“The collapse of the Twin Towers created massive dust clouds that filled the air and left hundreds of highly populated city blocks covered with ash, debris, and harmful particles.  In Lower Manhattan, the plane crashes—which resulted in the collapse of the Twin Towers—created massive dust clouds that filled the air and left hundreds of highly populated city blocks covered with ash, debris, and harmful particles, including asbestos, silica, metals, concrete, and glass. Fires within the debris pile and the collapse of 7 WTC burned through the end of December 2001 with continued flare-ups in 2002, releasing carcinogenic combustion by-products. These contaminants remained in Lower Manhattan and parts of Brooklyn for an undetermined amount of time after 9/11. Responders, local workers, residents, students, and others had potential for acute exposures in the early days and continuing exposure from residual materials—indoors and outside—as well as exposure to toxic gases, smoke, vapors, and combustion by-products from continuing fires. ”

Centers for Disease Control & Prevention (https://www.cdc.gov/wtc/exhibition/toxins-and-health-impacts.html)