Georgetown, Colo. ? When fire broke out deep underground at a hydroelectric plant in the Rockies, officials at the surface dropped a radio down to five trapped men in a tunnel and were relieved to learn they were OK.

But by the time emergency crews reached them six hours later, they were dead.

On Wednesday, a day after the tragedy more than 1,500 feet underground at Xcel Corp.’s Cabin Creek power plant, investigators struggled to figure out what went wrong. Crews began to remove the workers’ bodies.

The workers were identified as Donald Dejaynes, 43; Dupree Holt, 37; James St. Peters, 52; Gary Foster, 48; Anthony Aguirre, 18; all of California. Their hometowns weren’t immediately available.

The men, whose bodies were found scattered along a 200 foot length of the 12-foot-wide pipe, didn’t have any burn marks, indicating that they probably died from the smoke and fumes from the chemical fire, Clear Creek undersheriff Stu Nay said.

Authorities defended their rescue efforts, saying smoke, the complexities of the 4,000-foot tunnel’s design and uncertainties about the dangers prevented them from going in after the men for more than 3 1/2 hours after the blaze broke out.

“We didn’t know what was causing the fire, what was feeding the fire,” Nay said. “You never know, when you’re dealing with airflow and the intensity of the fire where we’re facing a backdraft situation, what we’re running into.”

He added: “It’s dangerous work. We can’t afford to have someone else go in and complicate the problem.”

The blaze erupted when a machine used by the workers to coat the tunnel with a mixture of paint and epoxy caught fire, Xcel Energy spokeswoman Ethnie Groves said.

Nay said the mixture is kept in a hopper to warm it up so it will flow throw a sprayer. He said they were having problems spraying it so they added a solvent to the hopper and the hopper’s heating element inadvertently turned on, igniting the vapors.

Nine employees of RPI Coating of Santa Fe Springs, Calif., had been sealing the inside of the pipe to prevent corrosion, a routine procedure that followed an annual inspection. Two others were working outside the pipe and one of them was injured when he ran back into the tunnel to help when the fire broke out.

The tunnel delivers water from a reservoir to turbines that generate electricity at the plant 30 miles west of Denver.

The smoldering fire broke out about 1,400 feet from the tunnel’s bottom and was reported about 2 p.m., authorities said.

Four RPI workers escaped from the tunnel and were treated at a hospital and released. Five others scrambled about 1,000 feet above the fire but were trapped by smoke and the steep, nearly impossible-to-climb slope at a spot where the tunnel bends from a 15-degree angle to a 55-degree one, Nay said.

Officials dropped a radio to the workers, who reported about 2:40 p.m. that they were uninjured, Nay said.

Rescuers also dropped breathing masks and air tanks into the tunnel but were unsure if the workers were able to find them or use them, Nay said. Powerful fans were used to drive air into the tunnel and clear it of smoke so that the trapped crew members could breathe.