Exceptions from liability under section 153
155The owner of a ship from which persistent oil has been discharged or has escaped shall not incur any liability under section 153 if he proves that the discharge or escape—
(a)resulted from an act of war, hostilities, civil war, insurrection or an exceptional, inevitable and irresistible natural phenomenon; or
(b)was due wholly to anything done or left undone by another person, not being a servant or agent of the owner, with intent to do damage; or
(c)was due wholly to the negligence or wrongful act of a government or other authority in exercising its function of maintaining lights or other navigational aids for the maintenance of which it was responsible.