Microscopic analysis of WTC dust by Nicholas Petraco, BS, MS, DABC, FAAFS, FNYMS at The New York Microscopic Society lecture held at AMNH 28 May 2003

45.1% Fiberglass, rock wool (insulation, fireproofing)
31.8% Plaster (gypsum), concrete products (calcium sulfate, selenite, muscodite)
7.1% Charred wood and debris
2.1% Paper fibers
2.1% Mica flakes
2.0% Ceiling tiles (fiberglass component)
2.0% Synthetic fibers
1.4% Glass fragments
1.3% Human remains
1.4% Natural fibers
trace asbestos (it became illegal to use during the construction of the WTC)
Other trace elements: aluminum, paint pigments, blood, hair, glass wool with resin, and prescription drugs were found.

NOTES:
Particles found were 1-4 micrometers in size. (In general, particles that are 5-8 microns are irritants, and those that are 104 microns are small enough to be airborne and ingested into the lungs.)

Fiberglass particles are smaller than asbestos and lodge deeper into lungs creating more serious long-term health hazards than asbestos like white lung disease which will become more evident 5, 10, 20 years from 11 Sep 2001.

Why do we still use so much fiberglass if it's bad for you?