The material life cycle

The material life cycle. Ore and feedstock are mined and processed to yield a material. This is manufactured into a product that is used and, at the end of its life, discarded or recycled. Energy and materials are consumed in each phase, generating waste heat and solid, liquid and gaseous emissions.

Ore and feedstock, drawn from the earth’s resources, are processed to give materials; these are manufactured into products that are used and, at the end of their lives, discarded, a fraction perhaps entering a recycling loop, the rest committed to incineration or landfill. Energy and materials are consumed at each point in this cycle (we shall call them ‘phases’), with an associated penalty of CO2, SOx, NOx and other emissions—heat, and gaseous, liquid and solid waste, collectively called environmental ‘stressors’. These are assessed by the technique of life-cycle analysis (LCA). A rigorous LCA examines the life cycle of a product and assesses in detail the eco-impact created by one or more of its phases of life, cataloging and quantifying the stressors. This requires information for the life history of the product at a level of precision that is only available after the product has been manufactured and used. It is a tool for the evaluation and comparison of existing products, rather than one that guides the design of those that are new. A full LCA is time-consuming and expensive, and it cannot cope with the problem that 80% of the environmental burden of a product is determined in the early stages of design, when many decisions are still fluid. This has led to the development of more approximate ‘streamline’ LCA methods that seek to combine acceptable cost with sufficient accuracy to guide decision-making, the choice of materials being one of these decisions. But even then there is a problem: a designer, seeking to cope with many interdependent decisions that any design involves, inevitably finds it hard to know how best to use data of this type.

How are CO2 and SOx emissions to be balanced against resource depletion,
toxicity or ease of recycling?

How are CO2 and SOx emissions to be balanced against resource depletion, toxicity or ease of recycling? This perception has led to efforts to condense the eco-information about a material production into a single measure or indicator, normalizing and weighting each source of stress to give the designer a simple, numeric ranking. The use of a single-valued indicator is criticized by some. The grounds for criticism are that there is no agreement on normalization or weighting factors, and that the method is opaque since the indicator value has no simple physical significance.
But on one point there is international agreement: the Kyoto Protocol of 1997 committed the developed nations that signed it to progressively reduce carbon emissions, meaning CO2. At the national level the focus is more on reducing energy consumption, but since this and CO2 production are closely related, they are nearly equivalent. Thus, there is a certain logic in basing
design decisions on energy consumption or CO2 generation; they carry more conviction than the use of a more obscure indicator. We shall follow this route, using energy as our measure.Ore and feedstock, drawn from the earth’s resources, are processed to give materials; these are manufactured into products that are used and, at the end of their lives, discarded, a fraction perhaps entering a recycling loop, the rest committed to incineration or landfill. Energy and materials are consumed at each point in this cycle (we shall call them ‘phases’), with an associated penalty of CO2, SOx, NOx and other emissions—heat, and gaseous, liquid and solid waste, collectively called environmental ‘stressors’. These are assessed by the technique of life-cycle analysis (LCA). A rigorous LCA examines the life cycle of a product and assesses in detail the eco-impact created by one or more of its phases of life, cataloging and quantifying the stressors. This requires information for the life history of the product at a level of precision that is only available after the product has been manufactured and used. It is a tool for the evaluation and comparison of existing products, rather than one that guides the design of those that are new. A full LCA is time-consuming and expensive, and it cannot cope with the problem that 80% of the environmental burden of a product is determined in the early stages of design, when many decisions are still fluid. This has led to the development of more approximate ‘streamline’ LCA methods that seek to combine acceptable cost with sufficient accuracy to guide decision-making, the choice of materials being one of these decisions. But even then there is a problem: a designer, seeking to cope with many interdependent decisions that any design involves, inevitably finds it hard to know how best to use data of this type.