“In Lower Manhattan on 9/11/01 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.

Officials declared the plane crash in Somerset County near Shanksville, Pennsylvania a crime scene; the crash created hazardous conditions—including fiery hot spots and smoke—for workers and volunteers. At the Pentagon in Arlington, Virginia, responders, cleanup crews, and construction workers were potentially exposed to smoke, jet fuel, heat from the fire, hazardous chemicals, and harmful debris.”

Center for Disease Control and Prevention-CDC / World Trade Health Center (Toxins and Health Impacts: Health Effects of 9/11 – WTC Health Program)