SEATTLE (AP) — Utility officials say an electrical equipment malfunction caused an explosion at a hydroelectric dam on Washington's Columbia River that injured six workers.

Grant Public Utility District spokesman Chuck Allen says the explosion happened Thursday afternoon in one of 10 generating units at the Priest Rapids Dam near the central Washington city of Mattawa.

Allen says the utility is investigating, along with state workplace regulators. He says they don't know yet what caused the equipment malfunction.

Five workers are being treated at Harborview Medical Center in Seattle. Spokeswoman Susan Gregg said Friday two men, both in their 40s, are in critical condition while three men are in satisfactory condition. All are being treated for burns.

Allen says the unit will be shut down until officials determine what happened. He says there was no structural damage to the facility and no threats to public safety.

A Grant County sheriff's spokesman says his agency won't be investigating because "there's no indication of criminal wrongdoing or terrorism."

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