When do you need this inspection?
If you’re a Canadian or foreign-flagged vessel that has unloaded a “Category X” noxious liquid substance at a port and plan to depart from the port, you will need this type of inspection. Before a vessel leaves the port of unloading, it is required to prewash the tank that held the noxious liquid substance and discharge the residues to a reception facility until the concentration level of the noxious substance is below the maximum allowable level, hence the term “prewash.” If residues of these substances are discharged into the sea from tank cleaning or deballasting operations, they are deemed to present a major hazard to either marine resources or human health and, therefore, it is prohibited to discharge them into the marine environment.
The Vessel Pollution and Dangerous Chemicals Regulations provide the authority to conduct prewash inspections or grant exemptions as per Annex II of MARPOL. Vessels that contained “Category X” substances require a prewash operation prior to leaving the port of unloading or must be granted an exemption under the list provided in the Regulations. Exemptions to the prewash requirement can be given for reasons such as reloading with the same or compatible substance, washing to occur at another port with an appropriate reception facility, or using various other approved methods of dealing with cargo residues. Exempted vessels are still required to have a TC inspector verify necessary procedures and documentation to support the exemption.