How do I work out the sulphur hexafluoride (SF6) my magnesium die casting shop emits from its cover gas?

SF6 is a cover gas that stops molten magnesium from burning. The method from the Intergovernmental Panel on Climate Change (IPCC) counts all the SF6 you consume as emitted, so your cylinder records are the figure. With no records, its default is 1.0 kilogram of SF6 per tonne of magnesium cast.

Why a casting shop emits SF6 at all

The IPCC guidelines say all molten magnesium spontaneously burns in the presence of atmospheric oxygen, so production and casting of all magnesium metal needs a protection system. Among the commonly used systems are gases with high global warming potential (GWP), such as SF6, which typically escape to the atmosphere. Casting by gravity, sand or die all count.

IPCC methods are written for national inventories and do not use Scopes. Reading them for one plant, SF6 escaping from your own melt shop is a direct emission from a source you control, which is Scope 1 in Greenhouse Gas (GHG) Protocol terms. That placement is our reading, not IPCC text. The same goes for the Tier 1 and Tier 2 methods below: they are written for national totals, and applying them to one plant is our reading.

Method 1: your own SF6 consumption (the IPCC's Tier 2)

1. Take the SF6 you used in the year: opening stock plus purchases minus closing stock, in kilograms. The guidelines say SF6 use is measured easily and accurately from purchase data.
2. Treat all of it as emitted. The Tier 2 equation is simply emissions equal consumption of SF6 in magnesium smelters and foundries.
3. Multiply the kilograms by the GWP of SF6 in the set your inventory uses to get carbon dioxide equivalent (CO2e).

Method 2: the default (Tier 1), only if you do not know your casting type

The Tier 1 equation multiplies the magnesium cast by a default factor of 1.0 kilogram of SF6 per tonne of magnesium casting, for all casting processes. The guidelines trace it to a die casting consumption rate of about 1 kilogram of SF6 per tonne of magnesium produced or smelted under recommended conditions. The IPCC gives one factor for all casting processes, taken from a die casting rate; it offers no die-casting-only factor.

They also say consumption varies substantially between casting operations, sometimes by orders of magnitude, and that Tier 1 should be used only when you do not know the type of operation (recycling, billet casting, die casting and so on). Our reading: a shop that has cylinder invoices should not use it, and a die casting shop knows its type.

How far to trust each number

• Purchase data: the guidelines call an uncertainty of less than 5 percent usually appropriate for directly reported data.
• The assumption that 100 percent of the SF6 is emitted: in a typical casting operation they say it should be within 30 percent.
• The Tier 1 default: they say uncertainty may range over orders of magnitude, so it is a very rough approximation.

What to keep for a reviewer

• Magnesium production volumes and process types.
• Cover gas consumption or composition, or the magnesium production where a factor is used.
• The calculation, the method and any assumptions.

One year at a die casting shop (example figures)

• SF6 used: opening stock 18.0 plus purchases 30.0 minus closing stock 21.0 = 27.0 kilograms
• Tier 2: 27.0 kilograms of SF6 emitted
• Magnesium cast in the year: 24 tonnes
• Tier 1 check: 24 x 1.0 = 24 kilograms of SF6
• Difference: 27.0 minus 24 = 3.0 kilograms, so records give 12.5 percent more than the default (3.0 / 24)

Stock, purchase and tonnage figures are an example. Multiply the kilograms by the SF6 GWP from the set you use for the rest of your inventory.

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 SF6 or other cover gas releases from documents, so work that line out from your own cylinder records as shown here.

• Which assessment report's global warming potential values to use
• What Senseible does not calculate
• SF6 leaks from switchgear in Scope 1
• Carbon footprint per kg of aluminium die casting

Sources: IPCC 2006 Guidelines, Volume 3, Chapter 4, Metal Industry Emissions, section 4.5 Magnesium production

Last reviewed 2026-11-05. Equations 4.30 and 4.31 and Table 4.20 are from the IPCC 2006 Guidelines. The GWP of SF6 depends on the assessment report you use, so check it against your buyer's or verifier's rule.