How do I estimate process carbon dioxide for bricks, tiles or refractories if I have no lab assay of the carbonate in my clay?

Use the Intergovernmental Panel on Climate Change (IPCC) Tier 1 defaults: clay used is 1.1 times product tonnes, carbonate is 10% of the clay, split 85% limestone and 15% dolomite. That is about 0.049 tonnes of carbon dioxide (CO2) per tonne of product. Real clays run from 0 to over 30% carbonate.

The Tier 1 recipe

1. Clay used = tonnes of fired product x 1.1, the default loss factor.
2. Carbonate in the clay = clay x 10%, the default carbonate content.
3. CO2 = carbonate x (0.85 x 0.43971 + 0.15 x 0.47732) = carbonate x 0.445. The 85 and 15 are the default split between limestone and dolomite, and the other numbers are the CO2 per tonne of each.

Which products it covers

The guide's ceramics group includes bricks and roof tiles, vitrified clay pipes, refractory products, expanded clay products, wall and floor tiles, table and ornamental ware, sanitary ware, technical ceramics and bonded abrasives. The CO2 comes from heating carbonates in the clay, shale, limestone, dolomite and witherite, and from limestone used as a flux.

Why an assay beats the default

The guide notes that carbonate in the clays used by the ceramics industry ranges from 0 to over 30%. At 30% the default answer triples; at a clean 3% it falls to under a third. An assay of your clay pit, or the supplier's analysis, replaces the 10%. Carbonates you add yourself, such as limestone or dolomite, count on top. If you only know the weight of carbonate rock, the guide assumes 95% purity.

Fuel is separate

Coal, wood, gas or oil burnt in the kiln is a separate Scope 1 line, worked out from your invoices. The default above is only the carbonate in the clay.

A brick unit firing 1,000 tonnes in a month

• Clay used: 1,000 x 1.1 = 1,100 tonnes
• Carbonate at the 10% default: 110 tonnes; CO2 = 110 x 0.445 = about 49 tonnes
• If an assay shows 3% carbonate: 33 tonnes x 0.445 = 14.7 tonnes
• At 30% carbonate: 330 tonnes x 0.445 = about 147 tonnes

The 1,000 tonnes and the assay values are example numbers. Kiln fuel is added separately.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so kiln fuel and site power are on file. The clay assay and tonnes fired come from your lab and production log.

• Carbon calculators
• Brick kiln emissions per 1,000 bricks
• Process CO2 from limestone calcination
• Morbi ceramic cluster carbon footprint

Sources: IPCC, 2006 Guidelines for National Greenhouse Gas Inventories, Volume 3, Chapter 2: Mineral Industry Emissions

Last reviewed 2026-11-04. The 2006 Guidelines are written for national inventories. A plant's own lab assay, production log and fuel invoices replace these defaults wherever you have them.