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How western wildfires spread harmful particles across U.S.
6m 26s
Raging wildfires are burning across parts of the western U.S. and Canada, pushing thousands of people to flee their homes and forcing Canada to call up the military to help. In addition to the physical devastation the flames are causing, researchers are getting a clearer picture of just how dangerous all that toxic smoke is to human health. William Brangham reports.