An LCA database is a generic name for a database that contains data that can be used for life cycle assessment. The data in an LCA database can consist of life cycle inventory data (LCI) and/or already characterized life cycle impact assessment data (LCIA). Data from an EPD is always LCIA data that is already characterized.

As any with LCA data, also EPDs are originally based on inventory data but the final document does not contain the original LCI data but just the LCIA results for that product. Some tools may provide users access to both original LCI data and LCIA results, in One Click LCA users normally only have access to the LCIA results.

LCI data is a list of all different inputs and outputs from the processes studied such as kg of methane emissions to air or phosphorus emissions to water.

LCIA data is LCI data transformed into environmental impacts using a characterization model. For instance, methane is one component that impacts GWP (Global warming potential impact category) and thus it is transformed into CO2 equivalents using a characterization method (such as CML, TRACI or ReCiPe).
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There are several different characterization models but in the European building sector, EN 15804 refers to CML which is the commonly used method and also globally most widely used one for construction. The EN 15804 standard is also in line with the ISO 14044/44 standard.
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To read more on what an EPD is, please check the following article: What is an EPD?