How much CO2 does acetylene used for cutting and welding emit?
Each kg of acetylene burnt in a cutting or welding torch releases about 3.38 kg CO2, because one molecule of acetylene (C2H2) burns to two molecules of CO2. A cylinder holding 7 cubic metres of gas, about 7.7 kg, gives roughly 26 kg CO2.
Where the 3.38 figure comes from
Acetylene is C2H2, with a molar mass of 26. Burning it fully gives 2 CO2, with a mass of 88. So 88 / 26 = 3.38 kg CO2 per kg of acetylene. This is a carbon balance, not a database default, so it holds for any supplier as long as the quantity is right.
Acetylene burnt in your own torches is stationary combustion in Scope 1 under the GHG Protocol Corporate Standard.
Converting the invoice quantity to kg
- Invoice in kg of gas: multiply by 3.38 directly.
- Invoice in cubic metres: multiply by about 1.1 kg per cubic metre (acetylene density near room temperature and normal pressure), then by 3.38. That is about 3.7 kg CO2 per cubic metre.
- Invoice by cylinder count only: ask the supplier for the gas content per cylinder, because sizes differ by supplier. Do not use the cylinder's gross weight; it includes the steel shell, the porous filler and the acetone the gas is dissolved in.
What not to add
- Oxygen cylinders used with the acetylene: oxygen releases no CO2 at the torch. The electricity used to make it at the gas plant belongs in Scope 3 purchased goods, not Scope 1.
- Acetone in the cylinder: it stays in the cylinder and goes back to the supplier, so it is not burnt.
- LPG used as a cutting fuel instead of acetylene: use the LPG factor, 2.98 kg CO2 per kg, on that line.
Is it worth counting
For most fabrication shops acetylene is a small line next to grid power and diesel. Count it anyway if your invoices show it, because it is easy and a buyer reviewing your Scope 1 will see the purchases. If it is below 1% of your total, you can note it as immaterial but keep the calculation.
Worked example: a month of cutting gas
- Acetylene invoices: 12 cylinders of 7 cubic metres = 84 cubic metres
- 84 x 1.1 kg per cubic metre = 92.4 kg acetylene
- 92.4 x 3.38 = 312.3 kg CO2 (Scope 1)
- One 7 cubic metre cylinder: 7.7 kg x 3.38 = 26.0 kg CO2
Cylinder content varies by size and supplier; use the quantity printed on your invoice where there is one.
What Senseible does here
Senseible reads the gas invoice from an image or PDF, classifies the line by HSN code and multiplies the printed quantity by a published factor. A gas line without a factor in its list shows no figure rather than a guess, so the 3.38 calculation above is the one to record for acetylene.
Sources: GHG Protocol Corporate Standard, 2006 IPCC Guidelines, Volume 2 Energy
Last reviewed 2026-10-17. Acetylene density varies with temperature; where the supplier states kg per cylinder, use that.