MARPOL Annex III Regulation 2.3 says “For the purposes of this Annex, empty packagings which have been used previously for the carriage of harmful substances shall themselves be treated as harmful substances unless adequate precautions have been taken to ensure that they contain no residue that is harmful to the marine environment. “

Further part 4 of the Code says “Empty packagings, including IBCs and large packagings, that have contained a dangerous substance shall be treated in the same manner as is required by this Code for a filled packaging, unless adequate measures have been taken to nullify any hazard.”

Empty chlorine cylinders are dangerous , unless the cylinders are purged and no chlorine gas is remaining inside, must be marked and labelled as full. Which means the existing marks and labels must not be removed. Additionally, for packagings, IBCs, bulk containers, portable tanks, road tank vehicles and railway tank wagons which contain the residue of dangerous goods of classes other than class 7 dangerous goods document must contain the words “EMPTY UNCLEANED” or “RESIDUE LAST CONTAINED” before or after the dangerous goods description.