# We are switching our magnesium foundry's cover gas from sulphur hexafluoride (SF6) to a hydrofluorocarbon (HFC) such as HFC-134a or a fluorinated ketone: what do we report?

Canonical: https://senseible.earth/answers/magnesium-cover-gas-switch-from-sf6-to-hfc-134a

The Intergovernmental Panel on Climate Change (IPCC) gives no default emission factor for HFC-134a or the fluorinated ketone FK 5-1-12 as cover gas because there are no data yet to base one on. They also react with molten magnesium, so for a national key category good practice is to measure the leaked gas and the perfluorocarbons (PFCs) formed.

## What the guidelines say about the new gases

- Both HFC-134a and FK 5-1-12 are less thermodynamically stable than SF6, and so have much lower global warming potential (GWP).
- The guidelines expect them to decompose or react extensively on contact with liquid or gaseous magnesium, producing various fluorinated gases, for example PFCs.
- As a rule of thumb from one study (Tranell et al., 2004), when SF6 is replaced by HFC-134a, less than half the amount of active fluorinated compound on a molar basis is needed to protect a given magnesium surface under otherwise identical conditions.
- For the ketone, the guidelines say PFC decomposition products would be more significant in carbon dioxide equivalent terms than the FK 5-1-12 itself (its own GWP is estimated to be similar to carbon dioxide).

## What you can and cannot calculate

For SF6 the guidelines give a default factor and a consumption method. For HFC-134a and FK 5-1-12 they say there are no data at this time on which to base emission factors, so it is not possible to develop a factor-based approach (their Tier 1 or Tier 2).

If the emission from magnesium cover gases is a national key category, their good practice is direct measurement, or meaningful indirect measurement, of the fugitive HFC-134a or FK 5-1-12 and of the PFCs formed, which is their Tier 3. They put the uncertainty of such monitoring at about plus or minus 10 percent.

The guidelines add that the contribution of carbon dioxide used as a carrier gas is normally a small fraction of the GWP and may generally be disregarded, though they call it the largest uncertainty in the simple approach if the blend is very rich in carbon dioxide.

## A practical order of work for the changeover

1. Keep the last year of SF6 consumption on cylinder records, so the before and after are on the same basis.
2. From the day of the switch, record each cover gas bought and used, with the carrier gas blend.
3. Ask your gas supplier whether it holds emission measurements from furnaces like yours. Treat any figure it gives as theirs, with its conditions, until you have measured your own exhaust.
4. In any report, state that the new gas has no IPCC default factor and show what you measured or did not measure. Do not describe the switch as a cut in carbon dioxide equivalent until measurements show it.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into a dated, fingerprinted record, so the fuel and power of the site show up once uploaded. It does not calculate or measure cover gas releases from documents, so the cover gas line comes from your own records and measurements.

- [Sulphur hexafluoride in magnesium die casting](https://senseible.earth/answers/magnesium-die-casting-sf6-cover-gas-emissions)
- [Netting off sulphur hexafluoride in the melt](https://senseible.earth/answers/magnesium-sf6-broken-down-in-furnace-can-i-subtract)
- [Which assessment report's global warming potential values to use](https://senseible.earth/answers/ar5-vs-ar6-gwp-which-to-use)

Sources: [IPCC 2006 Guidelines, Volume 3, Chapter 4, Metal Industry Emissions, section 4.5 Magnesium production](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_4_Ch4_Metal_Industry.pdf)

Last reviewed 2026-11-05. From section 4.5 of the IPCC 2006 Guidelines. Industry practice with these gases has moved since 2006, so ask your supplier and verifier whether newer measured factors exist before relying on this page.