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Old 27th August 2007, 08:45 PM   #46
Join Date: Apr 2006
Posts: 7,854
If I might clear something up for both sides...

The "low order of probability" comment comes from the FEMA investigation of WTC 7. NIST has never said any such thing. The FEMA report was completed years ago, and is quite cursory. The NIST report, as most are aware, has been repeatedly delayed as its scope has grown, and is now anticipated towards the end of this year.

FEMA did indeed state that their proposed collapse hypothesis was of "a low probability of occurrence." However, the report needs to be read in order to understand what that statement means. FEMA's words, in context, are as follows:

Originally Posted by FEMA
[Page 5-30] A further hypothesis that would help explain the long time lapse between the collapse of WTC 1 and the collapse of WTC 7 would be that the masonry wall and door resisted the fire for a number of hours, but eventually failed. The new opening then allowed the fire (still supplied with a continuous discharge of fuel oil) to flow into the mechanical equipment room, envelope elements of the fireproofed trusses, and eventually cause a buckling collapse of one or both of them. For the fire to last long enough for this to occur, the flow rate would have to be around 30 gpm. At a rate of 30 gpm, the fuel would last for about 7 hours and would produce a fire of about 60 MW. The possibility that such a scenario could occur would be dependent on the specific construction details of the wall, the door, and the fireproofing on the truss.

Another hypothesis that has been advanced is that the pipe was penetrated by debris at a point near the southwest corner where there was more damage caused by debris from the collapse of the towers. This would have resulted in fuel oil spilling onto the 5th floor, forming a large pool. At some point, this would have ignited and produced the required fire. This hypothesis has the advantage of assuming a pipe break in the area most severely impacted by the tower debris and accounts for the long delay from the initial incident to the collapse of WTC 7. The principal challenge is that such a fire would have more severely exposed Truss 3. If Truss 3 has been the point of collapse initiation, it is not expected that the first apparent sign of collapse would be the subsidence of the east penthouse. […]

Further investigation is required to determine whether the preceding scenarios did or could have actually occurred.

[Page 5-31] The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence. Further research, investigation, and analysis are needed to resolve this issue.

These scenarios involve a large number of steps. All the steps appear plausible, but FEMA was unable to properly investigate how the fueling system worked, etc., so the scenarios above were largely hypothetical at the time FEMA wrote it. If we were to investigate those steps, and find that FEMA's speculation was in fact predicted, then the scenarios would immediately go from "a low probability of occurrence" to a "high order of probability." This is part of NIST's investigation.

Also, since the FEMA report was published, we have learned much more about WTC 7:
  • The amount of damage caused by WTC 1's collapse has been understood to be much greater than previously thought
  • We have a better understanding of the collapse initiation
  • Many more videos of both impacts and collapse have been recovered
  • NIST has done an in-depth study of the emergency fueling systems

What this all goes to show is that you have to actually read the FEMA report to know what it contains. It is a very limited report, limited by time, money, and access. FEMA admits as much. There is no reason to take their statements -- that they could only propose speculative scenarios, and that such would be considered improbable without further work -- out of context.

If one really wants to understand, I suggest one go to the source.
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