A ship dispatched by the United Nations has arrived off the coast of Yemen to begin pumping over 1 million barrels of oil from a decaying supertanker anchored in the Red Sea. The ship was abandoned off the coast of Yemen in 2015, at the start of the U.S.-backed, Saudi-led war against Houthi rebels. It contains four times the amount of oil spilled off the coast of Alaska during 1989’s Exxon Valdez disaster. On Monday, U.N. humanitarian coordinator David Gressly said engineers had secured the rusting ship against a potential catastrophic spill or explosion.

David Gressly: “The structure of the FSO Safer, even though it is a decaying vessel, the hull is still very secure, which means that the transfer of the oil will be relatively low-risk.”