As per MARPOL Annex I, chapter 4, Regulation 18
Segregated ballast tanks:
- Every crude oil tanker of 20,000 t dwt and above and every product carrier of 30,000 t dwt and above delivered after 1 June 1982 shall be provided with segregated ballast tank.
- Every crude oil tanker or product carrier of 40,000 t dwt and above delivered on or before 1 June 1982 shall be provided with segregated ballast tank.
- The capacity of the ballast tanks shall be so determined that the ship may operate safely on ballast voyage without recourse to the use of cargo tanks for water ballast
It means the ballast water introduced into a tank which is completely segregated from the cargo oil and oil fuel system & which is permanently allocated to the carriage of ballast or to cargos other than oil & Noxious Liquid substances