Friday, June 20, 2014

Exploration in Life Cycle Assessment (LCA) : Part 1 Goal and Scope Definitions

Contained here are a series of my technical notes into the study and application of ISO 14040-14043 series of standards. These standards cover the environmental management of engineered products over their entire life cycle.

This "life cycle" as defined by ISO extends from raw material extraction and acquisition, through energy and material production and manufacturing, to use and end of life treatment and final disposal.

Its appropriate to start with Goal and Scope definition and it is nice to have a product entity for study. Let me first consider the product system "150g strawberry yogurt in a polypropylene (PP) cup with an aluminum cover", the first example suggested for review in the new book Life Cycle Assessment (LCA) by Walter Klopffer and Birgit Grahl.

ISO 14040:2006 section 5 gives the methodological framework for applying LCA. Applying sub-sections & to goal and scope definition, they are compiled below.


150 g strawberry yogurt in a polypropylene (PP) cup with an aluminum cover.


The intended application is that of a PP cup to store strawberry yogurt and hermetically seal it with a tear-off aluminum lidding. This is not a comparative study of two systems.

The reason for carrying out the study is only for information sharing and the intended audience are engineers and students of the LCA methodology. Using derivable facts for decision making and competitive assertions are beyond scope.

As far as possible, data for the study will be obtained from the internet.

I encourage readers to dispute the methods used or offer additional advice on improvements.


Identification of Functions :

The service delivered by the product system can be divided into primary and secondary functions.

Selection of Functions and Definition of Functional unit :

Within the scope of the study, functions above that are more relevant to the study must be identified according to Section 5.2.2.

The product system originally specified by Klopffer and Grahl is interpreted as pointing to a generic PP cup containing 150 g strawberry yogurt with the intent of storing and sealing.

We will assume that this product is intended to be made for distribution and so considered within the study scope is the labeling and printing of dates.

ISO defines a functional unit as the quantification of the relevant functions of the product in order to assign a reference to the inputs and outputs of the product system. For a start, we know that 150 g of strawberry yogurt is the unit to be stored.

But does assigning time to the functional unit matter?

Fruit yogurt would last 7-10 days past its sell date in a refrigerator and 1-2 months past its sell date when stored in a freezer. So for assigning a time to the PP container, what time is to be considered? This is a case for further discussion but for this post, I take 2 weeks of yogurt life past its sell date.

A note here is that it is not the product but the product system that is under consideration. So it is not necessarily the yogurt that has the maximum time.

Depending on the health and life of the cow and the constituents of the plastic cup, either the cow or the plastic may outlive each other to put the most environmental burden. For example, if the plastic cup is made of part recycled material that could break down sooner than conventional cups, perhaps the cow whose lifetime is 15 years would govern the LCA study as far as time goes. This given the idea that the time line that is important is the time necessary to remove the waste from the environment.

This is a significant factor and will be revisited in later parts of this post.

Identification of performance of the product and determination of the reference flow :

The quantity of product necessary to fulfil the defined functional unit constitutes its performance. The questions here is whether to define the reference flow to fulfil the "product system" or the product. The intent of defining the reference flow below is the quantity of product needed to hold 150g of strawberry yogurt.

With a small amount of research, I found that a standard cup of 150mL capacity with a heat sealable aluminum lid will do the trick.

Qualitative System Flowchart & System Boundary:

Below is what I consider to be a system flowchart (or product system tree) and system boundary for the yogurt product system. All man made products, systems and processes relevant to the product system are bounded by a dotted line, the region considered as the "Technosphere".

The product tree starts on the extreme left by considering all processes necessary to get raw materials used. This includes the polypropylene granules, the starter yogurt, the aluminum for the lidding, the strawberries.

As you move towards the right, you see process boxes for the production of the cups, the lidding and the strawberry yogurt. Distribution of the final product is followed by use, disposal and (perhaps) incineration or a trip to the landfill, or a reclamation process that puts back recycled raw material into the raw material box.
This is closed loop recycling. Any recycled product that is an input to external products flows out of the technosphere.

Cut-off Criteria:

For simplicity, the recommendations of Klopffer and Grahl will be followed by using the 1%-5% cut-off criteria. This means that any inputs to individual process boxes that constitute less than 1% by mass fraction can be safely ignored provided that the sum of the ignored inputs do not add up to more than 5% of the total mass of the output.

I would also like to add that for simplicity, the inputs to secure, maintain or repair capital goods used in the production processes, for example the injection molding machine , are not considered.

Geographical and Temporal System Boundaries:

It is assumed that all processes are within the boundaries of the United States of America. In analyzing the system, we'd also like to bound input data to a temporal boundary greater than year 2000. It hardly makes sense to consider outdated data for analysis when process technologies, energy efficiencies etc change year by year.

This concludes the goal and scope definition of the product system "150 g strawberry yogurt in a polypropylene (PP) cup with an aluminum cover".  It is not my intention to have neglected factoring in any important element to the scope but you are free to give your inputs and critique of the process thus far.

In part 2 of this series, I'll investigate the next phase of the ISO LCA methodology, which is Life Cycle Inventory.

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1 comment:

nahas said...

Thanks for the article , this was very informative