Look at all that black smoke!

On August 7, a small, "seemingly insignificant leak" was found at one of the country’s biggest oil refineries located near San Francisco. Though required by California law to “immediately” notify the public of any gas leak, fire or oil spill, Chevron did not consider the leak to be an immediate danger to residents nearby.

“At that point in time, there really wasn’t anything we could advise the
community to do,” said Mark Ayers, the refinery’s fire chief.

Yet some two hours later, that small leak became an intense fire that sent acrid black smoke into the sky and more than 1000 people went to hospitals with health complaints of eye irritation and breathing problems. All but a handful of patients were quickly treated and released, hospital officials said.

A county wide Level 3 Hazardous Material "Immediate-Extreme-Health-Hazard" alert was issued advising local residents to,

"shelter in place, go inside, close all windows and doors, turn off all
heaters, air conditioners and fans. If not using the fireplace, close fireplace dampers and vents, and cover cracks around doors and windows with tape or damped towels." [fireplaces? in California summer?]

That's a pretty rare alert. Consider this,

While Bay Area air quality officials excluded potentially toxic pollutants, their analysis did not say exactly what was in the smoke that boiled out of the refinery's No. 4 Crude Unit, only that the air around the refinery was unlikely to cause any long-term health effects.

Chevron admitted that the fire caused the refinery to emit large clouds of sulfuric acid, nitrogen dioxide, sulfur dioxide, nitrogen oxide and hydrogen oxide. "We apologize for the fire and smoke caused by yesterday's incident," the company said in a statement.