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Posted on Feb 4, 2016

Human error caused explosion at Priest Rapids Dam

MATTAWA — A lack of communication and failure to follow safety procedures caused the electrical explosion at Priest Rapids Dam in October that sent six Grant PUD employees to hospitals with burns, according to a report released this week by Grant PUD.
All injured employees, some of them who were seriously injured, have been released from hospitals. Two have returned to work. It is unknown when or if the other four will be able to return, PUD spokesman Chuck Allen said Monday.
The “arc flash” explosion happened the afternoon of Oct. 8 after crews had finished performing maintenance on the dam’s C-8 generating unit and were preparing to get it back on line.
The unit had been off line for several weeks. Under those circumstances it’s not unusual for the unit’s spring-loaded “breaker,” or on-off switch to become less responsive than usual, Allen said.
Through a breakdown in communication, a crew was dispatched to examine the breaker but didn’t know that the breaker still had power coming into it, Allen said.
“It wasn’t a single employee who did something wrong, it was a whole process,” he said.
The explosion occurred when the crew attempted to reset the breaker manually. This caused arcing within the breaker and damage to the breaker. To perform a manual reset of the breaker, power has to be completely shut off to it, Allen said.
Allen likened it to a homeowner doing work to a circuit breaker without first shutting off the power to the entire breaker panel.
An analysis by an independent lab concluded that the breaker functioned as designed. The cause of the explosion was a series of human and process errors, which included:
–Leadership not adequately setting and enforcing safety expectations.
–On-site leaders not controlling work activities or ensuring that energy sources were isolated before allowing the crew to work on the breaker.
–No pre-job brief was performed to outline known safety hazards.
–Employees lacked knowledge about how the breaker would operate under those conditions.
–The crew working on the breaker didn’t first verify that it was safe to work on before they began.
PUD officials said in an incident summary report that corrective measures include:
–Review and improve safety plans.
–Ensure a job brief happens in all hazardous situations.
–Improve crew training.
–Conduct more testing and safety audits.
Priest Rapids Dam is on the Columbia River near the community of Mattawa, 24 miles south of Vantage. It was built between 1956 and 1959. Along with Wanapum Dam, it is one of the PUD’s two Columbia River power plants that provide most of its generation.

 

— By Christine Pratt, Wenatchee World

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