The incident all began with a power outage that started at a PG&E substation, but there is no word on what caused that power outage. Tesoro doesn't know what happened, but the power outage caused a lot of problems.
It was alarming to see huge plume of black smoke billowing out of the Tesoro refinery in the late afternoon.
"We were kind of worried that something really bad was going on, but we don't know. So when we got home there was no power so we were asking all the neighbors if they knew why there was no power," said Concord resident Adrianna Ramirez.
The Tesero power plant would also like to know why there wasn't any power.
"We were affected by the power loss," said Tesoro refinery spokesman Ken Dami.
PG&E officials say the power went out at a substation and they're trying to figure out why. When the refinery lost power, workers had to shut down the plant and start burning the product they were in the process of making.
"The flares did what they were supposed to do, they released pressure from our system due to the sudden power outage which we're trying to understand where and how that occurred," said Dami.
They issued a shelter in place while the flares burned, but some people without power in their homes didn't receive the word.
"We didn't get a call or any notice of what was going on," said Ramirez.
Air quality experts are still trying to establish the impact of the smoke.
"It's going to descend gradually and as it peters out the risk will diminish, but right now best to shelter in place not take any chances," says Mark Ross from the Bay Area Air Quality District.
The Dreher Family actually headed out to the grocery store, where it smelled a little better than it did at home.
"At our house, in the backyard, it's really bad and I have to wear a mask out there," said Concord resident Debbie Dreher. When asked what it smelled like she said, "Wood smoke, only a little more toxic than that."
The shelter in place order has been lifted.
Tesoro says it doesn't have a backup power system, but that is something that it will look into as it tries to make sure this never makes sure this happens again.