9/11 WTC Dust & Environment Studies - Timeline

Mick West

Staff member
The purpose of this post is to provide a reference for the various studies of the WTC dust, with specific attention to anything relevant to supposed evidence of thermite or explosives (like iron microspheres, and flakes of red paint).

It's not light reading. I might summarize at some point.

2001 Oct 12 - Chatfield, E. J. and Kominsky, J. R., 2001 Characterization of Particulate Found in Apartments after Destruction of the World Trade Center
No discussion of iron or spheres. Lists iron elemental level at 0.86%, 0.41% and 1.2%. Samples taken 18 Dec 2001.
Metabunk 2018-10-15 23-33-41.jpg

2001 Nov 27 - Roger N. Clark, Robert O. Green, Gregg A. Swayze, Greg Meeker, et al (USGS)
Environmental Studies of the World Trade Center area after the September 11, 2001 attack.

Somewhat higher iron percentages. 1.41 to 4.13
Metabunk 2018-10-15 23-58-59.jpg

2002 - Paul J Lioy, Clifford Weisel, James R Millette, et al
Characterization of the Dust/Smoke Aerosol that Settled East of the World Trade Center (WTC) in Lower Manhattan after the Collapse of the WTC 11 September 2001. Environmental Health Perspectives
110(7):703-14 DOI:10.1289/ehp.02110703

Very brief mention of iron:
"In addition to the elements quantified by ICP/MS analyses, the SEM dispersive X-ray analyses showed large signals for iron and calcium, which are major components of construction materials. Similar observations were found for silicon, which is consistent with the glass fragments and fiberglass found in each sample."

2002 - Millette, J. R., Boltin, R., Few, P., & Turner, W. (2003).
Microscopical Studies of World Trade Center Disaster Dust Particles. Microscopy Today, 11(5), 32–37. doi:10.1017/s1551929500053220
(Originally published MICROSCOPE, Vol 50:1, 29-35 (2002)

Does not mention iron, but does mention "Metal Flakes" and "Paint Particles"

2003 April, EPA
World Trade Center Background Study Report

Focus on toxic substances. Does not mention iron or spheres.

2003 June, EPA
Chemical Analysis of World Trade Center Fine Particulate Matter for Use in Toxicologic Assessment


Metabunk 2018-10-15 23-47-44.jpg

Metabunk 2018-10-15 23-48-40.jpg

Values of iron are 0.36% to 1.51%. Much lower than the control samples which had 3%

2003 - R.J. Lee investigation of 130 Liberty Street (Samples after May 2002, published Dec 2003)
Various reports. Most famously for "Composition and Morphology", which has a figure of 5.87% next to "Fe Sphere" under "Mean of Composition" in a table described as "Statistical P-values for the comparison of TP-01 dust and dust in Background Buildings." (which seems wrong, as these are not p-values).
Metabunk 2018-10-16 11-29-01.jpg
The values in Lee are hard to interpret. What do they actually mean? Why is the combined Class A particle types 35.58? Other studies say mineral wool alone is over 50% of the composition.

2004-2005 - The EPA Expert technical review Panel.
Multiple meetings, with a variety of presentations and discussion on developing a signature for WTC dust. They did reference the Lee study a few times, but not in any great detail. I could find no mention of iron spheres, but I've been unable to do a comprehensive review, as there's a few hours of audio, and many pages of reports. This is from the final report, and is the only substantive mention I could find:
2005 - Heather A. Lowers and Gregory P. Meeker
Particle Atlas of World Trade Center Dust, USGS
"The primary metal and metal-oxide phases in WTC dust are Fe-rich and Zn-rich particles (Meeker and others, 2005b). "
Discusses glass spheres, but not iron spheres.
Contains four spectra of iron particles, two of which are spheres. All have lots of oxygen.

2005 - Gregory P. Meeker, Amy M. Bern*, Heather A. Lowers, and Isabelle K. Brownfield
Determination of a Diagnostic Signature for World Trade Center Dust using Scanning Electron Microscopy Point Counting Techniques

Does not mention spheres. Gives similar elemental compsition of Iron-rich to before
Metabunk 2018-10-15 23-41-03.jpg
"Data presented here suggest that the presence and relative abundance of the three MMVF components – slag wool, rock wool, and soda-lime glass – along with the presence of concrete particles and gypsum could be used as a primary diagnostic signature for WTC dust. Secondary signature components could include FeOx, ZnOx, silica, and chrysotile. "

2005 Peer Review of EPA report
Metabunk 2018-10-16 11-14-31.jpg
Which does not really seem to tally with:

2005 Nov 3, Meeker, Lioy, Lippman
Comments on WTC Signature Study and Peer Review

A very brief passing mention of "iron spheres" as a possible signature component. Probably based on the Lee report. Note it's lumped in with "trace elements", so the presence there does not indicate a lot of them.
Last edited:

Mick West

Staff member
2009 Lowers, Meeker, Lioy, Lippmann.
Summary of the development of a signature for detection of residual dust from collapse of the World Trade Center buildings

This revisits Samples from Clark 2001 and Swayze 2005, Lioy 2002, and Yiin 2004
Metabunk 2018-10-16 06-50-26.jpg
"Fe-rich = Primarily Fe metal and Fe oxide"
Iron rich "area percent coverage" is similar to numbers for other studies, 0.1 to 1.33%. Note it's "area", not mass.
No other mention of iron. No mention of spheres.
Concludes that slag wool is a good fingerprint for WTC dust.
Particles were binned (counted) by type, including morphology (shape). But no mention is made of spheres.

Mick West

Staff member
2004 - Summary Report of the World Trade Center Technical Review Panel Conference Call May 12, 2004

Note this is glass (vitreous) spheres. But it's interesting in the context of steel microspheres too. The largest component of the dust was slag wool, and "slag is simply a by-product of the steel industry", which means at some point it was in contact with iron microspheres. At the very least it will contain some iron compounds.

Verified somewhat by Meeker, 2004-05-25 Presentation

Looking at this sample, the fibers and the sphere were analyzed:

Metabunk 2018-10-16 10-11-04.jpg

And were found to be glass.
Metabunk 2018-10-16 10-16-22.jpg

The composition of the sphere matched the fibers. The FeO (Iron oxide) was <1% in everything except one fiber


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