A welder killed in a massive explosion at Philips Services Hawaii at Campbell Industrial Park on Oct. 7 accidentally caused the blast that took his life, a Honolulu Fire Department investigation concluded today.

Killed was Sean Norva, 23, of Waipahu.

"The accident occurred while the worker was welding part of a catwalk that was connected to the top of an oil storage tank," an HFD media release said. "The tank was approximately 15 feet tall and reportedly contained waste oil."

The release said that vapors from the tank were ignited by the welding activities and caused the explosion, the release said. Norva was thrown more than 100 feet from the point blast while the fractured tank was propelled approximately 30 feet.

"The explosion fatally injured the welder," the investigation concluded, according to the release. "Two other workers who were near the base of the tank when it exploded were seriously injured. A fourth worker at an adjacent business survived the blast with minor injuries."