# Impact methodology

Markdown version of https://bluegreenmaterials.com/en/impact-methodology. Updated on 2026-11-08.

Every lot we buy and pay for generates an environmental impact certificate with a folio. This page explains exactly how it is calculated, what is never done and how to use it in a sustainability report without inflating numbers.

## Three rules that are never broken

- **Real weight, not estimates**: Impact is calculated with the net scale weight of the lot once it is paid. The estimate in the offer never enters the certificate.
- **No factor without a source**: Each impact factor is tied to the publication it comes from and the date it was consulted. A factor without a source cannot be used: the system rejects it.
- **Nothing is overwritten**: If a weight is corrected later, a new version of the certificate is issued. The previous one stays in the history; it is not edited.

## The calculation, step by step

1. **The weight is closed**: The lot reaches paid status with its real net weight per material, backed by a scale ticket with a photo.
2. **It is split by family**: Each material is assigned to its family (for example carbon steel or stainless). A mixed lot does not use a single factor: each family is calculated with its own.
3. **The factor is applied**: For each family, impact = net tonnes × per tonne factor of the current version. Families are added up and rounded to the kilogram.
4. **The version is frozen**: The certificate records which factor version it used. If factors change later, earlier certificates do not change.
5. **Verification is published**: The certificate carries a folio. On its verification page anyone can check, without an account, that the document is authentic and unaltered.

> If a material has no factor in the current version, the calculation stops with an error. Another material's factor is never applied "for now": that would be an invented number.

## Where the factors come from

The factors compare making steel from scrap with making it from ore. As a public reference, worldsteel publishes the average CO₂ intensity of each route: 2.34 t per tonne in the blast furnace, 1.47 t with direct reduced iron and 0.69 t with scrap in the electric furnace (2024)[^ws-indicators]. Inputs per route (ore, coal, limestone and scrap) come from #SteelFacts[^ws-facts].

> **Current status of the factors** The platform's current factor version is **preliminary**: it is pending verification against the primary source and third party review. While it is, certificates say so and are not presented as verified. When the verified version is published, its figures, source and date will appear here.

We only publish metrics with a verifiable primary source. That is why we do not report water savings until we find a figure with that support. See [the published figures and their sources](https://bluegreenmaterials.com/en/impact).

## What the certificate does not say

- It is not a measurement at the mill's stack: it is an **estimate** of avoided emissions against a reference route.
- It does not say the resulting steel is carbon neutral: the electric furnace also emits.
- It is not a carbon credit or a tradable offset, and it cannot be sold or transferred.
- It does not cover transport of the lot or the emissions of the generator's own operations.

## How to use it in a sustainability report

For a greenhouse gas inventory, the GHG Protocol places the waste a company generates, including what is sent for recycling, in scope 3 category 5. It recommends the recycled content method: the emissions of the recycling process are allocated to whoever uses the recycled material, not to whoever generates it[^ghg-scope3].

On avoided emissions the GHG Protocol is clear: **they are not included in or deducted from the scope 3 inventory**, but they may be reported separately, documenting evidence that the material was collected, recycled and used, the methodology, sources, system boundaries, period and assumptions[^ghg-scope3].

The Bluegreen certificate is built for that: it carries net weight, material, period, folio, the factor version and its sources, and the chain of documents (CFDI, Carta Porte and scale ticket) that proves the material reached a mill. See [what each report includes](https://bluegreenmaterials.com/en/reports).

## Frequently asked questions

### Can I subtract the avoided CO₂ from my emissions?

No. The GHG Protocol asks for avoided emissions to be reported separately, without deducting them from the scope 3 inventory[^ghg-scope3].

### Why is the certificate only issued once the lot is paid?

Because only then is the real net weight closed. Calculating with the offer estimate would inflate or shrink the impact without support.

### What happens if a weight is corrected later?

A new version of the certificate is issued with the corrected weight. The previous version stays in the history.

### How does an auditor verify a certificate?

With the certificate folio, on its public verification page. No account is needed and no commercial data of the lot is shown, only the document fingerprint to compare with their copy.

## Sources

[^ws-indicators]: World Steel Association (worldsteel), «Sustainability Indicators Report 2025» (2025). https://worldsteel.org/wider-sustainability/sustainability-indicators/sustainability-indicators-report-2025/
[^ws-facts]: World Steel Association (worldsteel), «#SteelFacts, June 2026 update» (2026). https://worldsteel.org/wp-content/uploads/SteelFacts_update-June-2026.pdf
[^ghg-scope3]: GHG Protocol (WRI and WBCSD), «Technical Guidance for Calculating Scope 3 Emissions, version 1.0, category 5» (2013). https://ghgprotocol.org/sites/default/files/2023-03/Scope3_Calculation_Guidance_0%5B1%5D.pdf