Workers killed by an explosion of fireworks at an underground storage facility in Waikele on April 8 should not have been working on them in that bunker, according to a mainland-based fireworks expert who often serves as a consultant for fireworks firms.

Five employees of Donaldson Enterprises were killed and another worker injured when aerial fireworks stored in the concrete-lined, tunnel-like structure exploded as they were either in or just outside the bunker, police and fire officials said.

Don Holmstrom, lead investigator for the U.S. Chemical Safety Board on the Waikele incident, told the Star-Advertiser on Wednesday that the tunnel was being used not just for storage, but for preparation for demolition at another, unidentified location.

Holmstrom told The on Thursday that the workers "were in the process of dismantling some of the pyrotechnic devices that were in the storage area."

The board has yet to announce any conclusions, nor say what the men were doing specifically at the time of the blast.

But federal regulations bar the disassembling of fireworks or any other explosives within the same structures they are housed, pointed out Wisconsin-based fireworks expert Charley Weeth.

"The assembly or disassembly or the preparation of explosive materials is strictly prohibited in a magazine," said Weeth, who is not part of the Waikele investigation. "These are activities that are specifically limited to process buildings or areas, or the field."

Weeth, who has served on the National Fire Protection Association Technical Committee on Pyrotechnics, which helps develop national fire codes, pointed to regulations on the website of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives that specify fireworks are to be stored at least 200 feet away from facilities where they are being processed.

Standard practice also is to not try to dismantle fireworks until they are at or near the site where they are to be destroyed, he said.

Holmstrom and his staff went to the scene and also interviewed Donaldson employees, including a sixth man at the scene who is the sole survivor of the crew.

Holmstrom, as well as local authorities, have confirmed that Donaldson had a contract to dispose of confiscated aerial fireworks. But where they came from has not been made public.

Fireworks confiscated by the Honolulu Police Department are disposed of by HPD officers with proper expertise, a spokeswoman said. Donaldson officials have declined to speak to the media.

The Honolulu Fire Department said Donaldson Enterprises was given a permit to store aerial fireworks there after its inspectors visited the Waikele bunker last year.

Family and friends of the five men killed held a vigil near the gate to the storage facility Friday night.