SPOKANE, Wash. (AP) - One of the employees who was burned in an accident at Spokane's Waste-to-Energy Plant has been upgraded to serious condition and is breathing on his own.

The other worker remains in critical condition.

Craig Law and Larry Pratt were performing routine maintenance inside one of the facility's boilers on Tuesday when something went wrong and they were burned by steam.

They were first taken to Providence Sacred Heart Medical Center and then transferred to Seattle's Harborview Medical Center, the region's specialty trauma center.

The state Department of Labor and Industries has opened an investigation into the accident.

The city took over operation of the plant in 2014 from the former operator, Wheelabrator, a subsidiary of Waste Management.