VANCOUVER, BC – Emergency physician Courtney Howard vividly remembers the summer of 2014. Communities like Yellowknife, in the Northwest Territories. …That year, nearly 400 fires burned 3 million hectares. Smoke came at Yellowknife from all directions. …The 2017 fire season was even more extreme. …One community, Prince George, recorded levels of PM2.5 at 1000 parts per million. …Canada is leading our understanding of smoke’s impact on human health. That effort has been led by Sarah Henderson, a researcher at the British Columbia Centre for Disease Control. Her findings help illuminate who is most affected, and how that information can be used by local officials to determine what to do in a forest fire, such as requiring evacuations and opening “smoke shelters,” buildings with special air filters. …They found a 40% increase in asthma inhaler demand over the combined wildfire seasons, with about 43,000 extra inhalers given. Doctor visits for asthma surged nearly 20%.