MARPOL Annex VI Regulation 4: equivalent arrangements
Regulation 4 of MARPOL Annex VI lets an Administration accept a fitting or method at least as effective as the Annex requires, which is the legal basis of the scrubber.
MARPOL Annex VI Regulation 4 is the equivalence clause. It permits the Administration of a Party to allow a fitting, material, appliance, apparatus or alternative procedure in place of one the Annex requires, provided the substitute is at least as effective in terms of emission reductions. It is the provision under which an exhaust gas cleaning system is accepted as an alternative to burning fuel that meets the Regulation 14 sulphur limits , and the reason a scrubber ship is compliant rather than exempt.
The full article will set out the text of Reg.4.1 to 4.4, the difference between an equivalent and an exemption under Regulation 3 , what a Party must communicate to the Organization when it accepts one, and how the accepted arrangement is entered in section 2.6 of the Supplement to the International Air Pollution Prevention Certificate . It will also cover the other equipment accepted under the same clause, including the selective catalytic reduction and exhaust gas recirculation routes to NOx Tier III .
The practical point the clause turns on is that approval sits with the flag Administration, not with a classification society. Class type approval is a commercial convenience that most Administrations rely on, and it is not what the Annex requires.