The Bag: A Breakdown

How the Esquire sample from the heart of the dust cloud compares with the air given off by the smoldering pile three weeks after the attack

Initial Dust Cloud, 9/11/01

Coarse particles (12 to 2.5 microns), 85 percent of sample

Cahill hypothesizes that the large proportion of gypsum here (and in the smaller particles below) is due to the way the towers collapsed: As the concrete floors fell, the five million square feet of gypsum drywall were pulverized and pushed outward.

65% gypsum

22% cement

12.5% aggregate (sand and gravel particles)

0.5% other

Very fine aerosols (0.26 to 0.09 microns), 0.02%

Particles this size are the most dangerous because they can get trapped deep in the lungs and enter the bloodstream. These dangerous particles made up only a tiny percentage of the total sample, reducing their health threat.

63% Gypsum Drywall is made almost entirely of gypsum, a fire retardant with no know health threats. Because it is high in calcium, it is a common food additive.

21% Cement Because of its high pH, cement causes skin and nasal irritation. But most cases of WTC cough were reportedly caused by larger particles -- 10 microns or higher.

15% Aggregate Sand and gravel that were mixed to form the World Trade Center's concrete.

2% Other Slight traces of magnesium, phosphorus, chlorine, bromine, zinc, and lead were found, but probably not enough to cause lasting health problems.

Air Around the Pile, 10/3/01


As the pile burned, Cahill took samples from atop a six-story building one mile away. The sand, gravel, sulfur, and chlorine are not in themselves dangerous, but as they burn, they break down into smaller, more toxic particles.

70.1% aggregate

5.8% gypsum

4% cement

4% chlorine

3.9% sulfur

12.2% other

Very fine aerosols (0.26 to 0.09 microns), 20%

Many of the original materials broke down into smaller and more toxic elements and chemicals. When they are inhaled, they enter into the bloodstream, where they remain.

78% Sulfuric acid Formed from combustion. When inhaled, it paralyzes and kills cilia, tiny hairs in the lungs that defend against foreign matter, leaving the lungs more susceptible to toxic particles.

14% Metals Even if they're not toxic in raw form, when lead, mercury, arsenic, nickel, and vanadium enter the bloodstream, the body often attacks them as foreign objects, which could cause long-term health problems.

7% Glass fumes When paper and plastic burn at very high temperatures, they give rise to fumes containing very fine glass particles.

0.5% Chlorine, cement, and gypsum The chlorine involved in combustion is a key factor in the creation of ultra-fine toxic metals.

Source: Thomas Cahill, the DELTA Group, University of California, Davis

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