Six utility workers were injured in an electrical explosion at the Priest Rapids Dam in Washington state on Thursday.

All six were admitted to a Seattle medical center. One worker was kept overnight and then was released the next morning. The other five workers remain in the medical center with burn injuries. Two are in critical condition and are expected to be placed in intensive care.

A spokesperson for Grant County Public Utility District said that the explosion was due to a malfunction of electrical equipment. The incident was isolated to only one of ten generating units at the dam. He also said the structure of the dam was stable and no residents are at risk. Some residents reported power outage Thursday evening and also cell phone service outage in relation to the incident.

The generator voltage is between 13.2 kV and 13.8 kV.

The Grant County PUD states that there are no public safety issues or downstream flooding impacts. 

This Columbia River dam was built in 1961 and has a total powerhouse capacity of 955.6 MW. It is located near Mattawa, WA, about 150 miles southeast of Seattle. It is owned by the Grant County Public Utility District.

The cause of the explosion is under investigation and will probably take weeks to complete.

Update 10/13/15: The main circuit breaker, acting as the on/off switch for the generator, malfunctioned. The generating unit will not go back in operation until after the investigation is completed. One of the critically injured workers is now in serious condition; the other remains in critical condition. Only three remain in the hospital at this time.

For updates, visit the GCPUD website on their News Releases page.