According to DNV, even thoughthe total amount of methane slip might initially seem minor, it significantly impacts reported GHG emissions.
Methane slip, as based on standard factors, can account for up to 24% of GHG emissions from an LNG-fuelled vessel. As an alternative to using standard factors for the reporting of CO2 equivalents, direct methane emissions monitoring has the potential to positively impact a ship’s reported carbon footprint.
EU regulations and IMO guidelines account for methane slip from LNG-fuelled engines by using standard factors. The table shows the LNG standard correction factors as % of the mass of the fuel for three different engine types:
Considering the GWP of methane is 28 times that of CO2, these standard factors can result in methane slip contributing to up to 24% of the reported GHG emissions, which is accounted for in terms of CO2 equivalent.
Regulations allow for deviations from predefined standard factors if real figures can be certified by a direct emissions measurement.
In January 2025, a dedicated IMO Correspondence Group took a significant step towards standardizing the quantification of methane slip through direct measurement.
They submitted their report for MEPC 83, which includes proposed draft guidelines for test bed and onboard measurements of methane emissions from marine diesel engines.
These guidelines represent the first essential tool for reliably verifying methane slip measurements. DNV expects that the draft guidelines will be adopted by the IMO at MEPC 83 ending on 11 April 2025.
Direct measurements of methane emissions offer significant advantages over standardized factors, especially when the standardized methane slip factor seems excessively high for a specific engine type or when methane abatement technologies are used to further treat exhaust emissions.
Although the total amount of methane slip might initially seem minor, it significantly impacts reported GHG emissions. Methane’s GWP over a 100-year timescale is 28 times higher than CO2, meaning even minor adjustments in methane emissions can substantially affect the reported CO2 equivalent.
Furthermore, the reported GHG equivalent emissions caused by methane can be almost entirely mitigated by applying methane catalysts. The reduction potential of methane catalysts can only be accurately verified through measurements of methane slip.
Consider methane slip measurements as part of your strategy:
It is recommended to evaluate whether the standard methane slip factors significantly differ from those of your installed engine. Collaborate with the engine designer to assess potential improvements for reducing methane slip.
Any deviations from the standard factors can be verified by measuring methane slip on board your ship.
