The smoldering fire broke out about 1,400 feet from the tunnel’s bottom and was reported around 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 around 2:40 p.m. that they were uninjured, but that may have been the last contact rescuers had with them, Nay said.160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! 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. It was unclear whether the five maintenance workers were burned, suffocated or overcome by fumes from the highly flammable epoxy sealant they were using to coat the inside of the empty, 12-foot-wide water pipeline. 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 hours after the blaze broke out. “We didn’t know what was causing the fire, what was feeding the fire,” Undersheriff Stu 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 caught fire, Xcel Energy spokeswoman Ethnie Groves said. But exactly what burned after – the machine, the epoxy or both – was unclear, she said. Nine employees of RPI Coating of Santa Fe Springs had been sealing the inside of the pipe to prevent corrosion, a routine procedure that followed an annual inspection. The tunnel delivers water from a reservoir to turbines that generate electricity at the plant 30 miles west of Denver.