Scientists who have analysed the aftermath of the 11 September 2001 attacks on the World Trade Center say that workers at Ground Zero suffered "brutal" effects from the fumes coming out of the wreckage.
"The debris pile acted like a chemical factory," said Professor Thomas Cahill of the University of California at Davis.
Work at Ground Zero went on for months
"It cooked together the components of the buildings and their contents, including enormous numbers of computers, and gave off gases of toxic metals, acids and organics for at least six weeks," he said.
Professor Cahill heads a research group which collected over 8,000 air samples between 2 and 30 October 2001 a mile away from the collapsed Trade Center towers.
The group produced a report on those samples in 2002 but has now come up with a much more detailed explanation of what went on after the catastrophe.
Three months of fires
"When the towers burned and collapsed, tons of concrete, glass, furniture, carpets, insulation, computers and paper were reduced to enormous oxygen-poor debris piles that slowly burned until 19 December.
"In that hot pile, some of the constituent elements combined with organic matter and abundant chlorine from papers and plastics and then escaped to the surface as metal-rich gases.
"These then either burned or chemically decomposed into very fine particles capable of penetrating deeply into human lungs," the university explains.
Professor Cahill and his colleagues identified four classes of particles likely to damage human health.
- Fine and very fine transition metals, which interfere with lung chemistry
Sulphuric acid, which attacks cilia and lung cells directly
Very fine, insoluble glass particles which travel through the lungs to the bloodstream and heart
High-temperature organic matter, many components of which are known to be carcinogens
Conditions would have been "brutal" for people working at Ground Zero without respirators and slightly less so for those working or living in immediately adjacent buildings, Professor Cahill said.
The new data is being presented at the national meeting of the American Chemical Society in New York.