The previous day, a 36-compartment tanker, the S.S. Sansinena, had arrived at the Union Oil Company's bulk terminal at Berth 46, near the southern tip of the harbor. The mostly Italian crew had spent the majority of the day on the 17th loading fuel and ballast in preparation for an 11PM departure. The Sansinena was 810-feet long and 70,620 deadweight tons - the largest vessel of its kind when it was constructed in 1958.

At 7:33PM, an unknown ignition source created an explosion that acted like a surgeon's knife, lifting the center section of the ship - a section more than 500 feet long - into the air, leaving the bow and aft sections in the water. The midship section lifted off like a Saturn rocket and made it more than 700 feet into the air. As gravity took over, the center section of the Sansinena came crashing down on top of a guard shack 200 yards from where the ship was berthed. Most investigators believe that security guard Howard Dennis was in the shack. He was certainly killed and his body never found.

On the Princess Louise, it turned out that not one guest had been injured. They turned out to watch the glow in the sky from the explosion and fire. It was a night they would never forget.

OCD dispatched Task Force 38, Engine 53, Engine 101 and all five fireboats. Within the first 18 minutes of the incident, an additional nine task forces, nine rescue-ambulances, two helicopters, three triples, Light Water 100 and Crash 90 were added to the assignment. Chief Engineer Long was flown by helicopter to the harbor to take command and direct the crews.

When first-in Task Force 48 arrived on scene, it was still unclear to them what had happened. There was oil and flame extending along the Union Oil yard and the midship section of the Sansinena was not easily recognized. You wouldn't expect to see the middle of a ship sitting on a dock and this one was nearly concealed by flames and smoke. BC Christenson notified OCD of, "fire on a 900-foot front."

As Boat 5, berthed about a half mile from the explosion drew in close to the oil and fire covered water and stern of the ship, debris were still falling from the sky. The bow and stern were separated by more than 500 feet of open water, much of it covered with burning oil. Both sections of the ship were more than 60 feet from the concrete pier.

The three-man crew on board Fireboat 5 could hear screams and calls for help. Despite the threat of additional explosions, Fireboat Mate Walter Ball, and firefighters John Kemperman and Forrest Taylor worked Fireboat 5 into the area beneath the stern of the doomed ship and rescued four sailors from the water and 14 who slid down ropes and jumped into the fireboat. Once the crewmen were on board, Ball swung the fireboat around and sped for Berth 55 where Engine 101 had set up a command post for medical assessment. The engine company, along with RA staff were triaging victims before transporting them to local hospitals.

Land companies were forced to lay extremely long hose lays into the fire. Next to the Union Oil facility, the San Pedro Boat Works contained more than $1.5 million in small craft moorings. It was the most at-risk exposure. For three hours, firefighters battled the flames before bringing the major emergency fire under control. The pleasure craft at the Boat Works were saved.

As the sun came up on the morning of December 18, the toll was known. There were nine dead, plus 46 injured. Damage extended out in a six-mile radius from the explosion. The scene was almost unimaginable: two bits of ship sticking up from the shallow harbor and a smoking ruin on the dock adjacent.

The Coast Guard investigation indicated that the monetary loss exceeded $21 million. It also severely criticized the procedures used on board the Sansinena. Within a very short period of time, the Los Angeles Fire Department began a formal policy of inspecting every incoming tanker prior to offloading or onloading ballast or cargo. It was the first department in the United States to do so. Firefighters Kemperman, Ball, and Taylor were awarded Medals of Valor for saving the 18 crewmen on the ship.