On the morning of Sept. 11, 2001, I was working as a paramedic in Lower Manhattan. I responded to the attacks on the World Trade Center. In dust so thick it shrouded the sun, my fellow rescue workers and I picked our way through the rubble, looking for survivors. Very few of us had masks. When I got home and took a shower, the runoff clogged the drain and collected around my ankles like reconstituted cement. More.