What are the dangers of living near an oil refinery (that seems to have annual flares and explosions)?

I live in the SF Bay Area somewhat near a corridor of oil refineries. One in particular, the Shell refinery in Martinez, CA keeps on having accidents that send toxic fumes into the air. They had a fire a couple days ago which caused the county to put out a “shelter in place” order for the immediate area. They told people to turn off their HVAC and seal up their doors and windows. Last year the same thing happened and they told everyone not to eat the produce grown in this yards. But they only extended to warning to within the city limits basically.

What is the actual reach? What are the concerns? What about the produce grown within that reach? (There are many farms within the area.) How much air gets into our house with the windows and doors closed?