Officials say that the five workers who were killed by a fire at a hydroelectric plant near Georgetown, Colo., on Oct. 2 most likely died of smoke inhalation, according to a New York Times report.

State and federal investigators have traced the fire at the plant to a heated device being used to mix an epoxy-based sealant inside a steep underground water tunnel where the men were working.

Four workers who escaped the fire from a bottom entrance to the tunnel were treated at a Denver hospital and released.

The investigation process at the plant could take months, said Herb Gibson, the Denver area director for OSHA.

The agency released records two days after the incident showing that RPI Coating, a California-based contractor at the plant, had been fined 90 times since 1988 while operating under another name, Robison Prezioso Inc. The fines totaled $135,569, the agency said, and 27 of the violations were considered serious.

All five victims were employees of RPI, which had been hired by Xcel Energy to do routine anticorrosion maintenance on the 4,000-ft. tunnel.

The plant, located high in the mountains overlooking Georgetown, a rustic town about 45 miles west of Denver, is operated by Xcel.

Among the many issues likely to be raised during the investigation, according to the Times, will be RPI’s troubled track record.

“They have a history of citations with both state and federal OSHA,” Gibson said.

One occurrence, in 2002, involved a scaffolding collapse on the San Francisco-Oakland Bay Bridge that killed one RPI employee.

The company has also been fined hundreds of thousands of dollars in California and Hawaii for violating hazardous waste rules, according to the Times.