Under the Exhaust Gas Cleaning System Guidelines there are 2 schemes for approving a scrubbing system as an alternative method of compliance with MARPOL Annex VI regulation 14 fuel sulphur limits:

• ‘Scheme A’ – initial certification of exhaust gas cleaning performance, followed by periodic survey, with continuous monitoring of key system operating parameters and daily emission checks to confirm performance in service; and
• ‘Scheme B’ – performance confirmation by continuous monitoring of exhaust emissions using an approved system, which is also subject to periodic survey, with daily checks of key system operating parameters.

In practice, many scrubber systems are approved under both Scheme A and Scheme B. In addition, while Scheme B requires continuous monitoring of the SO₂/CO₂ ratio as the method of confirming compliance, most scrubber systems also have continuous monitoring and logging of all major system operating parameters (e.g. flow rates, temperatures & pressures, as well as the mandatory monitoring of wash water discharges), regardless of whether Scheme A approved.

In the unlikely event that the continuous emissions monitoring system (CEMS) should malfunction, the advice given to EGCSA by industry legal experts and regulators is that ship operators should be open and advise the vessel’s Flag State Administration and Port State Control what has happened and of any remedial action that is to be taken. CEMS must then be fixed soonest (i.e. before or at next port) or compliant fuel used.  For the period of downtime (i.e. between malfunction and fix), Port State Control could, if needed, use a comparison of logged system operating parameters with EGC System Technical Manual ‘Scheme B’ (ETM-B) to confirm that the scrubber continued to operate correctly and therefore that the vessel remained in compliance.