I’ve been doing a lot “deep-dives” into structural steel/steel construction data myself, and came across this same issue. After discussions with AISC’s team, I think I can resolve your question.
When structural steel is delivered to a site, it typically does NOT come directly from a steel mill. Rather, it gets fabricated at a fabrication shop using other structural elements (plate for example) to meet the drawing requirements. This is great from a construction standpoint, but a nightmare in terms of carbon counting as EPDs for the final fabricated member do not exist. However, in the scope of A1-A3, A1 would be the impacts for the steel mill (aka unfabricated, but then you also need to account for waste steel generated during fabrication), A2 would be the impacts from transportation to a fabrication shop, and A3 would be the impacts at the fabrication shop (excluding any coatings applied). Due to the relatively few steel mills compared to fabrication shops, what’s happened is that the steel mill companies have generated product specific EPDs with mill specific GWP values showing the mills impacts under A1, and then industry average fabrication values for A2 and A3. In some instances, the larger steel mill companies have begun to acquire fabrication shops, in which case they may end up using their own fabrication shops’ A2 and A3.
As you can see, the largest “unknown” is in what YOUR fabrication shops’ A2 and A3 is (your being the shop who is conducting the fabrication for any given project). If I had to guess, this is why BCCA listed both unfabricated and fabricated product specific GWP values. It is also important to note that even though there is uncertainty behind A2 and A3, all of the product-specific EPDs are third-party verified against ISO 14025 and 14044.
In order to accomplish your goal of incorporating GWP limits on steel products, what you would need to do is the following:
- Isolate the specific steel products you are looking for - the GWP varies greatly between product (product meaning…HSS, Plate, Hot-Rolled, Rebar, etc).
- Determine where your steel products are currently being sourced from - if it’s from within the US or North America, than using the AISC Industry Average values, or other steel product’s industry average would be relevant since it’s tied to the “local” (relative to the world) steel market.
- Use the Industry Average steel product EPD GWP value for A1-A3 (which would include fabrication) + a degree of uncertainty if you do not know which specific mills you are commonly sourced from. If you do know which steel mills your sourcing from, you can tailor your value to better suit what you actually receive. Or, you could come to release that adopting the BCCA limits for fabricated steel products would not be a challenge/reach for you/your firm.
- Rinse and repeat for EACH steel product.
On the implementation side, the best way to go about it would be to stay on top of the tonnage purchased per steel product per mill before it is fabricated. It can be a heavy data lift, but tracking the “as purchased” steel product tonnage is the best approach from my standpoint since you can then tie it back to a product specific EPD that lists the mill specific GWP values.