How do I account for industrial gases (LPG, acetylene, welding gas) in my carbon inventory?

Only some gases generate reportable Scope 1 emissions, and for some (e.g. welding gases) the amounts are usually very small and may be excluded from your calculations if justified.

What are industrial gases?

Industrial gases are supplied in cylinders, cylinder packs or bulk tanks. Common uses include welding and cutting, forklifts and heating, food and beverage, healthcare and dental, laboratories, manufacturing and fire suppression.

Emissions arise in two ways: the gas is burned (LPG, acetylene), or the gas itself is a greenhouse gas that is released (CO₂, nitrous oxide). Both are Scope 1 when they happen at sites you control.

Fugitive refrigerant emissions are recorded separately in Trace: How do I calculate emissions from refrigerants? 

Which gases release greenhouse gases?

A gas creates Scope 1 emissions if burning it produces CO₂, or if the gas itself is a greenhouse gas. Oxygen, nitrogen, argon, helium and hydrogen do neither.

The emissions from producing oxygen, nitrogen and argon sit in Scope 3 (purchased goods and services). They are almost always very small and are not part of this section.

Do I need to report these emissions?

Not always. Emissions from industrial gases are a Scope 1 source, so they should be considered, but whether you need to report them depends on how material they are. That depends on the gas and how much you use. Welding gases are often immaterial for many companies, while LPG can be significant. 

Welding gases such as acetylene and shielding gas are usually bought in small quantities, so their emissions are typically very small compared with other Scope 1 sources such as fuel and refrigerants. Many companies conclude they are immaterial and choose to exclude them. That is a reasonable approach if you can justify it.

LPG is different. Sites running forklifts or LPG heating can use several tonnes a year, so it should be treated like any other Scope 1 fuel. Nitrous oxide and bulk CO₂ can also be material.

Typical scale:

• Acetylene: 10 kg of net acetylene is about 34 kg CO₂.
• Shielding gas: a 15 m³ cylinder of argon with 16% CO₂ is about 4.5 kg CO₂e.
• LPG: a 45 kg cylinder is about 137 kg CO₂e, and one tonne of LPG is about 3 t CO₂e. Forklift fleets and LPG heating can be material.
• Nitrous oxide: because of its high GWP, 100 kg is about 27 t CO₂e.
• Pure CO₂: a 30 kg cylinder is 30 kg CO₂, which can add up quickly for bulk users such as beverage producers.

Questions to help you decide

• What gases do you buy, and roughly how much of each per year? A few cylinders of acetylene or shielding gas is likely very small, so you may be able to exclude it with a justification. If you buy LPG, nitrous oxide or bulk CO₂, include and assess them.
• Do you have the data to estimate them? Invoices or delivery records showing gas type, cylinder size and quantity are usually enough for a quick estimate. If you don’t have them, record the exclusion and the reason.
• Do you have manufacturing operations or significant on-site processing? If so, we suggest assessing these emissions where you have the data.

If you decide to exclude these emissions, keep a record of your estimate or reasoning if needed for an auditor. If you decide to report them, the sections below explain how to enter your data.

If you report these emissions...

Entering data in Trace: LPG cylinders

Enter LPG supplied in cylinders and bought by weight in the 'Industrial Gases' section, in kg. LPG delivered in bulk and billed in litres goes in 'Stationary Fuels'. Do not enter the same LPG in both places.

Trace converts the NGA per-litre LPG factor to kg using a standard density of 0.51 kg/L.

Reading your invoice: brands and product names

Suppliers sell shielding gas under brand names, so the invoice rarely includes the gas mix itself. To choose the right option in Trace, find the CO₂ percentage on the invoice, the cylinder label or the safety data sheet (SDS).

The table below maps BOC’s range, one of the most common in Australia, to the Trace options. BOC’s 2019 Essentials Guide lists each shielding gas with a gas code and a nominal mixture.

*For mixes without their own option, you can work out the CO₂ in kg and enter it under Pure CO₂ (direct-release) → m³ of mix x CO₂ % x 1.87 kg/m³.

For example, 15 m³ of a 10% CO₂ mix is 15 x 0.10 x 1.87 = about 2.8 kg. Oxygen, helium, hydrogen and nitrogen add no emissions, so ignore them.

Other suppliers use their own names. Some name mixes by composition, such as 5/2 for 5% CO₂ and 2% O₂, or 16/3 for 16% CO₂ and 3% O₂. Always check the supplier’s SDS, because composition can differ slightly between suppliers and over time.

Converting cubic metres (m³) to kilograms

Trace takes gas quantities in kg. Cylinder gases are often rated in cubic metres (m³), and the cylinder size letters (D, E, G) indicate size and volume. Compressed gas cylinders are identified by letter codes, while LPG cylinders are identified by the weight of their contents. CO₂ and LPG are usually already in kg.

kg = m³ x density (kg/m³)

Worked example 1: acetylene. A cylinder rated at 7 m³ holds about 7 x 1.10 = 7.7 kg.

Worked example 2: shielding gas. For a 15 m³ cylinder of argon with 16% CO₂:

1. Mix density = (0.84 x 1.69) + (0.16 x 1.87) = about 1.72 kg/m³
2. Mass = 15 x 1.72 = about 25.8 kg

Enter 25.8 kg against Shielding gas (Argon / 16% CO₂).

Use the density at the same temperature and pressure your supplier uses for the m³ rating. It is on the SDS. Mixing reference conditions (for example 0°C and 15°C) can introduce an error of up to about 7%.

Notes for data collection

• Net vs gross: Use the weight or volume of the gas only, not the gross weight of the cylinder (steel).
• Purchases vs consumption: We want to measure consumption for the reporting period but this can be hard to measure. Purchases are a reasonable proxy for consumption. If your stock changes materially over the year, use purchases plus opening stock less closing stock.
• Complete combustion: The factors assume all LPG and acetylene is burned and all CO₂ supplied is released. This slightly overstates emissions if some gas is leaked or left in returned cylinders.
• Other fuel gases: If you use another fuel gas, such as propylene cutting gas, speak to your Trace advisor. Entering it as LPG is a close approximation for propylene (within about 3%).