The life cycle assessment (LCA) process is a multi-step calculation that is challenging even for seasoned LCA professionals to recite with precision. Do not feel alone; it is a complex process. Let’s break it down into simpler bites by examining the components of the LCA calculations.

The LCA process follows four steps:
• Process inventory data collection
• Impact characterization
• Normalization
• Weighting

We consider each step, first individually; then combined, in a continuous calculation. Please keep in mind that each of these steps is included in every Okala Impact Factor. Designers and product teams need not take the time to understand them in depth. They are included here to show the rigor behind the single-score assessment process.

In the Process Inventory step, data is collected for a material or process in terms of cradle-to-gate emissions, land use changes and resource depletion. Without going into detail about how this mysterious process is accomplished, it is safe to say that the data includes a long list of substance flows, moving both into the process, and most importantly, out to the air, water and soil. In simple terms the latter flows can be considered as pollution. There are often hundreds or possibly more than a thousand data points for each material or process in an LCA.

You should not fret; designers are not asked to collect this information. It has already been collected by scientists for commodity materials and common processes. The process inventory data below – edited for this discussion -- represents the production and consumption (combustion) of ten gallons of lead-free gasoline.

The production and combustion of these ten gallons of lead-free gasoline emit considerable carbon dioxide (CO2) to air, less aluminum to water and even less lead to water. There are also 694 additional data points for other emissions, land use effects and resource depletion effects.

In the Impact Characterization step, the process inventory data just covered converts to discrete quantities of environmental impacts. This is arrived at using scientific formulae that teams of experts develop in each impact category. The impact categorization method used in this example and in the Okala Impact Factors is TRACI (Tool for Reduction and Assessment of Chemical other Environmental Impacts). Below we see how the three respective emissions were converted into impacts in three different impact categories. It is possible for an emission to have impacts in multiple impact categories (such as chlorinated fluorocarbons being both greenhouse gases and ozone-layer-depleting gases.)

Characterization of each impact type uses a different equivalency unit. Carbon dioxide is the equivalency unit for global warming impacts, so these values remain unchanged. Ecotoxicity is measured by a standard based on the herbicide 2,4-D, while human toxicity uses the solvent toluene as a metric. These impact values may be easier than the raw process inventory data to understand, since most people have difficulty in determining the relative significance of each impact.

Normalization is a step that allows us to compare apples to apples. It divides the impact in each category by the estimated impacts from a reference product or process. In the Okala Impact Factors, these are the estimated impacts in each impact category to be produced by the average person in the United States in one year. This somewhat abstract denominator creates normalized impact results that have the same units, measured in points.

The normalized impacts are now in the same units (normalized impact points) because their respective units are now the same. It becomes easier to compare the relative significance of each of these categories.

Weighting multiplies each impact by a percentage point to adjust the relative significance of each impact category. Weighting in general is a socially-defined step; the units used in Okala Impact Factors were defined by the US National Institute of Standards and Technology (NIST).

This last step makes a modest adjustment to the relative importance of the impact categories. It should be noted that normalization and weighting are not required by ISO 14040 series LCA standards, but their inclusion is allowed to assist in interpretation of the characterized impacts.

The unit is also adjusted by three digits to enable the measurement of smaller systems, by switching from a point to a millipoint (1/1000th of a point). If we used points for most products, they would be in miniscule numbers with many zeros after the decimal point; millipoints are more practical for most applications.

When this step is complete, the impact categories of all the individual impacts are totaled to deliver the Okala Impacts. Here we see 2252 Okala millipoints for the production and combustion of 10 gallons of unleaded gasoline; a common reference unit of consumption in the United States.

Why is this seemingly complex mathematical process necessary? For this reason: the unique contribution of Okala includes the ability of seeing, at a glance, in a single-score assessment based on scientific rigor, the relative sustainability of multiple product designs. The process actually reduces complexity by arriving at a quickly-comparable score.