Whenever a ship collision, stranding, or other incident of navigation or other occurrence on board a ship or external to it resulting in material damage or imminent threat of material damage to the ship or her cargo creates, as determined by the Secretary, a grave and imminent danger to the coastline or related interests of the United States from pollution or threat of pollution of the sea by convention oil or of the sea or atmosphere by a substance other than convention oil which may reasonably be expected to result in major harmful consequences, the Secretary may, except as provided for in section 1479 of this title, without liability for any damage to the owners or operators of the ship, to her cargo or crew, to underwriters or other parties interested therein, take measures on the high seas, in accordance with the provisions of the convention, the protocol and this chapter, to prevent, mitigate, or eliminate that danger.