What are Other Substances (OS) in Annex II?

• A. Substances indicated as OS in the pollution category column which have been evaluated and found to fall outside X, Y or Z because they present no harm; discharge not subject to Annex II.
• B. Substances indicated as OS that require the same restrictions as X.
• C. Substances OS only apply to ballast water.
• D. OS stands for Official Substances.

Answer: (A)

In MARPOL Annex II, noxious liquid substances carried in bulk are categorized by hazard levels. OS stands for Other Substances. These are substances that, after evaluation, have been found to fall outside the harm categories X, Y, or Z because they do not pose a harmful impact on the marine environment. Because of this assessment, discharging these substances is not subject to the discharge restrictions of Annex II.

This means OS represents items that have been deemed not to require Annex II controls, though ships still must follow any other applicable regulations and ensure the substance is properly listed as OS. The other options conflict with this understanding: one incorrectly says OS must follow the same restrictions as the highest hazard category, another claims OS applies only to ballast water (which is governed by different regulations), and the last is inaccurate about the abbreviation.