Section 11

Where a person is charged with an offence under section 10, it shall be a defence to prove that the discharge or escape of the substance mentioned in subsection (1) of that section was caused for the purpose of securing the safety of the vessel, the place on land, the installation, device or aircraft concerned, or for the purpose of saving life but a defence under this section shall not operate if the court is satisfied that the discharge or escape was not necessary for the alleged purpose or was not a reasonable step to take in the circumstances.