Co-product allocation under EN 15804:A2

Many production processes yield more than one product, especially chemical production processes. An oil refinery turns crude oil into petrol, diesel and kerosene in a single step. That raises the question of how you divide the environmental impact fairly across those co-products. EN 15804:A2 sets strict rules for this, so your EPD stays reliable and comparable with others.

Avoid allocation: subdivision first

The standard is clear: you avoid allocation wherever you can. If you can split the process into sub-processes and measure the inputs and outputs of each, you do exactly that. This subdivision assigns every flow directly to the product that causes it, without assumptions. Your result stays as factual as possible.

When you must divide: physical or economic

Can the process not be split or in principle yes, but the data per sub-process is missing? Then you divide the inputs and outputs between the products. Here the standard prescribes a fixed choice. When the co-products sit close together in revenue — think of petrol and diesel from the same refinery — you divide the impact by physical properties such as mass or volume. When revenue differs sharply, mass gives a distorted picture: in ore smelting, a kilo of precious metal and a kilo of residual material weigh the same, yet drive the process very differently. In that case you divide by economic value.

EN 15804 makes the boundary concrete: a revenue difference of more than 25% counts as high and calls for economic allocation. A co-product that contributes 1% or less to total revenue you may neglect.

One rule always sits above the method

Whichever method you choose, for specific inherent properties of a material flow you always follow the physical reality. Energy content and elementary composition — the biogenic carbon content, for instance — is accounted for according to the actual physical flows. This keeps a calculation method from distorting your carbon accounting.

The hierarchy is therefore fixed: subdivide first, then divide by physical properties, and only as a last step divide economically — with the inherent properties always following the physical flow. Every step up increases accuracy and narrows the room for interpretation. Document for each co-product situation which method you apply and why; that keeps your EPD traceable and comparable.

Sound allocation, sound EPD

Not sure which method your process calls for, or want your allocation choices checked against EN 15804:A2? R<THINK helps you with software, data and expertise to get your LCA and EPD right down to this level of detail.