If any oil is discharged from a ship, tanker or offshore installation the master of such ship, tanker or offshore installation and, if he is not the owner of such ship, tanker or offshore installation, also the owner thereof, shall be guilty of an offence unless-
(a) the oil in question was discharged for the purpose of securing the safety of such ship, tanker or offshore installation or of any other ship or tanker or of preventing damage to such ship, tanker or offshore installation or to any other ship or tanker or the cargo thereof, or of saving life, and such discharge of the oil was necessary for such purpose or was a reasonable step to take in the circumstances;
(b) the oil in question escaped from the ship, tanker or offshore installation in consequence of damage to the ship, tanker or offshore installation, and as soon as practicable after the damage occurred all reasonable steps were taken for preventing or (if it could not be prevented) for stopping or reducing the escape of the oil; or
(c) the oil in question escaped by reason of leakage, and neither such leakage nor any delay in discovering it was due to any lack of reasonable care, and as soon as practicable after the escape was discovered, all
reasonable steps were taken for stopping or reducing it.
