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Duke Energy blames steam sensor malfunction during start-up process for noise

SALISBURY — While Duke Energy said last week that loud noises emitted by its Buck Combined Cycle Station were part of the start-up process, it clarified that remark Thursday, saying the “explosion” was the result of a steam flow sensor malfunction. 

After the thunderous noises rang out from the plant on Thursday last week, reports that an explosion happened at the plant circulated on social media. Duke Energy Communications Manager Heather Danenhower said that those reporters were not true and that the sounds were merely the plant’s safety systems functioning correctly.

The plant, which was under a maintenance and inspection outage from Sept. 4 through Nov. 6, had recently been brought back online when a steam flow system sensor glitched.

“About 12 hours after restarting the station, there was a steam flow sensor malfunction and the control system is a massive computer that automates tens of thousands inputs and outputs,” Danenhower said. “That master computer closed a valve in response to that sensor malfunction. When that happened, steam built up in pipes because the plant continued to run and steam continued to build up. So the safety valves activated, venting excess steam from three vent lines.”

When the excess steam burst from the three vent lines, it created a noise that sounded like “bombs going off,” local resident Jack Nozell said. Danenhower said that steam was emitted for three or four minutes and that the vents were opening and closing during that time, which could have also contributed to the noise.

Nozell, who has lived near the plant for several years, said that local residents expressed their confusion about the noise on the Nextdoor neighborhood social network. He said that he hasn’t received any communication from Duke Energy about the event.

Danenhower said that Duke Energy did respond to several inquiries on social media about what caused the noise and that the company is apologetic that the noise disturbed neighbors.

Duke Energy is still investigating why the sensor malfunctioned, but Danenhower said that the malfunction did not lead to any physical harm to the plant’s employees. Duke Energy didn’t alert neighbors of the noise beforehand, Danenhower said, because the plant didn’t expect the noise itself.

“Though the outage was planned in a normal process, the noise that plant neighbors heard was not anticipated,” Danenhower said.

The noise made by the steam safety valve may have been jarring to nearby neighbors, but Danenhower said that they should take comfort knowing the system worked.

“Even though it was an inconvenience to plant neighbors and it was alarming to plant neighbors, we hope that they take comfort in knowing that the noise that they heard was the result of a carefully engineered safety system doing its job,” Danenhower said.

Neighbors may also take some solace in the fact that the loud noises are a rare occurrence.

“It is an infrequent event,” Danenhower said. “We’ve had smaller scale ones, but because it is so infrequent, that’s likely why it was startling to plant neighbors.”

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