Use some common sense. The chemicals would spread out over a massive area. A plume 150 miles away and 50 miles wide would be diluted in a huge amount of air of 7500 square miles. The number of toxic molecules is going to be on the order of one part per trillion and you are probably exposed to more toxic gases released from plastic items in your house. You should probably be more concerned about dozens of factories releasing toxic chemicals nonstop while the train burned for a couple days over a week ago.