Definition
The International Standards Organization (ISO) has defined LCA as :
"A technique for assessing the environmental aspects and potential impacts associated with a product by:
· Compiling an inventory of relevant inputs and outputs of a product system,
· Evaluating the potential environmental impacts associated with those inputs and outputs,
· Interpreting the results of the inventory analysis and impact assessment phases in relation to the objectives of the study" (ISO 14.040).
The technique examines every stage of the life cycle, from the winning of the raw materials, through manufacture, distribution, use, possible re-use/recycling and then final disposal.
For each stage, the inputs (in terms of raw materials and energy) and outputs (in terms of emissions to air, water, soil, and solid waste) are calculated, and these are aggregated over the Life Cycle.
These inputs and outputs are then converted into their effects on the environment, i.e. their environmental impacts.
The sum of these environmental impacts then represents the overall environmental effect of the Life Cycle of the product or service.
LCA Background
The concept of life-cycle assessment first emerged in the late 1960's but did not receive much attention until the mid-11980's
In 1989, the Society of Environmental Toxicology and Chemistry (SETAC) became the first international organization to begin oversight of the advancement of LCA.
In 1994, the International Standards Organization (ISO) began developing standards for the LCA as part of its 14000 series standards on environmental management. The standards address both the technical details and conceptual organization of LCA .
• ISO 14040-A standard on principles and framework
• ISO 14041-A standard on goal and scope definition and inventory analysis
• ISO 14042-A standard on life-cycle impact assessment
• ISO 14043-A standard on life-cycle interpretation
Several of the methods described as LCA methods follow the LCA framework defined in ISO 14040, involving an inventory similar to that described in ISO 14041, and assessment of impacts to some degree as described in ISO 14042, while a smaller number take on the normalization and weighting also discussed in ISO 14042.
Still, methods based on the ISO standards may differ greatly, given that the ISO standards allow flexibility to customize characterization and normalization factors and weighting methods to suit the values and conditions of a particular location or sector.
The International Standards Organization (ISO) has defined LCA as :
"A technique for assessing the environmental aspects and potential impacts associated with a product by:
· Compiling an inventory of relevant inputs and outputs of a product system,
· Evaluating the potential environmental impacts associated with those inputs and outputs,
· Interpreting the results of the inventory analysis and impact assessment phases in relation to the objectives of the study" (ISO 14.040).
The technique examines every stage of the life cycle, from the winning of the raw materials, through manufacture, distribution, use, possible re-use/recycling and then final disposal.
These inputs and outputs are then converted into their effects on the environment, i.e. their environmental impacts.
The sum of these environmental impacts then represents the overall environmental effect of the Life Cycle of the product or service.
LCA Background
The concept of life-cycle assessment first emerged in the late 1960's but did not receive much attention until the mid-11980's
In 1989, the Society of Environmental Toxicology and Chemistry (SETAC) became the first international organization to begin oversight of the advancement of LCA.
In 1994, the International Standards Organization (ISO) began developing standards for the LCA as part of its 14000 series standards on environmental management. The standards address both the technical details and conceptual organization of LCA .
• ISO 14040-A standard on principles and framework
• ISO 14041-A standard on goal and scope definition and inventory analysis
• ISO 14042-A standard on life-cycle impact assessment
• ISO 14043-A standard on life-cycle interpretation
Several of the methods described as LCA methods follow the LCA framework defined in ISO 14040, involving an inventory similar to that described in ISO 14041, and assessment of impacts to some degree as described in ISO 14042, while a smaller number take on the normalization and weighting also discussed in ISO 14042.
Still, methods based on the ISO standards may differ greatly, given that the ISO standards allow flexibility to customize characterization and normalization factors and weighting methods to suit the values and conditions of a particular location or sector.
Goal And Scope
This is the first stage of the study and probably the most important, since the elements defined here, such as purpose, scope, and main hypothesis considered are the key of the study.
The scope of the study usually implies defining the system, its boundaries (conceptual, geographical and temporal), the quality of the data used, the main hypothesis and a priori limitations.
A key issue in the scope is the definition of the functional unit.
This is the unit of the product or service whose environmental impacts will be assessed or compared.
It is often expressed in terms of amount of product, but should really be related to the amount of product needed to perform a given function.
During the goal definition process, the following issues should be considered:
System Boundaries
Definition of system boundaries
The scope of an LCA describes the boundaries which define the system being studied.
The scope should be well defined to ensure that the breadth and depth of the study are compatible with the stated goal.
For example, in a comparison of virgin and recycled systems, removal of downstream stages may not affect comparative rankings significantly.
However, if objectives go beyond comparative rankings to assessing environmental burdens throughout the life cycle, eliminating the downstream stages may exclude some environmental impacts that are unique to recycled systems and that have comparatively high burdens in the downstream stages.
System boundaries define the unit processes or activities that will be included in the system under study. Decisions must be made on which processes or activities will be included.
As noted above under consideration of the functional unit, it might be possible to eliminate those processes that are identical for all items under study.
Or, it might be possible to eliminate elements of the system that are beyond the purview of the study goal and purpose, i.e., those components of the system that cannot be affected by the decisions, actions, or activities that are driving the study.
The basis for the decisions should be clearly understood and described and should be consistent with the stated goal of the study. At the outset of an LCA, all life-cycle stages should be considered.
Upon careful review, it may be possible to eliminate the need to collect data from some of these stages or sub processes.
The study team should keep in mind, however, that Barnthouse et al. (1997) noted several features that are crucial to LCA
Any decisions that affect these features should be carefully documented.
A true life-cycle always starts with the extraction of the raw materials from the earth and ends with the final disposal of the refusals in the earth.
In practice every system can be described, but if the described system do not satisfy the condition illustrated above, it does not represent an LCA but an eco-balance or an eco-profile.
Kirk et al., 2005, have pointed out the influence of system boundaries on LCA results, since setting system boundaries in different ways can tip the scales in favor of one technology over another.
They showed how the concepts of system boundaries and parameters help illuminate why wastewater decisions may only move problems in time and space, rather than solve them.
This is the first stage of the study and probably the most important, since the elements defined here, such as purpose, scope, and main hypothesis considered are the key of the study.
The scope of the study usually implies defining the system, its boundaries (conceptual, geographical and temporal), the quality of the data used, the main hypothesis and a priori limitations.
A key issue in the scope is the definition of the functional unit.
This is the unit of the product or service whose environmental impacts will be assessed or compared.
It is often expressed in terms of amount of product, but should really be related to the amount of product needed to perform a given function.
During the goal definition process, the following issues should be considered:
- Why is the study being conducted (i.e., what decision, action, or activity will it contribute to or affect)?
- Why is LCA needed for this decision, action, or activity? What, specifically, is it expected to contribute?
- What additional analytical tools are needed and what will they be expected to contribute?
- Who is the primary target audience for the study (i.e., who will be making the decision, taking or directing the action, or organizing or participating in the activity)?
- What other audiences will have access to the study results? What uses might these audiences make of the study findings?
- What are the overall environmental goals, values, and principles of the sponsoring organization and intended audience?
- How does the intended application of the study relate to these goals, values, and principles?
System Boundaries
Definition of system boundaries
The scope of an LCA describes the boundaries which define the system being studied.
The scope should be well defined to ensure that the breadth and depth of the study are compatible with the stated goal.
For example, in a comparison of virgin and recycled systems, removal of downstream stages may not affect comparative rankings significantly.
However, if objectives go beyond comparative rankings to assessing environmental burdens throughout the life cycle, eliminating the downstream stages may exclude some environmental impacts that are unique to recycled systems and that have comparatively high burdens in the downstream stages.
System boundaries define the unit processes or activities that will be included in the system under study. Decisions must be made on which processes or activities will be included.
As noted above under consideration of the functional unit, it might be possible to eliminate those processes that are identical for all items under study.
Or, it might be possible to eliminate elements of the system that are beyond the purview of the study goal and purpose, i.e., those components of the system that cannot be affected by the decisions, actions, or activities that are driving the study.
The basis for the decisions should be clearly understood and described and should be consistent with the stated goal of the study. At the outset of an LCA, all life-cycle stages should be considered.
Upon careful review, it may be possible to eliminate the need to collect data from some of these stages or sub processes.
The study team should keep in mind, however, that Barnthouse et al. (1997) noted several features that are crucial to LCA
- a system-wide perspective embodied in the term "cradle-to-grave" that implies efforts to assess the multiple
- operations and activities involved in providing a product or services;
- a multimedia perspective that suggests that the system include resource inputs as well as wastes and emissions to all environmental media, i.e., air, water, and land; and
- a functional unit accounting system that normalizes energy, materials, emissions, and wastes across the system and media to the service or product provided.
Any decisions that affect these features should be carefully documented.
A true life-cycle always starts with the extraction of the raw materials from the earth and ends with the final disposal of the refusals in the earth.
In practice every system can be described, but if the described system do not satisfy the condition illustrated above, it does not represent an LCA but an eco-balance or an eco-profile.
Kirk et al., 2005, have pointed out the influence of system boundaries on LCA results, since setting system boundaries in different ways can tip the scales in favor of one technology over another.
They showed how the concepts of system boundaries and parameters help illuminate why wastewater decisions may only move problems in time and space, rather than solve them.
System Function And Functional Unit
The functional unit is a measure of the performance of the product system. The primary purpose of the functional unit is to provide a reference to which the inputs and outputs are related and is necessary to ensure comparability of results.
The function is related directly to the questions that the study is designed to answer, and the functional unit must be selected as the basis for the study.
One of the primary purposes for a functional unit is to provide a reference for the system inputs and outputs.
A well-defined functional unit that assures equivalence also allows for more meaningful comparisons between alternative systems.
In their study of Life cycle assessment of wastewater treatment technologies treating petroleum process waters, Vlaopolous et al. 2006 have considered a process water flow of 10,000 m3/day for a time period of 15 years (system design life) as the function unit used in order to compare the different wastewater treatment processes.
The functional unit is a measure of the performance of the product system. The primary purpose of the functional unit is to provide a reference to which the inputs and outputs are related and is necessary to ensure comparability of results.
The function is related directly to the questions that the study is designed to answer, and the functional unit must be selected as the basis for the study.
One of the primary purposes for a functional unit is to provide a reference for the system inputs and outputs.
A well-defined functional unit that assures equivalence also allows for more meaningful comparisons between alternative systems.
In their study of Life cycle assessment of wastewater treatment technologies treating petroleum process waters, Vlaopolous et al. 2006 have considered a process water flow of 10,000 m3/day for a time period of 15 years (system design life) as the function unit used in order to compare the different wastewater treatment processes.
Inventory Analysis
The inventory analysis is a technical process of collecting data, in order to quantify the inputs and outputs of the system, as defined in the scope.
Energy and raw materials consumed, emissions to air, water, soil, and solid waste produced by the system are calculated for the entire life cycle of the product or service.
The inventory analysis is a technical process of collecting data, in order to quantify the inputs and outputs of the system, as defined in the scope.
Energy and raw materials consumed, emissions to air, water, soil, and solid waste produced by the system are calculated for the entire life cycle of the product or service.
In order to make this analysis easier, the system under study is split up in several subsystems or processes and the data obtained is grouped in different categories in a LCI table.
Impact Assessment
Life Cycle Impact Assessment (LCIA) is a process to identify and characterize the potential effects produced in the environment by the system under study.
The starting point for LCIA is the information obtained in the inventory stage, so the quality of the data obtained is a key issue for this assessment.
LCIA is considered to consist of four steps that are briefly described below.
The first step is Classification, in which the data originated in the inventory analysis are grouped in different categories, according to the environmental impacts they are expected to contribute.
Indicators of impact categories include:
Climate change
Acidification
Eutrophication
Photochemical smog
Fossil fuel depletion
Ecotoxicity
Ozone depletion
Human toxicity
The second step, called Characterization, consists of weighting the different substances contributing to the same environmental impact.
Thus, for every impact category included in LCIA, an aggregated result is obtained, in a given unit of measure.
The third step is Normalization, which involves relating the characterized data to a broader data set or situation, for example, relating SOx emissions to a country's total SOx emissions.
The last step is weighting, where the results for the different impact categories are converted into scores, by using numerical factors based on values.
This is the most subjective stage of an LCA and is based on value judgments and is not scientific.
For instance, a panel of experts or public could be formed to weight the impact categories.
The advantage of this stage is that different criteria (impact categories) are converted to a numerical score of environmental impact, thus making it easier to make decisions.
Impact Assessment
Life Cycle Impact Assessment (LCIA) is a process to identify and characterize the potential effects produced in the environment by the system under study.
The starting point for LCIA is the information obtained in the inventory stage, so the quality of the data obtained is a key issue for this assessment.
LCIA is considered to consist of four steps that are briefly described below.
The first step is Classification, in which the data originated in the inventory analysis are grouped in different categories, according to the environmental impacts they are expected to contribute.
Indicators of impact categories include:
Climate change
Acidification
Eutrophication
Photochemical smog
Fossil fuel depletion
Ecotoxicity
Ozone depletion
Human toxicity
The second step, called Characterization, consists of weighting the different substances contributing to the same environmental impact.
Thus, for every impact category included in LCIA, an aggregated result is obtained, in a given unit of measure.
The third step is Normalization, which involves relating the characterized data to a broader data set or situation, for example, relating SOx emissions to a country's total SOx emissions.
The last step is weighting, where the results for the different impact categories are converted into scores, by using numerical factors based on values.
This is the most subjective stage of an LCA and is based on value judgments and is not scientific.
For instance, a panel of experts or public could be formed to weight the impact categories.
The advantage of this stage is that different criteria (impact categories) are converted to a numerical score of environmental impact, thus making it easier to make decisions.
Interpretation
This is the last stage of the LCA, where the results obtained are presented in a synthetic way, presenting the critical sources of impact and the options to reduce these impacts.
Interpretation involves a review of all the stages in the LCA process, in order to check the consistency of the assumptions and the data quality, in relation to the goal and scope of the study.
Elements of the Study Design
The study designers and sponsors consider numerous elements of the study design.
The following questions are considered during this process.
Benefits and limitations of the life cycle approach
Life Cycle Assessment is an inclusive tool.
All necessary inputs and emissions in many stages and operations of the life cycle are considered to be within the system boundaries. This includes not only inputs and emissions for production, distribution, use and disposal, but also indirect inputs and emissions - such as from the initial production of the energy used - regardless of when or where they occur.
If real environmental improvements are to be made by changes in the product or service, it is important not to cause greater environmental deteriorations at another time or place in the Life Cycle.
LCA offers the prospect of mapping the energy and material flows as well as the resources, solid wastes, and emissions of the total system, i.e. it provides a "system map" that sets the stage for a holistic approach.
The power of LCA is that it expands the debate on environmental concerns beyond a single issue, and attempts to address a broad range of environmental issues, by using a quantitative methodology, thus providing an objective basis for decision making.
Unfortunately, LCA is not able to assess the actual environmental effects of the system.
ISO 14.042 standard, dealing with Life Cycle Impact Assessment, specially cautions that LCA does not predict actual impacts or assess safety, risks, or whether thresholds are exceeded.
The actual environmental effects of emissions will depend on when, where and how they are released into the environment, and other assessment tools must be utilized.
For example, an aggregated emission released in one event from one source, will have a very different effect than releasing it continuously over years from many diffuse sources.
Clearly no single tool can do everything, so a combination of complementary tools is needed for overall environmental management.
LCA in waste management
LCA has begun to be used to evaluate a city or region's future waste management options.
The LCA, or environmental assessment, covers the environmental and resource impacts of alternative disposal processes, as well as those other processes which are affected by disposal strategies such as different types of collection schemes for recyclables, changed transport patterns and so on.
The complexity of the task, and the number of assumptions which must be made, is shown by the simplified diagram (above) showing some of the different routes which waste might take, and some of the environmental impacts incurred along the way.
Those shown are far from exhaustive.
This is the last stage of the LCA, where the results obtained are presented in a synthetic way, presenting the critical sources of impact and the options to reduce these impacts.
Interpretation involves a review of all the stages in the LCA process, in order to check the consistency of the assumptions and the data quality, in relation to the goal and scope of the study.
Elements of the Study Design
The study designers and sponsors consider numerous elements of the study design.
The following questions are considered during this process.
- Depth and detail
- -What level of depth and detail of data does the application require?
- -Are these requirements greater for some data categories and issues than for others?
- Breadth and completeness
- - Does the application require that all aspects of the life cycle be included, or can some be eliminated or examined less exhaustively?
- - What inventory and impact-category indicators must be included to meet the purpose of the study?
- - Where are the systems boundaries drawn and why?
- Transparency
- - What degree of openness and comprehensiveness is required in the presentation of data or study results?
- - Who will see the products of the study, including underlying data as well as results, and how much transparency will they require?
- - Will proprietary data be used that must be shielded from some users?
- Data sources
- - Where are the data to be collected?
- - Are publicly available data sources appropriate for the study?
- -Are primary data required?
- - Is a mix of approaches appropriate for the study?
- Data quality
- -How much confidence should the potential users have in the data and in the study's conclusions?
- - How much uncertainty can they tolerate?
- Modeling allocation conventions
- -How is recycling to be treated?
- -How are burdens of a process to be allocated among co-products?
- Site specificity
- -Does the application require that the study produce information about specific sites or facilities?
- -Is site-specific information needed for any of the planned supplemental analyses, such as risk assessment?
- Scale
- -Does the application require data on a global, continental, regional, and local scale?
- - Which biological scales are most relevant-ecosystems, populations, individual organisms, physiological systems, or molecular systems?
- -Are users of the study interested only, or primarily, in impacts that occur at a particular scale?
- Level of aggregation
- -What level and types of aggregation are most appropriate to support the study decision needs?
- - Will the traditional LCA approach of aggregating all data throughout the life cycle by functional unit be sufficient, or will the user require some data to be retrievable in a disaggregated form (e.g., by industrial process)?
- LCA limitations
- -How environmentally relevant is the modeling that was used in the impact assessment?
- - Does the intended application require more precise modeling of risk or hazard?
- Temporal specificity
- -Does the application require that the study produce information on the time frame for when potential impacts or their associated inventory items occurred?
Benefits and limitations of the life cycle approach
Life Cycle Assessment is an inclusive tool.
All necessary inputs and emissions in many stages and operations of the life cycle are considered to be within the system boundaries. This includes not only inputs and emissions for production, distribution, use and disposal, but also indirect inputs and emissions - such as from the initial production of the energy used - regardless of when or where they occur.
If real environmental improvements are to be made by changes in the product or service, it is important not to cause greater environmental deteriorations at another time or place in the Life Cycle.
LCA offers the prospect of mapping the energy and material flows as well as the resources, solid wastes, and emissions of the total system, i.e. it provides a "system map" that sets the stage for a holistic approach.
The power of LCA is that it expands the debate on environmental concerns beyond a single issue, and attempts to address a broad range of environmental issues, by using a quantitative methodology, thus providing an objective basis for decision making.
Unfortunately, LCA is not able to assess the actual environmental effects of the system.
ISO 14.042 standard, dealing with Life Cycle Impact Assessment, specially cautions that LCA does not predict actual impacts or assess safety, risks, or whether thresholds are exceeded.
The actual environmental effects of emissions will depend on when, where and how they are released into the environment, and other assessment tools must be utilized.
For example, an aggregated emission released in one event from one source, will have a very different effect than releasing it continuously over years from many diffuse sources.
Clearly no single tool can do everything, so a combination of complementary tools is needed for overall environmental management.
LCA in waste management
LCA has begun to be used to evaluate a city or region's future waste management options.
The LCA, or environmental assessment, covers the environmental and resource impacts of alternative disposal processes, as well as those other processes which are affected by disposal strategies such as different types of collection schemes for recyclables, changed transport patterns and so on.
The complexity of the task, and the number of assumptions which must be made, is shown by the simplified diagram (above) showing some of the different routes which waste might take, and some of the environmental impacts incurred along the way.
Those shown are far from exhaustive.
References
Azapagic, A., (1999). Life cycle assessment and its implications to process selection, design and optimization, Chemical Engineering Journal, 3, 73, pp1-21.
Barnthouse L, Fava J, Humphreys K, Hunt R, Laibson L, Noesen S, Owens JW, Todd JA, Vigon B, Weitz K, Young J, editors. 1997. Life-cycle impact assessment: the state-of-the-art. Pensacola FL: Society of Environmental Toxicology and Chemistry
(SETAC).
Fava J, Jensen A.A., Lindfors L., Pomper S., De Smet B., Warren J., Vigon B., eds. (1994)
SETAC, Life-cycle assessment data quality: a conceptual framework Workshop report,
Wintergreen, OOctober 1992. Pensacola: SETAC.
Huppes, G., Francois, S., (eds) (1994). Proceedings of the European Workshop on allocation in LCA, 24-25 FFebruary1994, Leiden, the Netherlands, SETAC- Europe, BBrussels Belgium
Kirk, B., Etnier, C., Kärrman, E., and Johnstone, S. (2005), Methods for Comparison of Wastewater Treatment Options. Project No. WU-HT-03-33. Prepared for the National Decentralized Water Resources Capacity Development Project. Washington University, St. Louis, MO, by Ocean Arks International, Burlington, VT.
Miettinen, P. and Hamalainen, R., (1997). How to benefit from decision analysis in environmental life ccycleassessment "European Journal of Operational Research. Vol 102,2, pp279-294
Udo de Haes, H., (1994). Guidelines for the application of life - cycle assessment in the European Union ecolabelling programme SPOLD, Brussels, Belgium.
Vlasopoulos, N.,Memon, F.,Butler, Murphy, R., (2006), Life Cycle Assessment of Wastewater Treatment Technologies, Treating Petroleum Process Waters. Sci.Total Environm.,(367), 58-70.
Introductory reading:
1. From the LCAccess website (U.S. EPA), http://www.epa.gov/ORD/NRMRL/lcaccess/
Read the "Why LCA?" section. Other browsing is optional.
2. "How is a Life Cycle Assessment Made?" pp. 11-24 in Life Cycle Assessment: What it is and how to do it; UNEP, 1996.
3. Masters, GM (1998): Introduction to Environmental Engineering and Science (2nd
edition); extract from ch. 9 "An example of life cycle assessment: Polystyrene cups",
p562-565.
Further LCA Resources
1. Books
Ciambrone, DF, Environmental Life Cycle Analysis, Lewis Publishers, 1997
Curran, MA, Environmental Life Cycle Assessment, McGraw-Hill, 1996
Graedel, TE, Streamlined Life-Cycle Assessment, Prentice Hall, 1998
Vigon, BW et.al., Life-Cycle Assessment: Inventory Guidelines and Principles, USEPA Risk
Reduction, Lewis Publishers, 1994
Weidema, BP (ed.), Environmental Assessment of Products: a Handbook on Life Cycle Assessment,
2nd edition, UETP-EEE, Finnish Association of Graduate Engineers, Helsinki, 1993
2. Journal Articles and ISO Standard
ISO 14040 series of standards: SABS ISO 14040 (1998), SABS ISO 14041 (1999), ISO 14042 (1999),
ISO 14043 (2000) and ISO14044. Some Case Studies:
_ Vollebregt, LHM and J Terwoert, LCA of Cleaning and Degreasing Agents in the Metal Industry, Int. J. of LCA, 3 (1), 12-17, 1998.
_ Andersson, K and T Ohlsson, Life Cycle Assessment of Bread Produced on Different Scales, Int. J. of LCA, 4 (1), 25-40, 1999.
3. LCA Websites
UNEP/SETAC Life Cycle Initiative: http://www.uneptie.org/pc/sustain/lcinitiative/
U.S. EPA, NRMRL: LCAccess: http://www.epa.gov/ORD/NRMRL/lcaccess/
CML - Centre for Environmental Science: http://www.leidenuniv.nl/interfac/cml/
SETAC Foundation for Environmental Education: http://www.setac.org/lca.html
Pre Product Ecology Consultants: http://www.pre.nl/
Ecobilan (Software Developers and Consultants): http://www.ecobilan.com
The International Journal of LCA: http://www.ecomed.de/journals/lca/
4. Software Tools and Data Libraries
CML LCA - free LCA software
Commercial software: SimaPro, GABI, Umberto
EcoInvent database represents the state of the art - at cost
BUWAL, IVAM, USA I/O, US database project, ETH - some free, some not
Danish food and agriculture database - freesment, McGraw-Hill, 1996
Graedel, TE, Streamlined Life-Cycle Assessment, Prentice Hall, 1998
Vigon, BW et.al., Life-Cycle Assessment: Inventory Guidelines and Principles, USEPA Risk
Reduction, Lewis Publishers, 1994
Weidema, BP (ed.), Environmental Assessment of Products: a Handbook on Life Cycle Assessment,
2nd edition, UETP-EEE, Finnish Association of Graduate Engineers, Helsinki, 1993
http://grimstad.uia.no/puls/climatechange/nns05/13nns05a.htm
http://grimstad.uia.no/puls/climatechange/nns05/13nns05a.htm
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