The "Deep Mystery" of Melted Steel

The "Deep Mystery" of Melted Steel
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There is no indication that any of the fires in the World Trade Center buildings were hot enough to melt the steel framework. Jonathan Barnett, professor of fire protection engineering, has repeatedly reminded the public that steel--which has a melting point of 2,800 degrees Fahrenheit--may weaken and bend, but does not melt during an ordinary office fire. Yet metallurgical studies on WTC steel brought back to WPI reveal that a novel phenomenon--called a eutectic reaction--occurred at the surface, causing intergranular melting capable of turning a solid steel girder into Swiss cheese.

Materials science professors Ronald R. Biederman and Richard D. Sisson Jr. confirmed the presence of eutectic formations by examining steel samples under optical and scanning electron microscopes. A preliminary report was published in JOM, the journal of the Minerals, Metals & Materials Society. A more detailed analysis comprises Appendix C of the FEMA report. The New York Times called these findings "perhaps the deepest mystery uncovered in the investigation." The significance of the work on a sample from Building 7 and a structural column from one of the twin towers becomes apparent only when one sees these heavy chunks of damaged metal.

A one-inch column has been reduced to half-inch thickness. Its edges--which are curled like a paper scroll--have been thinned to almost razor sharpness. Gaping holes--some larger than a silver dollar--let light shine through a formerly solid steel flange. This Swiss cheese appearance shocked all of the fire-wise professors, who expected to see distortion and bending--but not holes.

A eutectic compound is a mixture of two or more substances that melts at the lowest temperature of any mixture of its components. Blacksmiths took advantage of this property by welding over fires of sulfur-rich charcoal, which lowers the melting point of iron. In the World Trade Center fire, the presence of oxygen, sulfur and heat caused iron oxide and iron sulfide to form at the surface of structural steel members. This liquid slag corroded through intergranular channels into the body of the metal, causing severe erosion and a loss of structural integrity.

"The important questions," says Biederman, "are how much sulfur do you need, and where did it come from? The answer could be as simple--and this is scary- as acid rain."

Have environmental pollutants increased the potential for eutectic reactions? "We may have just the inherent conditions in the atmosphere so that a lot of water on a burning building will form sulfuric acid, hydrogen sulfide or hydroxides, and start the eutectic process as the steel heats up," Biederman says. He notes that the sulfur could also have come from contents of the burning buildings, such as rubber or plastics. Another possible culprit is ocean salts, such as sodium sulfate, which is known to catalyze sulfidation reactions on turbine blades of jet engines. "All of these things have to be explored," he says.

From a building-safety point of view, the critical question is: Did the eutectic mixture form before the buildings collapsed, or later, as the remains smoldered on the ground. "We have no idea," admits Sisson. "To answer that, we would need to recreate those fires in the FPE labs, and burn fresh steel of known composition for the right time period, with the right environment." He hopes to have the opportunity to collaborate on thermodynamically controlled studies, and to observe the effects of adding sulfur, copper and other elements. The most important lesson, Sisson and Biederman stress, is that fail-safe sprinkler systems are essential to prevent steel from reaching even 1,000 degrees Fahrenheit, because phase changes at the 1,300-degree mark compromise a structure's load-bearing capacity.

The FEMA report calls for further metallurgic investigations, and Barnett, Biederman and Sisson hope that WPI will obtain NIST funding and access to more samples. They are continuing their microscopic studies on the samples prepared by graduate student Jeremy Bernier and Marco Fontecchio, the 2001–02 Helen E. Stoddard Materials Science and Engineering Fellow. (Next year's Stoddard Fellow, Erin Sullivan, will take up this work as part of her graduate studies.) Publication of their results may clear up some mysteries that have confounded the scientific community.

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[NOTE in this eyewitness account, how the ENTIRE BUILDING of WTC tower 2
experienced an internal EXPLOSION when the second aircraft hit the
second WTC tower. Notice the PHYSICAL DAMAGE to the building, quite
apart from the fires. From the lobby level, damage to the ENTIRE
building included all the way down in the LOBBY on the GROUND FLOOR :
"the marble veneer was cracking and falling off the walls; the
chandeliers shattered on the floors along with the plaster ceiling, and
the force imploded in at about 50 mph, pulling metal, balled safety
glass, and other material with it. The pipes were bursting over my head
and dense materials were flying around me as if they were being pureed
in a blender. In the next instant came a horrible noise and a flash of
extreme heat and light blown directly over my head.]

[ALSO NOTE the major debris flying off of the building, causing damage]

http://www.rightnation.us/inhouse/tilly.htm

I exited the emergency stairwell into the 1st floor lobby center
elevator vestibule servicing floors 3 thought 43 about eight seconds
before the second hijacked plane went through my Tower 2. I didn't think
of it until later, but now as I recall, at this point I lost track of Karen.

What followed was unlike anything I have ever experienced, or could
imagine experiencing; the only thing that comes close is the movie Die
Hard. When that plane blew through upstairs the repercussions only took
about 25 seconds, but it all seemed in slow motion to me, as if I was
watching myself on a movie screen. All of the oxygen was sucked out of
the building and my lungs (like being in a vacuum). I felt doomed
because the turnstile exiting the elevator bank would not unlock for me
to get out and run for the revolving doors leading out of the lobby and
into the mall under the plaza level. I could not have known at that
panic-filled moment, but that locked-up turnstile would save my life.
Instead I'm thinking, "This is where I will die," because I can hear an
explosion roaring downward inside the building. Yet somehow I looked
over to see that the end turnstile wraps around a support beam forming
about a two-square-foot space, but there is only about six inches to
squeeze through between the end of the turnstile and wall beam.
Something inside me told me to get in there. I'm about 100 pounds
soaking wet, so I pressed myself through and balled up facing the
support beam with the steel barrier wrapped around my back giving me a
little protected cubby hole.

This is when the explosion came.

It progressed down the building, breaking the windows as it went; the
entire building was groaning, an unnatural, unearthly sound, much like a
can squeezing, or cracking uncooked spaghetti. By the time it reached
the lobby, the marble veneer was cracking and falling off the walls; the
chandeliers shattered on the floors along with the plaster ceiling, and
the force imploded in at about 50 mph, pulling metal, balled safety
glass, and other material with it. The pipes were bursting over my head
and dense materials were flying around me as if they were being pureed
in a blender. In the next instant came a horrible noise and a flash of
extreme heat and light blown directly over my head. I concluded later in
the day that this was from the huge airplane fireball sent down the
78-110 elevator shaft that exploded out into the lobby, and blew around
the walls and curled into the center vestibule where I was taking cover.
The third and last explosion occurred when a huge chunk of burning
wreckage fell to Liberty Street, which runs parallel along the south
side of the South Tower, and crashed through the building into the lobby
behind me, bringing metal, glass, marble and revolving doors with it.
There had been four security men and some fleeing WTC workers behind me
near those revolving doors; I realized that they were all taken out by
either a huge chunk of the building exploding outwards or the tail end
of the plane falling to the street. I now know that there were nine of
us in the lobby that day when the plane hit, two NYPD officers on the
44-77 elevator side, and two others coming out of emergency stairwells
on the 78-110 elevator side. The two officers and I were the only ones
who made it out alive.

[snip]

I started for the Borders at top speed, while hearing secondary
explosions going off above my head, almost like an .08 gage gun or
larger. All this made me want to hit the floor and all I could think
was, "What in God's name is happening up there?"

[snip. Notice CONTINUING explosions]

The explosions above our heads on the plaza were scaring them and they
kept stopping. I grabbed one of their hands and told them to hold on and
keep up.

[snip. Notice STRUCTURAL DAMAGE quite apart from the fires

There was a massive, black gaping hole in the north side of the WTC 1
around the 94th floor to 104th floor, and a massive section missing,
wrapping around the east and north sides of WTC 2 at about the 80th to
90th floors. We were just 20 floors below where that fire was burning,
and I thank God we moved when we did. We still heard the secondary
explosions consistently so I continued to look back at the WTC and
noticed that people were jumping out of both towers from above the fire
lines!