KALAELOA — One man was killed and three others were injured yesterday in an explosion at a Campbell Industrial Park company that processes used fuel oil.

The blast was centered on a 9,500-gallon tank at PSC Industrial Outsourcing Co., or Philip Services Corp.

The man who was killed had been welding around the tank just before the blast, Honolulu police said. He had paused and asked a co-worker to adjust the welding machine, and seconds later the tank containing used motor oil exploded a few feet from the victim, police said last night.

The dead man's identity was not released last night. His age was variously given as 22 and 23.

He and two of the injured men were contract employees of PSC. Another man who works at an adjacent business, Bonded Materials, also was injured.

The force of the explosion propelled the welder 75 to 100 feet, and he landed on or near a pickup truck in the parking lot of the Bonded property. The truck had major damage to its bed and sides.

The tank that exploded holds used fuel oil and was blown from its scaffolding and landed about 30 feet away.

The contractors doing the renovations were not authorized to be "where they were," said Jess Keopke, the plant's general manager.

He declined to elaborate.

The facility was being renovated at the time of the explosion but was not operating.

"The plant was shut down," Keopke said.

He declined to identify the workers' contract company.

Houston-based PSC has been modernizing its Campbell Industrial Park facility and "various contractors have been in and out of the plant," said Mike Leonelli, area manager for PSC, who was flying to Honolulu last night from Salt Lake City, Utah, because of the accident.

The suspect tank "is one of many tanks in the facility," Leonelli said. "It's a very unfortunate situation."

The explosion could be heard several blocks away.

Vincent Nihipali, owner of nearby VNC Drywall, said he heard a "big, hollow boom."

"This is too close to home," he said. "This is nuts."

After the blast, family members and co-workers rushed to the site and some were visibly shaken and crying. They declined to speak to the media.

Fire investigators were at the scene yesterday to try to determine how the explosion happened.

It occurred around 1:30 p.m. along the 91-400 block of Komohana Street, near the intersection of Kauhi Street. It did not cause a fire, said Honolulu Fire Capt. Terry Seelig.

The injuries involved a man in his late 40s and another in his early 20s, who were both taken in stable condition to a trauma center, said Bryan Cheplic, spokes- man for the city's Emergency Services Department.

Another man, in his late 20s or early 30s, was taken in stable condition to a different hospital, Cheplic said.

The man who died suffered "extensive multisystem trauma," Cheplic said. Paramedics pronounced him dead at 1:36 p.m., he said. An autopsy was pending today.

The death comes as Hawai'i has seen a drop in occupational deaths. Last year, 23 people died because of job-related injuries in the Islands, compared with 30 in 2006.

In the 2007 fatalities, seven workers died in falls, three were killed after coming in contact with "objects or equipment" and five of the fatalities occurred after exposure to harmful substances, according to statistics from the U.S. Bureau of Labor. The remaining eight were killed in traffic-related incidents or assaults.

PSC Industrial Services provides industrial cleaning and environmental services and is one of two operating groups of Philip Services Corp.