In the early evening of August 6, a series of explosions at the Richmond Chevron oil refinery in the San Francisco Bay Area sparked a huge fire that burned for hours.
The fire sent a huge black cloud that went for miles over densely populated areas. Tens of thousands of residents were ordered to stay in their homes, with windows and doors closed.
Local authorities issued a level three warning, meaning the cloud would cause eye, skin, nose and respiratory sickness.