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Introduction
There are a few concepts that needed to be addressed in Life-Cycle audit. The first concept is I=PAT. The second concept is embodied energy. The third one is Life-Cycle Assessment which includes 4 steps namely goal and scope, Life-Cycle Inventory, Life-Cycle impact assessment and Life-Cycle interpretation.
IPAT
The equation, I=PAT, where I is Human Impact, P is population, A is Affluence and T is Technology. I= PAT was developed in the early 1970s during the course of a debate between Barry Commoner, who argued that the environmental impacts in the US were primarily due to post war changes in production technology, and Paul Ehrlich and John Holdren, who argued that all three factors were important and important and emphasized in particular the role of population growth. The equation indicates that global environmental pressures can be alleviated by implementing policies to slow population growth, to reduce or slow the growth of consumption per capita (afflence), or to decrease the environment impact of production. Usually, reducing consumption growth is considered as a potential policy only in more developed countries (MDCs) but it is hardly an option for less developed countries (LDCs). The combined effect of all these policies must therefore be sufficient to allow for improvement in LDC living standards. (O'Neil, MacKellar & Lutz 2001)
Embodied energy
Embodied energy is the amount of energy that is consumed during its production. This concept is used when determining the suitable material for a design. When producing certain materials, energy required to make the product emit greenhouse gas which contribute to global warming. The idea is to choose the material that save much more energy so that little impact on the environment and save the planet. Embodied energy of some materials is shown in table 12.
Table 12: embodied energy of some material (wikipedia, 2013)
Application
If we are going to make a table or chair of certain dimensions with Timber, the embodied energy is 8.5 MJ per kg and carbon dioxide is 0.46 MJ/kg. For the same dimensions of chair and table, if we use Aluminium embodied energy is 155 MJ per kg and carbon dioxide is about 8.24 MJ/kg. Thus, It is a good idea to use Timber to make table and chair as it has lower embodied energy and carbon dioxide emission to the environment.
Life-Cycle Assessment
Life-Cycle Assessment (LCA) is defined as the "compilation and evaluation of the inputs , outputs and potential environmental impacts of a product system throughout its life cycle" (ISO 14040 cited in Guinee 2002). LCA is a tool for analysis of the environmental burden of products at all stages in their life cycle from extraction of resources through production of materials to discarding (Guinee 2002). It is very complicated to go through all the 4 steps of LCA. Instead, we will focus on Life-Cycle Inventory. The first step in Life-Cycle Inventory is material auditing.
Common Mistake
Life-Cycle Audit is not the same as Material audit. Life-Cycle Audit a combination of techniques and tools for this topic. Material audit is the first step in Life-Cycle Inventory. Material audit uses embodied energy to audit.
Material Audit
Material audit is about identifying inputs and outputs of the product. Inputs will involve resources such as fuel, water required for each material of a product. Outputs will consist of carbon dioxide emission, water emission, etc.
For this analysis, we will assume that we would like to compare the 2 table; one entirely made of wood and other entire made of aluminium with the same dimensions. The data for this analysis is obtained from US life-cycle inventory database which material audits are shown in table 13 and 14.
Table 13: Material audit of Aluminium production(US life-cycle inventory database, 2008)
Table 14: Material audit of planted dried lumber processing (US life-cycle inventory database, 2011)
From the material audit, we can clearly aluminium processing requires much more resources and embodied energy. Thus, it is a wise choice to design a table with lumber in order to reduce resource consumption and energy usage. We need to note that the choice of material for a design will have great impact on our planet and thus we have to consider about what materials to be used in our design carefully.

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