The Functional Unit: the Heart of all Life Cycle Assessments

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

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

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

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

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