(KRON) — Flaring at the Phillips 66 refinery Wednesday afternoon prompted health officials to monitor air quality in Rodeo.

The Crockett-Carquinez Fire Department said residents may see black smoke in the area. The Level 1 flaring incident happened around 3:30 p.m.

The Bay Area Air Quality Management District said it dispatched inspectors to investigate. “We are responding to complaints, documenting any violations of air quality regulations, and assisting first responders,” air district officials wrote.

A spokesperson for the refinery told KRON4 that the Phillips 66 refinery experienced a “steam process upset.”

“All refinery safety systems functioned as designed. Flares are important safety devices used in refineries and petrochemical facilities. They safely burn excess hydrocarbon gases which cannot be recovered or recycled. Excess hydrocarbon gases are burned in the flare systems,” the refinery’s spokesperson wrote.

Refinery workers are also investigating to pinpoint what caused Wednesday’s flaring.

“There were no injuries, and all personnel are safe,” the spokesperson wrote. “The safety of the community, the environment, and our people are of the utmost importance to our company, and these priorities will guide our efforts as we investigate the cause of the flaring.”