Flaring at the Chevron Refinery in Richmond, California this week caused employees to be evacuated and disruptions in operations, according to news sources. Flaring is a refinery safety mechanism that burns gases that would otherwise be released into the atmosphere.

No injuries were reported.

The flaring occurred two days in a row. A spokeswoman for Chevron said the flaring happened during the startup of a process unit and was quickly addressed and stopped by refinery employees.

Local authorities issued a low level warning to area residents. Black smoke was visible in the air surrounding the refinery.

During Monday’s flaring incident, fewer than one hundred employees were evacuated from the refinery.

Unknown quantities of sulfur dioxide and hydrogen sulfide may have been released into the atmosphere during the incidents. Health officials said there were no reports of health problems stemming from the flaring.