The best compositional match for the majority (>85%) of WTC glass fibers is slag wool, a by-product of pig iron production (TIMA, 1991). Pieces of yellow thermal insulation found in bulk samples are composed of soda-lime glass fibers (Meeker and others, 2005b). Very few fibers of this composition exist in the fine (<150 m) microscopic portion of the dust. Rock wool is also present as a trace constituent of the fine dust portion.
Rock wool and slag wool can have similar EDS spectra. The two can be distinguished based on the presence of iron. Slag wool will generally have less than 2 weight percent FeO whereas rock wool contains from 3 to 12 weight percent FeO (TIMA, 1991). Soda-lime glass has a distinct EDS spectrum from both slag wool and rock wool. The Na peak is higher and Ca, Mg, and Al peaks are smaller in the soda-lime glass spectrum than the slag wool and rock wool spectra.
Glass shards, fragments, and spheres are also present in the dust samples. The microscopic glass shards and fragments are less abundant than the ubiquitous slag wool fibers in the fine dust (<150 m). Most of the glass fragments fall within the compositional range for soda lime glass, a common type used as window glass (TIMA, 1991). Other glass fragments are present which contain mostly Si with trace amounts of Na, K, and/or Al. The majority (> 90%) of glass spheres, generally less than 500 m in diameter, are of slag wool composition.
Where does all the slag wool (not rock wool) come from? Insulation? Fire-proofing? It does stand out in the USGS Report: http://pubs.usgs.gov/of/2005/1165/508OF05-1165.html
According to NAIMA, the North American trade association for manufactures of fiber glass, slag & rock wool are used for building insulation or other industrial uses:
o they are a primary constituent of ceiling tile and sprayed fire proofing for commericial buildings.
o they are non-combustible with melting temp close to 2000 deg F and have excellent thermal resisitance
See www.naima.org and the links and resources they have.
One other comment: Fires were definitely retarded when this dust with a high concentration of slag wool was spread over the place. This answers the mystery Judy Wood raises in her web page such as in Figure 66g in which she notes "the fire seems to be very selective" and Figure 66o asks "Why doesn't the paper burn". The reason is in both figures everything is covered with this highly non-combustible dust. Fires are confined very locally to highly flammable sources and cannot easily spread.
