San Francisco-area residents were allowed to leave their homes late Monday night after a fire at a nearby refinery was contained, but not before it led to a scare in local emergency rooms.

According to KRON-TV, officials at Chevron say a diesel seal broke at the company’s refinery in Richmond, in the East Bay, causing a fuel spill, which may have sparked with heated metal, leading to the fire erupting around 6:30 p.m. Monday night.

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As black smoke escaped the facility, residents in Contra Costa County were ordered to confine themselves and their pets indoors. The Contra Costa Times reported that about three dozen people were treated at a local hospital for respiratory problems. The smoke could reportedly be seen from as far as Oakland.

“We heard the sirens go off and I said, ‘Thunderdome blew,'” Richmond resident Emmett Zediker said Monday night. “We call Chevron ‘Thunderdome’ because when it blows, it blows. So we cracked open a bottle of vintage wine and we are having an apocalypse party.”

This was the first explosion and fire at the refinery in five years. The San Francisco Chronicle reported that residents and environmental activists have long opposed Chevron’s attempts to upgrade the facility, saying it would only make pollution in the area worse. A renovation project approved by the local city council four years ago was curtailed after it was determined the company had left some key questions unanswered.

Watch KRON’s Tuesday morning update on the fire’s containment below:

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[h/t NPR]