Battery storage is considered crucial for feeding clean electricity onto the grid when the sun is not shining or the wind is not blowing, and it has been used in significant amounts only in the last couple of years. But the batteries are nearly all lithium, which has a tendency toward "thermal runaway," meaning it can catch fire and burn very hot, releasing toxic gases. Vistra sells energy to Pacific Gas & Electric, one of the nation's largest utilities. The blaze did not spread beyond the facility, according to Monterey County spokesperson Nicholas Pasculli. Evacuation orders for from 1,200 to 1,500 people were lifted Friday evening after officials confirmed there was "no threat to human health," the Monterey County Sheriff's Office said in a statement. But residents were advised to close their windows and turn off their air conditioning.