How do we count flared gas under UK CBAM if we cannot meter the flare accurately?

The technical guide from HM Revenue and Customs (HMRC) says flare monitoring must cover routine and operational flaring. If accurate monitoring is not technically feasible or costs unreasonably, the reference emission factor of 0.00393 tonnes of carbon dioxide (tCO2) per normal cubic metre (Nm3) should be used.

What the monitoring must cover

• Routine flaring and operational flaring: trips, start-up and shutdown, and emergency reliefs in production processes.
• Emissions from the flared gas when combusted.
• Emissions from fuels needed to run the flare, for example the pilot flame and fuels used to combust the flared gas.
• Inherent carbon dioxide (CO2) in the gas source stream.

If you cannot meter it well

The guide says that if accurate monitoring of a flare is not possible because of technical feasibility or unreasonable costs, the reference emission factor of 0.00393 tCO2/Nm3 should be used. HMRC's draft force of law notice words this as "must" and says the value comes from pure ethane used as a conservative proxy for flare gases.

The guide lists three items to include in flare emissions, and does not say whether the reference factor also covers the pilot fuel. Ask your verifier before you assume it does.

Doing better than the reference factor

• Use process modelling based on industry standard models.
• Weigh the molecular weight of each contributing stream by its share, to get a weighted annual average for the flare gas.
• For activity data, the guide says a higher measurement of uncertainty than for other fuels combusted would be acceptable.
• Write the approach into the monitoring plan.

Example: a year of flared gas

• Estimated flared volume: 200,000 Nm3 over the monitoring year
• Reference factor: 0.00393 tCO2/Nm3
• 200,000 x 0.00393 = 786 tCO2 from the flared gas
• If the plant models its stream and gets a lower factor, it needs evidence the verifier accepts

The volume is an example, not a plant's figure.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. The standard product does not meter flares (metering is a custom installation on request) or model flare gas. Fuel purchase records cover bought fuels such as pilot gas, not the gas flared. A verifier accredited for UK CBAM must still verify the figure.

• Waste gas used as fuel
• Fuel sampling when unsafe
• What a UK CBAM monitoring plan holds
• UK CBAM for Indian exporters

Sources: HMRC, Carbon Border Adjustment Mechanism (CBAM): technical guide for monitoring, reporting and verification, HMRC, The Carbon Border Adjustment Mechanism (Emissions and Verification) Force of Law Notice (Draft)

Last reviewed 2026-11-06. Read from technical guide section D4.8.5.2.1 and the draft Emissions and Verification notice section B.9.1.3 on 6 November 2026. HMRC may change both before 1 January 2027.