Section 18 Defences.
Where a person is charged with an offence under section 3(5), (6) or (7), 4(3) or (4), 5(4) or 13(2) it shall be a defence to prove that the contravention in question occurred by reason of matters outside his control and that he took all reasonable precautions to avoid such a contravention.
Subject to subsection (3), where a person is charged with an offence under this Part it shall be a defence to prove that the contravention in question occurred in a case of emergency relating to—
the safety of human life, vessels or aircraft,
the safety of equipment and facilities of high value, or
the protection of the environment.
Subsection (2) does not apply where the contravention in question is a contravention of section 6(1) or of a condition attached to a permit granted under section 6(3).
Where a person is charged with an offence under section 7(2) in respect of a contravention of section 7(1)(a), it shall be a defence to prove that the act in question was done for the relief of the suffering of the mammal or bird in question.