HONOLULU -- The Honolulu Medical Examiner's Office on Wednesday released the identity of the worker killed in an explosion at a Campbell Industrial Park business Tuesday.

Sean Miguel Norva, 23, of Waipahu, died in the blast. Norva died from multiple internal injuries, the medical examiner said.

Investigators were on the scene of the explosion Wednesday at Philip Services Corp. in Campbell Industrial Park.

A 9,500-gallon waste oil tank exploded when Norva was welding a metal footbridge near the tank. The blast threw Norva nearly 100 feet. Three others were injured.

Welding near oil or gas tanks can be dangerous work. There are regulations that cover such work.

Sam Dannaway, a fire protection engineer, said Honolulu fire codes require a permit for welding near oil tanks.

"Waste oil storage, when we're dealing with it in terms of looking safety items, we always consider it as volatile flammables unless its tested and proven otherwise because by nature of being a waste, you don't know what type of liquid has been dumped into a waste oil tank," Dannaway said.

Officials said the tank that exploded held used fuel oil.

"We have to assume that the tank is going to contain flammable liquids, and if there's openings near the tank, there will be flammable vapors present," Dannaway said.

Fire officials said the investigation will be meticulous because there was a fatality. They said there are multiple possible sources of ignition and they want to get it right.