OSHA has fined two companies more than $1 million for alleged serious and willful violations of federal workplace safety and health standards following a tunnel fire last year that killed five employees.

The fire occurred at Xcel Energy’s Cabin Creek hydroelectric plant near Georgetown, Colo., on Oct. 2 after vapors from a flammable solvent ignited inside a tunnel. The five workers, who were trapped in the tunnel, died from asphyxiation.

RPI Coating Inc. of Santa Fe Springs, Calif., was fined $845,100. OSHA cited the company for using unsafe electrical equipment, failing to install carbon monoxide alarms and other violations. Public Service Co. of Colorado, doing business as Xcel Energy, was cited for failing to employ proper safety and rescue precautions and incurred proposed fines of $189,900.

The fire began at the hydroelectric plant while employees were in a tunnel cleaning a sprayer with a flammable solvent. Vapor from the solvent ignited, causing the fire. Four workers escaped, but five employees working deeper inside the tunnel were unable to escape and were asphyxiated.