From a testimony by a firefighter at WTC
Report from Ground Zero: The World Trade Center Collapse
Account of FDNY Lieutenant Brenda Berkman by Linda Willing, Associate Editor, WFS Publications (Women in the Fire Service, Inc.)
[…] Even as the search continued at the site, the funerals had begun. "There’s eight a day," Brenda said grimly. But hopes of finding even identifiable body parts are fading. "There’s no concrete there," Brenda said. "You’d expect that there would be enormous pieces of concrete. There are just tiny chunks. The rebar has been stripped clean. It’s just pieces of twisted metal, packed down dust and paper, and rubbish, and that’s it. There is no glass — not a piece of glass, and the World Trade Center Towers were 20% glass. Everything was just pulverized."