Updated -- Officials with the Grant County Public Utility District say an electrical equipment failure is to blame for an explosion at Priest Rapids Dam Thursday that injured six workers, two critically.
The PUD said the injured employees are power plant electricians and operators. Their names have not been released.
Five of the injured workers are being treated for burns at Harborview Medical Center in Seattle. Besides the two in critical condition, three are satisfactory, according to a hospital spokeswoman. A sixth worker has been released from a local hospital, the PUD said.
"This is a difficult day for everyone here at Grant PUD," said acting general manager Kevin Nordt in a statement Friday morning. "Our primary focus will continue to be taking care of our people."
The explosion happened around 4:15 p.m. in P-8, one of the dam's 10 generating units which officials said had recently been under repair.
"This is a nightmare to us," Grant PUD hydro manager Kevin Marshall said at the scene Thursday night. "This is the last thing we want to happen with our people. It's the one thing we talk about a lot and we want everybody to go home safely and we weren't able to do that today."
On Friday, inspectors from Washington's Department of Labor and Industries arrived at the dam to begin an investigation. An L&I spokeswoman said it appeared that her agency had not inspected the Priest Rapids Dam in the past six years.
The dam is located about 20 miles south of Interstate 90 on the Columbia River in Grant County near the town of Mattawa.
Priest Rapids Dam has been generating hydroelectric power on the Columbia River since 1959.
Olympia Correspondent Austin Jenkins contributed to this report.