Life Cycle Analysis (LCA), originally derived to assess the carbon footprint of manufactured goods, is being applied to production processes where it can be manipulated in a variety of ways each yielding a different result to claim the lowest carbon footprint for a particular process. This paper uses the example of blast furnace slag as a replacement for cement clinker and shows, depending on the method of allocation, a saving of 0.24tCO2/t of steel produced or 0.64tCO2/t of cement produced. By J P Birat*