New Guidelines Aim to Tackle Methane Slip Emissions
As the maritime industry increasingly turns to liquefied natural gas (LNG) as a cleaner fuel alternative, the challenge of methane slip—unburnt methane released during combustion—has come to the forefront. This phenomenon can account for up to 24% of greenhouse gas (GHG) emissions from LNG-fueled vessels. In a significant development, the International Maritime Organization (IMO) is moving towards standardizing direct methane emissions monitoring, which could greatly enhance the accuracy of reported carbon footprints for ships.
Understanding Methane Slip and Its Impact
Methane slip occurs when LNG engines fail to achieve complete combustion, resulting in unburnt methane being emitted into the atmosphere. This is a critical issue, as methane possesses a global warming potential (GWP) over 25 times greater than that of carbon dioxide (CO2). Consequently, the emissions from methane slip can significantly inflate a vessel’s GHG footprint, making it essential for the industry to address this challenge effectively.
Current EU regulations and IMO guidelines utilize standard factors to account for methane slip emissions from LNG engines. These factors can lead to methane slip contributing to a substantial portion of reported GHG emissions, calculated in CO2 equivalents. However, the regulations also allow for deviations from these standard factors if actual emissions can be verified through direct measurement.
In January 2025, a dedicated IMO Correspondence Group made strides towards standardizing the quantification of methane slip through direct measurement. Their report, submitted for MEPC 83, includes proposed guidelines for both test bed and onboard measurements of methane emissions from marine diesel engines. This initiative represents a crucial step in providing a reliable method for verifying methane slip measurements, with DNV anticipating the adoption of these guidelines by the IMO at the MEPC 83 meeting, concluding on April 11, 2025.
Benefits of Direct Methane Emissions Measurement
DNV, a leading classification society, is offering support for accurate methane slip measurements through its accredited emissions laboratory, Envilab. Their services comply with the new IMO draft guidelines and can be conducted on test beds or directly onboard vessels. The results are documented in an official emissions report, which certifies reduced methane slip factors for verification.
Direct measurement of methane emissions provides significant advantages over standardized factors, particularly when the standard methane slip factor appears excessively high for specific engine types or when methane abatement technologies are employed. Even minor adjustments in methane emissions can lead to substantial changes in reported CO2 equivalents due to methane’s high GWP. Furthermore, the application of methane catalysts can nearly eliminate the reported GHG emissions associated with methane, but this reduction can only be validated through accurate methane slip measurements.
As the maritime industry navigates the complexities of GHG emissions reporting, it is recommended that operators evaluate whether standard methane slip factors differ significantly from those of their installed engines. Collaborating with engine designers to explore potential improvements for reducing methane slip is also advisable. DNV is ready to assist with these critical measurements, paving the way for a more sustainable maritime future.
