe, 

it was called an Ecobalance. With the formation of public interest groups encouraging industry to 

ensure the accuracy of information in the public domain, and with the oil shortages in the early 

1970’s, approximately 15 REPAs were performed between 1970 and 1975. Through this period, a 

protocol or standard research methodology for conducting these studies was developed. This multistep methodology involves a number of assumptions. During these years, the assumptions and 

techniques used underwent considerable review by EPA and major industry representatives, with the 

result that reasonable methodologies were evolved. 

From 1975 through the early 1980’s, as interest in these comprehensive studies waned because of the 

fading influence of the oil crisis, environmental concerns shifted to issues of hazardous and 

household waste management. However, throughout this time, life cycle inventory analysis 

continued to be conducted and the methodology improved through a slow stream of about two studies 

per year, most of which focused on energy requirements. During this time, European interest grew 

with the establishment of an Environment Directorate (DG X1) by the European Commission. 

European LCA practitioners developed approaches parallel to those being used in the USA. Besides 

working to standardize pollution regulations throughout Europe, DG X1 issued the Liquid Food 

Container Directive in 1985, which charged member companies with monitoring the energy and raw 

materials consumption and solid waste generation of liquid food containers. 
When solid waste became a worldwide issue in 1988, LCA again emerged as a tool for analyzing 

environmental problems. As interest in all areas affecting resources and the environment grows, the 

methodology for LCA is again being improved. A broad base of consultants and researchers across 

the globe has been further refining and expanding the methodology. The need to move beyond the 

inventory to impact assessment has brought LCA methodology to another point of evolution (SETAC 

1991; SETAC 1993; SETAC 1997). 

In 1991, concerns over the inappropriate use of LCAs to make broad marketing claims made by

product manufacturers resulted in a statement issued by eleven State Attorneys General in the USA 

denouncing the use of LCA results to promote products until uniform methods for conducting such 

assessments are developed and a consensus reached on how this type of environmental comparison 

can be advertised non-deceptively. This action, along with pressure from other environmental 

organizations to standardize LCA methodology, led to the development of the LCA standards in the 

International Standards Organization (ISO) 14000 series (1997 through 2002). 

In 2002, the United Nations Environment Programme (UNEP) joined forces with the Society of 

Environmental Toxicology and Chemistry (SETAC) to launch the Life Cycle Initiative, an 

international partnership. The three programs of the Initiative aim at putting life cycle thinking into 

practice and at improving the supporting tools through better data and indicators. The Life Cycle 

Management (LCM) program creates awareness and improves skills of decision-makers by producing 

information materials, establishing forums for sharing best practice, and carrying out training

programs in all parts of the world. The Life Cycle Inventory (LCI) program improves global access to 

transparent, high quality life cycle data by hosting and facilitating expert groups whose work results 

in web-based information systems. The Life Cycle Impact Assessment (LCIA) program increases the 

quality and global reach of life cycle indicators by promoting the exchange of views among experts 

whose work results in a set of widely accepted recommendations.

Limitations of Conducting an LCA 

Performing an LCA can be resource and time intensive. Depending upon how thorough an LCA the user 

wishes to conduct, gathering the data can be problematic, and the availability of data can greatly impact 

the accuracy of the final results. Therefore, it is important to weigh the availability of data, the time 

necessary to conduct the study, and the financial resources required against the projected benefits of the 

LCA. 

LCA will not determine which product or process is the most cost effective or works the best. Therefore, 

the information developed in an LCA study should be used as one component of a more comprehensive 

decision process assessing the trade-offs with cost and performance, e.g., Life Cycle Management. 

Life Cycle Management 

Life Cycle Management (LCM) is the application of life cycle thinking to modern business practice, 

with the aim to manage the total life cycle of an organization’s product and services toward more 

sustainable consumption and production (Jensen and Remmen 2004). It is an integrated framework 

of concepts and techniques to address environmental, economic, technological, and social aspects of 

products, services, and organizations. LCM, as any other management pattern, is applied on a 

voluntary basis and can be adapted to the specific needs and characteristics of individual 

organizations (SETAC 2004). 

5
There are a number of ways to conduct Life Cycle Impact Assessment. While the methods are typically

scientifically-based, the complexity of environmental systems has led to the development of alternative 

impact models. Chapter 4 expands on this. 

As mentioned earlier, an LCA can help identify potential environmental tradeoffs. However, 

converting the impact results to a single score requires the use of value judgments, which must 

be applied by the commissioner of the study or the modeler. This can be done in different ways 

such as through the use of an expert panel, but it cannot be done based solely on natural science. 

6
Chapter 2 

Goal Definition and Scoping 

What is Goal Definition and Scoping? 

Goal definition and scoping is the phase of the LCA process that defines the purpose and method of 

including life cycle environmental impacts into the decision-making process. In this phase, the following 

items must be determined: the type of information that is needed to add value to the decision-making 

process, how accurate the results must be to add value, and how the results should be interpreted and 

displayed in order to be meaningful and usable. 

How Does Goal Definition and Scoping Affect the LCA Process? 

The LCA process can be used to determine the potential environmental impacts from any product, 

process, or service. The goal definition and scoping of the LCA project will determine the time and 

resources needed. The defined goal and scope will guide the entire process to ensure that the most 

meaningful results are obtained. Every decision made throughout the goal definition and scoping phase 

impacts either how the study will be conducted, or the relevance of the final results. The following 

section identifies the decisions that must be made at the beginning of the LCA study and the impact of 

these decisions on the LCA process. 

Getting Started 

The following six basic decisions should be made at the beginning of the LCA process to make effective 

use of time and resources: 

1. Define the Goal(s) of the Project 

2. Determine What Type of Information Is Needed to Inform the Decision-Makers 

3. Determine the Required Specificity

4. Determine How the Data Should Be Organized and the Results Displayed 

5. Define the Scope of the Study

6. Determine the Ground Rules for Performing the Work

Each decision and its associated impact on the LCA process are explained below in further detail. 

Define the Goal(s) of the Project 

LCA is a versatile tool for quantifying the overall (cradle-to-grave) environmental impacts from a 

product, process, or service. The primary goal is to choose the best product, process, or service with the 

least effect on human health and the environment. Conducting an LCA also can help guide the 

development of new products, processes, or activities toward a net reduction of resource requirements and 

emissions. There may also be secondary goals for performing an LCA, which would vary depending on 

the type of project. The following are examples of possible applications for life-cycle inventories, most 

of which require some level of impact assessment in addition to the inventory: 

• Support broad environmental assessments - The results of an LCA are valuable in understanding the 

relative environmental burdens resulting from evolutionary changes in given processes, products, or 

packaging over time; in understanding the relative environmental burdens between alternative 

processes or materials used to make, distribute, or use the same product; and in comparing the 

environmental aspects of alternative products that serve the same use. 

• Establish baseline information for a process - A key application of an LCA is to establish a baseline 

of information on an entire system given current or predicted practices in the manufacture, use, and 

disposal of the product or category of products. In some cases, it may suffice to establish a baseline 

for certain processes associated with a product or package. This baseline would consist of the energy 

7
and resource requirements and the environmental loadings from the product or process systems that 

are analyzed. The baseline information is valuable for initiating improvement analysis by applying 

specific changes to the baseline system.

• Rank the relative contribution of individual steps or processes - The LCA results provide detailed 

data regarding the individual contributions of each step in the system studied to the total system. 

The data can provide direction to efforts for change by showing which steps require the most energy

or other resources, or which steps contribute the most pollutants. This application is especially

relevant for internal industry studies to support decisions on pollution prevention, resource 

conservation, and waste minimization opportunities. 

• Identify data gaps - The performance of an LCA for a particular system reveals areas in which data 

for particular processes are lacking or are of uncertain or questionable quality. Inventory followed 

by impact assessment aids in identifying areas where data augmentation is appropriate for both 

stages. 

• Support public policy - For the public policymaker, LCA can help broaden the range of 

environmental issues considered in developing regulations or setting policies. 

• Support product certification - Product certifications have tended to focus on relatively few criteria. 

LCA, only when applied using appropriate impact assessment, can provide information on the

individual, simultaneous effects of many product attributes. 

• Provide information and direction to decision-makers - LCA can be used to inform industry,

government, and consumers on the tradeoffs of alternative processes, products, and materials. The 

data can give industry direction in decisions regarding production materials and processes and create 

a better informed public regarding environmental issues and consumer choices. 

• Guide product and process development - LCA can help guide manufacturers in the development of 

new products, processes, and activities toward a net reduction of resource requirements and 

emissions. 

Determine What Type of Information Is Needed to Inform the Decision-Makers 

LCA can help answer a number of important questions. Identifying the questions that the decisionmakers care about will help define the study parameters. Some examples include: 

• What is the impact to particular interested parties and stakeholders?

• Which product or process causes the least environmental impact (quantifiably) overall or in each 

stage of its life cycle?

• How will changes to the current product/process affect the environmental impacts across all life 

cycle stages?

• Which technology or process causes the least amount of acid rain, smog formation, or damage to 

local trees (or any other impact category of concern)? 

• How can the process be changed to reduce a specific environmental impact of concern (e.g., global 

warming)? 

Once the appropriate questions are identified, it is important to determine the types of information needed 

to answer the questions. 

8
Attributional LCA versus Consequential LCA 

During a workshop held in 2003, specifically on life cycle inventory for electricity generation,

participants recognized the need to choose an allocation method depending considerably upon 

whether the life cycle assessment is being performed from an attributional or a consequential point of 

view. The term “attributional life cycle assessment” was defined as an attempt to answer “how are 

things (i.e. pollutants, resources, and exchanges among processes) flowing within the chosen 

temporal window?” while “consequential life cycle assessment” attempts to answer “how will flows 

beyond the immediate system change in response to decisions?” For example, an attributional LCA 

would examine the consequences of using green power compared to conventional sources. A 

consequential LCA would consider the consequences of this choice in that only a certain amount of 

green power may be available to customers, causing some customers to buy conventional energy

once the supply of greener sources was gone. The choice between conducting an attributional or a 

consequential assessment depends on the stated goal of the study (Curran, Mann, & Norris 2005).

Determine the Required Specificity 

At the outset of every study, the level of specificity must be decided. In some cases, this level will be 

obvious from the application or intended use of the information. In other instances, there may be several 

options to choose from, ranging from a completely generic study to one that is product-specific in every

detail. Most studies fall somewhere in between. 

An LCA can be envisioned as a set of linked activities that describe the creation, use, and ultimate 

disposal of the product or material of interest. At each life cycle stage, the analyst should begin by

answering a series of questions: Is the product or system in the life cycle stage specific to one company or 

manufacturing operation? Or does the product or system represent common products or systems generally

found in the marketplace and produced or used by a number of companies? 

Such questions help determine whether data collected for the inventory should be specific to one 

company or manufacturing facility, or whether the data should be more general to represent common 

industrial practices. 

The appropriate response to these questions often rests on whether the life cycle is being performed for 

internal organizational use or for a more public purpose. Accessibility to product- or facility-specific data 

may also be a factor. A company may be more interested in examining its own formulation and assembly

operations, whereas an industry group or government agency may be more interested in characterizing 

industry-wide practice. LCAs can have a mix of product-specific and industry-average information. For 

example, a cereal manufacturer performing an analysis of using recycled paperboard for its cereal boxes 

might apply the following logic. For operations conducted by the manufacturer, such as box printing, set 

up, and filling, data specific to the product would be obtained because average data for printing and filling 

across the cereal industry or for industry in general would not be as useful. 

Stepping back one stage to package manufacturing, the cereal manufacturer is again faced with the 

specificity decision. The data could be product-specific, or generic data for the manufacturing stage 

could be used. The product-specific approach has these advantages: the aggregated data reflect the 

operations of the specific paper mills supplying the recycled board, and the energy and resources 

associated with this stage can be compared with those of similar specificity for the filling, packaging, and 

distribution stage. A limitation of this option is the additional cost and time associated with collecting 

9
product-specific data from the mills and the level of cooperation that needs to be established with the 

upstream vendors. Long-term confidentiality agreements with vendors may also represent unacceptable 

burdens compared with the value added by the more specific data.

Determine the Data Requirements 

The required level of data accuracy for the project depends on the use of the final results and 

the intended audience (i.e. will the results be used to support decision-making in an internal 

process or in a public forum?). For example, if the intent is to use the results in a public 

forum to support product/process selection to a local community or regulator, then estimated 

data or best engineering judgment for the primary material, energy, and waste streams may

not be sufficiently accurate to justify the final conclusions. In contrast, if the intent of 

performing the LCA is for internal decision-making purposes only, then estimates and best 

engineering judgment may be applied more frequently. This may reduce the overall cost and 

time required to perform the LCA, as well as enable completion of the study in the absence of

precise, first-hand data. 

In addition to the intended audience, the required level of data accuracy could be based on 

the criticality of the decision to be made and the amount of money involved in the decision. 

The alternative decision path, using industrial average data for making recycled paperboard, has a parallel 

mix of advantages and limitations. Use of average, or generic, data may be advantageous for a 

manufacturer considering use of recycled board for which no current vendors have been identified. If the 

quality of these average data can be determined and is acceptable, their use may be preferable. The 

limitation is that data from this stage may be less comparable to that of more product-specific stages. 

This limitation is especially important in studies that mix product-specific and more general analyses in 

the same life-cycle stage. For example, comparing virgin and recycled paperboard using product-specific 

data for one material and generic data for the other could be problematic. 

Another limitation is that the generic data may mask technologies that are more environmentally 

burdensome. Even with some measure of data variability, a decision to use a particular material made on 

the basis of generic data may misrepresent true loadings of the actual suppliers. Opportunities to identify 

specific facilities operating in a more environmentally sound manner are lost. Generic data do not 

necessarily represent industry-wide practices. The extent of representation depends on the quality and 

coverage of the available data and is impossible to state as a general rule. 

It is recommended that the level of specificity be very clearly defined and communicated so that readers 

are more able to understand the differences in the final results. Before initiating data collection and 

periodically throughout the study, the analyst should revisit the specificity decision to determine if the 

approach selected for each stage remains valid in view of the intended use. 

Foreground and Background Data 

An important element in LCA practice is the distinction that has been made between foreground and 

background data. The foreground system refers to the system of primary concern. The background 

system delivers energy and materials to the foreground system as aggregated data sets in which 

individual plants and operations are not identified. The selection of foreground or background data 

decides if either marginal or average data are to be used. 

10
Determine How the Data Should Be Organized and the Results Displayed 

LCA practitioners define how data should be organized in terms of a functional unit that appropriately

describes the function of the product or process being studied. Careful selection of the functional unit to

measure and display the LCA results will improve the accuracy of the study and the usefulness of the 

results. 

When an LCA is used to compare two or more products, the basis of comparison should be equivalent 

use, i.e., each system should be defined so that an equal amount of product or equivalent service is 

delivered to the consumer. In the handwashing example, if bar soap were compared to liquid soap, the 

logical basis for comparison would be an equal number of handwashings. Another example of equivalent 

use would be in comparing cloth diapers to disposable diapers. One type of diaper may typically be 

changed more frequently than the other, and market/use studies show that often cloth diapers are doubled, 

whereas disposables are not. Thus, throughout a day, more cloth diapers will be used. In this case, a 

logical basis for comparison between the systems would be the total number of diapers used over a set 

period of time. 

Equivalent use for comparative studies can often be based on volume or weight, particularly when the 

study compares packaging for delivery of a specific product. A beverage container study might consider 

1,000 liters of beverage as an equivalent use basis for comparison, because the product may be delivered 

to the consumer in a variety of different-size containers having different life-cycle characteristics. 

An Example of Selecting a Functional Unit 

An LCA study comparing two types of wall insulation to determine environmental preferability must 

be evaluated on the same function, the ability to decrease heat flow. Six square feet of four-inch 

thick insulation Type A is not necessarily the same as six square feet of four-inch thick insulation 

Type B. Insulation type A may have an R factor equal to ten, whereas insulation type B may have an 

R factor equal to 20. Therefore, type A and B do not provide the same amount of insulation and 

cannot be compared on an equal basis. If Type A decreases heat flow by 80 percent, you must 

determine how thick Type B must be to also decrease heat flow by 80 percent. 

Define the Scope of the Study 

As Chapter 1 explained, an LCA includes all four stages of a product or process life cycle: raw material 

acquisition, manufacturing, use/reuse/maintenance, and recycle/waste management. These product stages 

are explained in more detail below. To determine whether one or all of the stages should be included in 

the scope of the LCA, the following must be assessed: the goal of the study, the required accuracy of the 

results, and the available time and resources. Exhibit 2-1 provides an example of life cycle stages that 

could be included in a project related to treatment technologies. 

Raw Materials Acquisition 

The life cycle of a product begins with the removal of raw materials and energy sources from the earth. 

For instance, the harvesting of trees or the mining of nonrenewable materials would be considered raw 

materials acquisition. Transportation of these materials from the point of acquisition to the point of 

processing is also included in this stage. 

11
Manufacturing 

During the manufacturing stage, raw materials are transformed into a product or package. The product or 

package is then delivered to the consumer. The manufacturing stage consists of three steps: materials 

manufacture, product fabrication, and filling/packaging/distribution.

Materials Manufacture - The materials manufacture step involves the activities that convert raw 

materials into a form that can be used to fabricate a finished product. 

Product Fabrication - The product fabrication step takes the manufactured material and processes it 

into a product that is ready to be filled or packaged. 

Filling/Packaging/Distribution - This step finalizes the products and prepares them for shipment. It 

includes all of the manufacturing and transportation activities that are necessary to fill, package, and 

distribute a finished product. Products are transported either to retail outlets or directly to the

consumer. This stage accounts for the environmental effects caused by the mode of transportation, 

such as trucking and shipping. 

Use/Reuse/Maintenance 

This stage involves the consumer’s actual use, reuse, and maintenance of the product. Once the product is 

distributed to the consumer, all activities associated with the useful life of the product are included in this 

stage. This includes energy demands and environmental wastes from both product storage and 

consumption. The product or material may need to be reconditioned, repaired or serviced so that it will 

maintain its performance. When the consumer no longer needs the product, the product will be recycled 

or disposed. 

Recycle/Waste Management 

The recycle/waste management stage includes the energy requirements and environmental wastes 

associated with disposition of the product or material.

12
Each step in the life cycle of a product, package, or material can be categorized within one and only one 

of these life-cycle stages. Each step or process can be viewed as a subsystem of the total product system. 

Viewing the steps as subsystems facilitates data gathering for the inventory of the system as a whole. The 

boundaries of subsystems are defined by life-cycle stage categories in Chapter 3. The rest of this chapter 

deals with defining boundaries of the whole product system. Many decisions must be made in defining 

the specific boundaries of each system. 

Product systems are easier to define if the sequence of operations associated with a product or material is 

broken down into primary and secondary categories. The primary, or zero-order, sequence of activities 

directly contributes to making, using, or disposing of the product or material. The secondary category

includes auxiliary materials or processes that contribute to making or doing something that in turn is in 

the primary activity sequence. Several tiers of auxiliary materials or processes may extend further and 

13
further from the main sequence. In setting system boundaries, the analyst must decide where the analysis 

will be limited and be very clear about the reasons for the decision. The following questions are useful in 

setting and describing specific system boundaries: 

• Does the analysis need to cover the entire life cycle of the product? A theoretically complete lifecycle system would start with all raw materials and energy sources in the earth and end with all 

materials back in the earth or at least somewhere in the environment but not part of the system. Any

system boundary different from this represents a decision by the analyst to limit it in some way. 

Understanding the possible consequences of such decisions is important for evaluating tradeoffs 

between the ability of the resulting inventory to thoroughly address environmental attributes of the 

product constraints on cost, time, or other factors that may argue in favor of a more limited boundary. 

Too limited a boundary may exclude consequential activities or elements. 

Depending on the goal of the study, it is possible to exclude certain stages or activities and still 

address the issues for which the life-cycle assessment is being performed. For example, it may be 

possible to exclude the acquisition of raw materials without affecting the results. Suppose a company

wishes to perform an LCA to evaluate alternative drying systems for formulating a snack food 

product. If the technologies are indifferent to the feedstock, it is possible to assume the raw materials 

acquisition stage will be identical for all options. If the decision will be based on selecting a drying 

system with lower energy use or environmental burdens, it may be acceptable to analyze such a 

limited system. However, with this system boundary, the degree of absolute differences in the overall 

system energy or environmental impact cannot be determined. The difference in the product 

manufacturing stage may represent a minor component of the total system. Therefore, statements 

about the total system cannot be made. 

• What will be the basis of use for the product or material? Is the study intended to compare different 

product systems? If the products or processes are used at different rates, packaged in varying 

quantities, or come in different sizes, how can one accurately compare them? Can equivalent use 

ratios be developed? Should market shares be considered to estimate proportionate burden form each 

product in a given category? Is the study intended to compare service systems? Are the service 

functions clearly defined so that the input and outputs are properly proportioned? 

• What ancillary materials or chemicals are used to make or package the products or run the 

processes? Might these ancillary materials or chemicals contribute more than a minor fraction of the 

energy or emissions of the system to be analyzed? How do they compare by weight with other 

materials and chemicals in the product systems?

• In a comparative analysis, are any extra products required to allow one product to deliver equivalent 

or similar performance to another? Are any extra materials or services required for one service to be 

functionally equivalent to another or to a comparable product?

Exhibit 2-2 shows an example of setting system boundaries for a product baseline analysis for a 

hypothetical bar soap system. Tallow is the major raw material for soap production, and its primary raw 

material source is the grain fed to cattle. Production of paper for packaging soap is also included. The 

fate of both the soap and its packaging end the life cycle of this system. Minor inputs could include, for 

example, the energy required to fabricate the tires on the combine used to plant and harvest the grain. 

14
Exhibit 2-2. Example Flow Diagram of a Hypothetical Bar Soap System 

In an LCA to create a baseline for future product development or improvement, the unit upon which the 

analysis is performed can be almost anything that produces internally consistent data. In the bar soap 

example, one possible usage unit could be a single bar. However, if the product packaging were being 

analyzed at the same time, it would be important for consistency to consider packaging in different 

amounts such as single bars, three-packs, and so on. 

If the LCA were intended to analyze whether bar soap should be manufactured using an animal-derived or 

vegetable-derived raw material source, the system boundaries and units of analysis would be more 

complicated. First, the system flow diagram would have to be expanded to include the growing, 

harvesting, and processing steps for the alternative feedstock. Then the performance of the finished 

product would have to be considered. Do the options result in a bar that gets used up at different rates 

when one material or the other is chosen? If this were the case, a strict comparison of equal-weight bars 

would not be appropriate. 

Suppose an analyst wants to compare bar soap made from tallow with a liquid hand soap made from

synthetic ingredients. Because the two products have different raw material sources (cattle and 

petroleum), the analysis should begin with the raw materials acquisition step. Because the two products 

are packaged differently and may have different chemical formulas, the materials manufacture and 

packaging steps would need to be included. Consumer use and waste management options also should be 

examined because the different formulae could result in varying usage patterns. Thus for this 

comparative analysis, the analyst would have to inventory the entire life cycle of the two products. 

15
Again, the analyst must determine the basis of comparison between the systems. Because one soap is a 

solid and the other is a liquid, each with different densities and cleansing abilities per unit amount, it

would not make sense to compare them based on equal weights or volumes. The key factor is how much 

of each is used in one handwashing to provide an equivalent level of function or service. An acceptable 

basis for comparison might be equal numbers of handwashings. Because these two products may be used 

at different rates, it would be important to find data that give an equivalent use ratio. For example, a 

research lab study may show that five cubic millimeters of bar soap and ten cubic millimeters of liquid 

soap are used per handwashing. If the basis for comparison were chosen at 1,000 handwashings, 5,000 

cubic millimeters of bar soap would be compared to 10,000 cubic millimeters of liquid soap. Thus, the 

equivalent use ratio is 1 to 2. 

Because the two soap product types are packaged in different quantities and materials, the analyst would 

need to include packaging in the system. Contributions of extra ingredients, such as perfumes, might also 

be considered. The analyst may or may not find that any extra raw materials are used in one or the other. 

Soaps typically must meet a minimum standard performance level. 

However, if the liquid hand soap also had a skin moisturizer in its formula, the analyst would need to 

include a moisturizing lotion product in the boundary of the bar soap system on two conditions. The first 

condition would apply if the environmental issues associated with this component were germane to the 

purpose of the LCA. The second condition, which is not as clear-cut, is if there is actual value received 

by the consumer from inclusion of the moisturizer. If market studies indicate that consumers purchase the 

product in preference to an identical product without a moisturizer, or if they subsequently use a 

moisturizing lotion after using a non-moisturizing soap, then equivalent use would entail including the 

separate moisturizing lotion. Including the moisturizing lotion would move the comparison beyond

equivalent handwashing to equivalent hand washing and skin moisturizing. 

In defining system boundaries, it is important to include every step that could affect the overall 

interpretation or ability of the analysis to address the issues for which it is being performed. Only in 

certain well-defined instances can life-cycle elements such as raw materials acquisition or waste 

management be excluded. In general, only when a step is exactly the same in process, materials, and 

quantity in all alternatives considered, can that step be excluded from the system. In addition, the 

framework for the comparison must be recognized as relative because the total system values exclude 

certain contributions. This rule is especially critical for LCAs used in public forums rather than for 

internal company decision making. For example, a company comparing alternative processes for 

producing one petrochemical product may not need to consider the use and disposal of the product if the 

final composition is identical. The company may also find that each process uses exactly the same 

materials in the same amounts per unit of product output. Therefore, the company may consider the 

materials it uses as having no impact in the study results. Another example is a filling operation for 

bottles. A company interested in using alternative materials for its bottles while maintaining the same 

size and shape may not need to include filling bottles. However, if the original bottles were compared to 

boxes of a different size and shape, the filling step would need to be included. 

16
Applications of System Expansion 

System expansion broadens the system boundaries and introduces a new functional unit to make the 

two systems being compared equal in scope. Take for example Product A which is produced by

Process AB along with co-product B. Product A is to be compared to Product C which is the only

product to be produced by Process C. Using system expansion, an alternative way to produce 

Product B is added to Process C. The comparison is now between Process AB and Process C plus 

Process D. 

Another approach to applying system expansion is by subtracting the environmental burdens of an 

alternative way of producing Product B (using the same example as before) so that only Product A is 

compared to Product C. This approach is also referred to as the avoided burden approach since it is 

reasoned that the production of any alternative products is no longer needed and the resultant 

environmental burdens are avoided. The environmental burdens allocated to the product of interest 

are then calculated as the burdens from the process minus the burdens of an alternative co-product. 

For example, a process that also generates heat, such as a refrigerator, offsets some of the need for 

space heating which would be supplied by some other source. The emissions avoided through this 

reduced demand might include emissions such as carbon dioxide, sulfur dioxide, nitrogen oxide, 

carbon monoxide and hydrocarbons that are typically emitted from power generation facilities. This 

process can result in negative accounting of burdens if the subtracted releases do not occur in the 

main product system. 

Resource constraints for the life-cycle inventory may be considerations in defining the system boundaries, 

but in no case should the scientific basis of the study be compromised. The level of detail required to 

perform a thorough inventory depends on the size of the system and the purpose of the study. In a large 

system encompassing several industries, certain details may not be significant contributors given the 

defined intent of the study. These details may be omitted without affecting the accuracy or application of 

the results. However, if the study has a very specific focus, such as a manufacturer comparing alternative 

processes or materials for inks used in packaging, it would be important to include chemicals used in very 

small amounts. 

Additional areas to consider in setting boundaries include the manufacture of capital equipment, energy

and emissions associated with personnel requirements, and precombustion impacts for fuel usage. These 

are discussed later. 

After the boundaries of each system have been determined, a system flow diagram, as shown in Exhibit 2-

2, can be developed to depict the system and direct efforts to gather data for the life cycle inventory.

17
Each system step should be represented individually in the diagram, including the production steps for 

ancillary inputs or outputs such as chemicals and packaging. 

Determine the Ground Rules for Performing the Work 

Prior to moving on to the inventory analysis phase it is important to define some of the logistical 

procedures for the project. 

1. Documenting Assumptions - All assumptions or decisions made throughout the entire project must be 

reported along side the final results of the LCA project. If assumptions are omitted, the final results 

may be taken out of context or easily misinterpreted. As the LCA process advances from phase to 

phase, additional assumptions and limitations to the scope may be necessary to accomplish the 

project with the available resources. 

2. Quality Assurance Procedures - Quality assurance procedures are important to ensure that the goal 

and purpose for performing the LCA will be met at the conclusion of the project. The level of 

quality assurance procedures employed for the project depends on the available time and resources 

and how the results will be used. If the results are to be used in a public forum, a formal review 

process is recommended. A formal review process may consist of internal and external review by 

LCA experts and/or a review by interested parties to better ensure their support of the final results. If 

the results are to be used for internal decision-making purposes only, then an internal reviewer who 

is familiar with LCA practices and is not associated with the LCA study may effectively meet the 

quality assurance goals. It is recommended that a formal statement from the reviewer(s) 

documenting their assessment of each phase of the LCA process be included with the final report for 

the project. 

3. Reporting Requirements - Defining “up front” how the final results should be documented and 

exactly what should be included in the final report helps to ensure that the final product meets the 

appropriate expectations. When reporting the final results, or results of a particular LCA phase, it is 

important to thoroughly describe the methodology used in the analysis. The report should explicitly

define the systems analyzed and the boundaries that were set. The basis for comparison among 

systems and all assumptions made in performing the work should be clearly explained. The 

presentation of results should be consistent with the purpose of the study. The results should not be 

oversimplified solely for the purposes of presentation. 

18
Chapter 3 

Life Cycle Inventory 

What is a Life Cycle Inventory (LCI)? 

A life cycle inventory is a process of quantifying energy and raw material requirements, atmospheric 

emissions, waterborne emissions, solid wastes, and other releases for the entire life cycle of a product, 

process, or activity.

Why Conduct an LCI? 

In the life cycle inventory phase of an LCA, all relevant data is collected and organized. Without an LCI, 

no basis exists to evaluate comparative environmental impacts or potential improvements. The level of 

accuracy and detail of the data collected is reflected throughout the remainder of the LCA process. 

Life cycle inventory analyses can be used in various ways. They can assist an organization in comparing 

products or processes and considering environmental factors in material selection. In addition, inventory 

analyses can be used in policy-making, by helping the government develop regulations regarding resource 

use and environmental emissions. 

What Do the Results of the LCI Mean? 

An inventory analysis produces a list containing the quantities of pollutants released to the environment 

and the amount of energy and material consumed. The results can be segregated by life cycle stage, 

media (air, water, and land), specific processes, or any combination thereof. 

Key Steps of a Life Cycle Inventory 

EPA’s 1993 document, “Life-Cycle Assessment: Inventory Guidelines and Principles,” and 1995 

document, “Guidelines for Assessing the Quality of Life Cycle Inventory Analysis,” provide the 

framework for performing an inventory analysis and assessing the quality of the data used and the results. 

The two documents define the following four steps of a life cycle inventory:

1. Develop a flow diagram of the processes being evaluated. 

2. Develop a data collection plan. 

3. Collect data. 

4. Evaluate and report results. 

Each step is summarized below. 

Step 1: Develop a Flow Diagram

A flow diagram is a tool to map the inputs and outputs to a process or system. The “system” or “system

boundary” varies for every LCA project. The goal definition and scoping phase establishes initial 

boundaries that define what is to be included in a particular LCA; these are used as the system boundary

for the flow diagram. Unit processes inside of the system boundary link together to form a complete life 

cycle picture of the required inputs and outputs (material and energy) to the system. Exhibit 3-1 

illustrates the components of a generic unit process within a flow diagram for a given system boundary. 

19
Exhibit 3-1. Generic Unit Process

Transportation

Materials/Parts/Components Finished Parts/Components Process

Non-Hazardous Material Outputs Hazardous Material Outputs

Electricity

Water

Gas

The more complex the flow diagram, the greater the accuracy and utility of the results. Unfortunately, 

increased complexity also means more time and resources must be devoted to this step, as well as the data 

collecting and analyzing steps. 

Flow diagrams are used to model all alternatives under consideration (e.g., both a baseline system and 

alternative systems). For a comparative study, it is important that both the baseline and alternatives use 

the same system boundary and are modeled to the same level of detail. If not, the accuracy of the results 

may be skewed. 

For data-gathering purposes it is appropriate to view the system as a series of subsystems. A “subsystem” 

is defined as an individual step or process that is part of the defined production system. Some steps in the 

system may need to be grouped into a subsystem due to lack of specific data for the individual steps. For 

example, several steps may be required in the production of bar soap from tallow (see Exhibit 3-2). 

However, these steps may all occur within the same facility, which may not be able to or need to break 

data down for each individual step. The facility could however, provide data for all the steps together, so 

the subsystem boundary would be drawn around the group of soap production steps and not around each 

individual one. 

Each subsystem requires inputs of materials and energy; requires transportation of product produced; and 

has outputs of products, co-products, atmospheric emissions, waterborne wastes, solid wastes, and 

possibly other releases. For each subsystem, the inventory analyst should describe materials and energy

sources used and the types of environmental releases. The actual activities that occur should also be 

described. Data should be gathered for the amounts and kinds of material inputs and the types and 

quantities of energy inputs. The environmental releases to air, water, and land should be quantified by

type of pollutant. Data collected for an inventory should always be associated with a quality measure. 

Although formal data quality indicators (DQIs) such as accuracy, precision, representativeness, and 

20
completeness are strongly preferred, a description of how the data were generated can be useful in 

judging quality. 

Exhibit 3-2. Detailed System Flow Diagram for Bar Soap 

Co-products from the process should be identified and quantified. Co-products are process outputs that 

have value, i.e., those not treated as wastes. The value assigned to a co-product may be a market value 

(price) or may be imputed. In performing co-product allocation, some means must be found to

objectively assign the resource use, energy consumption, and emissions among the co-products, because 

there is not a physical or chemical way to separate the activities that produce them. Generally, allocation 

should allow technically sound inventories to be prepared for products or materials using any particular 

output of a process independently and without overlap of the other outputs. 

21
In the meat packing step of the bar soap example, several co-products could be identified: meat, tallow, 

bone meal, blood meal, and hides. Other examples of co-products are the trim scraps and off-spec 

materials from a molded plastic plate fabricator. If the trim scraps and off-spec materials are used or 

marketed to other manufacturers, they are considered as co-products. Industrial scrap is the common 

name given to such materials. If the trim is discarded into the solid waste stream to be landfilled, it 

should be included in the solid waste from the process. If the trim or off-spec materials are reused within 

the process, they are considered “home scrap,” which is part of an internal recycling loop. These 

materials are not included in the inventory, because they do not cross the boundaries of the subsystem.

All transportation from one process location to another is included in the subsystem. Transportation is 

quantified in terms of distance and weight shipped, and identified by the mode of transport used. 

Step 2: Develop an LCI Data Collection Plan

As part of the goal definition and scoping phase (discussed in Chapter 2), the required accuracy of data 

was determined. When selecting sources for data to complete the life cycle inventory, an LCI data 

collection plan ensures that the quality and accuracy of data meet the expectations of the decision-makers. 

Key elements of a data collection plan include the following: 

• Defining data quality goals 

• Identifying data sources and types 

• Identifying data quality indicators 

• Developing a data collection worksheet and checklist. 

Each element is described below. 

Define Data Quality Goals - Data quality goals provide a framework for balancing available time and 

resources against the quality of the data required to make a decision regarding overall environmental or 

human health impact (EPA 1986). Data quality goals are closely linked to overall study goals and serve

two primary purposes: 

• Aid LCA practitioners in structuring an approach to data collection based on the data quality needed 

for the analysis. 

• Serve as data quality performance criteria. 

No pre-defined list of data quality goals exists for all LCA projects. The number and nature of data 

quality goals necessary depends on the level of accuracy required to inform the decision-makers involved 

in the process. 

Examples of Data Quality Goals 

The following is a sample list of hypothetical data quality goals: 

• Site-specific data are required for raw materials and energy inputs, water consumption, air 

emissions, water effluents, and solid waste generation. 

• Approximate data values are adequate for the energy data category. 

• Air emission data should be representative of similar sites in the U.S. 

• A minimum of 95 percent of the material and energy inputs should be accounted for in the LCI.

22
Identify Data Quality Indicators - Data quality indicators are benchmarks to which the collected data can 

be measured to determine if data quality requirements have been met. Similar to data quality goals, there 

is no pre-defined list of data quality indicators for all LCIs. The selection of data quality indicators 

depends upon which ones are most appropriate and applicable to the specific data sources being 

evaluated. Examples of data quality indicators are precision, completeness, representativeness, 

consistency, and reproducibility.

Identify Data Sources and Types - For each life cycle stage, unit process, or type of environmental 

release, specify the necessary data source and/or type required to provide sufficient accuracy and quality

to meet the study’s goals. Defining the required data sources and types prior to data collection helps to 

reduce costs and the time required to collect the data. 

Examples of data sources include the following: 

• Meter readings from equipment 

• Equipment operating logs/journals 

• Industry data reports, databases, or consultants 

• Laboratory test results 

• Government documents, reports, databases, and clearinghouses 

• Other publicly available databases or clearinghouses 

• Journals, papers, books, and patents 

• Reference books 

• Trade associations 

• Related/previous life cycle inventory studies 

• Equipment and process specifications 

• Best engineering judgment. 

Examples of data types include: 

• Measured 

• Modeled 

• Sampled 

• Non-site specific (i.e., surrogate data) 

• Non-LCI data (i.e., data not intended for the purpose of use in an LCI) 

• Vendor data. 

The required level of aggregated data should also be specified, for example, whether data are 

representative of one process or several processes. 

A number of sources should be used in collecting data. Whenever possible, it is best to get wellcharacterized industry data for production processes. Manufacturing processes often become more

efficient or change over time, so it is important to seek current data. Inventory data can be facilityspecific or more general and still remain current. 

Several categories of data are often used in inventories. Starting with the most disaggregated, these are: 

• Individual process- and facility-specific: data from a particular operation within a given 

facility that are not combined in any way. 

• Composite: data from the same operation or activity combined across locations. 

23
• Aggregated: data combining more than one process operation. 

• Industry-average: data derived from a representative sample of locations and believed to 

statistically describe the typical operation across technologies. 

• Generic: data whose representativeness may be unknown but which are qualitatively 

descriptive of a process or technology. 

Complete and thorough inventories often require use of data considered proprietary by either the 

manufacturer of the product, upstream suppliers or vendors, or the LCA practitioner performing the study.

Confidentiality issues are not relevant for life-cycle inventories conducted by companies using their own 

facility data for internal purposes. However, the use of proprietary data is a critical issue in inventories 

conducted for external use and whenever facility-specific data are obtained from external suppliers for 

internal studies. As a consequence, current studies often contain insufficient source and documentation 

data to permit technically sound external review. Lack of technically sound data adversely affects the 

credibility of both the life-cycle inventories and the method for performing them. An individual 

company’s trade secrets and competitive technologies must be protected. When collecting data (and later 

when reporting the results), the protection of confidential business information should be weighed against 

the need for a full and detailed analysis or disclosure of information. Some form of selective 

confidentiality agreements for entities performing life-cycle inventories, as well as formalization of peer 

review procedures, is often necessary for inventories that will be used in a public forum. Thus, industry

data may need to undergo intermediate confidential review prior to becoming an aggregated data source 

for a document that is to be publicly released. 

The purpose, scope, and boundary of the inventory help the analyst determine the level or type of 

information that is required. For example, even when the analyst can obtain actual industry data, in what 

form and to what degree should the analyst show the data (e.g., the range of values observed, industry

average, plant-specific data, and best available control techniques)? These questions or decisions can 

usually be answered if the purpose or scope has been well defined. Typically, most publicly available 

life-cycle documents present industry averages, while many internal industrial studies use plant-specific 

data. Recommended practice for external life-cycle inventory studies includes the provision of a measure

of data variability in addition to averages. Frequently, the measure of variability will be a statistical 

parameter, such as a standard deviation. 

Examples of private industry data sources include independent or internal reports, periodic measurements, 

accounting or engineering reports or data sets, specific measurements, and machine specifications. One 

particular issue of interest in considering industrial sources, whether or not a formal public data set is 

established, is the influence of industry and related technical associations to enhance the accuracy, 

representativeness, and currentness of the collected data. Such associations may be willing, without 

providing specific data, to confirm that certain data (about which their members are knowledgeable) are 

realistic. 

Government documents and data bases provide data on broad categories of processes and are publicly

available. Most government documents are published on a periodic basis, e.g., annually, biennially, or 

every four years. However, the data published within them tend to be at least several years old. 

Furthermore, the data found in these documents may be less specific and less accurate than industry data 

for specific facilities or groups of facilities. However, depending on the purpose of the study and the 

specific data objectives, these limitations may not be critical. All studies should note the age of the data 

used. Some useful government documents include: 

• U.S. Department of Commerce, Census of Manufacturers 

• U.S. Bureau of Mines, Census of Mineral Industries 

24
• U.S. Department of Energy, Monthly Energy Review 

• U.S. Environmental Protection Agency, Toxics Release Inventory (TRI) Database. 

Government data bases include both non-bibliographic types where the data items themselves are 

contained in the data base and bibliographic types that consist of references where data may be found. 

Technical books, reports, conference papers, and articles published in technical journals can also provide 

information and data on processes in the system. Most of these are publicly available. Data presented in 

these sources are often older, and they can be either too specific or not specific enough. Many of these 

documents give theoretical data rather than real data for processes. Such data may not be representative 

of actual processes or may deal with new technologies not commercially tested. In using the technical 

data sources in the following list, the analyst should consider the date, specificity, and relevancy of the 

data: 

• Encyclopedia of Chemical Technology, Kirk-Othmer

• Periodical technical journals such as Journal of the Water Environment Federation

• Proceedings from technical conferences 

• Textbooks on various applied sciences. 

Surveys designed to capture information on a representative sample of end users can provide current 

information on the parameters of product or service use. Surveys typically center around a question: 

• How long or how many times is a product or service used before it is discarded (e.g., the number of 

years a television set has been in use and is expected to be in use)?

• What other materials and what quantities of these materials are used in conjunction with product use 

or maintenance (e.g., moisturizing lotion used after hand washing)? 

• How frequent is the need for product repair or maintenance (e.g., how often is an appliance repaired 

over its lifetime, and who does the repair)? 

• What other uses does the product have beyond its original purpose? 

• What does the end user do with the product when he or she is through with it? 

Frequently, the end user will not be able to supply specific information on inputs and outputs. However, 

the end user can provide data on user practices from which inputs and outputs can be derived. Generally, 

the end user can be the source of related information from which the energy, materials, and pollutant 

release inventory can be derived. (An exception would be an institutional or commercial end user who 

may have some information on energy consumption or water effluents.) Market research firms can often 

provide qualitative and quantitative usage and customer preference data without the analyst having to

perform independent market surveys. 

Recycling provides an example of some of the strengths and limitations encountered in gathering data. 

For some products, economic-driven recycling has been practiced for many years, and an infrastructure 

and markets for these materials already exist. Data are typically available for these products, including 

recycling rates, the consumers of the reclaimed materials, and the resource requirements and 

environmental releases form the recycling activities (collection and reprocessing). Data for materials 

currently at low recycling rates with newly forming recycling infrastructures are more difficult to obtain. 

In either case, often the best source for data on resource requirements and environmental releases is the 

processors themselves. For data on recycling rates and recycled material, consumers and processors may

be helpful, but trade associations as well as the consumers of the recycled materials can also provide data. 

For materials that are recycled at low rates, data will be more difficult to find. 

25
Two other areas for data gathering relate to the system as a whole and to comparisons between and among 

systems. It is necessary to obtain data on the weights of each component in the product evaluated, either 

by obtaining product specifications from the manufacturer or by weighing each component. These data 

are then used to combine the individual components in the overall system analysis. Equivalent use ratios 

for the products compared can be developed by surveying retailers and consumers, or by reviewing 

consumer or trade association periodicals. 

Develop a Data Collection Spreadsheet – The next step is to develop a life cycle inventory spreadsheet 

that covers most of the decision areas in the performance of an inventory (see Appendix A which shows a

sample inventory spreadsheet). A spreadsheet can be prepared to guide data collection and validation and 

to enable construction of a database to store collected data electronically. The following eight general

decision areas should be addressed in the inventory spreadsheet: 

• Purpose of the inventory

• System boundaries 

• Geographic scope 

• Types of data used 

• Data collection procedures 

• Data quality measures 

• Computational spreadsheet construction 

• Presentation of results. 

The spreadsheet is a valuable tool for ensuring completeness, accuracy, and consistency. It is especially 

important for large projects when several people collect data from multiple sources. The spreadsheet

should be tailored to meet the needs of a specific LCI. 

The overall system flow diagram, derived in the previous step, is important in constructing the 

computational spreadsheets because it numerically defines the relationships of the individual subsystems

to each other in the production of the final product. These numerical relationships become the source of 

“proportionality factors,” which are quantitative relationships that reflect the relative contributions of the 

subsystems to the total system. For example, data for the production of a particular ingredient X of bar 

soap are developed for the production of 1,000 tons of X. To produce 1,000 tons of bar soap, 250 tons of 

X are needed, accounting for losses and inefficiencies. Thus, to find the contributions of X to the total 

system, the data for 1,000 tons of X are multiplied by 0.250. 

The spreadsheet can be used to make other computations beyond weighting the contributions of various 

subsystems. It can be used to translate energy fuel value to a standard energy unit, such as million British 

thermal unit (Btu) or gigajoule (GJ). Precombustion or resource acquisition energy can be computed by

applying a standard factor to a unit quantity of fuel to account for energy used to obtain and transport the 

fuel. Energy sources, as well as types of wastes, can be categorized. Credits or charges for incineration 

can be derived. Fuel-related wastes should also be calculated based on the fuels used throughout the 

system. The spreadsheet should also incorporate waste management options, such as recycling, 

composting, and landfilling. 

It is important that each subsystem be incorporated in the spreadsheet with its related components and that 

each be linked together in such as way that inadvertent omissions and double-counting do not occur. The 

spreadsheet can be organized in several different ways to accomplish this purpose. These can include 

allocating certain fields or areas in the spreadsheet to certain types of calculations or using one type of 

spreadsheet software to actually link separate spreadsheets in hierarchical fashion. It is imperative, 

26
however, once a system of organization is used, that it be employed consistently. Haphazard organization 

of data sets and calculations generally leads to faulty inventory results. 

Many decisions must be made in every life-cycle inventory analysis. Every inventory consists of a mix of 

factual data and assumptions. Assumptions allow the analyst to evaluate a system condition when factual 

data either cannot be obtained within the context of the study or do not exist. Each piece of information 

(e.g., the weight of paperboard used to package the soap, type of vehicle and distance for shipping the 

tallow, losses incurred when rendering tallow, or emissions resulting from the animals at the feedlot), fall 

into one or the other category and each plays a role in developing the overall system analysis. Because 

assumptions can substantially affect study results, a series of “what if” calculations or sensitivity analyses 

are often performed on the results to examine the effect of making changes in the system. A sensitivity

analysis will temporarily modify one or more parameters and affect the calculation of the results. 

Observing the change in the results will help determine how important the assumptions are with respect to 

the results. The computational spreadsheet is also used to perform these sensitivity analysis calculations. 

Decision Points within Life Cycle Inventory 

During the 2003 InLCA/LCM conference in Seattle, Washington, a session was organized with the 

specific intent of initiating open discussion on inventory methodology and determining if there was 

support behind the idea of developing international procedural guidelines for inventory, going beyond 

the ISO 14040 and 14041 guidance. The general consensus of the group in Seattle was that there is a 

need and desire for more detailed guidance, especially around the following list of suggested key

decision points within life cycle inventory:

• Co-product allocation 

• Recycling allocation 

• Exclusion of small amounts 

• Exclusion of spills and losses 

• Age-appropriateness of data

• Surrogate and estimated data 

• Inventory for impact assessment 

• Matching the goal to the method 

• Collecting primary data 

• Report format 

• Iterative procedure for data collection 

• Choosing boundaries 

• Capital equipment/infrastructure exclusions 

• Time and location meta data. 

Sometimes it is helpful to think ahead about how the results will be presented. This can direct some

decisions on how the spreadsheet output is specified. The analyst must remember the defined purpose for 

performing the analysis and tailor the data output to those expressed needs. For example, the analyst 

might ask: Is the purpose of the life-cycle inventory to evaluate the overall system results? Or is it 

expected that detailed subsystem information will be analyzed in relation to the total? Will the study be 

used in a public forum? If so, how? How much detail is required? Answers to questions such as these 

will help determine the complexity and the degree of generalization to build into the spreadsheet, as well 

as the appropriate presentation of results. 

27
Step 3: Collect Data 

Data collection efforts involve a combination of research, site-visits and direct contact with experts, 

which generates large quantities of data. As an alternative, it may be more cost effective to buy a 

commercially available LCA software package (see Appendix B). Prior to purchasing an LCA software 

package the decision-makers or LCA practitioner should insure that it will provide the level of data 

analysis required. 

A second method to reduce data collection time and resources is to obtain non-site specific inventory

data. Several organizations have developed databases specifically for LCA that contain some of the basic 

data commonly needed in constructing a life cycle inventory. Some of the databases are sold in 

conjunction with LCI data collection software; others are stand-alone resources (see Appendix B). Many

companies with proprietary software also offer consulting services for LCA design. The use of 

commercial software risks losing transparency in the data. Often there is no record of assumptions or 

computational methods that were used. This may not be appropriate if the results are to be used in the 

public domain. Revisiting the goal statement is needed in order to determine if such data are appropriate. 

All industrial processes have multiple input streams and many generate multiple output streams. Usually

only one of the outputs is of interest for the life cycle assessment study being conducted, so the analyst 

needs to determine how much of the energy and material requirements and the environmental releases 

associated with the process should be attributed, or allocated, to the production of each co-product. For 

example, steam turbine systems may sell both electricity and low-pressure steam as useful products. 

When co-products are present, the practitioner must determine how much of the burdens associated with 

operating and supplying the multi-output process should be allocated to each co-product. The practitioner 

must also decide how to allocate environmental burdens across co-products when one is a waste stream

that can be sold for other uses. 

The guidance provided by the International Standards Organization (ISO) recognizes the variety of 

approaches that can be used to treat the allocation issue and, therefore, requires a step-wise approach (see 

text box on ISO 14041). The standard calls for practitioners to avoid allocation if possible; and secondly,

to model approaches which reflect the physical relationships between the process outputs and its inputs. 

Proper application of the ISO guidelines on allocation requires a good understanding of the physical 

relationships between co-products in a process. 

Although avoiding allocation is favored by the ISO standard, it is not always possible to expand systems 

in all cases. And, as alluded to earlier, allocation cannot be totally avoided even in a system expansion 

approach. Therefore, other options must be used. 

Although mass has most often been used as a basis for allocation, allocation by volume is done in a 

similar way. Methods based on market value usually include expected economic gain based on gross 

sales. However, none of these methods offers a general solution. Allocation may seem impractical in 

cases where one product far outweighs another. Although market value in most cases reflects the use of 

energy and therefore many of the associated burdens, allocation on this basis covers only one aspect of 

the system. Also, market value is highly variable over time, sometimes up to 50 percent in a short time 

period. Allocation on an equal basis (50/50) or on an “all or none” basis (100 percent to one product) can 

be considered to be a highly arbitrary choice. 

Environmental burdens related to the alternative systems must still be modeled using an appropriate 

method where co-products are generated. A lot has been published in the open literature on the subject in 

an effort to better understand the consequences of allocation choices. 

28
ISO 14041: 6.5.3 Allocation Procedure 

On the basis of the principles mentioned above, the following stepwise procedure shall be applied. 

Step 1: Wherever possible, allocation should be avoided by: 

1) Dividing the unit process to be allocated into two or more subprocesses and collecting the input 

and output data related to these subprocesses. 

2) Expanding the product system to include the additional functions related to the co-products, 

taking into account the requirements of (function, functional unit, and reference flow). 

Step 2: Where allocation cannot be avoided, the inputs and outputs of the system should be 

partitioned between its different products or functions in a way which reflects the underlying physical 

relationships between them, i.e., they shall reflect the way in which the inputs and outputs are 

changed by quantitative changes in the products or functions delivered by the system. The resulting 

allocation will not necessarily be in proportion to any simple measurement such as mass or molar 

flows of coproducts. 

Step 3: Where physical relationship alone cannot be established or used as the basis for allocation, the 

inputs should be allocated between the products and functions in a way which reflects other 

relationships between them. For example, input and output data might be allocated between 

coproducts in proportion to the economic value of the products. 

The flow diagram(s) developed in Step 1 provides the road map for data to be collected. Step 2 specifies 

the required data sources, types, quality, accuracy, and collection methods. Step 3 consists of finding and 

filling in the flow diagram and worksheets with numerical data. This may not be a simple task. Some

data may be difficult or impossible to obtain, and the available data may be difficult to convert to the 

functional unit needed. Therefore, the system boundaries or data quality goals of the study may have to

be refined based on data availability. This iterative process is common for most LCAs. 

Inputs in the Product Life-Cycle Inventory Analysis 

The decision on which raw/intermediate material requirements to include in a life-cycle inventory is 

complex, but several options are available: 

• Incorporate all requirements, no matter how minor, on the assumption that it is not possible a 

priori to decide to exclude anything. 

• Within the defined scope of the study, exclude inputs of less than a predetermined and clearly

stated threshold. 

• Within the defined scope of the study, exclude inputs determined likely to be negligible, relative 

to the intended use of the information, on the basis of a sensitivity analysis. 

• Within the defined scope, consistently exclude certain classes or types of inputs, such as capital 

equipment replacement. 

The advantage of the first option is that no assumptions are made in defining and drawing the system

boundary. The analyst does not have to explain or defend what has been included or excluded. The 

disadvantage is that application of this approach could be an endless exercise. The number of inputs 

could be very large and could include some systems only distantly related to the product system of 

29
interest. Besides the computational complexity, interpretation of the results with respect to the single 

desired product, package, or activity could be difficult.

The second option, if implemented with full explanation of what the threshold is and why it was selected, 

would have the advantages of consistency and lower cost and time investments. Two suboptions can be 

identified, depending on the nature of the threshold. One suboption is to specify a percentage 

contribution below which the material will be excluded, for example, one percent of the input to a given 

subsystem or to the entire system. The one percent rule historically has been useful in limiting the extent 

of the analysis in inventories where the environmental consequences of quantitatively minor materials are 

not considered. The disadvantage of the one percent rule is that the possible presence of an 

environmentally damaging activity associated with these materials could be overlooked. Also, when used 

with mixed percentages (e.g., percent of system energy, percent of subsystem input), the result may be 

confusing or inconsistent. The scoping analysis should provide a rationale for choosing to apply such a 

rule. 

The second suboption is to set a threshold based on the number of steps that the raw/intermediate material 

is removed from the main process sequence. Consider the bar soap example discussed earlier. Caustic 

manufacture from brine electrolysis is part of the main process sequence and would clearly be included. 

Sodium carbonate is an input material for the production of caustic is therefore a secondary input. 

Applying a “one-step back” decision rule would include the steps associated with sodium carbonate 

production. Ammonium chloride is an input material for the production of sodium carbonate using the 

Solvay process. Relative to caustic, ammonium chloride is a tertiary input and would be excluded if a 

“one-step back” decision rule were applied. As in the first option, the “one-step back” decision rule has 

the advantages of clarity and consistent application. For some inputs that are analyzable in exact 

mathematical terms, the “one-step back” rule may be justifiable. If the inputs to a given process bear a 

fixed relationship to the next-tier process, one step is all that may be necessary to obtain a sufficiently

accurate value (Boustead and Hancock 1979). 

Consider the example of a refinery. Most of the refinery’s output is sold for production of petroleumbased materials. However, a small portion, say eight percent, is used to run the refinery. This portion, 

termed the parasitic fraction, is mathematically related to the refinery output as: 

M(1+f) 

where: 

M is the output product and 

f is the parasitic fraction (0.08) 

For a life-cycle inventory on a petroleum-based plastic, the primary output of the refinery clearly would 

be included within the system boundary. Suppose the data quality indicators showed that the data were 

accurate to + 5 percent. Because of the first-tier use of the material represents an eight percent difference, 

a “one-step back” rule would include the refinery material (fuel) output used to run the refinery.

However, to produce the material (fuel) to run the refinery requires a further fraction of the output two 

steps back for the plastic raw material. This is calculated as: 

M(1+f+f2

). 

Thus, the incremental contribution of the second step back is 0.6 percent, which is less than the data 

accuracy. That is, there is no significant difference in the system data after the first step. Disadvantages 

of this approach include the lack of simple geometric relationships for many inputs and the increased 

effort to analyze more tiers as data quality increases.

30
The third option, drawing boundaries based on sensitivity analysis, adds the advantage of being 

systematic rather than arbitrary in assigning the threshold. The disadvantages of a sensitivity analysisbased approach are that the analyst needs to be very clear in describing how the analysis was used and, 

unless a large existing database is available to supply preliminary values that can be used in the sensitivity

analysis, the required analysis effort may not be limited by a very large amount. A more in-depth 

discussion of sensitivity analysis is provided later in this chapter. 

The final option, excluding certain classes or types of input, also has been found through experience to 

apply to many systems. For example, in the bar soap inventory, a decision may be made to exclude the 

equipment used to cut the bars of soap. The justification is that the allocation of inputs and outputs from

the manufacture of the machine is minuscule when the millions of bars of soap produced by the machine 

are considered. The advantage of this option is that many complex subsystems can often be excluded. 

The disadvantages are the same as those for the first option, namely, that a highly significant activity may

be eliminated. Capital equipment is the most commonly excluded input type. The analyst should 

perform a preliminary analysis to characterize the basic activities in each class or type of input to ensure 

that a significant contribution is not left out. 

Energy

Energy represents a combination of energy requirements for the subsystem. Three categories of energy 

are quantifiable: process, transportation, and energy of material resources (inherent energy). 

Process energy is the energy required to operate and run the subsystem process(es), including such items

as reactors, heat exchangers, stirrers, pumps, blowers, and boilers. Transportation energy is the energy 

required to power various modes of transportation such as trucks, rail carriers, barges, ocean vessels, and 

pipelines. Conveyors, forklifts, and other equipment that could be considered with transportation or 

process are labeled according to their role in the subsystem. For example, power supplied to a conveyor 

used to carry material from one point in the subsystem would be labeled process energy. On the other 

hand, the power supplied to a conveyor used to transport material from one subsystem to a different 

subsystem would be considered transportation energy. 

Two alternatives exist for incorporating energy inputs in a subsystem module. One is to report the actual 

energy forms of the inputs, e.g., kilowatt-hours (kWh) of electricity or cubic feet of natural gas. The 

other is to include the specific quantities of fuels used to generate the produced energy forms in the 

module. 

The advantage of the first approach is that the specific energy mix is available for each subsystem. For 

example, a company may want to evaluate the desirability of installing a natural gas-fired boiler to 

produce steam compared to using its electrically heated boiler powered by a combination of purchased 

and on-site generated electricity. A specific fuel mix could be applied to compute the energy and fuel 

resource use. The second approach, incorporating specific fuel quantities, allows a subsystem comparison 

of primary energy fuels. For example, “x” kilowatt-hours of electricity would be specified as “y” cubic 

feet of natural gas and “z” pounds of uranium.

Within each subsystem, the energy input data should be given as specific quantities of fuel and then 

converted into energy equivalents according to the conversion factors discussed in the following two 

sections. For example, the energy requirements attributed to a polyethylene resin plant may be specified 

as 500 pounds of ethylene for feedstock, 500 cubic feet of natural gas, 50 kilowatt-hours of electricity to

run the process equipment, and 50 gallons of diesel fuel to transport the resin to consumers. In this case, 

the 50 kilowatt-hours would be converted to 180 megajoules. 

31
Combustion and Precombustion Values

To report all energy usage associated with the subsystem of concern, the analyst may need to consider 

energy data beyond the primary process associated with combustion of the fuel. The energy used in fuel 

combustion is only part of the total energy associated with the use of fuel. The amount of energy

expended to acquire the fuel also may be significant in comparison to other energy expenditures. Energy

to acquire fuel raw materials (e.g., mining coal or drilling for oil), process these raw materials into usable 

fuels, and transport them is termed by various practitioners as “precombustion energy” or “energy of fuel 

acquisition.” Precombustion energy is defined as the total amount of energy necessary to deliver a usable 

fuel to the consumer of the fuel. 

Including precombustion energy is analogous to extending the system boundaries for fuels to raw material 

inputs. For example, suppose the combustion of fuel oil in an industrial boiler results in the release of 

about 150,000 Btu per gallon. However, crude oil drilling and production, refining, and transporting the 

fuel oil require an additional 20,000 Btu per gallon. This additional energy is the precombustion energy. 

Thus, the total energy expended (precombustion energy plus combustion energy) when a gallon of fuel oil 

is consumed would be 170,000 Btu. Generally, a complete inventory will include precombustion energy

contributions because they represent the true energy demand of the system. Inclusion or exclusion of this 

contribution should be clearly stated. 

Energy Sources

Energy is obtained from a variety of sources, including coal, nuclear power, hydropower, natural gas, 

petroleum, wind, solar energy, solid waste, and wood biomass. Fuels are interchangeable, to a high 

degree, based on their energy content. For example, an electric utility decides which fuel or other energy

source to use based on the cost per energy unit. Utilities can and do use multiple forms of energy sources, 

making possible an economic decision based on the energy cost per kilowatt-hour of electricity generated. 

Manufacturing companies also choose among energy sources on the same basis. However, reasons other 

than cost, such as scarcity or emissions to the environment, also affect the energy source decision. For 

example, during periods of petroleum shortages, finding products that use predominantly non-petroleum

energy sources may be desirable. For that reason, the inventory should characterize energy requirements 

according to basic sources of energy. Thus, it would consider not only electricity, but also the basic 

sources (such as coal, nuclear power, hydropower, natural gas, and petroleum) that produce the 

electricity. 

Electricity: Considerations associated with electricity include the source of fuel used to generate the 

electricity and the efficiency of the generating system. Power utilities typically use coal, nuclear power, 

hydropower, natural gas, or oil to generate electricity. Non-utility generation sources can include wind 

power, waste-to-energy, and geothermal energy. Accurately determining electrical energy use and 

associated emissions raises several complications, such as relating the actual electricity use of a single 

user to the actual fuel used. 

Although a given company pays its bills to a particular utility, the company is not simply purchasing 

power from the nearest plant. Once electricity is generated and fed into power lines, it is 

indistinguishable from electricity from any other source. Individual generating stations owned by a given 

utility may use different fuels. The electricity generated by these stations is “mixed” in the transmission 

lines of that utility. The utility is interconnected with neighboring utilities (also using various types of 

fuel), to form regional grids, which then interconnect to form a national grid. 

Computational models currently used to perform life-cycle inventories of electricity in the United States 

are based on the fuel mix in regional grids or on a national average. In many cases where an industry is 

scattered throughout the United States, the fuel mix for the national grid (available from the U.S. 

32
Department of Energy) can be used, making calculations easier without sacrificing accuracy. Data for 

2004 are shown in Table 3-1. 

Table 3-1. U.S. National Electrical Grid Fuel Mix for 2004 

Fuel Gigawatt-hours 

(GWh) Percent 

Coal 1,976,333 50

Nuclear 788,556 19.9

Hydro 261,545 6.6

Natural Gas 714,600 18.1

Oil 117,591 3

Biomass 60,042 1.5

Other* 34,741 0.9

Total 3,953,408 100

Source: Edison Electric Institute, 

http://www.eei.org/industry_issues/industry_overview_and_statistics/industry_statis

tics/index.htm#fuelmix

* Includes geothermal, solar and wind power. 

One exception to the national grid assumption is the electroprocess industries which use vast amounts of 

electricity. Aluminum smelting is the primary example. It and the other electroprocessing industries are 

not distributed nationally, so a national electricity grid does not give a reasonable approximation of their 

electricity use. They are usually located in regions of inexpensive electric power. Some plants have 

purchased their own electric utilities. In recognition of this fact, specific regional grids or data from onsite facilities are commonly used for life-cycle inventories of the electroprocessing industries. 

The energy efficiency of the electricity-generating and delivery system must also be considered. The 

theoretical conversion from the common energy unit of kilowatt-hour to common fuel units (megajoules) 

is 3.61 MJ per kWh. Ideally, the analyst would compute a specific efficiency based on the electrical 

generation fuel mix actually used. This value is derived by comparing the actual fuels consumed by the 

electricity-generating industry in the appropriate regional or national grid to the actual kilowatt-hours of 

electricity delivered for useful work. The value includes boiler inefficiencies and transmission line losses. 

However, a conversion of 11.3 MJ per kWh may be used in most cases to reflect the actual use of fuel to 

deliver electricity to the consumer from the national grid. 

Nuclear Power: Nuclear power substitutes for fossil fuels in the generation of electricity. There is no 

measurement of nuclear power directly equivalent to the joules of fossil fuel, so nuclear power typically is 

measured as its fossil fuel equivalency. The precombustion energy of nuclear power is usually added to 

the fuel equivalency value. The precombustion energy includes that for mining and processing, as well as

the increased energy requirement for power plant shielding. 

Hydropower: Most researchers traditionally have counted hydropower at its theoretical energy

equivalence of 3.61 MJ per kWh, with no precombustion impacts included. No precombustion factors are 

used for hydropower because water does not have an inherent energy value from which line transmission 

losses, etc., can be subtracted. The contribution of the capital equipment is small in light of the amount of 

hydroelectric energy generated using the equipment. Disruption to ecosystems typically has not been 

considered in the inventory. However, quantitative inventory measures that may be suitable for 

characterizing related issues, such as habitat loss due to land use conversion, potentially could be 

included. Factors addressing area damage, recovery time, and ecosystem function are under consideration 

for inclusion in the impact analysis. 

33
Water

Water volume requirements should be included in a life-cycle inventory analysis. In some locations, 

water is plentiful. Along the coasts, seawater is usable for cooling or other manufacturing purposes. 

However, in other places water is in short supply and must be allocated for specific uses. Some areas 

have abundant water in some years and limited supplies in other years. Some industrial applications reuse 

water with little new or makeup water required. In other applications, however, tremendous amounts of 

new water inputs are required. 

How should water be incorporated in an inventory? The goal of the inventory is to measure, per unit of

product, the gallons of water required that represent water unavailable for beneficial uses (such as 

navigation, aquatic habitat, and drinking water). Water withdrawn from a stream, used in a process, 

treated, and replaced in essentially the same quality and in the same location should not be included in the 

water-use inventory data. Ideally, water withdrawn from groundwater and subsequently discharged to a 

surface water body should be included, because the groundwater is not replaced to maintain its beneficial 

purposes. Data to make this distinction may be difficult to obtain in a generic study where site-specific 

information is not available. 

In practice, the water quantity to be estimated is net consumptive usage. Consumptive usage as a lifecycle inventory input is the fraction of total water withdrawal from surface or groundwater sources that 

either is incorporated into the product, co-products (if any), or wastes, or is evaporated. As in the general 

case of renewable versus nonrenewable resources, valuation of the degree to which the water is or is not 

replenishable is best left to the impact assessment. 

Outputs of the Product Life-Cycle Inventory Analysis 

A traditional inventory qualifies three categories of environmental releases or emissions: atmospheric 

emissions, waterborne waste, and solid waste. Products and co-products also are quantified. Each of 

these areas is discussed in more detail in the following sections. Most inventories consider environmental 

releases to be actual discharges (after control devices) of pollutants or other materials from a process or 

operation under evaluation. Inventory practice historically has included only regulated emissions for each 

process because of data availability limitations. It is recommended that analysts collect and report all 

available data in the detailed tabulation of subsystem outputs. In a study not intended for product 

comparisons, all of these pollutants should be included in the summary presentations. 

A comparative study offers two options. The first is to include in the summary presentation only data 

available for alternatives under consideration. The advantage of this option is that it gives a comparable 

presentation of the loadings from all the alternatives. The disadvantage is that potentially consequential 

information, which is available only for some of the alternatives, may not be used. The second option is 

to report all data whether uniformly available or not. In using this option, the analyst should caution the 

user not to draw any conclusions about relative effects for pollutants where comparable data are not 

available. “Comparable” is used here to mean the same pollutant. For example, in a summary of data on 

a bleached paper versus plastic packaging alternatives, data on dioxin emissions may be available only for 

the paper product. The second option is recommended for internal studies and for external studies where 

proper context can be provided. 

Atmospheric Emissions

Atmospheric emissions are reported in units of weight and include all substance classified as pollutants 

per unit weight of product output. These emissions generally have included only those substances 

required by regulatory agencies to be monitored but should be expanded where feasible. The amounts 

reported represent actual discharges into the atmosphere after passing through existing emission control 

devices. Some emissions, such as fugitive emissions from valves or storage areas, may not pass through 

control devices before release to the environment. Atmospheric emissions from the production and 

34
combustion of fuel for process or transportation energy (fuel-related emissions), as well as the process 

emissions, are included in the life-cycle inventory. 

Typical atmospheric emissions are particulates, nitrogen oxides, volatile organic compounds (VOCs), 

sulfur oxides, carbon monoxide, aldehydes, ammonia, and lead. This list is neither all-inclusive nor is it a 

standard listing of which emissions should be included in the life-cycle inventory. Recommended 

practice is to obtain and report emissions data in the most speciated form possible. Some air emissions, 

such as particulates and VOCs, are composites of multiple materials whose specific makeup can vary 

from process to process. All emissions for which there are obtainable data should be included in the 

inventory. Therefore, the specific emissions reported for any system, subsystem, or process will vary 

depending on the range of regulated and nonregulated chemicals. 

Certain materials, such as carbon dioxide and water vapor losses due to evaporation (neither of which is a 

regulated atmospheric emission for most processes), have not been included in most inventory studies in 

the past. Regulations for carbon dioxide are changing as the debate surrounding the greenhouse effect 

and global climate change continues and the models used for its prediction are modified. Inclusion of 

these emerging emissions of concern is recommended. 

Waterborne Wastes

Waterborne wastes are reported in units of weight and include all substances generally regarded as 

pollutants per unit of product output. These wastes typically have included only those items required by 

regulatory agencies, but the list should be expanded as data are available. The effluent values include 

those amounts still present in the waste stream after wastewater treatment, and represent actual discharges 

into receiving waters. For some releases, such as spills directly into receiving waters, treatment devices 

do not play a role in what is reported. For some materials, such as brine water extracted with crude oil 

and reinjected into the formation, current U.S. regulations do not define such materials as waterborne 

wastes, although they may be considered in solid waste regulations under the Resource Conservation and 

Recovery Act (RCRA). Other liquid wastes may also be deep well injected and should be included. In 

general, the broader definition of emissions in a life-cycle inventory, in contrast to regulations, would 

favor inclusion of such streams. It can be argued, from a systems analysis standpoint, that materials such 

as brine should count as releases from the subsystem because they cross the subsystem boundary. If 

wastes and spills that occur are discharged to the ocean or some other body of water, these values are 

always reported as wastes.

As with atmospheric wastes, waterborne wastes from the production and combustion of fuels (fuel-related 

emissions), as well as process emissions, are included in the life-cycle inventory.

Some of the most commonly reported waterborne wastes are biological oxygen demand (BOD), chemical 

oxygen demand (COD), suspended solids, dissolved solids, oil and grease, sulfides, iron, chromium, tin, 

metal ions, cyanide, fluorides, phenol, phosphates, and ammonia. Again, this listing of emissions is not 

meant to be a standard for what should be included in an inventory. Some waterborne wastes, such as 

BOD and COD, consist of multiple materials whose composition can vary from process to process. 

Actual waterborne wastes will vary for each system depending on the range of regulated and nonregulated 

chemicals. 

Solid Waste

Solid waste includes all solid material that is disposed from all sources within the system. U.S. 

regulations include certain liquids and gases in the definition as well. Solid wastes typically are reported 

by weight. A distinction is made in data summaries between industrial solid wastes and post-consumer 

solid wastes, as they are generally disposed of in different ways and, in some cases, at different facilities. 

Industrial solid waste refers to the solid waste generated during the production of a product and its 

35
packaging and is typically divided into two categories: process solid waste and fuel-related solid waste. 

Post-consumer solid waste refers to the product/packaging once it has met its intended use and is 

discarded into the municipal solid waste stream. 

Process solid waste is the waste generated in the actual process, such as trim or waste materials that are 

not recycled, as well as sludges and solids from emissions control devices. Fuel-related waste is solid 

waste produced from the production and combustion of fuels for transportation and operating the process. 

Fuel combustion residues, mineral extraction wastes, and solids from utility air control devices are 

examples of fuel-related wastes. 

In the United States, mine tailings and overburden generally are not regulated as solid waste. However, 

the regulations require overburden to be replaced in the general area from which it was removed. 

Furthermore, environmental consequences associated with the removal of mine tailings and overburden 

should be included. The regulations do not require industrial solid waste to be handled off site. 

Therefore, researchers try to report all solid waste from industrial processes destined for disposal, whether 

off site or local. Historically, no distinctions have been made between hazardous and nonhazardous solid 

waste, nor have individual wastes been specifically characterized. However, in view of the potentially

different environmental effects, analysts will find it useful to account for these wastes separately, 

especially if an impact assessment is to be conducted. 

Products

The products are defined by the subsystem and/or system under evaluation. In other words, each 

subsystem will have a resulting product, with respect to the entire system. This subsystem product may

be considered either a raw material or intermediate material with respect to another system, or the 

finished product of the system. 

Again using the bar soap example, when examining the meat packaging subsystem, meat, tallow, hides, 

and blood would all be considered product outputs. However, because only tallow is used in the bar soap 

system, tallow is considered the only product from that subsystem. All other material outputs (not 

released as wastes or emissions) are considered co-products. If the life-cycle assessment were performed 

on a product such as a leather purse, hides would be considered the product from the meat packaging 

subsystem, and all other outputs would be considered co-products.

Although for bar soap the tallow is considered the product from the meat packaging subsystem, it is 

simultaneously an intermediate material within the bar soap system. Thus, from these examples one can 

see that classifying a material as a product in a life-cycle study depends, in part, on the extent of the 

system being examined, i.e., the position from which the material is viewed or the analyst’s point of view. 

Transportation

The life-cycle inventory includes the energy requirements and emissions generated by the transportation 

requirements among subsystems for both distribution and disposal of wastes. Transportation data are 

reported in miles or kilometers shipped. This distance is then converted into units of ton-miles or tonnekilometers, which is an expression involving the weight of the shipment and the distance shipped. 

Materials typically are transported by rail, truck, barge, pipeline, and ocean transport. The efficiency of 

each mode of transport is used to convert the units of ton-miles into fuel units (e.g., gallons of diesel fuel). 

The fuel units are then converted to energy units, and calculations are made to determine the emissions 

generated from the combustion of the fuels. 

Exhibit 3-2 shows that transportation is evaluated for the product leaving each subsystem. This method 

of evaluating transportation avoids any inadvertent double-counting of transportation energy or emissions. 

Transportation is reported only for the product of interest from a subsystem and not for any co-products 

36
of the subsystem, because the destination of the co-products is not an issue. The raw materials for the bar 

soap production system, for example, include salt from salt mining and trees from natural forest 

harvesting. Applying the template to these two subsystems shows that the transport of salt from the 

mining operation and the transport of trees from the logging operation must be included in the data 

collected for these subsystems. 

The salt is transported to chlorine/sodium hydroxide plants, and the trees are transported to pulp mills. 

Applying the template to these subsystems shows that the transport of chlorine and sodium hydroxide 

from those plants to pulp mills is part of the chlorine production and sodium hydroxide subsystems. 

Likewise, the transport of pulp to paper mills is part of the pulp mill subsystem. The transport of raw 

materials, salt, and trees into the subsystems (chlorine production, sodium hydroxide production, and pulp 

mills) now being evaluated has already been accounted for in the evaluation of the salt mining and natural 

forest harvesting subsystems. Applying the template throughout the bar soap system shows the 

evaluation of transportation ending with the post-consumer waste management subsystem, where wastes 

may be transported to a final disposal site. 

Backhauling may be a situation where there is some overlap between the transportation associated with 

product distribution and the transportation associated with recycling of the product or a different product 

after consumer use. A backhaul has been described as occurring when a truck or rail carrier has a 

profitable load in one direction and is willing to accept a reduced rate for a move in the return direction. 

Backhaul opportunities occur when the demand for freight transportation in one area is relatively low and 

carriers have a financial incentive to move their vehicles, loaded or empty, to a place where the demand 

for freight transportation is higher. Due to the lowered transportation rates, recycled materials, especially

paper and aluminum, are often transported by backhauling. Thus, a carrier may take a load of new paper 

from a mill to customers in a metropolitan area and pick up loads of scrap paper in the same area to bring 

them back to the mill. In this scenario, backhauling may reduce the energy and emissions associated with

distribution of a product (made from new paper) by assigning energy and emissions associated with an 

empty return trip to the recycled scrap paper. 

Co-Product Allocation

Most industrial processes are physical and/or chemical processes. The fundamentals of life-cycle 

inventory are based on modeling a system in such a way that calculated values reasonably represent actual 

(measurable) occurrences. Some processes generate multiple output streams in addition to waste streams. 

In attributional LCAs, only certain of these output streams are of interest with respect to the primary

product being evaluated (see the text box in Chapter 2 on the distinction between attributional and 

consequential LCAs). The term co-product is used to define all output streams other than the primary

product that are not waste streams and that are not used as raw materials elsewhere in the system

examined in the inventory. Co-products are of interest only to the point where they no longer affect the 

primary product, i.e. the product that is part of the life cycle system being studied. Subsequent refining of 

co-products is beyond the scope of the analysis, as is transport of co-products to facilities for further 

refining. A basis for co-product allocation needs to be selected with careful attention paid to the specific 

items calculated. Each industrial system must be handled on a case-by-case basis since no allocation 

basis exists that is always applicable. 

37
Exhibit 3-3. Allocating Resources and Environmental Burdens on a Mass Basis for a Product and 

Co-Product (Source: EPA 1993) 

Co-Product Allocation for Product “A” and Product “B” 

Co-Product Allocation for Product “A”

Co-Product Allocation for Product “B”

38
In effect, the boundary for the analysis is drawn between the primary product and co-products, with all 

materials and environmental loadings attributed to co-products being outside the scope of the analysis. 

For example, the production of fatty acids from tallow for soap manufacture generates glycerine, a 

secondary stream that is collected and sold. Glycerine, therefore, is considered a co-product, and its 

processing and use would be outside the scope of the bar soap analysis. 

Basis for Co-Product Allocation

The first step is to investigate any complex process in detail and attempt to identify unit subprocesses that 

produce the product of interest. If sufficient detail can be found, no co-product allocation will be 

necessary. The series of subprocesses that produce the product can simply be summed. Many metal 

manufacturing plants illustrate this approach. In steel product manufacture, all products are made by 

melting the raw materials, producing iron, and then producing raw steel. These steps are followed by a 

series of finishing operations that are unique to each product line. It is generally possible to identify the 

particular subprocesses in the finishing sequence of each product and to collect sufficient data to carry out 

the life-cycle inventory without co-product allocation. In many cases, a careful analysis of unit systems 

will avoid the need to make co-product allocations. Still, in some cases, such as a single chemical 

reaction vessel that produces several different products, there is no analytical method for cleanly 

separating the subprocesses. In this example, co-product allocation is necessary.

The analyst needs to determine the specific resource and environmental categories requiring study. For a 

given product, different co-product allocations may be made for different resource and environmental 

categories. To find the raw materials needed to produce a product, a simple mass balance will help track 

the various input materials into the output materials. For instance, if a certain amount of wood is needed 

to produce several paper products, and the analysis concerns only one of the products, then a mass 

allocation scheme, as demonstrated in Exhibit 3-3, will be used to determine the amount of wood required 

for the target product. 

If a process produces several different chemical products, care must be taken in the analysis. It will be 

necessary to write balanced chemical equations and trace the chemical stoichiometry from the raw 

materials into the products. A simple mass allocation method frequently gives reasonable results, but not 

always. In calculating energy, heat of reaction may be the appropriate basis for allocating energy to the 

various co-products. 

If the various co-product chemicals are quite different in nature, some other allocation method may be 

needed. For example, an electrolytic cell can produce hydrogen and oxygen from water. Each water 

molecule requires two electrons to produce two hydrogen atoms and one oxygen atom. On a macroscopic 

basis, electricity that produces one mole (or two grams) of hydrogen only produces one-half mole (or 16 

grams) of oxygen. Thus, the input electrical energy would be allocated between the hydrogen and oxygen

co-products on a molar basis. That is, two-thirds of the energy would be allocated to the hydrogen and 

one-third to the oxygen, resulting in an energy per unit mass for hydrogen that is 16 times that of oxygen. 

However, conservation of mass is used to determine the material requirements. Each mole of water (18 

grams) contains two grams of hydrogen atoms and 16 grams of oxygen atoms, and the dissociation of the 

water results in two grams of hydrogen and 16 grams of oxygen. Thus, a mass allocation would be 

appropriate for raw material calculations in this example. 

For environmental emissions from a multiple-product process, allocation to different co-products may not 

be possible. For example, in a brine cell that produces sodium, chlorine, and hydrogen as co-products, it 

may be tempting to associate any emissions containing chlorine with the chlorine co-product alone. 

However, because the sodium and hydrogen are also produced by the same cell and cannot be produced 

from this cell without also producing chlorine, all emissions should be considered as joint wastes. The 

question arises as to how to allocate chlorine emissions (as well as other emissions) to all three products. 

39
It has been suggested that the selling price of the co-products could be used as a basis for this allocation. 

Because the selling prices of the various co-products can vary greatly with time and with independent 

competitive markets for each co-product, a market-based approach would have to accommodate such 

variations, by using an average value ranged over several years, or similar method. 

Further, it has been suggested that the notion of ‘demand product’ could be used to avoid allocation. The 

idea is to recognize when a process was created with the intent of producing a single main product of 

interest, i.e. the one in demand. By-products and wastes that are created as a result of manufacturing this 

demand product are considered to be incidental, including those that may have found a market over the 

years. Therefore, all of the environmental burdens are allocated to the demand product. 

One final issue is the distinction between marginal wastes and co-products. In some cases it is not clear 

whether a material is a waste or a co-product. A hypothetical example might be a valuable mineral that 

occurs as 0.1 percent of an ore. For each pound of mineral product, 999 pounds of unneeded material is 

produced. This discarded material might find use as a road aggregate. As such, it has value and displaces 

other commercial aggregates and appears to be a co-product along with the valuable mineral. However, 

its value is so low that in some cases it may simply be dumped back on the ground because of limited 

markets. Whether this material is considered a waste or a co-product may have a significant effect on the 

results of a product life-cycle inventory. It does not seem reasonable to use a simple mass allocation 

scheme here. It is more reasonable to assume that all of the energy and other resources and emissions 

associated with this process are incurred because of the desire for the valuable product mineral. However, 

there are some cases where the “waste” has marginal, but greater value than the example used here. 

It becomes difficult in some instances to determine precisely which of the co-product allocation 

methodologies discussed above is most “correct.” One important role of an inventory is to provide 

information upon which impact assessment and improvement analysis can be based. In cases where there 

is no clear methodological solution, the inventory should include reasonable alternative calculations or 

apply sensitivity analysis to determine the effect of allocation on the final results. It remains at some later 

time to make the judgments as to which of several reasonable alternatives is the correct one. In any event, 

it should be made clear what assumptions were made and what procedures were used. 

Industrial Scrap

One co-product stream of particular interest is industrial scrap. This term is used to specifically identify

process wastes of value (trim scraps and off-spec materials) that are produced as an integral part of a 

manufacturing process. Further, the wastes have been collected and used as input materials for additional 

manufacturing processes. The last criterion is that these scrap materials have never been used as 

originally intended when manufactured. For example, a common polyurethane foam product is seat 

cushions for automobiles. The trim from cutting the cushions is never incorporated into seat cushions. 

Likewise, off-spec seat cushions sold as industrial scrap are never used as seat cushions, but are used as 

input material for another process. 

A careful distinction must be made between industrial scrap and post-consumer waste for proper 

allocation in the inventory. If the industrial scrap is to be collected and used as a material input to a 

production system or process, it is credited in the life-cycle inventory as a co-product at the point where it 

was produced. Unfortunately, systems that use material more efficiently, i.e., that produce lesser amounts 

of salable co-products, assume a higher percentage of the upstream energy and releases using the 

criterion. 

When the consumption of a co-product falls within the boundaries of the analysis, it must no longer be 

considered as a co-product, but as a primary product carrying with it all the energy requirements and 

40
environmental releases involved with producing it, beginning with raw materials acquisition. For 

example, a study of carpet underlayment made from polyurethane scrap would include the manufacturing 

steps for producing the polyurethane scrap. Its production must be handled, as is any other subsystem of 

a life-cycle inventory. Industrial scrap does not displace virgin raw materials, because the consumption 

of the industrial scrap redefines the system to include the virgin materials for its production (isocyanates 

and polyalcohols in the case of polyurethane foam). Tallow is another example of a material that would 

be defined as an industrial scrap/co-product. Historically, the thinking has been that once a material shifts 

from the waste category to being a utilized material, or a co-product, then it should bear some of the 

burden (energy, raw/intermediate material input, and environmental releases) for its own production. 

Data Time Period

The time period that data represents should be long enough to smooth out any deviations or variations in 

the normal operations of a facility. These variations might include plant shutdowns for routine 

maintenance, startup activities, and fluctuation in levels of production. Often data are available for a 

fiscal year of production, which is usually a sufficient time period to cover such variations. 

Specific Data versus Composite Data

When the purpose of the inventory is to find ways to improve internal operations, it is best to use data 

specific to the system that is being examined. These types of data are usually the most accurate and also 

the most helpful in analyzing potential improvements to the environmental profile of a system. However, 

private data typically are guarded by a confidentiality agreement, and must be protected from public use 

by some means. Composite, industry-average data are preferable when the inventory results are to be 

used for broad application across the industry, particularly in studies performed for public use. Although 

composite data may be less specific to a particular company, they are generally more representative of an 

industry as a whole. Such composite data can also be made publicly available, are more widely usable, 

and are more general in nature. Composite data can be generated from facility-specific data in a 

systematic fashion and validated using a peer review process. Variability, representativeness, and other 

data quality indicators can still be specified for composite data. 

Geographic Specificity

Natural resource and environmental consequences occur at specific sites, but there are broader 

implications. It is important to define the scope of interest (regional vs. national vs. international) in an 

inventory. A local community may be more interested in direct consequences to itself than in global 

concerns. 

In general, most inventories done domestically relate only to that country. However, if the analysis 

considers imported oil, the oilfield brines generated in the Middle East should be considered. It has been 

suggested that the results of life-cycle inventories indicate which energy requirements and environmental 

releases (of the total environmental profile of a product) are local. However, due to the fact that 

industries are not evenly distributed, this segmenting can be done only after an acceptable level of 

accuracy is agreed on. The United States, Canada, Western Europe, and Japan have the most accurate 

and most readily available information on resource use and environmental releases. Global aspects 

should be considered when performing a study on a system that includes foreign countries or products, or 

when the different geographic locations are a key difference among products or processes being 

compared. As a compromise, when no specific geographical data exist, practices that occur in other 

countries typically are assumed to be the same as for their domestic counterparts. These assumptions and 

the inherent limitations associated with their application should be documented within the inventory

report. In view of the more stringent environmental regulations in developed countries, this assumption, 

while necessary, often is not correct. Energy use and other consequences associated with importing 

materials should also be included. 

41
Technology Mixes/Energy Types

For inventory studies of processes using various technology mixes, market share distribution of the 

technologies may be necessary to accurately portray conditions for the industry as a whole. The same is 

true of energy sources. Most inventories can be based on data involving the fuel mix in the national grid 

for electricity. There are exceptions, such as the aluminum electroprocessing industry previously

discussed. Variations of this kind must be taken into account when applying the life-cycle inventory

methodology. Also, as previously mentioned, conditions can differ greatly across international borders. 

Data Categories

Environmental emission databases usually cover only those items or pollutants required by regulatory

agencies to be reported. For example, as previously mentioned, the question of whether to report only

regulated emissions or all emissions is complicated by the difficulty in obtaining data for unregulated 

emissions. In some cases, emissions that are suspected health hazards may not be required to be reported 

by a regulatory agency because the process of adding them to the list is slow. A specific example of an 

unregulated emission is carbon dioxide, which is a greenhouse gas suspected as a primary agent in global 

warming. There is no current requirement for reporting carbon dioxide emissions, and it is difficult to 

obtain measured data on the amounts released from various processes. Thus, results for emissions 

reported in a life-cycle inventory may not be viewed as comprehensive, but they can cover a wide range 

of pollutants. As a rule, it is recommended that data be obtained on as broad a range as possible. 

Calculated or qualitative information, although less desirable and less consistent with the quantitative 

nature of an inventory, may still be useful. 

Routine/Fugitive/Accidental Releases

Whenever possible, routine, fugitive, and accidental emissions data should be considered in developing 

data for a subsystem. If data on fugitive and accidental emissions are not available, and quantitative 

estimates cannot be obtained, this deficiency should be noted in the report on the inventory results. Often 

estimates can be made for accidental emissions based on historical data pertaining to frequency and 

concentrations of accidental emissions experienced at a facility. 

When deciding whether to include accidents, they should be divided into two categories based on 

frequency. For the low-frequency and high-magnitude events, e.g., major oil spills, tools other than lifecycle inventory may be appropriate. Unusual circumstances are difficult to associate with a particular 

product or activity. More frequent, lower magnitude events should be included, with perhaps some

justification for keeping their contribution separate from routine operations. 

Special Case Boundary Issues

In all studies, boundary conditions limiting the scope must be established. The areas of capital 

equipment, personnel issues, and improper waste disposal typically are not included in inventory studies, 

because they have been shown to have little effect on the results. Earlier studies did consider them in the 

analysis; later studies have verified their minimal contribution to the total system profile. Thus, exclusion 

of contributions from capital equipment manufacture, for example, is not excluded a priori. The decision 

to include or not to include them should be clearly noted by the analyst. 

Capital Equipment - The energy and resources that are required to construct buildings and to build 

process equipment should be considered. However, for most systems, capital expenditures are allocated 

to a large number of products manufactured during the lifetime of the equipment. Therefore, the resource 

use and environmental effluents produced are usually small when attributed to the system of interest. The 

energy and emissions involved with capital equipment can be excluded when the manufacture of the item

itself accounts for a minor fraction of the total product output over the life of the equipment. 

42
Personnel Issues - Inventory studies focus on the comprehensive results of product consumption, 

including manufacturing. At any given site, there are personnel-related effluents from the manufacturing 

process as well as wastes from lunchroom trash, energy use, air conditioning emissions, water pollution 

from sanitary facilities, and others. In addition, inputs and outputs during transportation of personnel 

from their residence to the workplace can be significant, depending on the purpose and scope of the 

inventory. In many situations, the personnel consequences are very small and would probably occur 

whether or not the product was manufactured. Therefore, exclusion from the inventory may be justified. 

The analyst should be explicit about including or excluding this category. For these issues, the goals of 

the study should be considered. If the study is comparative, and one option is significantly different in 

personnel or capital equipment requirements, then at least a screening-level evaluation should be 

performed to support an inclusion or exclusion decision. 

Improper Waste Disposal - For most studies it is assumed that wastes are properly disposed into the 

municipal solid waste stream or wastewater treatment system. Illegal dumping, littering, and other 

improper waste disposal methods typically are not considered in life-cycle inventories as a means of solid 

waste disposal. Where improper disposal is known to occur and where environmental effects are known 

or suspected, a case may be made to include these activities. 

Economic Input/Output Approach to Life Cycle Inventory 

Economic Input/Output offers an alternative way to create life cycle inventory. The input/output 

model divides an entire economy into distinct sectors and represents them in table, or matrix, form

so that each sector is represented by one row and one column. The matrix represents sales from one 

sector to another. Most nations have created input/output tables although few are as detailed as the 

U.S. model which provides 480 sectors. The economic input-output model is linear so that the 

effects of purchasing $1,000 from one sector will be ten times greater than the effects of purchasing 

$100 from that sector. 

In order to create life cycle inventory, the economic output for each sector is first calculated, then 

the environmental outputs are calculated by multiplying the economic output at each stage by the 

environmental impact per dollar of output. The advantage of the economic input/output approach is 

that it quickly covers an entire economy, including all the material and energy inputs, thereby

simplifying the inventory creation process. Its main disadvantage is that the data are created at high 

aggregate levels for an entire industry, such as steel mills, rather than particular products, such as 

the type of steel used to make automobiles. 

“Hybrid” models which combine the economic input/output model with process models have also 

been proposed in order to utilize the advantages offered by both approaches. 

(Hendrickson et al 2006) 

43
Step 4: Evaluate and Document the LCI Results 

When writing a report to present the final results of the life-cycle inventory, it is important to thoroughly 

describe the methodology used in the analysis. The report should explicitly define the systems analyzed 

and the boundaries that were set. All assumptions made in performing the inventory should be clearly

explained. The basis for comparison among systems should be given, and any equivalent usage ratios that 

were used should be explained. 

Life-cycle inventory studies generate a great deal of information, often of a disparate nature. The analyst 

needs to select a presentation format and content that are consistent with the purpose of the study and that 

do not arbitrarily simplify the information solely for the sake of presenting it. In thinking about 

presentation of the results, it is useful to identify the various perspectives embodied in life-cycle inventory

information. These dimensions include, but may not be limited to, the following: 

• Overall product system

• Relative contribution of stages to the overall system

• Relative contribution of product components to the overall system 

• Data categories within and across stages, e.g., resource use, energy consumption, and 

environmental releases 

• Data parameter groups within a category, e.g., air emissions, waterborne wastes, and solid 

waste types 

• Data parameters within a group, e.g., sulfur oxides, carbon dioxide, chlorine, etc. 

• Geographic regionalization if relevant to the study, e.g., national versus global 

• Temporal changes. 

The life-cycle analyst must select among these dimensions and develop a presentation format that 

increases comprehension of the findings without oversimplifying them. Two main types of format for 

presenting results are tabular and graphical. 

Sometimes it is useful to report total energy results while also breaking out the contributions to the total 

from process energy and energy of material resources. Solid wastes can be separated into postconsumer 

solid waste and industrial solid waste. Individual atmospheric and water pollutants should be reported 

separately. Atmospheric emissions, waterborne wastes, and industrial solid wastes can also be

categorized by process emissions/wastes and fuel-related emissions/wastes. Such itemized presentations 

can assist in identifying and subsequently controlling certain energy consumption and environmental 

releases. 

The results from the inventory can be presented most comprehensibly in tabular form. The choice of how 

the tables should be created varies, based on the purpose and scope of the study. If the inventory has been 

performed to help decide which type of package to use for a particular product, showing the overall 

system results will be the most useful way to present the data. On the other hand, when an analysis is 

performed to determine how a package can be changed to reduce its releases to the environment, it is 

important to present not only the overall results, but also the contributions made by each component of 

the packaging system. For example, in analyzing a liquid delivery system that uses plastic bottles, it may

be necessary to show how the bottle, the cap, the label, the corrugated shipping box, and the stretch wrap 

around the boxes all contribute to the total results. The user can thus concentrate improvement efforts on 

the components that make a substantial contribution when evaluating proposed changes. 

Graphical presentation of information helps to augment tabular data and can aid in interpretation. Both

bar charts (either individual bars or stacked bars) and pie charts are valuable in helping the reader 

visualize and assimilate the information from the perspective of “gaining ownership or participation in 

life-cycle assessment” (Werner 1991). However, the analyst should not aggregate or sum dissimilar data 

when creating or simplifying a graph. 

44
For internal industrial use by product manufacturers, pie charts showing a breakout by raw materials, 

process, and use/disposal have been found useful in identifying waste reduction opportunities. 

For external studies, the data must be presented in a format that meets one fundamental criterion - clarity. 

Ensuring clarity requires that the analyst ask and answer questions about what each graph is intended to 

convey. It may be necessary to present a larger number of graphs and incorporate fewer data in each one. 

Each reader should understand the desired response after viewing the information. 

Now that the data has been collected and organized into one format or another, the accuracy of the results 

must be verified. The accuracy must be sufficient to support the purposes for performing the LCA as 

defined in the goal and scope (see Chapter 2 for a discussion on goal definition). 

Steps 1 and 2 of Chapter 5, Life Cycle Interpretation, describe how to efficiently assess the accuracy of 

the LCI results. As illustrated in Exhibit 1-2, Phases of an LCA, in Chapter 1, LCA is an iterative 

process. Determining the sensitivity of the LCI data collection efforts in regard to data accuracy prior to 

conducting the saves time and resources. Otherwise, the life cycle impact assessment effort may have to

be repeated if it is later determined that the accuracy of the data is insufficient to draw conclusions. 

When documenting the results of the life cycle inventory, it is important to thoroughly describe the 

methodology used in the analysis, define the systems analyzed and the boundaries that were set, and all 

assumptions made in performing the inventory analysis. Use of the worksheet (see Step 2) supports a 

clear process for documenting this information. 

The outcome of the inventory analysis is a list containing the quantities of pollutants released to the 

environment and the amount of energy and materials consumed. The information can be organized by

life cycle stage, media (air, water, and land), specific process, or any combination thereof that is 

consistent with the ground rules defined in Chapter 2, Goal Definition and Scoping, for reporting 

requirements. 

45
Chapter 4 

Life Cycle Impact Assessment 

What is a Life Cycle Impact Assessment (LCIA)? 

The Life Cycle Impact Assessment (LCIA) phase of an LCA is the evaluation of potential human health 

and environmental impacts of the environmental resources and releases identified during the LCI. Impact 

assessment should address ecological and human health effects; it should also address resource depletion. 

A life cycle impact assessment attempts to establish a linkage between the product or process and its 

potential environmental impacts. For example, what are the impacts of 9,000 tons of carbon dioxide or 

5,000 tons of methane emissions released into the atmosphere? Which is worse? What are their potential 

impacts on smog? On global warming? 

LCA versus Risk Assessment 

An important distinction exists between life cycle impact assessment (LCIA) and other types of 

impact analysis. LCIA does not necessarily attempt to quantify any specific actual impacts 

associated with a product, process, or activity. Instead, it seeks to establish a linkage between a 

system and potential impacts. The models used within LCIA are often derived and simplified 

versions of more sophisticated models within each of the various impact categories. These simplified 

models are suitable for relative comparisons of the potential to cause human or environmental 

damage, but are not indicators of absolute risk or actual damage to human health or the environment. 

For example, risk assessments are often very narrowly focused on a single chemical at a very specific 

location. In the case of a traditional risk assessment, it is possible to conduct very detailed modeling 

of the predicted impacts of the chemical on the population exposed and even to predict the probability

of the population being impacted by the emission. In the case of LCIA, hundreds of chemical 

emissions (and resource stressors) which are occurring at various locations are evaluated for their 

potential impacts in multiple impact categories. The sheer number of stressors being evaluated, the 

variety of locations, and the diversity of impact categories makes it impossible to conduct the 

assessment at the same level of rigor as a traditional risk assessment. Instead, LCIA models are 

based on the accepted models within each of the impact categories using assumptions and default 

values as necessary. The resulting models that are used within LCIA are suitable for relative 

comparisons, but not sufficient for absolute predictions of risk. 

The key concept in this component is that of stressors. A stressor is a set of conditions that may lead to 

an impact. For example, if a product or process is emitting greenhouse gases, the increase of greenhouse 

gases in the atmosphere may contribute to global warming. Processes that result in the discharge of 

excess nutrients into bodies of water may lead to eutrophication. An LCIA provides a systematic 

procedure for classifying and characterizing these types of environmental effects. 

Why Conduct an LCIA?

Although much can be learned about a process by considering the life cycle inventory data, an LCIA 

provides a more meaningful basis to make comparisons. For example, although we know that 9,000 tons 

of carbon dioxide and 5,000 tons of methane released into the atmosphere are both harmful, an LCIA can 

determine which could have a greater potential impact. Using science-based characterization factors, an 

LCIA can calculate the impacts each environmental release has on problems such as smog or global 

warming. 

46
Midpoint versus Endpoint Modeling 

Midpoint impact assessment models reflect the relative potency of the stressors at a common 

midpoint within the cause-effect chain. Analysis at a midpoint minimizes the amount of forecasting 

and effect modeling incorporated into the LCIA, thereby reducing the complexity of the modeling 

and often simplifying communication. Midpoint modeling can minimize assumptions and value 

choices, reflect a higher level of societal consensus, and be more comprehensive than model coverage 

for endpoint estimation. (Bare et al 2003) 

What Do the Results of an LCIA Mean? 

The results of an LCIA show the relative differences in potential environmental impacts for each option. 

For example, an LCIA could determine which product/process causes more global warming potential. 

Key Steps of a Life Cycle Impact Assessment 

The following steps comprise a life cycle impact assessment. 

1. Selection and Definition of Impact Categories - identifying relevant environmental impact

categories (e.g., global warming, acidification, terrestrial toxicity). 

2. Classification - assigning LCI results to the impact categories (e.g., classifying carbon dioxide 

emissions to global warming). 

3. Characterization - modeling LCI impacts within impact categories using science-based 

conversion factors (e.g., modeling the potential impact of carbon dioxide and methane on global 

warming). 

4. Normalization - expressing potential impacts in ways that can be compared (e.g. comparing the

global warming impact of carbon dioxide and methane for the two options). 

47
5. Grouping - sorting or ranking the indicators (e.g. sorting the indicators by location: local, 

regional, and global). 

6. Weighting - emphasizing the most important potential impacts. 

7. Evaluating and Reporting LCIA Results - gaining a better understanding of the reliability of the 

LCIA results.

ISO developed a standard for conducting an impact assessment entitled ISO 14042, Life Cycle Impact

Assessment (ISO 1998), which states that the first three steps – impact category selection, classification, 

and characterization – are mandatory steps for an LCIA. Except for data evaluation (Step 7), the other 

steps are optional depending on the goal and scope of the study. 

Step 1: Select and Define Impact Categories

The first step in an LCIA is to select the impact categories that will be considered as part of the overall 

LCA. This step should be completed as part of the initial goal and scope definition phase to guide the 

LCI data collection process and requires reconsideration following the data collection phase. The items

identified in the LCI have potential human health and environmental impacts. For example, an

environmental release identified in the LCI may harm human health by causing cancer or sterility, or 

affect workplace safety. Likewise, a release identified in the LCI could also affect the environment by

causing acid rain, global warming, or endangering species of animals. 

For an LCIA, impacts are defined as the consequences that could be caused by the input and output 

streams of a system on human health, plants, and animals, or the future availability of natural resources. 

Typically, LCIAs focus on the potential impacts to three main categories: human health, ecological 

health, and resource depletion. Exhibit 4-1 shows some of the more commonly used impact categories. 

Step 2: Classification 

The purpose of classification is to organize and possibly combine the LCI results into impact categories. 

For LCI items that contribute to only one impact category, the procedure is a straightforward assignment. 

For example, carbon dioxide emissions can be classified into the global warming category.

For LCI items that contribute to two or more different impact categories, a rule must be established for 

classification. There are two ways of assigning LCI results to multiple impact categories (ISO 1998): 

• Partition a representative portion of the LCI results to the impact categories to which they contribute. 

This is typically allowed in cases when the effects are dependent on each other. 

• Assign all LCI results to all impact categories to which they contribute. This is typically allowed 

when the effects are independent of each other. 

For example, since nitrogen dioxide could potentially affect both ground level ozone formation and 

acidification (at the same time), the entire quantity of nitrogen dioxide would be assigned to both impact 

categories (e.g., 100 percent to ground level ozone and 100 percent to acidification). This procedure must 

be clearly documented. 

48
Exhibit 4-1. Commonly Used Life Cycle Impact Categories 

Impact

Category

Scale Examples of LCI Data 

(i.e. classification)

Common Possible 

Characterization 

Factor

Description of 

Characterization 

Factor

Global 

Warming 

Global Carbon Dioxide (CO2) 

Nitrogen Dioxide (NO2) 

Methane (CH4) 

Chlorofluorocarbons (CFCs)

Hydrochlorofluorocarbons

(HCFCs) 

Methyl Bromide (CH3Br) 

Global Warming 

Potential 

Converts LCI data to

carbon dioxide (CO2) 

equivalents 

Note: global warming

potentials can be 50, 

100, or 500 year

potentials. 

Stratospheric 

Ozone 

Depletion 

Global Chlorofluorocarbons (CFCs)

Hydrochlorofluorocarbons

(HCFCs) 

Halons 

Methyl Bromide (CH3Br) 

Ozone Depleting

Potential 

Converts LCI data to

trichlorofluoromethane 

(CFC-11) equivalents. 

Acidification Regional 

Local 

Sulfur Oxides (SOx) 

Nitrogen Oxides (NOx) 

Hydrochloric Acid (HCL) 

Hydroflouric Acid (HF) 

Ammonia (NH4) 

Acidification

Potential 

Converts LCI data to

hydrogen (H+) ion 

equivalents. 

Eutrophication Local Phosphate (PO4) 

Nitrogen Oxide (NO) 

Nitrogen Dioxide (NO2) 

Nitrates 

Ammonia (NH4) 

Eutrophication

Potential 

Converts LCI data to

phosphate (PO4) 

equivalents. 

Photochemical 

Smog 

Local Non-methane hydrocarbon

(NMHC) 

Photochemical 

Oxident Creation 

Potential 

Converts LCI data to

ethane (C2H6) 

equivalents. 

Terrestrial 

Toxicity 

Local Toxic chemicals with a reported 

lethal concentration to rodents 

LC50 Converts LC50 data to

equivalents; uses multimedia modeling, 

exposure pathways. 

Aquatic 

Toxicity 

Local Toxic chemicals with a reported 

lethal concentration to fish

LC50 Converts LC50 data to

equivalents; uses multimedia modeling, 

exposure pathways. 

Human Health Global 

Regional 

Local 

Total releases to air, water, and

soil. 

LC50 Converts LC50 data to

equivalents; uses multimedia modeling, 

exposure pathways. 

Resource 

Depletion 

Global 

Regional 

Local 

Quantity of minerals used

Quantity of fossil fuels used

Resource Depletion 

Potential 

Converts LCI data to a 

ratio of quantity of

resource used versus 

quantity of resource left 

in reserve. 

Land Use Global 

Regional 

Local 

Quantity disposed of in a landfill 

or other land modifications 

Land Availability Converts mass of solid 

waste into volume using 

an estimated density. 

Water Use Regional 

Local 

Water used or consumed Water Shortage

Potential 

Converts LCI data to a 

ratio of quantity of

water used versus 

quantity of resource left 

in reserve.

49
Step 3: Characterization

Impact characterization uses science-based conversion factors, called characterization factors, to convert 

and combine the LCI results into representative indicators of impacts to human and ecological health. 

Characterization factors also are commonly referred to as equivalency factors. Characterization provides 

a way to directly compare the LCI results within each impact category. In other words, characterization 

factors translate different inventory inputs into directly comparable impact indicators. For example, 

characterization would provide an estimate of the relative terrestrial toxicity between lead, chromium, and 

zinc. 

Impact Categories and Associated Endpoints 

The following is a list of several impact categories and endpoints that identify the impacts. 

Global Impacts 

Global Warming - polar melt, soil moisture loss, longer seasons, forest loss/change, and change in 

wind and ocean patterns. 

Ozone Depletion - increased ultraviolet radiation. 

Resource Depletion -decreased resources for future generations. 

Regional Impacts

Photochemical Smog - “smog,” decreased visibility, eye irritation, respiratory tract and lung 

irritation, and vegetation damage. 

Acidification - building corrosion, water body acidification, vegetation effects, and soil effects. 

Local Impacts

Human Health - increased morbidity and mortality. 

Terrestrial Toxicity - decreased production and biodiversity and decreased wildlife for hunting or

viewing. 

Aquatic Toxicity - decreased aquatic plant and insect production and biodiversity and decreased 

commercial or recreational fishing. 

Eutrophication – nutrients (phosphorous and nitrogen) enter water bodies, such as lakes, estuaries 

and slow-moving streams, causing excessive plant growth and oxygen depletion.

Land Use - loss of terrestrial habitat for wildlife and decreased landfill space. 

Water Use - loss of available water from groundwater and surface water sources.

Impact indicators are typically characterized using the following equation: 

Inventory Data × Characterization Factor = Impact Indicators 

For example, all greenhouse gases can be expressed in terms of CO2 equivalents by multiplying the 

relevant LCI results by a CO2 characterization factor and then combining the resulting impact indicators 

to provide an overall indicator of global warming potential. 

Characterization can put these different quantities of chemicals on an equal scale to determine the amount 

of impact each one has on global warming. The calculations show that ten pounds of methane have a 

larger impact on global warming than twenty pounds of chloroform. 

50
Characterization of Global Warming Impacts 

The following calculations demonstrate how characterization factors can be used to estimate the 

global warming potential (GWP) of defined quantities of greenhouse gases: 

Chloroform GWP Factor Value* = 9 Quantity = 20 pounds 

Methane GWP Factor Value* = 21 Quantity = 10 pounds 

Chloroform GWP Impact = 20 pounds x 9 = 180 

Methane GWP Impact = 10 pounds x 21 = 210 

*Intergovernmental Panel on Climate Change (IPCC) Model 

The key to impact characterization is using the appropriate characterization factor. For some impact 

categories, such as global warming and ozone depletion, there is a consensus on acceptable 

characterization factors. For other impact categories, such as resource depletion, a consensus is still being 

developed. Exhibit 4-1 describes possible characterization factors for some of the commonly used life 

cycle impact categories. 

A properly referenced LCIA will document the source of each characterization factor to ensure that they

are relevant to the goal and scope of the study. For example, many characterization factors are based on 

studies conducted in Europe. Therefore, the relevancy of the European characterization factors must be 

investigated before they can be applied to American data. 

TRACI 

EPA’s Tool for the Reduction and Assessment of Chemical and other environmental Impacts 

(TRACI) is an impact assessment tool that will support consistency in environmental decision 

making. TRACI allows the examination of the potential for impacts associated with the raw material 

usage and chemical releases resulting from the processes involved in producing a product. It allows 

the user to examine the potential for impacts for a single life cycle stage, or the whole life cycle, and 

to compare the results between products or processes. The purpose of TRACI is to allow a 

determination or a preliminary comparison of two or more options on the basis of the following

environmental impact categories: ozone depletion, global warming, acidification, eutrophication, 

photochemical smog, human health cancer, human health noncancer, human health criteria, 

ecotoxicity, fossil fuel use, land use, and water use (EPA 2003).

Step 4: Normalization 

Normalization is an LCIA tool used to express impact indicator data in a way that can be compared 

among impact categories. This procedure normalizes the indicator results by dividing by a selected 

reference value. 

There are numerous methods of selecting a reference value, including: 

• The total emissions or resource use for a given area that may be global, regional or local 

51
• The total emissions or resource use for a given area on a per capita basis 

• The ratio of one alternative to another (i.e., the baseline) 

• The highest value among all options. 

The goal and scope of the LCA may influence the choice of an appropriate reference value. Note that 

normalized data can only be compared within an impact category. For example, the effects of

acidification cannot be directly compared with those of aquatic toxicity because the characterization 

factors were calculated using different scientific methods. 

Step 5: Grouping 

Grouping assigns impact categories into one or more sets to better facilitate the interpretation of the 

results into specific areas of concern. Typically, grouping involves sorting or ranking indicators. The 

following are two possible ways to group LCIA data (ISO 1998): 

• Sort indicators by characteristics such as emissions (e.g., air and water emissions) or location (e.g., 

local, regional, or global). 

• Sort indicators by a ranking system, such as high, low, or medium priority. Ranking is based on 

value choices. 

Step 6: Weighting 

The weighting step (also referred to as valuation) of an LCIA assigns weights or relative values to the 

different impact categories based on their perceived importance or relevance. Weighting is important 

because the impact categories should also reflect study goals and stakeholder values. As stated earlier,

harmful air emissions could be of relatively higher concern in an air non-attainment zone than the same 

emission level in an area with better air quality. Because weighting is not a scientific process, it is vital

that the weighting methodology is clearly explained and documented. 

Although weighting is widely used in LCAs, the weighting stage is the least developed of the impact

assessment steps and also is the one most likely to be challenged for integrity. In general, weighting 

includes the following activities: 

• Identifying the underlying values of stakeholders 

• Determining weights to place on impacts 

• Applying weights to impact indicators. 

Weighted data could possibly be combined across impact categories, but the weighting procedure must be 

explicitly documented. The un-weighted data should be shown together with the weighted results to 

ensure a clear understanding of the assigned weights. 

Note that in some cases, the presentation of the impact assessment results alone often provides sufficient 

information for decision-making, particularly when the results are straightforward or obvious. For 

example, when the best-performing alternative is significantly and meaningfully better than the others in 

at least one impact category, and equal to the alternatives in the remaining impact categories, then one 

alternative is clearly better. Therefore, any relative weighting of the impact assessment results would not 

change its rank as first preference. The decision can be made without the weighting step. 

Several issues exist that make weighting a challenge. The first issue is subjectivity. According to ISO 

14042, any judgment of preferability is a subjective judgment regarding the relative importance of one 

impact category over another. Additionally, these value judgments may change with location or time of 

year. For example, someone located in Los Angeles, CA, may place more importance on the values for 

52
photochemical smog than would a person located in Cheyenne, Wyoming. The second issue is derived 

from the first: how should users fairly and consistently make decisions based on environmental 

preferability, given the subjective nature of weighting? Developing a truly objective (or universally

agreeable) set of weights or weighting methods is not feasible. However, several approaches to weighting 

do exist and are used successfully for decision-making, such as the Analytic Hierarchy Process, the 

Modified Delphi Technique, and Decision Analysis Using Multi-Attribute Theory. 

Step 7: Evaluate and Document the LCIA Results

Now that the impact potential for each selected category has been calculated, the accuracy of the results 

must be verified. The accuracy must be sufficient to support the purposes for performing the LCA as 

defined in the goal and scope. When documenting the results of the life cycle impact assessment, 

thoroughly describe the methodology used in the analysis, define the systems analyzed and the boundaries 

that were set, and all assumptions made in performing the inventory analysis. 

The LCIA, like all other assessment tools, has inherent limitations. Although the LCIA process follows a 

systematic procedure, there are many underlying assumptions and simplifications, as well subjective 

value choices. 

Depending on the LCIA methodology selected, and/or the inventory data on which it is based, some of 

the key limitations may include: 

• Lack of spatial resolution – e.g., a 4,000-gallon ammonia release is worse in a small stream than in a 

large river. 

• Lack of temporal resolution – e.g., a five-ton release of particulate matter during a one month period 

is worse than the same release spread through the whole year. 

• Inventory speciation – e.g., broad inventory listing such as “VOC” or “metals” do not provide 

enough information to accurately assess environmental impacts. 

• Threshold and non-threshold impact – e.g., ten tons of contamination is not necessarily ten times 

worse than one ton of contamination. 

The selection of more complex or site-specific impact models can help reduce the limitations of the 

impact assessment’s accuracy. It is important to document these limitations and to include a 

comprehensive description of the LCIA methodology, as well as a discussion of the underlying 

assumptions, value choices, and known uncertainties in the impact models with the numerical results of 

the LCIA to be used in interpreting the results of the LCA. 

53
Chapter 5 

Life Cycle Interpretation 

What is Life Cycle Interpretation? 

Life cycle interpretation is a systematic technique to identify, quantify, check, and evaluate information 

from the results of the LCI and the LCIA, and communicate them effectively. Life cycle interpretation is 

the last phase of the LCA process. 

ISO has defined the following two objectives of life cycle interpretation: 

1. Analyze results, reach conclusions, explain limitations, and provide recommendations based on 

the findings of the preceding phases of the LCA, and to report the results of the life cycle 

interpretation in a transparent manner. 

2. Provide a readily understandable, complete, and consistent presentation of the results of an LCA

study, in accordance with the goal and scope of the study. (ISO 1998b) 

Comparing Alternatives Using Life Cycle Interpretation 

Interpreting the results of an LCA is not as simple as two is better then three, therefore Alternative A is 

the best choice! While conducting the LCI and LCIA it is necessary to make assumptions, engineering 

estimates, and decisions based on your values and the values of involved stakeholders. Each of these 

decisions must be included and communicated within the final results to clearly and comprehensively 

explain conclusions drawn from the data. In some cases, it may not be possible to state that one 

alternative is better than the others because of the uncertainty in the final results. This does not imply that 

efforts have been wasted. The LCA process will still provide decision-makers with a better understanding 

of the environmental and health impacts associated with each alternative, where they occur (locally, 

regionally, or globally), and the relative magnitude of each type of impact in comparison to each of the 

proposed alternatives included in the study. This information more fully reveals the pros and cons of each 

alternative. 

Can I Select an Alternative Based Only on the Results of the LCA? 

The purpose of conducting an LCA is to better inform decision-makers by providing a particular type of 

information (often unconsidered), with a life cycle perspective of environmental and human health 

impacts associated with each product or process. However, LCA does not take into account technical 

performance, cost, or political and social acceptance. Therefore, it is recommended that LCA be used in 

conjunction with these other parameters. 

Key Steps to Interpreting the Results of the LCA 

The guidance provided in this chapter is a summary of the information provided on life cycle 

interpretation from the ISO standard entitled “Environmental Management - Life Cycle Assessment - Life 

Cycle Interpretation,” ISO 14043 (ISO 1998b). Within the ISO standard, the following steps to

conducting a life cycle interpretation are identified and discussed: 

1. Identification of the Significant Issues Based on the LCI and LCIA. 

2. Evaluation which Considers Completeness, Sensitivity, and Consistency Checks. 

3. Conclusions, Recommendations, and reporting. 

54
Exhibit 5-1 illustrates the steps of the life cycle interpretation process in relation to the other phases of the 

LCA process. Each step is summarized below. 

Step 1: Identify Significant Issues 

The first step of the life cycle interpretation phase involves reviewing information from the first three 

phases of the LCA process in order to identify the data elements that contribute most to the results of both 

the LCI and LCIA for each product, process, or service, otherwise known as “significant issues.” 

The results of this effort are used to evaluate the completeness, sensitivity, and consistency of the LCA 

study (Step 2). The identification of significant issues guides the evaluation step. Because of the 

extensive amount of data collected, it is only feasible within reasonable time and resources to assess the 

data elements that contribute significantly to the outcome of the results. 

Before determining which parts of the LCI and LCIA have the greatest influence on the results for each 

alternative, the previous phases of the LCA should be reviewed in a comprehensive manner (e.g., study 

goals, ground rules, impact category weights, results, external involvement, etc.). 

Review the information collected and the presentations of results developed to determine if the goal and 

scope of the LCA study have been met. If they have, the significance of the results can then be 

determined. 

55
Determining significant issues of a product system may be simple or complex. For assistance in 

identifying environmental issues and determining their significance, the following approaches are 

recommended: 

• Contribution Analysis - the contribution of the life cycle stages or groups of processes are compared

to the total result and examined for relevance. 

• Dominance Analysis - statistical tools or other techniques, such as quantitative or qualitative ranking 

(e.g., ABC Analysis), are used to identify significant contributions to be examined for relevance. 

• Anomaly Assessment - based on previous experience, unusual or surprising deviations from expected

or normal results are observed and examined for relevance. 

Significant issues can include: 

• Inventory parameters like energy use, emissions, waste, etc. 

• Impact category indicators like resource use, emissions, waste, etc.

• Essential contributions for life cycle stages to LCI or LCIA results such as individual unit processes

or groups of processes (e.g., transportation, energy production). 

Step 2: Evaluate the Completeness, Sensitivity, and Consistency of the Data 

The evaluation step of the interpretation phase establishes the confidence in and reliability of the results 

of the LCA. This is accomplished by completing the following tasks to ensure that products/processes are 

fairly compared: 

1. Completeness Check - examining the completeness of the study.

2. Sensitivity Check - assessing the sensitivity of the significant data elements that influence the results 

most greatly. 

3. Consistency Check - evaluating the consistency used to set system boundaries, collect data, make 

assumptions, and allocate data to impact categories for each alternative. 

Each technique is summarized below. 

Completeness Check - The completeness check ensures that all relevant information and data needed for 

the interpretation are available and complete. A checklist should be developed to indicate each significant 

area represented in the results. Data can be organized by life cycle stage, different processes or unit 

operations, or type of data represented (raw materials, energy, transportation, environmental release to air, 

land, or water). Using the established checklist, it is possible to verify that the data comprising each area 

of the results are consistent with the system boundaries (e.g., all life cycle stages are included) and that 

the data is representative of the specified area (e.g., accounting for 90 percent of all raw materials and 

environmental releases). The result of this effort will be a checklist indicating that the results for each 

product/process are complete and reflective of the stated goals and scope of the LCA study. If 

deficiencies are noted, then a fair comparison cannot be performed and additional efforts are required to 

fill the gaps. In some cases, data may not be available to fill the data gaps; under these circumstances, it 

is necessary to report the differences in the data with the final results and estimate the impact to the 

comparison either quantitatively (percent uncertainty) or qualitatively (Alternative A’s reported result 

may be higher because “X” is not included in its assessment). 

Sensitivity Check - The objective of the sensitivity check is to evaluate the reliability of the results by

determining whether the uncertainty in the significant issues identified in Step 1 affect the decision56
maker’s ability to confidently draw comparative conclusions. A sensitivity check can be performed on 

the significant issues using the following three common techniques for data quality analysis: 

1. Contribution Analysis – Identifies the data that has the greatest contribution on the impact indicator 

results. 

2. Uncertainty Analysis – Describes the variability of the LCIA data to determine the significance of 

the impact indicator results. 

3. Sensitivity Analysis – Measures the extent that changes in the LCI results and characterization 

models affect the impact indicator results. 

Additional guidance on how to conduct a contribution, uncertainty, or sensitivity analysis can be found in 

the EPA document entitled “Guidelines for Assessing the Quality of Life Cycle Inventory Analysis,” 

April 1995, EPA 530-R-95-010. As part of the LCI and LCIA phases, a sensitivity, uncertainty, and/or

contribution analysis may have been conducted. These results can be used as the sensitivity check. As 

part of the goal, scope, and definition phase of the LCA process, the data quality and accuracy goals were 

defined. Verify that these goals have been met with the sensitivity check. If deficiencies exist, then the 

accuracy of the results may not be sufficient to support the decisions to be made and additional efforts are 

required to improve the accuracy of the LCI data collected and/or impact models used in the LCIA. In 

some cases, better data or impact models may not be available. Under these circumstances, report the 

deficiencies for each relevant significant issue and estimate the impact to the comparison either 

quantitatively or qualitatively. 

Consistency Check - The consistency check determines whether the assumptions, methods, and data used 

throughout the LCA process are consistent with the goal and scope of the study, and for each 

product/process evaluated. Verifying and documenting that the study was completed as intended at the 

conclusion increases confidence in the final results. 

A formal checklist should be developed to communicate the results of the consistency check. Exhibit 5-2 

provides examples of the types of information to be included in the checklist. The goal and scope of the 

LCA determines which categories should be used. 

Depending upon the goal and scope of the LCA, some inconsistency may be acceptable. If any

inconsistency is detected, document the role it played in the overall consistency evaluation. 

After completing steps 1 and 2, it has been determined that the results of the impact assessment and the 

underlying inventory data are complete, comparable, and acceptable to draw conclusions and make 

recommendations. If this is not true, stop! Repeat steps 1 and 2 until the results will be able to support 

the original goals for performing the LCA. 

57
Exhibit 5-2. Examples of Checklist Categories and Potential Inconsistencies 

Category Example of Inconsistency

Data Source Alternative A is based on literature and Alternative B is based on measured data. 

Data Accuracy For Alternative A, a detailed process flow diagram is used to develop the LCI data. 

For Alternative B, limited process information was available and the LCI data

developed was for a process that was not described or analyzed in detail. 

Data Age Alternative A uses 1980's era raw materials manufacturing data. Alternative B used a 

one year-old study.

Technological 

Representation 

Alternative A is bench-scale laboratory model. Alternative B is a full-scale

production plant operation.

Temporal 

Representation 

Data for Alternative A describe a recently developed technology. Alternate B 

describes a technology mix, including recently built and old plants. 

Geographical 

Representation 

Data for Alternative A were data from technology employed under European

environmental standards. Alternative B uses the data from technology employed 

under U.S. environmental standards. 

System

Boundaries, 

Assumptions, 

& Models 

Alternative A uses a Global Warming Potential model based on 500 year potential. 

Alternative B uses a Global Warming Potential model based on 100 year potential. 

Step 3: Draw Conclusions and Recommendations 

The objective of this step is to interpret the results of the life cycle impact assessment (not the LCI) to 

determine which product/process has the overall least impact to human health and the environment, 

and/or to one or more specific areas of concern as defined by the goal and scope of the study.

Depending upon the scope of the LCA, the results of the impact assessment will return either a list of unnormalized and un-weighted impact indicators for each impact category for the alternatives, or it will 

return a single grouped, normalized, and weighted score for each alternative, or something in between, 

e.g., normalized but not weighted. 

In the case where a score is calculated, the recommendation may be to accept the product/process with the 

lowest score. Or, it could be to investigate the reasons how the process could be modified to lower the 

score. However, do not forget the underlying assumptions that went into the analysis. 

If an LCIA stops at the characterization stage, the LCIA interpretation is less clear-cut. The conclusions 

and recommendations rest on balancing the potential human health and environmental impacts in the light 

of study goals and stakeholder concerns. 

A few words of caution should be noted. It is important to draw conclusions and provide 

recommendations based only on the facts. Understanding and communicating the uncertainties and 

limitations in the results is equally as important as the final recommendations. In some instances, it may

not be clear which product or process is better because of the underlying uncertainties and limitations in 

the methods used to conduct the LCA or the availability of good data, time, or resources. In this situation, 

the results of the LCA are still valuable. They can be used to help inform decision-makers about the 

human health and environmental pros and cons, understanding the significant impacts of each, where they

are occurring (locally, regionally, or globally), and the relative magnitude of each type of impact in 

comparison to each of the proposed alternatives included in the study. 

58
Reporting the Results 

Now that the LCA has been completed, the materials must be assembled into a comprehensive report 

documenting the study in a clear and organized manner. This will help communicate the results of the 

assessment fairly, completely, and accurately to others interested in the results. The report presents the 

results, data, methods, assumptions, and limitations in sufficient detail to allow the reader to comprehend 

the complexities and trade-offs inherent in the LCA study. 

If the results will be reported to someone who was not involved in the LCA study, i.e., third-party

stakeholders, this report will serve as a reference document and should be provided to them to help 

prevent any misrepresentation of the results. 

The reference document should consist of the following elements (ISO 1997): 

1. Administrative Information 

a. Name and address of LCA practitioner (who conducted the LCA study)

b. Date of report 

c. Other contact information or release information 

2. Definition of Goal and Scope 

3. Life Cycle Inventory Analysis (data collection and calculation procedures) 

4. Life Cycle Impact Assessment (methodology and results of the impact assessment that was 

performed) 

5. Life Cycle Interpretation 

a. Results 

b. Assumptions and limitations 

c. Data quality assessment 

6. Critical Review (internal and external) 

a. Name and affiliation of reviewers 

b. Critical review reports 

c. Responses to recommendations 

Critical Review 

The desirability of a peer review process has been a major focus of discussion in many life-cycle analysis 

forums. The discussion stems from concerns in four areas; lack of understanding regarding the 

methodology used or the scope of the study, desire to verify data and the analyst’s compilations of data, 

questioning key assumptions and the overall results, and communication of results. For these reasons, it 

is recommended that a peer review process be established and implemented early in any study that will be 

used in a public forum. 

The following discussion is not intended to be a blueprint of a specific approach. Instead, it is meant to 

point out issues that the practitioner or sponsor should keep in mind when establishing a peer review 

procedure. Overall, a peer review process should address the four areas previously identified: 

• Scope/boundaries methodology

• Data acquisition/compilation 

• Validity of key assumptions and results 

• Communication of results.

59
The peer review panel should participate in all phases of the study: (1) reviewing the purpose, system

boundaries, assumptions, and data collection approach; (2) reviewing the compiled data and the

associated quality measures; and, (3) reviewing the draft inventory report, including the intended 

communication strategy. 

A spreadsheet, such as the one presented in Appendix A would be useful in addressing many of the issues 

surrounding scope/boundaries methodology, data/compilation of data, and validity of assumptions and 

results. Criteria may need to be established for communication of results. These criteria could include 

showing how changes in key assumptions could affect the study results, and guidance on how to publish 

and communicate results without disclosing proprietary data. 

It is generally believed that the peer review panel should consist of a diverse group of three to five 

individuals representing various sectors, such as federal, state, and local governments, academia, industry,

environmental or consumer groups, and LCA practitioners. Not all sectors need be represented on every

panel. The credentials or background of individuals should include a reputation for objectivity, 

experience with the technical framework or conduct of life-cycle analysis studies, and a willingness to 

work as part of a team. Issues for which guidelines are still under development include panel selection, 

number of reviews, using the same reviewers for all life-cycle studies or varying the members between 

studies, and having the review open to the public prior to its release. The issue of how the reviews should 

be performed raises a number of questions, such as these: Should a standard spreadsheet be required? 

Should oral as well as written comments from the reviewers be accepted? How much time should be 

allotted for review? Who pays for the review process?

The peer review process should be flexible to accommodate variations in the application or scope of lifecycle studies. Peer review should improve the conduct of these studies, increase the understanding of the 

results, and aid in further identifying and subsequently reducing any environmental consequences of 

products or materials. EPA supports the use of peer reviews as a mechanism to increase the quality and 

consistency of life-cycle inventories. 

Conclusion 

Adding life cycle assessment to the decision-making process provides an understanding of the human 

health and environmental impacts that traditionally is not considered when selecting a product or process. 

This valuable information provides a way to account for the full impacts of decisions, especially those 

that occur outside of the site that are directly influenced by the selection of a product or process. 

Remember, LCA is a tool to better inform decision-makers and should be included with other decision 

criteria, such as cost and performance, to make a well-balanced decision. 

60
References

Bare, J.C., Norris, G.A., Pennington, D.W., and McKone, T. 2003. “TRACI – The Tool for the 

Reduction and Assessment of Chemical and Other Environmental Impacts.” Journal of Industrial 

Ecology. 6(3-4), pp 49-78. The MIT Press. http://mitpress.mit.edu/jie

Boustead, I., and Hancock, G.F. 1979. Handbook of Industrial Energy Analysis. Chichester: Ellis 

Horwood and New York: John Wiley. ISBN 0-470-26492-6. Chapter 3, “Real Industrial Systems,” p. 76. 

Goldsmith, E and R Allen. 1972. “A Blueprint for Survival.” The Economist 2(1). 

Guinee et al. 2001. An Operational Guide to the ISO Standards. 

http://www.leidenuniv.nl/cml/ssp/projects/lca2/lca2.html

Curran, M.A. (ed) 1996. Environmental Life Cycle Assessment. ISBN 0-07-015063-X, McGraw-Hill. 

Curran, M.A., Mann, M., and Norris, G. 2005. “International Workshop on Electricity Data for Life Cycle 

Inventories.” J Cleaner Production. 13(8), pp 853-862. 

Environmental Protection Agency. 2003. Tool for the Reduction and Assessment of Chemical and Other 

Environmental Impacts (TRACI): User’s Guide and System Documentation. EPA 600/R-02/052. National 

Risk Management Research Laboratory. Cincinnati, Ohio, USA. 

Environmental Protection Agency. 1995. Guidelines for Assessing the Quality of Life Cycle Inventory 

Analysis. EPA/530/R-95/010. Office of Solid Waste. Washington, DC. USA. 

Environmental Protection Agency. 1993. Life Cycle Assessment: Inventory Guidelines and Principles. 

EPA/600/R-92/245. Office of Research and Development. Cincinnati, Ohio, USA. 

Environmental Protection Agency. 1986. EPA Quality Assurance Management Staff. Development of 

Data Quality Objectives: Description of Stages I and II. 

Hendrickson, C.T., Lave L., and Matthews, H.S. 2006. Environmental Life Cycle Assessment of Goods 

and Services: An Input-Output Approach. Resources for the Future, Washington, DC, ISBN 1-933115-

23-8. 

International Standards Organization. 1997. Environmental Management - Life Cycle Assessment - 

Principles and Framework ISO 14040.

International Standards Organization. 1998. Life Cycle Assessment - Impact Assessment ISO 14042.

International Standards Organization. 1998b. Environmental Management - Life Cycle Assessment - Life 

Cycle Interpretation ISO 14043.

Jensen, A.A. and Remmen, A. 2004. “Background Report for a UNEP Guide to Life Cycle Management 

- A Bridge to Sustainable Products.” Final draft 30 December 2004. UNEP/SETAC Life Cycle Initiative. 

Available from: 

http://www.uneptie.org/pc/sustain/reports/lcini/Background%20document%20Guide%20LIFE%20CYCL

E%20MANAGEMENT%20rev%20final%20draft.pdf. Accessed 08 June 2005. 

61
Meadows, D.H. et al. 1972. The Limits to Growth: A Report for the Club of Rome’s Project on the 

Predicament of Mankind. Universe Books, New York. P. 205. 

Society of Environmental Toxicology and Chemistry. 1991. A Technical Framework for Life Cycle 

Assessment. Fava, J., Denison, R., Jones, B., Curran, M.A., Vigon, B., Selke, S., and Barnum, J. (eds). 

Society of Environmental Toxicology and Chemistry. 1993. Guidelines for Life Cycle Assessment: A 

‘Code of Practice.’ Consoli, F., Allen, D., Boustead, I., Fava, J., Franklin, W., Jensen, A.A., Oude, N., 

Parrish, R., Perriman, R., Postlethwaite, D., Quay, B., Seguin, J., and Vigon, B. (eds). 

Society of Environmental Toxicology and Chemistry. 1997. Life Cycle Impact Assessment: The State-ofthe-Art. Barnthouse, L., Fava, J., Humphreys, K., Hunt, R., Laibson, L., Noessen, S., Owens, J.W., Todd, 

J.A., Vigon, B., Wietz, K., and Young, J. (eds). 

Society of Environmental Toxicology and Chemistry. 2004. Life-Cycle Management. Hunkeler, D., 

Rebitzer, G., Finkbeiner, M., Schmidt W-P., Jensen, A.A., Stranddorf, H., and Christiansen, K. 

Werner, A.F. 1991. Product Lifecycle Assessment: A Strategic Approach. Proceedings of the 

Global Pollution Prevention ’91 Conference, Washington, D.C.

62
Appendix A 

Sample Inventory Spreadsheet 

(This is a fictitious example of the life cycle inventory 

for a gasoline system and does not represent real data). 

63
PROCESS NAME: Fictitious Gasoline Life Cycle Inventory 

PROCESS ID: Gasoline REFERENCE FLOW: 1000 Units: gallons of: GPROCESS DESCRIPTION: Summary of LCI to extract, produce, and distribute 1,000 gallon

to fuel a typical passenger automobile in the US. 

BASIS OF CALCULATIONS 

Summer Winter Average Units Re

 Oxygen Content 2.1 1.9 0.02 percent EP

Molecular Weight 88 g/mol ww

Oxygenate Content by Volume 11.05 percent by volOxygenate Content by Weight 11.15 percent by weFuel Economy Estimated for Average Car By Fuel Type 20.22 miles/gal MPetroleum Refining Process Efficiency (mass outputs/mass inputs) 

Petroleum Refinery Process Efficiency (mass basis) 92 percent EI

GREET v1.6 Published Petroleum Refinery Efficiency 85 percent G

Process Efficiency Used in Calculations 85 percent 

Process Inputs 

Material Coal 9.88E+01 lb 

Crude Oil 5.64E+02 ga

Natural Gas 3.23E+02 SC

Uranium 6.69E-02 lb 

Wood 3.99E+00 lb Drilling Fluids Unknown 

Process Outputs 

Product Gasoline 594 ga

Co-Product N/A Air Emissions 

64
Mat. P&D Fuel P&D Fuel Use Process Total U

Volatile Organic Compounds (VOC) 1.86E-01 1.49E-01 2.98E-01 1.36E+01 1.42E+01 lb 

Carbon Monoxide (CO) 4.69E-01 4.78E-01 2.32E+00 3.00E+02 3.03E+02 lb Nitrogen Oxides (NOx) 1.51E+00 1.64E+00 8.33E+00 2.26E+01 3.41E+01 lb 

PM10 6.16E-02 2.06E-01 2.45E-01 6.79E-01 1.19E+00 lb 

Sulfur Oxides (SOx) 6.41E-01 2.17E+00 2.52E+00 1.44E+00 6.77E+00 lb 

Methane 5.60E-01 1.26E+00 3.18E-01 1.70E+00 3.84E+00 lb 

Nitrous Oxide (N2O) 3.91E-03 4.38E-03 2.85E-02 3.68E-02 lb 

Carbon Dioxide (CO2) 2.20E+02 3.75E+02 1.56E+03 1.20E+04 1.41E+04 lb 

VOC loss: evaporation 1.39E+01 1.39E+01 lb VOC loss: spillage 2.70E-04 2.36E-03 2.62E-03 lb 

1 1 1-Trichloroethane 2.19E-05 2.19E-05 lb 

1 2 3-Trichloropropane 9.67E-06 9.67E-06 lb 1 2 4-Trichlorobenzene 5.8E-07 5.8E-07 lb 1 2 4-Trimethylbenzene 1.07E-04 1.02E-04 1.23E-01 1.23E-01 lb 

1 2-Dibromoethane 1.24E-06 1.19E-06 1.61E-05 1.86E-05 lb 1 2-Dichloroethane 3.2E-06 3.06E-06 4.15E-05 4.78E-05 lb 1 3-Butadiene 2.9E-05 2.77E-05 8.39E-02 8.40E-02 lb 

2 2 4-TM-Pentane 1.20E+00 1.20E+00 lb 2 2 5-TM-Hexane 1.39E-01 1.39E-01 lb 2 3 3-TM-Pentane 2.22E-01 2.22E-01 lb 2 3 4-TM-Pentane 2.21E-01 2.21E-01 lb 

2 3-Dimethylbutane 1.39E-01 1.39E-01 lb 

2 4-Dimethylphenol 1.01E-07 1.01E-07 lb 

2-Methyl-2-butene 9.19E-02 9.19E-02 lb 

2-Methylhexane 1.57E-01 1.57E-01 lb 

2-Methylpentane 2.84E-01 2.84E-01 lb 3-Methylhexane 1.64E-01 1.64E-01 lb 3-Methylpentane 1.82E-01 1.82E-01 lb 

Acenaphthene 9.23E-05 9.23E-05 lb 

Acenaphthylene 5.20E-04 5.20E-04 lb Acetonitrile 4.29E-06 4.29E-06 lb 

Acetophenone 2.75E-06 2.75E-06 lb 

Acreolin 4.29E-07 3.2E-06 1.57E+03 8.21E-03 8.21E-03 lb 

Aluminum (fume or dust) 2.36E-08 2.36E-08 lb 

65
Ammonia 1.32E-03 2.43E-03 2.68E+00 2.68E+00 lb 

Anthracene 5.88E-07 5.62E-07 1.14E-04 1.16E-04 lb Antimony 2.17E-07 1.62E-06 1.85E-06 3.69E-06 lb Antimony Compounds 5.9E-07 5.64E-07 7.65E-06 8.80E-06 lb Arsenic 9.85E-07 7.34E-06 7.60E-05 8.43E-05 lb Asbestos (friable) 0.00E+00 lb Barium 8.80E-08 8.80E-08 lb Barium Compounds 1.05E-06 1.05E-06 lb Benzene 1.60E-03 2.26E-03 6.38E-01 6.42E-01 lb Benzo(a)anthracene 1.30E-05 1.30E-05 lb Benzo(a)pyrene 1.30E-05 1.30E-05 lb 

Benzo(b)fluoranthene 1.54E-05 1.54E-05 lb 

Benzo(g,h,i)perylene 3.24E-05 3.24E-05 lb Benzo(k)fluoranthene 1.54E-05 1.54E-05 lb Beryllium 1.12E-07 8.35E-07 9.47E-07 lb Biphenyl 2.31E-05 1.05E-05 3.73E-04 4.06E-04 lb 

Butraldehyde 5.58E-06 5.58E-06 lb 

Cadmium 2.14E-07 1.6E-06 2.79E-08 1.84E-06 lb Carbon Disulfide 1.89E-06 1.81E-06 2.45E-05 2.83E-05 lb 

Carbon Tetrachloride 2.43E-06 7.29E-06 2.16E-05 3.13E-05 lb 

Carbonyl Sulfide 5.23E-05 5.01E-05 7.58E-05 1.78E-04 lb 

Certain Glycol Ethers 3.11E-05 3.11E-05 lb 

Chlorine 4.06E-05 3.97E-05 5.25E-04 6.05E-04 lb 

Chlorine Dioxide 4.29E-09 4.29E-09 lb 

Chlorobenzene 0.00E+00 lb 

Chlorodifluoromethane 8.34E-06 7.99E-06 1.08E-04 1.25E-04 lb 

Chloromethane 2.97E-06 2.97E-06 lb 

Chromium 1.28E-06 9.52E-06 7.51E-08 1.09E-05 lb 

Chromium Compounds 9.85E-08 9.42E-08 1.28E-06 1.47E-06 lb Chromium III 7.85E-05 7.85E-05 lb 

Chromium VI 5.23E-05 5.23E-05 lb Chrysene 1.30E-05 1.30E-05 lb Cobalt 7.22E-07 4.86E-06 3.22E-08 5.62E-06 lb 

Cobalt Compounds 2.48E-09 2.38E-09 1.02E-06 1.03E-06 lb 

Copper 3.01E-08 3.01E-08 lb 

66
Copper Compounds 3.2E-07 3.07E-07 4.16E-06 4.78E-06 lb 

Cresol (mixed Isomers) 3.87E-06 3.7E-06 5.02E-05 5.78E-05 lb Cumene 1.42E-03 3.36E-03 5.10E-03 9.88E-03 lb 

Cumene Hydroperoxide 1.09E-05 1.09E-05 lb 

Cyanide Compounds 8.07E-05 8.07E-05 lb Cyclohexane 2.54E-04 2.43E-04 3.30E-03 3.79E-03 lb Dibenz(a,h)anthracene 0.00E+00 lb Dicyclopentadiene 3.94E-06 3.94E-06 lb Diethanolamine 2.94E-05 2.82E-05 3.82E-04 4.40E-04 lb Dioxins 2.36E-12 1.76E-11 1.99E-11 lb Ethylbenzene 7.00E-04 1.11E-03 3.44E-01 3.46E-01 lb Ethylene 3.62E-04 3.46E-04 4.69E-03 5.40E-03 lb Ethylene Glycol 1.89E-05 1.81E-05 2.45E-04 2.82E-04 lb Ethylene Oxide 4.29E-06 4.29E-06 lb Formaldehyde 2.93E-05 3.95E-05 2.32E-01 2.32E-01 lb 

Fluoranthene 1.15E-04 1.15E-04 lb 

Fluorene 1.91E-04 1.91E-04 lb 

Hydrazine 1.63E-06 1.63E-06 lb 

Hydocarbons (non CH4) 2.49E-02 1.86E-01 2.11E-01 lb 

Hydrochloric Acid 2.27E-03 1.63E-02 1.26E-03 1.98E-02 lb 

Hydrogen Cyanide 4.21E-05 4.21E-05 lb Hydrogen Fluoride 3.50E-04 2.28E-03 6.52E-04 3.28E-03 lb 

Indeno(123cd)pyrene 9.71E-06 9.71E-06 lb 

Isopentane 4.1E-07 4.55E-01 4.55E-01 lb 

Isopropyl Alcohol 3.59E-06 3.59E-06 lb 

Kerosene 1.09E-05 8.09E-05 9.18E-05 lb 

Lead 1.73E-06 1.29E-05 1.29E-08 1.46E-05 lb 

Lead Compounds 2.08E-07 1.99E-07 2.69E-06 3.10E-06 lb 

m-Xylene 9.61E-04 1.66E-03 4.01E-03 6.63E-03 lb 

Manganese 2.97E-06 2.21E-05 4.43E-05 6.94E-05 lb 

Manganese Compounds 2.23E-06 2.23E-06 lb 

Mercury 8.13E-07 6.06E-06 2.31E-05 3.00E-05 lb Mercury Compounds 1.29E-07 1.29E-07 lb 

Metals 4.5E-06 3.35E-05 3.80E-05 lb 

Methanol 1.05E-03 1.00E-03 1.36E-02 1.57E-02 lb 

67
Methyl Ethyl Ketone 4.91E-04 4.70E-04 6.37E-03 7.33E-03 lb 

Methyl Isobutyl Ketone 3.37E-05 3.22E-05 4.37E-04 5.03E-04 lb 

Methyl Tert-Butyl Ether 3.42E-04 3.27E-04 2.30E+00 2.30E+00 lb 

Methylene Chloride 1.85E-06 1.38E-05 0.00E+00 1.56E-05 lb 

Molybdenum Trioxide 4.50E-07 4.31E-07 5.84E-06 6.72E-06 lb 

n-Butane 1.10E-01 1.10E-01 lb n-Butyl Alcohol 2.45E-05 2.45E-05 lb n-Pentane 7.21E-04 5.29E-04 1.91E-01 1.92E-01 lb 

n-Hexane 7.21E-04 6.90E-04 4.13E-01 4.14E-01 lb 

n-Heptane 1.90E-01 1.90E-01 lb n-Octane 4.12E-03 4.12E-03 lb 

n-nonane 3.19E-03 3.19E-03 lb 

n-Decane 3.07E-03 3.07E-03 lb n-Undecane 1.75E-03 1.75E-03 lb n-Dodecane 2.31E-03 2.31E-03 lb 

n-Tridecane 2.74E-03 2.74E-03 lb 

n-Tetradecane 2.97E-03 2.97E-03 lb 

n-Pentadecane 2.83E-03 2.83E-03 lb n-Hexadecane 2.67E-03 2.67E-03 lb 

n-Heptadecane 2.62E-03 2.62E-03 lb 

n-Octadecane 1.60E-03 1.60E-03 lb n-Nonadecane 1.95E-03 1.95E-03 lb n-Icosane 1.79E-03 1.79E-03 lb 

n-Henicosane 1.66E-03 1.66E-03 lb 

n-Docosane 1.62E-03 1.62E-03 lb n-Methyl-2-Pyrrolidone 3.8E-05 3.64E-05 4.93E-04 5.67E-04 lb n-Nitrodimethylamine 9.06E-08 6.75E-07 7.66E-07 lb 

Naphthalene 7.36E-05 5.09E-05 1.76E-02 1.77E-02 lb 

Nickel 6.68E-06 4.83E-05 9.81E-05 1.53E-04 lb Nickel Compounds 5.81E-06 5.56E-06 7.53E-05 8.67E-05 lb 

Nitrate Compounds 0.00E+00 lb 

o-Xylene 9.39E-04 1.64E-03 3.73E-03 6.31E-03 lb Other Aldehydes 8.17E-05 6.08E-04 6.90E-04 lb Other Organics 1.24E-04 9.27E-04 1.05E-03 lb p-Xylene 9.94E-04 1.69E-03 1.61E-03 4.30E-03 lb 

68
Particulates (total) 3.61E-02 2.69E-01 0.00E+00 3.05E-01 lb 

Perchloroethylene 4.10E-07 3.05E-06 0.00E+00 3.46E-06 lb Phenanthrene 3.00E-05 1.31E-05 4.81E-04 5.24E-04 lb 

Phenols 2.52E-05 3.15E-05 3.12E-04 3.69E-04 lb 

Polycyclic Aromatic Compounds 7.74E-06 7.41E-06 1.00E-04 1.16E-04 lb 

Propionaldehyde 8.97E-03 8.97E-03 lb 

Propylene 6.65E-04 6.36E-04 8.63E-03 9.93E-03 lb Pyrene 1.57E-04 1.57E-04 lb 

Quinoline 1.01E-05 1.01E-05 lb 

Radionuclides (Ci) 8.90E-06 6.63E-05 7.52E-05 lb 

Selenium 3.09E-06 2.30E-05 2.61E-05 lb Selenium Compounds 1.07E-07 1.07E-07 lb Styrene 1.23E-06 1.18E-06 4.10E-02 4.10E-02 lb Sulfuric Acid 1.36E-03 1.30E-03 1.76E-02 2.03E-02 lb 

Tert-Butyl Alcohol 9.20E-07 8.81E-07 1.19E-05 1.37E-05 lb 

Tetrachloroethylene 1.03E-05 9.81E-06 1.33E-04 1.53E-04 lb 

Toluene 3.36E-03 4.36E-03 2.00E+00 2.00E+00 lb 

Toluene-2 6-Diisocyanate 4.14E-06 4.14E-06 lb Trichloroethylene 1.08E-05 1.30E-05 1.35E-04 1.59E-04 lb Vanadium 5.93E-06 5.93E-06 lb Vinyl Acetate 1.51E-05 1.51E-05 lb 

Xylene (mixed isomers) 5.52E-04 5.28E-04 1.31E+00 1.31E+00 lb Zinc (fume or dust) 1.09E-06 1.05E-06 1.42E-05 1.63E-05 lb 

Zinc Compounds 8.05E-06 7.71E-06 1.04E-04 1.20E-04 lb 

Acetaldehyde 0.00E+00 0.00E+00 6.72E-02 6.72E-02 lb Total 2.24E+02 3.85E+02 1.57E+03 1.24E+04 1.45E+04 lb 

Water Emissions 

Mat. P&D Fuel P&D Fuel Use Process Total U

1 1 1-Trichloroethane 0.00E+00 lb 

1 2 3-Trichloropropane 0.00E+00 lb 

1 2 4-Trichlorobenzene 0.00E+00 lb 

1 2 4-Trimethylbenzene 3.99E-07 1.6E-06 2.17E-01 2.17E-01 lb 

1 2-Dibromoethane 9.6E-10 9.41E-10 1.29E-08 1.48E-08 lb 1 2-Dichloroethane 2.15E-09 2.15E-09 lb 1 3-Butadiene 1.27E-07 1.25E-07 1.70E-06 1.96E-06 lb 

69
2 2 4-TM-Pentane 7.97E-01 7.97E-01 lb 

2 2 5-TM-Hexane 2.49E-01 2.49E-01 lb 2 3 3-TM-Pentane 3.96E-01 3.96E-01 lb 2 3 4-TM-Pentane 3.95E-01 3.95E-01 lb 

2 3-Dimethylbutane 2.49E-01 2.49E-01 lb 

2 4-Dimethylphenol 2.25E-07 2.25E-07 lb 

2-Methyl-2-Butene 1.64E-01 1.64E-01 lb 2-Methylhexane 2.80E-01 2.80E-01 lb 2-Methylpentane 5.07E-01 5.07E-01 lb 3-Methylhexane 2.93E-01 2.93E-01 lb 3-Methylpentane 3.25E-01 3.25E-01 lb Acetaldehyde 5.25E-07 5.25E-07 lb Acetonitrile 0.00E+00 lb Acetophenone 0.00E+00 lb Acid 4.96E-10 3.7E-09 4.19E-09 lb 

Aluminum (fume or dust) 0.00E+00 lb 

Ammonia 1.02E-04 2.25E-04 1.11E-03 1.44E-03 lb 

Anthracene 8.07E-07 8.07E-07 lb 

Antimony 9.17E-07 9.17E-07 lb 

Antimony Compounds 1.51E-07 1.48E-07 2.03E-06 2.33E-06 lb 

Arsenic 8.37E-08 8.37E-08 lb Barium 3.99E-06 3.99E-06 lb Barium Compounds 1.37E-05 1.37E-05 lb Benzene 4.25E-04 1.16E-03 8.58E-02 8.73E-02 lb 

Beryllium 4.94E-08 4.94E-08 lb 

Biphenyl 0.00E+00 1.15E-06 7.19E-07 1.87E-06 lb 

Biological Oxygen Demand (BOD) 1.11E-03 8.31E-03 9.42E-03 lb 

Boron 5.46E-06 4.07E-05 4.62E-05 lb Cadmium 3.60E-04 2.83E-04 1.63E-03 2.27E-03 lb 

Carbon Disulfide 8.59E-09 8.59E-09 lb 

Certain Glycol Ethers 3.33E-06 3.33E-06 lb 

Chlorine 2.56E-06 2.51E-06 3.43E-05 3.94E-05 lb 

Chromates 5.46E-06 4.07E-05 4.62E-05 lb 

Chromium 5.65E-07 5.65E-07 lb 

Chromium Compounds 9.24E-07 9.05E-07 1.24E-05 1.42E-05 lb 

70
Cobalt 4.81E-06 4.81E-06 lb 

Cobalt Compounds 3.18E-06 3.18E-06 lb 

Copper 1.07E-08 1.07E-08 lb Copper Compounds 3.42E-07 3.35E-07 4.59E-06 5.27E-06 lb 

Cresol (mixed isomers) 3.43E-07 3.36E-07 4.60E-06 5.28E-06 lb 

Cumene 7.80E-04 4.13E-03 1.92E-03 6.83E-03 lb Cyclohexane 3.15E-07 3.09E-07 4.23E-06 4.85E-06 lb Diethanolamine 1.21E-01 9.00E-01 2.55E-05 1.02E+00 lb Ethylbenzene 2.26E-04 7.83E-04 1.40E-01 1.41E-01 lb Ethylene 1.42E-06 1.42E-06 lb Ethylene Glycol 4.48E-05 3.24E-04 2.02E-05 3.89E-04 lb Fluorine 5.71E-05 5.71E-05 lb 

Hydrogen Fluoride 1.52E-07 1.52E-07 lb Iron 6.62E-01 4.03E-01 3.08E+00 4.14E+00 lb Isopentane 9.86E-01 9.86E-01 lb 

Lead 1.42E-07 1.42E-07 lb 

Lead Compounds 1.40E-07 1.37E-07 1.87E-06 2.15E-06 lb 

m-Xylene 1.41E-03 1.41E-03 lb 

Manganese 2.64E-02 1.61E-02 1.23E-01 1.65E-01 lb Manganese Compounds 3.41E-06 3.41E-06 lb 

Mercury 4.65E-05 9.99E-05 1.68E-04 3.14E-04 lb Methanol 3.15E-04 1.95E-04 1.55E-03 2.06E-03 lb Methyl Ethyl Ketone 1.32E-06 1.29E-06 1.77E-05 2.03E-05 lb 

Methyl Isobutyl Ketone 4.96E-09 4.86E-09 6.65E-08 7.64E-08 lb 

Methyl Tert-Butyl Ether 1.88E-05 2.57E-05 1.32E+00 1.32E+00 lb 

Molybdenum Trioxide 5.99E-07 5.87E-07 8.03E-06 9.22E-06 lb 

n-Butane 1.96E-01 1.96E-01 lb n-Butyl Alcohol 2.58E-08 2.58E-08 lb 

n-Pentane 3.75E-01 3.75E-01 lb n-Hexane 3.38E-07 2.07E-06 3.14E-01 3.14E-01 lb 

n-Heptane 1.74E-01 1.74E-01 lb n-Methyl-2-Pyrrolidone 6.72E-05 6.72E-05 lb n-Octane 1.65E-02 1.65E-02 lb 

n-Nonane 1.28E-02 1.28E-02 lb 

n-Decane 1.23E-02 1.23E-02 lb 

71
n-undecane 7.00E-03 7.00E-03 lb 

n-Dodecane 9.24E-03 9.24E-03 lb 

n-Tridecane 1.10E-02 1.10E-02 lb 

n-Tetradecane 1.19E-02 1.19E-02 lb 

n-Pentadecane 1.13E-02 1.13E-02 lb n-Hexadecane 1.07E-02 1.07E-02 lb 

n-Heptadecane 1.05E-02 1.05E-02 lb 

n-Octadecane 6.39E-03 6.39E-03 lb n-Nonadecane 7.80E-03 7.80E-03 lb n-Icosane 7.16E-03 7.16E-03 lb 

n-Henicosane 6.63E-03 6.63E-03 lb 

n-Docosane 6.46E-03 6.46E-03 lb 

Naphthalene 1.47E-04 4.13E-04 6.59E-04 1.22E-03 lb 

Nickel 4.06E-07 4.06E-07 lb Nickel Compounds 5.53E-06 3.18E-05 1.95E-05 5.69E-05 lb Nitrates 2.73E-03 2.68E-03 3.67E-02 4.21E-02 lb 

o-Xylene 1.41E-03 1.41E-03 lb 

Oil 5.58E-04 4.16E-03 0.00E+00 4.72E-03 lb 

p-Cresol 7.83E-07 7.83E-07 lb 

p-Xylene 1.41E-03 1.41E-03 lb Phenanthrene 9.23E-08 9.23E-08 lb 

Phenol 1.35E-04 1.00E-03 2.07E-05 1.16E-03 lb 

Polycyclic Aromatic Compounds 4.98E-08 4.88E-08 6.68E-07 7.66E-07 lb 

Propylene 1.43E-06 1.43E-06 lb Selenium 6.12E-07 6.12E-07 lb 

Selenium Compounds 4.94E-06 4.94E-06 lb 

Sodium Nitrite 6.01E-05 6.01E-05 lb Styrene 1.01E-07 1.01E-07 lb 

Sulfates 2.68E-04 2.00E-03 0.00E+00 2.27E-03 lb Sulfuric Acid 2.04E-02 1.52E-01 0.00E+00 1.73E-01 lb Tert-Butyl Alcohol 1.76E-05 1.76E-05 lb Tetrachloroethylene 1.07E-06 1.07E-06 lb 

Toluene 9.15E-04 2.65E-03 6.30E-01 6.33E-01 lb 

Vanadium 7.08E-08 7.08E-08 lb 

Xylene (mixed Isomers) 3.84E-06 1.94E-05 6.22E-01 6.22E-01 lb 

72
Zinc Compounds 1.32E-01 8.05E-02 6.15E-01 8.27E-01 lb 

Volatile Organic Compounds (VOC) 5.05E-07 9.08E-02 9.09E-02 lb 

Total 9.70E-01 1.58E+00 1.28E+01 1.54E+01 lb 

Solid Waste 

Mat. P&D Fuel P&D Fuel Use Process Total U

Sludge 2.52E+01 1.54E+01 1.17E+02 1.58E+02 lb 

Solid Waste #1 5.50E+00 4.08E+01 4.63E+01 lb 

Disposal Off-site, Subtitle D Landfill 7.73E-03 5.78E-03 1.70E-02 3.05E-02 lb Disposal Off-site, Subtitle C Landfill 3.04E-03 2.27E-03 6.68E-03 1.20E-02 lb Disposal On-site, Subtitle D Landfill 1.34E-03 1.00E-03 2.94E-03 5.28E-03 lb Disposal On-site, Subtitle C landfill 3.41E-04 2.55E-04 7.50E-04 1.35E-03 lb 

Total: 3.08E+01 5.61E+01 1.17E+02 2.04E+02 lb 

Raw Materials Extracted 

Fossil Fuel Mat. P&D Fuel P&D Fuel Use Process Total U

Coal 1.08E+05 8.06E+05 9.14E+05 BtCrude Oil 1.19E+07 4.73E+06 5.67E+07 7.33E+07 BtNatural Gas 3.54E+04 2.64E+05 3.00E+05 Bt

Non-Fossil Fuel 

Uranium 4.72E-05 6.69E-02 6.69E-02 lb Wood 3.79E-01 3.61E+00 3.99E+00 lb 

Water Consumption 

Mat. P&D Fuel P&D Fuel Use Process Total U

Public Supply 0.00E+00 ga

River/Canal 0.00E+00 gaSea 0.00E+00 gaUnspecified 2.27E+02 2.27E+02 gaWell 0.00E+00 gaTotal: 2.27E+02 2.27E+02 ga

Land Use 

Mat. P&D Fuel P&D Fuel Use Process Total U

Unknown ac

73
Appendix B 

LCA and LCI Software Tools 

Tool Vendor URL 

BEES 3.0 NIST Building and Fire http://www.bfrl.nist.gov/oae/software/bees.html 

Research Laboratory 

Boustead Model Boustead Consulting http://www.boustead-consulting.co.uk/products.htm 

5.0 

CMLCA 4.2 Centre of Environmental http://www.leidenuniv.nl/cml/ssp/software/cmlca/index.ht 

Science ml 

Dubo-Calc Netherlands Ministry of http://www.rws.nl/rws/bwd/home/www/cgiTransport, Public Works and bin/index.cgi?site=1&doc=1785 

Water Management 

Ecoinvent 1.2 Swiss Centre for Life Cycle http://www.ecoinvent.ch 

Inventories 

Eco-Quantum IVAM http://www.ivam.uva.nl/uk/producten/product7.htm 

EDIP PC-Tool Danish LCA Center http://www.lca-center.dk 

eiolca.net Carnegie Mellon University http://www.eiolca.net 

Environmental ATHENATM Sustainable http://www.athenaSMI.ca 

Impact Indicator Materials Institute 

EPS 2000 Design Assess Ecostrategy Scandinavia http://www.assess.se/ 

System AB 

GaBi 4 PE Europe GmbH and IKP http://www.gabi-software.com/software.html 

University of Stuttgart 

GEMIS Öko-Institut http://www.oeko.de/service/gemis/en/index.htm 

GREET 1.7 DOE’s Office of Transportation http://www.transportation.anl.gov/software/GREET/index. 

html 

IDEMAT 2005 Delft University of Technology http://www.io.tudelft.nl/research/dfs/idemat/index.htm 

KCL-ECO 4.0 KCL http://www1.kcl.fi/eco/softw.html 

LCAIT 4.1 CIT Ekologik http://www.lcait.com/01_1.html 

LCAPIX v1.1 KM Limited http://www.kmlmtd.com/pas/index.html 

MIET 3.0 Centre of Environmental http://www.leidenuniv.nl/cml/ssp/software/miet/index.htm 

Science l 

REGIS Sinum AG http://www.sinum.com/htdocs/e_software_regis.shtml 

SimaPro 6.0 PRé Consultants http://www.pre.nl/simapro.html 

SPINE@CPM Chalmers http://www.globalspine.com 

SPOLD The Society for Promotion of http://lca-net.com/spold/ 

Life-Cycle Assessment 

TEAMTM 4.0 Ecobalance http://www.ecobalance.com/uk_lcatool.php 

Umberto ifu Hamburg GmbH http://www.ifu.com/en/products/umberto 

US LCI Data National Renewable Energy http://www.nrel.gov/lci 

Lab 

BEES 3.0. Created by the National Institute for Standards and Technology (NIST) Building and Fire 

Research Laboratory, the BEES (Building for Environmental and Economic Sustainability) software can 

be used for balancing the environmental and economic performance of building products. Version 3.0 of 

the WindowsTM-based decision support software, aimed at designers, builders, and product 

74
manufacturers, includes actual environmental and economic performance data for 200 building products. 

BEES 3.0 can be downloaded free of charge from the NIST website. 

Boustead Model 5.0. Created by Boustead Consulting, the Boustead Model is an extensive database in 

which data such as fuels and energy use, raw materials requirements, and solid, liquid, and gaseous 

emissions are stored. It also includes software which enables the user to manipulate data in the database 

and to select a suitable data presentation method from a host of options. 

CMLCA 4.2. Created by the Centre of Environmental Science (CML) at Leiden University, Chain 

Management by Life Cycle Assessment (CMLCA) is a software tool that is intended to support the 

technical steps of the LCA procedure. The program can be downloaded from the CML website. 

Dubo-Calc. The Netherlands Ministry of Transport, Public Works, and Water Management has created a 

database containing LCI data of construction materials which are used in civil works. Data included are 

secondary data, derived from other databases, brought together in a set to use with their software for 

designers. 

Ecoinvent Database v1.2. The ecoinvent data v1.2 comprises more than 2700 datasets with 

global/European/Swiss coverage. About 1000 elementary flows are reported for each dataset, including 

emissions to air, water, and soil, mineral and fossil resources, and land use. Several actual and 

widespread impact assessment methods, namely the cumulative energy demand, climate change, CML 

2001, Eco-indicator 99, the ecological scarcity method 1997, EDIP 1997, EPS 2000, and Impact 2002+ 

are implemented. The ecoinvent data are available through EMIS, GaBi, Regis, SimaPro, and Umberto 

and are importable into CMLCA, KCL-eco, and TEAM. 

Eco-Quantum. Eco-Quantum is a calculating tool on the basis of LCA which serves actors in the 

building sector with quantitative information on the environmental impact of buildings as a whole. The 

added value of Eco-Quantum in this context is the database with composition data of about 1000 building 

components. Eco-Quantum is available only in Dutch. 

EDIP PC-Tool. Developed for the Danish EPA, the EDIP PC-Tool is a user friendly Windows 

application and database that supports the LCA process carried out according to the EDIP method. To 

carry out an LCA, detailed information on all the processes and materials included in the life cycle of the 

product is needed. Therefore, the tool has been equipped with a relational database, close in structure to 

the internationally recognized SPOLD format. 

eiolca.net. Created by the Green Design Institute of Carnegie Mellon, this web site allows users to 

estimate the overall environmental impacts from producing a certain dollar amount of a commodity or 

service in the United States. The database first was made publicly available in 1999; since then two 

major and several minor updates have been conducted. The web-based model provides rough guidance 

on the relative impacts of different types of products, materials, services, or industries with respect to 

resource use and emissions. The latest version is based on the 1997 industry benchmark input-output 

accounts compiled by the Bureau of Economic Analysis of the U.S. Department of Commerce. It 

incorporates emissions and resource use factors estimated for all 491 sectors of the U.S economy, using 

publicly available electricity and fuel consumption data compiled by the U.S. Census Bureau, the U.S. 

Departments of Energy and Transportation, and environmental databases created by the U.S. EPA. 

Environmental Impact Indicator. Developed by the Athena Institute, the Estimator was prepared for 

architects, engineers, and researchers to get LCA answers about conceptual designs of new buildings or 

renovations to existing buildings. The Estimator assesses the environmental implications of industrial, 

institutional, office, or both multi-unit and single-family residential designs. The Estimator incorporates 

75
the Institute’s inventory databases that cover more than 90 structural and envelope materials. Released in 

2002, it simulates over 1,000 different assembly combinations and is capable of modeling 95 percent of 

the building stock in North America. Athena has also developed databases for energy use and related air 

emissions for on-site construction of building assemblies; maintenance, repair and replacement effects 

though the operating life; and, demolition and disposal. 

EPS 2000 Design System. Created by Assess Ecostrategy Scandinavia AB, EPS (Environmental Priority 

Strategies) is a life cycle impact assessment software for sustainable product development. A demo 

version can be ordered from the website. 

GaBi 4 Software System and Database. GaBi is supported jointly by PE Europe GmbH and IKP 

University of Stuttgart. Different versions are available from educational to professional use of Life Cycle 

Analysis to evaluate life cycle environmental, cost, and social profiles of products, processes and 

technologies. GaBi offers databases with worldwide coverage as well as Ecoinvent data. A demo version 

is available for download. 

GEMIS (Global Emission Model for Integrated Systems). The Öko-Institut’s GEMIS is a life cycle 

analysis program and database for energy, material, and transport systems. The GEMIS database offers 

information on fossil fuels, renewables, processes for electricity and heat, raw materials, and transports. 

The GEMIS database can be downloaded for free from the website. 

GREET 1.7. The U.S. Department of Energy's Office of Transportation Technologies fuel-cycle model 

called GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation) allows 

researchers to evaluate various engine and fuel combinations on a consistent fuel-cycle basis. 

IDEMAT 2005. Created by Delft University of Technology, IDEMAT is a tool for material selections in 

the design process. It provides a database with technical information about materials, processes and 

components and allows the user to compare information. A demo version can be downloaded from the 

DTU website. 

KCL-ECO 4.0. KCL-ECO can be used to apply LCA to complicated systems with many modules and 

flows. It includes allocation, impact assessment (characterization, normalization, and weighting), and 

graphing features. A demo version can be downloaded from the KCL website. 

LCAIT 4.1. Offered by CIT Ekologik since 1992, LCAit has been used for the environmental 

assessment of products and processes. It includes an impact assessment database, including 

characterization factors and weighting factors. A demo version can be downloaded from the CIT 

website. 

LCAPIX. Offered by KM Limited, the LCAPIX v1.1 software combines LCA and Activity Based 

Costing (ABC) to help businesses assure environmental compliance while assuring sustained profitability. 

It allows for a quantitative measurement which can indicate the potential burden of any product. A 

licensing fee is required, but a demo version can be downloaded from the KM Ltd. website. 

MIET 3.0. – Missing Inventory Estimation Tool. Created by the Centre of Environmental Science 

(CML), MIET is a Microsoft Excel spreadsheet that enables LCA practitioners to estimate LCI of 

missing flows that were truncated. MIET is based on the most up-to-date U.S. input-output table and 

environmental data. MIET covers about 1,200 different environmental interventions including air, water, 

industrial and agricultural soil emissions, and resource use by various industrial sectors. MIET can be 

downloaded for free from the CML website after filling out a short questionnaire. 

76
REGIS. Developed by Sinum AG, REGIS is a software tool for creating corporate ecobalances and 

improving corporate environmental performance according to ISO14031. A demo version can be 

downloaded from the Sinum website. 

SimaPro 6.0. Created by PRé Consultants, SimaPro is a professional LCA software tool that contains 

several impact assessment methods and several inventory databases, which can be edited and expanded 

without limitation. It can compare and analyze complex products with complex life cycles. A demo 

version can be downloaded from the web site link provided above. 

SPINE@CPM. Maintained by IMI, Industrial Environmental Informatics at Chalmers University of 

Technology, LCI@CPM is a web portal for LCI information. The portal provides the possibility to: 

search for specific LCI-data in the database; purchase LCI-data sets; and convert SPINE data sets into 

ISO/TS 14048 automatically. The database contains more than 500 data sets. SPINE@CPM is the ISO/TS 

14048 version of the Swedish national database. Some of the data sets in the database are reported as full 

flow-charts where each included process or transport is separately stored in the database. The data 

published in LCI@CPM are reviewed in order to ensure that the quality requirements according to 

ISO/TS 14048 have been fulfilled. 

SPOLD Data Exchange Software. The Society for Promotion of Life Cycle Development, a now 

defunct group, lives on in memory through this software that can be used to create, edit, import, and 

export data in the SPOLD '99 format. It can be downloaded from the 2.-0 LCA consultants website. 

TEAMTM 4.0. Offered by Pricewaterhouse Coopers Ecobilan Group (also known as Ecobalance), 

TEAMTM 3.0 is a professional tool for evaluating the life cycle environmental and cost profiles of 

products and technologies. It contains comprehensive database of over 600 modules with worldwide 

coverage. An online demo is available from the website. 

Umberto. Created by the Institute for Environmental Informatics (ifeu) in Hamburg, Germany, Umberto 

serves to visualize material and energy flow systems. Data are taken from external information systems 

or are newly modeled and calculated. 

US LCI Data. In May 2001, NREL and its partners created the U.S. Life-Cycle Inventory (LCI) 

Database to provide support to public, private, and non-profit sector efforts in developing product life 

cycle assessments and environmentally-oriented decision support systems and tools. The objective of the 

U.S. LCI Database Project is to provide LCI data for commonly used materials, products and processes 

following a single data development protocol consistent with international standards. Since the goal is to 

make the creation of LCIs easier, rather than to carry out full product LCIs, database modules provide 

data on many of the processes needed by others for conducting LCIs. However, the modules do not 

contain data characterizing the full life cycles of specific products. The data protocol is based on ISO 

14048 and is compatible with the EcoSpold format. The LCI data are available in several formats: a 

streamlined spreadsheet, an EcoSpold format spreadsheet, an EcoSpold XML file, and a detailed 

spreadsheet with all the calculation details. 

77
Glossary 

Accidental Emission An unintended environmental release. 

Allocation Partitioning the input or output flows of a unit process to the product of 

interest. 

Attributional LCA An LCA that accounts for flows/impacts of pollutants, resources, and 

exchanges among processes within a chosen temporal window. 

Background Data The background data include energy and materials that are delivered to 

the foreground system as aggregated data sets in which individual plants 

and operations are not identified. 

Brines (oilfield) Wastewater produced along with crude oil and natural gas from oilfield 

operations. 

By-Products an incidental product deriving from a manufacturing process or chemical 

reaction, and not the primary product or service being produced. A byproduct can be useful and marketable, or it can have negative ecological 

consequences. 

Characterization Characterization is the second step of an impact assessment and 

characterizes the magnitude of the potential impacts of each inventory 

flow to its corresponding environmental impact. 

Characterization Factor Factor derived from a characterization model which is applied to convert 

the assigned LCI results to the common unit of the category indicator. 

Classification Classification if the first step of an impact assessment and is the process 

of assigning inventory outputs into specific environmental impact 

categories. 

Composite Data Data from multiple facilities performing the same operation that have 

been combined or averaged in some manner. 

Consequential LCA An LCA that attempts to account for flows/impacts that are caused 

beyond the immediate system in response to a change to the system. 

Co-Product A product produced together with another product. 

Environmental Aspects Elements of a business’ products, actions, or activities that may interact 

with the environment. 

Environmental Loadings Releases of pollutants to the environment, such as atmospheric and 

waterborne emissions and solid wastes. 

78
Equivalency Factor An indicator of the potential of each chemical to impact the given 

environmental impact category in comparison to the reference chemical 

used. 

Equivalent Usage Ratio A basis for comparing two or more products that fulfill the same 

function. For example, comparing two containers based on a set 

volume of beverage to be delivered to the customer. 

Facility-Specific Data Data from a particular operation within a given facility that are not 

combined in any way. 

Foreground Data Data from the foreground system that is the system of primary concern to 

the analyst. 

Fuel P&D Activities involved in the processing and delivery of fuel used to run a 

process; also called Precombustion Energy. 

Functional Unit The unit of comparison that assures that the products being compared 

provide an equivalent level of function or service. 

Green Technology A technology that offers a more environmentally benign approach 

compared to an existing technology. 

Impact Assessment The assessment of the environmental consequences of energy and natural 

resource consumption and waste releases associated with an actual or 

proposed action. 

Impact Categories Classifications of human health and environmental effects caused by a 

product throughout its life cycle. 

Impact Indicators Impact indicators measure the potential for an impact to occur rather than 

directly quantifying the actual impact. 

Industrial System A collection of operations that together perform some defined function. 

Inventory Analysis The identification and quantification of energy, resource usage, and 

environmental emissions for a particular product, process, or activity. 

Interpretation The evaluation of the results of the inventory analysis and impact 

assessment to reduce environmental releases and resource use with a 

clear understanding of the uncertainty and the assumptions used to 

generate the results. 

Life Cycle Assessment A cradle-to-grave approach for assessing industrial systems that 

evaluates all stages of a product’s life. It provides a comprehensive view 

of the environmental aspects of the product or process. 

Material P&D Activities involved in the processing and delivery of materials to a 

process. 

79
Normalization Normalization is a technique for changing impact indicator values with 

differing units into a common, unitless format by dividing the value(s) by 

a selected reference quantity. This process increases the comparability 

of data among various impact categories. 

Precombustion Energy The extraction, transportation, and processing of fuels used for power 

generation, including adjusting for inefficiencies in power generation and 

transmission losses. 

Product Life Cycle The life cycle of a product system begins with the acquisition of raw 

materials and includes bulk material processing, engineered materials 

production, manufacture and assembly, use, retirement, and disposal of 

residuals produced in each stage. 

Routine emissions Those releases that normally occur from a process, as opposed to 

accidental releases that proceed from abnormal process conditions. 

Sensitivity Analysis A systematic evaluation process for describing the effect of variations of 

inputs to a system on the output. 

Specific data Data that are characteristic of a particular subsystem, or process. 

Stressors A set of conditions that may lead to an environmental impact. For 

example, an increase in greenhouse gases may lead to global warming. 

System Flow Diagram A depiction of the inputs and outputs of a system and how they are 

connected. 

Weighting The act of assigning subjective, value-based weighting factors to the 

different impact categories based on their perceived importance or 

relevance. 

80