The U.S. National Transportation Safety Board says leaking fuel that touched a hot surface caused the August 2016 fire that injured dozens aboard the Caribbean Fantasy ship that grounded near Puerto Rico.

Officials said Tuesday the fire caused some $20 million in damage and spread quickly because fuel and lube oil valves were intentionally blocked open. They also blamed the failure of firefighting systems, a poor safety culture and a lack of inspection to ensure the safety management system was working.

The board said more than 45 of the 511 passengers and crew were treated for minor injuries. Six other injuries were reported as serious.

The fire burned for three days aboard the combination cruise and ferry vessel that was traveling from the Dominican Republic to Puerto Rico.