What action is prohibited in regard to oil and HAZMAT on a vessel?

The action that is prohibited in regard to oil and HAZMAT on a vessel is draining oil into bilges. This practice is strictly regulated since bilges are areas where water and oil typically collect and could pose significant environmental hazards if discharged improperly. When oil is drained into bilges, there is a risk that it could be released into the sea during normal operations or maintenance, leading to marine pollution and violation of international regulations such as MARPOL.

Discharging oil into the sea is also prohibited, but it is typically associated with operational discharges rather than the improper disposal of oil into bilges. Storing oil in cargo tanks can be permissible under certain conditions if done according to regulations, while mixing HAZMAT with ballast water is another hazardous practice that must be avoided to prevent environmental contamination. However, the action of draining oil directly into bilges poses a clear and immediate risk and is therefore strictly forbidden.