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Old 29th July 2011, 10:22 AM   #1270
alienentity
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Hi Chris,

Sound Pressure Levels for hypothetical explosives are detailed in NCSTAR 1-9, p 693 under
'Appendix D
HYPOTHETICAL BLAST SCENARIOS '

I can't quote the whole document here, it's too long. But relevant to questions regarding the accuracy of the estimate, I venture that there is simply no comparison between the NIST study and typical truther arguments from incredulity. It's not even a fair contest in terms of reliability - not that this will have an effect on truthers...

'D.3.1 SHAMRC Blast Modeling Code
SHAMRC (Crepeau 1998, Crepeau 2001) is a U.S. government-owned hydrocode solver that is used for analysis of explosive detonations, shock propagation, and structure loads due to blast and fragments. SHAMRC has a proven record of accurate calculations of airblast structural loading for explosive weights of less than one pound to more than 4,000 tons. SHAMRC has also been used to calculate the formation
and propagation of shaped charge jets and their interaction with structures. The code was well suited for the blast propagation analysis performed on WTC 7.
For the blast modeling effort, detailed two-dimensional SHAMRC hydrodynamic calculations were performed. The interior building layout was modeled to determine the transient pressure load inside the building after detonation. A two-dimensional analysis was sufficient to estimate pressures at window
locations for a small charge constrained between floors. The pressure histories were then used to determine whether windows would have broken, which would have provided visible evidence of a small charge detonation outside of the building. The window fragility analysis was conducted with a separate computational tool, SFOM, using window geometry, material properties, and construction information as
inputs to the model. The output from SFOM was Pressure-Impulse (P-I) failure curve predictions for WTC 7 windows. The SHAMRC-generated pressure histories were compared to the failure curves to predict window failure for each scenario considered. '

Effects on glass windows:

'D.3.3 Estimation of WTC 7 Perimeter Window Fragility
A Shard Fly-out Model (SFOM) (Meyer 2002∗) was used to predict window breakage, based on the pressure profiles from the SHAMRC analysis. The SFOM was originally developed for the Defense Threat Reduction Agency (DTRA) to predict window breakage as well as size and shape of shards created by blast loading'


'D.4 PHASE III: 1-D ACOUSTIC ANALYSIS
Based on the results from Phase II, representative overpressure waveforms from the predicted broken windows on the north and east faces, as well as from open areas at the southwest corner from WTC 1 debris damage, were used to make sound-distance propagation predictions. '

SUMMARY

...'In Phase III, an acoustic analysis was performed to assess the distance from the building that the blast would have been audible. Analyses were performed for both layout scenarios, using the pressure history and window failure location predictions generated during Phase II. For all scenarios and charge sizes, significant audible sound was predicted from all building faces. For locations where sound propagation
was unobstructed, the sound level from all building perimeter openings at 1 km would have been approximately 130 dB to140 dB. '

In the case of the Ashley Banfield video, there is a direct line of sight to WTC 7 which is just a few blocks away. This would indicate a real explosive demolition as hypothesized by 9/11 Truthers would have easily reached 110db to 120db at the location of Ms Banfield and her microphone.
There is simply no plausible explanation as to how this could have happened without being clearly recorded by her microphone.

Similarly for the second clip I provided, there is a direct line-of-sight to WTC 7, but not for its entire length. Again, at a distance of less than 1/2 mile (approx. 2000 ft) a conservative SPL level would be in the 110db to 130db range.

To put this in perspective for the microphone, this is louder than a jackhammer at 1 metre, and roughly equivalent to a jet engine at 100m or a vuvuzela horn at 1m.

Again, an explosive controlled demolition is not a realistic scenario from this data alone, and truthers have not even attempted to validate their claims in a scientific manner. Instead they continue to make what are essentially bare assertions with no data in support.
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