…Toxic chemicals on the very equipment meant to protect [fire fighter’s] lives could instead be making them gravely ill. This week, Captain Mitchell and other members of the International Association of Fire Fighters, the nation’s largest firefighters’ union, are demanding that union officials take action. They want independent tests of PFAS, the chemicals in their gear, and for the union to rid itself of sponsorships from equipment makers and the chemical industry. …The demands come as the safety of firefighters has become an urgent concern amid the worsening effects of climate change, which bring rising temperatures that prime the nation for increasingly devastating fires. …But over the past three decades, cancer has emerged as the leading cause of death for firefighters across the country, making up 75 percent of active-duty firefighter deaths in 2019. …The chemicals in question are called per- and polyfluoroalkyl substances, found in a range of products including fast-food containers and furniture.