Russia’s record-breaking heat and massive fires are stoking a new fear—that radioactive smoke could be coming from areas coated by fallout from the Chernobyl disaster. Three heavily radiated sites, and four other areas, have seen several fires, and only the wind will determine how far radioactive traces will spread. What health risks such smoke would cause are unclear. Trees and grass were contaminated in Russia, Belarus, and Ukraine after the 1986 disaster, and when those plants burn they can send the contaminants into the air and people’s lungs. Russia’s chief sanitary doctor warned against panic, though officials have admitted radioactive smoke could be released.