RODEO -- A hydrogen plant unit's startup led to a burst of noise that was audible in some West County homes Tuesday evening, officials said.

Just after 7 p.m., Air Liquide staff started up a unit that provides the company's Rodeo refinery with hydrogen, spokesman Paul Adler said.

"There was overpressuring, and the start-up created a boom sound, and flaring did occur," Adler said.

The unit, which was being started up for the first time, was immediately shut down so workers could investigate.

On social media, residents in Rodeo and Hercules took note of the loud burst.

"We believe that there is no more noise occurring, but it probably was loud," Adler said. "We've got superintendents monitoring, and I can understand why the community is wondering what is going on."

There were no injuries related to the incident.

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