EPD: Achieving Green Goals With HSS

By Cathleen Jacinto, PE, SE
Technical Consultant, Steel Tube Institute

Update: The State of California has pushed back the date of the Buy Clean California legislation to now become effective on July 1, 2022. STI and AISC will continue to provide updates as more information becomes available.

Figure 1: Steel mill photo courtesy of Nucor

When we think of a steel mill, one might imagine a picture of dark skies, rusty exposed steel, and billowing smokestacks. There is a long-held preconceived notion that steel mills are ‘dirty.’ However, this is a reality that is becoming part of the past. Over the past 30 years, modern technology has advanced the steel industry a great deal and has significantly reduced greenhouse gas emissions. In one sector of today’s steel mill, we will instead find cleaner and more controlled electric or induction furnaces, a larger amount of recycled steel scraps, less raw materials, and overall smaller steel mill footprints. Steel mills are now surrounded by green landscapes, a sign of sustainability. Structural steel that is produced in the United States contains an industry average recycled content of 93%. The most recyclable material by weight in the world is steel, and it can be repeatedly recycled without property loss. For these reasons, steel is a premier green construction material, and should be considered alongside any other material when designing for sustainability.

In recent years, there has been a stronger legislative push to lower embodied carbon in buildings by affecting the procurement process of building materials. The Buy Clean California Act was enacted into law in 2017, which limits the amount of embodied carbon allowed in public projects. Effective July 1, 2021, projects entering contracts with the state of California must meet the embodied carbon thresholds. This is the first-ever legislation to target carbon emissions for select construction materials. Hot rolled sections, HSS, and plates, among other materials, fall under the purview of Buy Clean California. Environmental legislation is only growing and trending to other states and initiatives as we take greater strides to reduce global warming. This article will discuss a few fundamentals behind embodied carbon, focus on the story behind HSS environmental impacts, and what designers/steel suppliers need to know going forward. 

Understanding the basics of EPDs

Figure 2: AISC Industry-Average EPD for Fabricated HSS

An Environmental Product Declaration (EPD) reports the impact a building material has on the environment. An EPD is technically a third-party verified document that summarizes the environmental impacts of a product, resulting from a science-based life cycle assessment (LCA). In simpler terms, EPDs are often likened to nutrition labels for a food product, conveying how environmentally healthy a building material is.

One of the key ways an EPD measures environmental impact is by reporting a Global Warming Potential (GWP) number for the material. The GWP number for steel is equivalent to measuring the relative amount of embodied carbon expended to manufacture the steel product. As greenhouse gases linger in the atmosphere, they act as a blanket, insulating and warming the Earth. The lower the GWP number, the lower the embodied carbon resulting from that product, leading to less potential for global warming.

How are EPDs and GWPs developed?

Figure 3: How to Develop an Environmental Product Declaration (EPD) and Global Warming Potential (GWP) thresholds

ISO 14025 and ISO 21930 Standards are a set of international standards that control environmental product declarations. These Standards establish a core set of requirements to be considered in a Product Category Rule (PCR).

The Product Category Rule (PCR) provides the rules, requirements, and guidelines for developing an EPD for a specific product category. The PCR instructs how the life cycle assessment (LCA) should be conducted.

The Life Cycle Assessment (LCA) is the systematic analysis of the potential environmental impact of a product during its entire life cycle.

An Environmental Product Declaration (EPD) is a third-party verified document that summarizes the environmental impacts of a product (i.e. steel HSS) as a result of the LCA. There are different types of EPDs:

  • Facility-specific EPD: An EPD from a single manufacturer and manufacturing facility of a product. A manufacturer of steel coil can have several steel mills. A facility-specific EPD must come from only one of a manufacturer’s steel mill facilities.
  • Industry-average EPD: An EPD reporting the average EPD results developed from multiple manufacturers and multiple facilities of a steel product. Refer to Figure 2 for an example of an industry-average EPD by STI and AISC for HSS.

The Global Warming Potential (GWP) is a threshold value reported in a product’s EPD, which, for steel, is measured in tons of C02 equivalent per ton of steel. The GWP is a relative measure of how much energy the emissions of 1 ton of a greenhouse gas will absorb over a period of time, compared to the emission of 1 ton of carbon dioxide (C02). For example, say the GWP for HSS is 2.83 tons of C02 equivalent per ton of steel. This means that the emissions to manufacture 1 metric ton of HSS are equivalent to emissions of 2.83 metric tons of carbon dioxide. A product compliant with Buy Clean California requires an EPD reporting a GWP value for that product or material less than the threshold GWP value required by Buy Clean for that product.

Buy Clean California

Now that we’ve laid the groundwork for embodied carbon and EPDs, let’s explore current environmental legislation affecting building construction. The Buy Clean California Act (BCCA) requires that public projects in the state of California are to purchase only building material products with a GWP level below the mandated threshold, as set by the Department of General Services. Essentially, its goal is to lower embodied carbon by affecting purchasing practices in building materials. There are a few items to note in the Buy Clean California Act:

  • BCCA legislation was passed in 2017, and is effective starting July 1, 2021
  • Applies to public projects in the state of California
  • Applies only to structural steel (HSS, plates, and hot-rolled sections such as WF, angles, channels, and WT), concrete reinforcing steel, flat glass, and mineral wool board insulation 
  • Does not apply to other building materials including, but not limited to, concrete, wood, concrete masonry, clay masonry, cold-formed steel, etc. Legislation is currently pending to include other materials.
  • BCCA requires a facility-specific EPD. The EPD must not be an industry-average EPD or an average reported GWP from multiple manufacturing facilities.

Buy Clean California is a change to the material procurement process, not necessarily the design process. In California, when those in the steel supply chain submit a project bid, they must also submit steel EPD(s) demonstrating that the steel material that will be supplied for the project falls below the GWP threshold.

STI, AISC, CRSI, and AISI have developed a Quick Guide to Buy Clean California’s Steel Provisions. This document summarizes the maximum GWP threshold values required by Buy Clean in units of tons of C02 equivalent per tons of steel, and these are also listed in Table 1 below. Also listed in the Quick Guide are specific structural steel and steel rebar products that fall under Buy Clean provisions. Refer to the link at the end of this article to download the Quick Guide from the Steel Tube Institute website.

Table 1: Excerpt from A Quick Guide to Buy Clean California’s Steel Provisions by STI, AISC, CRSI, and AISI: Maximum GWP-100 Thresholds per Buy Clean California

Now that we know what the maximum GWP values are, how do we find the GWP values for the steel used for our project? The actual GWP values for steel products will be found in facility-specific EPDs published by steel mills for your project. AISC has also developed industry-average fabrication values which are added to the product EPDs, resulting in an industry-wide fabricated steel products EPD. Note that the AISC EPDs are industry-average values, not facility-specific as required by Buy Clean California, and are used to determine the GWP thresholds for Buy Clean. However, fabricators who are eligible to use an industry-wide EPD published by AISC may submit the AISC EPDs as appropriate representation for their steel product in applications outside of Buy Clean California. Also, the AISC EPDs can offer a good sense of where steel products fall on the embodied carbon spectrum. Table 2 is an excerpt from the AISC EPD for Fabricated Hollow Structural Sections dated December 15, 2016 (the current version when this article was written). Please refer to AISC or STI for any potentially newer EPDs starting on July 1, 2021.

Table 2: Excerpt from Environmental Product Declaration for Fabricated Hollow Structural Sections by AISC dated December 15, 2016: Life Cycle Assessment showing industry-average GWP results for HSS

As an example, let us compare the AISC industry-average EPD for HSS with the required GWP threshold per Buy Clean. Since the AISC EPD reports fabricated HSS per Table 2, we compare this to fabricated GWP thresholds per Buy Clean California in Table 1. 

Industry-average fabricated HSS GWP per AISC EPD = 2.39 tons C02 eq / tons of steel

is less than Fabricated GWP Threshold per Buy Clean California Act = 3.19 tons C02 eq / tons of steel

We find that the AISC EPD industry average GWP for HSS is within acceptable GWP thresholds of Buy Clean. A similar evalulation would be performed for facility-specific EPDs received by mills and/or service centers to confirm compliance with Buy Clean California.

What is the story behind the HSS EPD numbers and where are we headed?

Since this legislation is fairly new, there has been a push in recent years to coordinate the several steps behind the GWP numbers – PCRs and LCAs – to prepare for the July 1, 2021 milestone for Buy Clean. For this reason, it is important to understand how the current GWP numbers were developed in 2016, and what direction we anticipate we are headed.

For steel, the measure of carbon levels is taken ‘at the mill gate.’ That means that the majority of the impact of steel to global warming comes from the production of steel at the mill.  Effectively, when we try to reduce the embodied carbon of steel, we need to look at its life before it leaves the mill gate, before fabrication, before erection, and before its final service life in a structure. 90% of the environmental impact of steel occurs before the steel piece leaves the mill gate, and 10% results from the fabricator part of the steel supply process.

Figure 4: Steel coil used to produce HSS sections

Therefore, understanding the embodied carbon levels in HSS requires background knowledge of the manufacturing of HSS at the mill. HSS is typically produced from a flat sheet of steel, or steel coil, that is cold-rolled into the HSS shapes we specify for our structures. There are two primary methods to manufacture steel coil, which is used to produce HSS sections – Blast Oxygen Furnace (BOF) and Electric Arc Furnace (EAF). Historically, HSS has been produced from steel coils that were manufactured using the old open-hearth BOF method. The BOF method melts raw iron-ore to extract pig ironto create new steel. A small percentage of scrap is used in this process. The EAF method uses recycled steel scrap to manufacture steel coil and utilizes a cleaner electric grid, resulting in an overall lower amount of embodied carbon in HSS production. In recent years, coil manufacturers have found ways to overcome material ductility challenges inherent in EAF production, resulting in an increase in HSS production using EAF-manufactured coil domestically in the United States. However, the majority of global HSS manufacturers outside of the United States is largely dependent on BOF-manufactured coil.

It is important to parallel this HSS manufacturing discussion with the timeline for EPD and GWP numbers. In 2016, when the first EPD was developed, the majority of coils used in global HSS production were produced from BOF-manufactured coils. At that time, domestic HSS producers did not have data from a life cycle assessment (LCA), and the HSS EPD was based on global LCA data and a global-average GWP number. This global GWP number in 2016 was heavily influenced by BOF manufacturers across the globe, which has resulted in the GWP threshold reported in the HSS EPD – 2.83 tons of C02 equivalent/tons of steel at mill gate per Table 1. 

In an effort to prepare for Buy Clean California to come into effect on July 1, 2021, HSS producers decided to develop a new industry-wide EPD by July 2021. The new EPD will now use a North American steel number for the LCA coil data, not global, which would represent a shift towards EAF-produced coils as the feed stock for HSS. In addition, there are also ongoing efforts to increase efficiency in the electric grid that powers EAF manufacturing. As the electric grid becomes more energy efficient and more fossil-free, the impact of steel HSS production on global warming would decrease. For all of these reasons, there is potential for the new GWP, and the amount of embodied carbon used to manufacture domestic HSS, to decrease. During the time this article is written, it remains to be seen if the new GWP number will be lower than the previous 2016 number. 

What do designers need to know about EPD for HSS?

When selecting materials for a project, we cannot only compare raw GWP numbers in EPDs between different materials (steel to concrete) or even within steel materials (WF to HSS). GWP numbers are based on the material’s unit of measurement – tons for steel, cubic yards for concrete, etc. The quantity of material used on a project to resist the same loading will vary greatly due to the difference in strength and stiffness of the materials. Therefore, to compare apples to apples, the structure as a whole would need to be analyzed and designed in each material separately to result with an estimated quantity for each material. Multiplying each material quantity by its corresponding GWP number would result in a final embodied carbon level for that material. We can then compare these final carbon levels more accurately across materials. In essence, the GWP numbers shown on EPDs for different materials (steel versus concrete, HSS versus WF) cannot be directly compared to each other when deciding what material is more environmentally friendly. The decision needs to be made in context to the quantity each material will require on a project.

Figure 5: Anaheim Regional Transportation Intermodal Center
Image courtesy of AISC/Thorton Tomasetti

To take this a step further, it is more appropriate to conduct a full life cycle assessment (LCA) for each material under consideration to fully understand its environmental impacts. GWP/Weight of materials is only one of several environmental impacts to consider. Finishes, cladding, and maintenance are a few examples of items that could change depending on the material selected and would impact a whole building LCA.  Therefore, only comparing GWP numbers amongst different materials is not recommended to select a material during design.

Buy Clean California is more so a change to the procurement of materials rather than a change to the design process – the Contractor and subcontractors need to ensure that the steel supplier chosen is compliant with Buy Clean California. That said, designers can optimize materials in an effort to reduce environmental impacts on a project, and minimizing steel tonnage is not always the most effective way to optimize. When we look at the full project life beyond design, a lighter steel member may require additional reinforcing at connections and thus, additional fabrication work. Specifically, for HSS, an effective way to optimize HSS design is to check HSS wall thicknesses at connections during design.

In conclusion, previous misconceptions of ‘dirty’ steel mills are a thing of the past. The steel industry has evolved a great deal to now stand in the forefront due to use of recycled steel, and push towards more efficient manufacturing methods to result in a cleaner steel production process. It is important to understand where the GWP numbers have come from, and the positive direction the steel industry is headed. For additional information on environmental impacts to HSS and other steel materials, please see the list of resources offered below. Feel free to also place an inquiry on the STI website at https://steeltubeinstitute.org/contact-us/.

Free Webinars

Webinar On Demand

Watch the recorded webinar on the introduction to Buy Clean California and the Steel Supply Chain.

Webinar On Demand

Watch the second recorded webinar in this series, Next Installment of Buy Clean California and the Steel Supply Chain.

Additional EPD Resources:

References

AISC and STI, 2016. “Environmental Product Declaration Fabricated Hollow Structural Sections,” American Institute of Steel Construction and the Steel Tube Institute.

Cross, J., Puchtel, M., and Anderson, J. (May, 2021). “Buy Clean California and the Steel Supply Chain,” Webinar, Steel Tube Institute.

Department of General Services Procurement Division. “Buy Clean California Act,” https://www.dgs.ca.gov/PD/Resources/Page-Content/Procurement-Division-Resources-List-Folder/Buy-Clean-California-Act. Accessed 05-28-2021.

(May 2021). “A Quick Guide to Buy Clean California’s Steel Provisions,” American Institute of Steel Construction, Steel Tube Institute, Concrete Reinforcing Steel Institute, and the American Iron and Steel Institute.

Johnson, L. 2019. “An Accurate Declaration,” Modern Steel Construction, American Institute of Steel Construction, July issue.

The International EPD System, https://www.environdec.com/home. Accessed 05-28-2021.

June 2021

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