Questions, but No Answers

"27. Why didn't the investigators look at actual steel samples from WTC 7?

Steel samples were removed from the site before the NIST investigation began. In the immediate aftermath of Sept. 11, 2001, debris was removed rapidly from the site to aid in recovery efforts and to facilitate emergency responders' efforts to work around the site. Once it was removed from the scene, the steel from WTC 7 could not be clearly identified. Unlike the pieces of steel from WTC 1 and WTC 2, which were painted red and contained distinguishing markings, WTC 7 steel did not contain such identifying characteristics."

'''We built in enough redundancy to allow entire portions of floors to be removed without affecting the building's structural integrity, on the assumption that someone might need double-height floors,' said Larry Silverstein, president of the company...MORE than 375 tons of steel - requiring 12 miles of welding - will be installed to reinforce floors for Salomon's extra equipment."

"Dr. Astaneh-Asl's project is one of eight financed by the National Science Foundation to study the World Trade Center disaster. He is also a member of a team assembled by the American Society of Civil Engineers to investigate the trade center site, and the society is dispatching a team to examine damage to the Pentagon.

One piece Dr. Astaneh-Asl saw was a charred horizontal I-beam from 7 World Trade Center, a 47-story skyscraper that collapsed from fire eight hours after the attacks. The beam, so named because its cross-section looks like a capital I, had clearly endured searing temperatures. Parts of the flat top of the I, once five-eighths of an inch thick, had vaporized.

Less clear was whether the beam had been charred after the collapse, as it lay in the pile of burning rubble, or whether it had been engulfed in the fire that led to the building's collapse, which would provide a more telling clue.

The answer lay in the beam's twisted shape. As weight pushed down, the center portion had buckled outward.

''This tells me it buckled while it was attached to the column,' not as it fell, Dr. Astaneh-Asl said, adding, 'It had burned first, then buckled.'

Engineers believe they have a general understanding of why the World Trade Center towers fell. Fires stoked by the jetliners' fuel weakened the structural columns. When one floor collapsed, its weight collapsed the floor beneath it, starting a catastrophic series of failures.

But they do not know the details. How many of the interior steel columns were severed by the crashes of the jets? How hot did the fires burn? Did the jet fuel play a central role or would an ordinary fire have also led to collapse? Was the steel as strong as it was supposed to be?

By comparing the beam's specifications with architectural drawings, Dr. Astaneh-Asl said he would be able to tell roughly where the beam came from.

'I want to know which ones buckled and which ones did not,' he said. ''That will lead you to the sequence of events. I can tell you exactly what happened there.''

For now, however, his impromptu inspections have ended. The trucks now take a different route, and there has been some concern whether there would be another chance before the steel is destroyed.

The wreckage of the World Trade Center could also provide unique insight to what happens to building materials like concrete, steel and fireproofing insulation under extreme conditions that are not tested in the laboratory. Dr. Astaneh-Asl said that in some places, the fireproofing melted into a glassy residue.

Dr. Astaneh-Asl also hopes to send samples of steel to Dr. Claudia P. Ostertag, a professor of civil engineering at Berkeley, for metallurgical testing. Above about 1,600 degrees Fahrenheit, the crystal structure of steel shifts to a softer, weaker form.

It is not possible to see this change of crystal structure directly, but with an electron microscope it is possible to deduce how much a piece of steel has been heated for how long.

Molten steel does not solidify all at once, but as many little specks, or grains, that grow until they mesh together, each less than a hundredth of an inch wide. When the steel is heated again, the tiny grain structures merge. Thus, comparing the grain sizes in the charred steel beams with pristine samples, Dr. Ostertag believes she will be able to tell how much the fires heated the steel.

Both Dr. Corley and Dr. Astaneh-Asl said their data gathering efforts would not delay the recycling efforts by much, although they would like to set aside pieces that were near the impacts and fires.

The steel scrap is worth only a few million dollars, a tiny fraction of the billions of dollars the cleanup will cost, Dr. Astaneh-Asl said. The knowledge that can be gained from it could save lives in a future disaster." - NY Times

"13. Did investigators consider the possibility that an explosion caused or contributed to the collapse of WTC 7?

Yes, this possibility was investigated carefully. NIST concluded that blast events inside the building did not occur and found no evidence supporting the existence of a blast event.

In addition, no blast sounds were heard on the audio tracks of video recordings during the collapse of WTC 7 or reported by witnesses. According to calculations by the investigation team, the smallest blast capable of failing the building's critical column would have resulted in a sound level of 130 decibels (dB) to 140 dB at a distance of at least half a mile, if unobstructed by surrounding buildings. This sound level is consistent with a gunshot blast, standing next to a jet plane engine, and more than 10 times louder than being in front of the speakers at a rock concert.

For the building to have been prepared for intentional demolition, walls and/or column enclosures and fireproofing would have to be removed and replaced without being detected. Preparing a column includes steps such as cutting sections with torches, which produces noxious and odorous fumes. Intentional demolition usually requires applying explosive charges to most, if not all, interior columns, not just one or a limited set of columns in a building.

14. Is it possible that thermite or thermate contributed to the collapse of WTC 7?

NIST has looked at the application and use of thermite and has determined that it was highly unlikely that it could have been used to sever columns in WTC 7 on Sept. 11, 2001.

Thermite is a combination of aluminum powder and a metal oxide that releases a tremendous amount of heat when ignited. It is typically used to weld railroad rails together by melting a small quantity of steel and pouring the melted steel into a form between the two rails. Thermate also contains sulfur and sometimes barium nitrate, both of which increase the compound's thermal effect, create flame in burning, and significantly reduce the ignition temperature.

To apply thermite to a large steel column, approximately 0.13 lb. of thermite would be needed to heat and melt each pound of steel. For a steel column that weighs approximately 1,000 lbs. per foot, at least 100 lbs. of thermite would need to be placed around the column, ignited, and remain in contact with the vertical steel surface as the thermite reaction took place. This is for one column; presumably, more than one column would have been prepared with thermite, if this approach were to be used.

It is unlikely that 100 lbs. of thermite, or more, could have been carried into WTC 7 and placed around columns without being detected, either prior to Sept. 11, 2001, or during that day.

Given the fires that were observed that day, and the demonstrated structural response to the fires, NIST does not believe that thermite or thermate was used to fail any columns in WTC 7.

Analysis of the WTC steel for the elements in thermite/thermate would not necessarily have been conclusive. The metal compounds also would have been present in the construction materials making up the WTC buildings, and sulfur is present in the gypsum wallboard used for interior partitions."