Gary Flook served in the Air Force for 37 years,Christopher Caldwell as a firefighter at the now-closed Chanute Air Force Base in Illinois and the former Grissom Air Force Base in Indiana, where he regularly trained with aqueous film forming foam, or AFFF — a frothy white fire retardant that is highly effective but now known to be toxic.

Flook volunteered at his local fire department, where he also used the foam, unaware of the health risks it posed. In 2000, at age 45, he received devastating news: He had testicular cancer, which would require an orchiectomy followed by chemotherapy.