The underground storage facility in Waikele where five Donaldson Enterprises employees were killed during a violent explosion Friday morning was being used by the company to prepare highly explosive fireworks for final disposal, an investigator from the U.S. Chemical Safety Board said yesterday.

But federal and local officials have yet to determine exactly what the men were doing when the explosion occurred.

Don Holmstrom, investigator-in-charge for the U.S. Chemical Safety Board, said that from what he was told, "generally … there were several steps in the process of destroying the fireworks." Preparation work was done at the scene, but the actual destruction of the fireworks, through burning, took place elsewhere, he said. Holmstrom declined to go into specifics of the predisposal work being done in the concrete-fortified tunnel. The space is one of 130 built into the mountains between Waikele and Kunia by the military in World War II and now being used as commercial storage lockers.

Officials of Waipio-based Donaldson Enterprises, the ordnance and fireworks disposal company that leases the bunker, have not commented publicly on the tragedy.

Holmstrom’s four-person team arrived Sunday on Oahu and has been interviewing witnesses and key employees of the different companies involved. The team has also been working with other government agencies investigating the incident.

Donaldson Enterprises was contracted by VSE Corp., a federal contractor, to store and destroy the fireworks, Holmstrom said.

"We don’t have any preliminary findings," Holmstrom said. "It’s too early."

"It appears to have been an industrial accident,"  he added.

The Chemical Safety Board is an independent federal agency tasked with investigating the root causes of chemical accidents at fixed industrial sites, the chemical accident equivalent of the National Transportation Safety Board. But unlike the NTSB, the Chemical Safety Board does not issue fines or citations. It will, however, offer recommendations to plants and regulatory agencies including the Occupational Safety and Health Administration and the Environmental Protection Agency.

Holmstrom is an investigations supervisor and heads the board’s Denver office.

The Honolulu Medical Examiner’s Office came to the same conclusion in stating that all five men died from an accidental explosion of fireworks in a confined area. Four died apparently after inhaling carbon monoxide.

The office identified four of the men: Robert Kevin Freeman, 24, of Aiea; Bryan Cabalce, 25, of Wahiawa; Neil Sprankle, 24, of Mililani; and Justin Kelii, 29, of Kaneohe. The fifth man has been identified by family members as Robert Leahey, 50.

The bodies of Freeman and Leahey were recovered soon after the accident at about 9 a.m. Friday. Examiners said the cause of death for both men was thermal burns and the toxic effects of carbon monoxide inhalation due to an explosion in a confined space.

Cabalce, who was taken to Straub Clinic & Hospital in critical condition, died at 5:50 p.m. Friday of burns due to the explosion.

The bodies of Sprankle and Kelii were removed from the cave Saturday. Examiners said the two men died of asphyxia due to the toxic effects of carbon monoxide inhalation caused by the explosion.

Police and fire crews said the unstable environment of the cave, where explosions continued through much of Friday, prevented them from going into the cave to retrieve Sprankle and Kelii until the following day.

A sixth man, also a Donaldson Enterprises employee, refused treatment at the scene.