Abstract: At 9:15 a.m. on January 19, 2018, work was being conducted in the William E Strait, a line haul vessel. Several tradesmen from multiple employers were working on the vessel. While Employees #1 and #2 were taking a break inside the upper engine room of the vessel, Employees #3 and #4 were installing pipes in the lower engine room. Earlier that morning, around 7:03 a.m., two employees from another employer found that the gas line for their cutting torch had been left inside an enclosed space located below deck. The employees reported that they smelled gas and vented the space for about an hour and a half before beginning work; however, did not have the space tested. Propylene and oxygen from the release entered into the forward portable water tank. After performing cutting and welding operations for a period of time in the enclosed space, located in front of the forward tank, an explosion occurred. Where employees #1 and #2 were taking their break was the deck level above where the explosion occurred, and Employees #3 and #4 were on the starboard side of the affected area with only a bulkhead in between. Employee #1 and #2 suffered body trauma and severe burns, resulting in their death. Employee #3 sustained a concussion, hearing loss, and burns to his hand, while Employee #4 sustained injury to his neck, head, back, and foot, as well as hearing loss.