The man died at Straub Clinic and Hospital Friday evening after arriving in critical condition, Hawaii Pacific Health spokeswoman Shawn Nakamoto told The Associated Press. He apparently had been burned.
She did not release the victim's identity. The man was among two people injured in the Friday morning blast near the Waikele Business Center.
Two others died in the blast. Two others are missing.
The Honolulu Department of the Medical Examiner said it did not expect to release victims' names until Monday.
But the Honolulu Star-Advertiser reports that sports broadcaster Jim Leahey has identified one of the two who died in the explosion as his brother, 50-year-old Robert Leahey.
A police robot was expected to begin searching the facility Saturday morning to see whether explosions had stopped and whether the temperature had dropped low enough for rescuers to enter and look for the two missing people.
They were last seen inside the bunker before the blast, but high temperatures prevented rescuers from entering to look for them, said Honolulu Fire Capt. Terry Seelig.
All the victims were employees of Donaldson Enterprises, an environmental services and unexploded ordnance disposal company, said Peter Savio, who handles the leases for the facility. The company couldn't immediately be reached for comment.
The storage facility was authorized by the fire department to hold fireworks.