Senseible

Which slope factor does the European Union (EU) Carbon Border Adjustment Mechanism (CBAM) method use for each aluminium smelter pot type, and how is it applied?

The Commission's aluminium guide prints a slope factor for each pot type, from 0.058 for vertical stud Søderberg to 0.233 for side worked prebake. Multiply it by your anode effect minutes per cell-day and your tonnes of aluminium to get carbon tetrafluoride (CF4), then add the hexafluoroethane (C2F6) share.

In plain words: what is being counted

A smelter makes aluminium in big electric pots, called cells. Now and then a pot has a short upset, called an anode effect, when the aluminium oxide it feeds on runs low (our background explanation, not the guide's words). For those few minutes it gives off two very strong warming gases, CF4 and C2F6. Together they are the perfluorocarbons (PFCs). CBAM is the EU's charge on the carbon built into imported goods, like a toll on the smoke behind a product.

Think of a car engine that coughs out a puff of dirty smoke each time it is starved of fuel. The more coughs, and the longer each lasts, the more smoke. The slope method counts the coughing minutes and turns them into gas.

The factors the guide prints, by pot type

The three steps

  1. Work out anode effect minutes per cell-day (AEM): how often anode effects happen per cell-day, times the average length of each one in minutes.
  2. CF4 in tonnes = AEM x (factor / 1,000) x tonnes of primary aluminium made in the period.
  3. C2F6 in tonnes = CF4 tonnes x the C2F6 share. Then turn both into carbon dioxide equivalent (CO2e) with the guide's global warming potentials: 6,630 tonnes of CO2e per tonne of CF4 and 11,100 per tonne of C2F6.

Minimum and better

The guide's minimum requirement is the technology factors above, which come from Annex II, section B.7 of the Methodology Act. Its recommended improvement is to set your own factors from continuous or intermittent field measurements at least every 3 years, or after significant changes in the installation, with a maximum uncertainty of plus or minus 15% each.

If you have seen other tables

Our page on the Intergovernmental Panel on Climate Change (IPCC) defaults prints a different slope table for some pot types. Each table is printed in its own source, and we did not re-check the IPCC figures here. For a CBAM report, use the table the Commission prints for CBAM, and confirm it against the Methodology Act with your verifier.

A centre worked prebake line making 100,000 tonnes a year (example)

Output and anode effect minutes are example numbers. The factors and global warming potentials are the guide's printed values.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. Reading anode effect minutes from a pot line is custom, on request. Senseible builds the verifier-ready file and checks every figure in-house; an accredited verifier Senseible partners with signs it off, or the client sends it to their own.

Sources: European Commission, CBAM Guidance No. 5e, aluminium (14 August 2026)

Last reviewed 2026-11-07. Check Tables 3-1 and 3-3 of the guide against Annex II, section B.7 of Implementing Regulation (EU) 2025/2547 before you file. The guide says it is not legally binding.