The cargo holds on bulk carriers and the cargo tanks on oil tankers need to be cleaned between jobs.
If a hold was previously used to carry minerals and the next cargo to
be transported is wheat, the hold will need to be cleaned until it is
spotless. Cleaning crews wearing protective clothing and breathing
equipment will move into the holds with large machines to help them
clean every surface and corner.
Any waste must be stored and placed in a proper container when on shore. No dust is allowed to escape to pollute the air.
It is not safe to clean the tanks inside tankers so it is never done in
port. Small amounts of vapour in tanks can be explosive. Tankers must
go to sea where chemicals are used to remove any materials in the
tanks. The waste that comes from the tanks must be stored and disposed
of properly back on shore.