In a rare criminal indictment over workplace deaths, Xcel Energy Inc. and a repair firm it hired are facing federal charges in the case of five workers killed in a 2007 chemical fire at a hydroelectric power plant in Colorado.

Also named in the indictment are Xcel's Colorado subsidiary, Public Service Co. of Colorado, repair firm RPI Coating of Santa Fe Springs, Calif., and two executives of RPI Coating.

Minneapolis-based Xcel issued a statement Friday that said the fire was an accident, not a criminal act.

Xcel and Public Service Co. of Colorado could be liable for as much as $5 million in fines if found guilty.

The October 2007 fire at Xcel's Cabin Creek Hydro Plant, in the mountains near Georgetown, Colo., occurred during the renovation of a large empty metal pipe down which water normally flowed to create hydroelectric power. Five employees of RPI Coating were trapped in the pipe when chemicals being used in the renovation caught fire and blocked their only exit.

The Occupational Safety and Health Administration (OSHA) ruled that violations of OSHA safety rules resulted in the fire and the men being trapped. Workers on the other side of the fire were able to escape.

The U.S. Department of Justice obtained the indictment from a Colorado grand jury based on the OSHA ruling and OSHA's resulting decision to refer the case to the Justice Department for criminal prosecution.

The New York Times reported in 2003 that OSHA rarely seeks Justice Department prosecution in cases where worker deaths resulted. Between 1982 and 2002, OSHA did so in only 7 percent of worker deaths, the Times reported.

Xcel's general counsel, Michael Connelly, said in a prepared statement: "The general public is familiar with the legal system, and people understand that accidents are treated differently from criminal acts. This was an accident -- a tragic accident. We reject any attempt to characterize the Cabin Creek events in any other way, and we look forward to the opportunity to present our case."

Xcel Energy, Public Service Co. of Colorado and RPI Coating were each charged with five counts of violating OSHA regulation and causing death, which is punishable by a fine of as much as $500,000 per count.

Philippe Goutagny, RPI Coating owner and president, and James Thompson, RPI vice president, were each charged with five counts of the same violation. If convicted, each could be sentenced to as much as six months in prison and be fined as much as $1.25 million.

Steve Alexander • 612-673-4553