An arc flash explosion occurred at the Priest Rapids hydroelectric dam in Eastern Washington leaving six employees injured of which, two of them were critically injured.
The employees were attempting to troubleshoot the circuit breaker on P08, which was one of ten generators at the dam. The repair work to the generator was not on the regular work schedule, and as it was towards the end of the work day, certain safety precautions were bypassed. The assumption was made that the power was cut off to the circuit, but it was never verified.
The circuit breaker was manually slow closed while energized with generator unit P08 in a stopped position. This caused an arc within the breaker, resulting in an explosion.
Analysing the Root Cause:
- Circuit breaker malfunction
- Human errors in operating procedures
- Arc flash/ Explosion
- 6 employees with various levels of injury had to be taken to regional medical facilities via airlift and ground ambulance.
What could have been done to avoid this?
- Safe practices should have been enforced by themanagement.
- Managers onsite should have ensured that the power was truly disconnected before working on the breaker.
- Use of warning labels on the circuit breaker equipment.
- Employees should have been provided with protective gear (PPE)
- Employees that have in-depth knowledge about how the breaker works, or what the potential risks associated with troubleshooting the breaker should have been assigned the task.
What should be done to avoid such incidents in the future:
To ensure safety of your employees and electrical infrastructure it is advised to get the following tests done:
- Relay Co-ordination Study: To determine the characteristics, ratings, and settings of overcurrent protective devices which will ensure that minimum unfaulty load is interrupted when protective devices isolate a fault or overload anywhere in the system.
- Short Circuit Study:To verify that each device of the electrical distribution system, including service equipment, breakers, branch panel boards and connected equipment meets the minimum requirements of short circuit energy at their connection point in the electrical distribution system.
- Arc Flash Hazard Study and Analysis: To assess the risks involved with incident energy released by an arc flash, propose preventive measures to eliminate the risk of incident energy exposure and provide adequate safety equipment and clothing for those operating on electrically energized
Further, only qualified personnel with the proper training should work on electrical equipment with appropriate electrical safety garments and tools.
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