No excuse for not testing for explosives

[aggle-rithm]

Perhaps he has seen the error of his ways.

Ha! No.

 

[ElMondoHummus]

I don't mean to beat a dead horse, but I just can't let this go by:

People like me would speculate less if the investigators had simply followed national fire standards and tested for and ruled out the possibility of explosives or incendiary devices.

The possibility of explosives or incendiary devices is ruled out. By NIST. Read NCSTAR 1-3C and tell me which of those components were affected by either blast or incendiaries.

"But it's not all the steel pieces!", so the truther reply will go. Yes, of course not. But most of them are pieces from the collapse initiation zone. It's proven that the collapse wasn't initiated by explosives or incendiaries because the state of the steel recovered from there disproves any such use.

"But it's still not all the steel pieces!", so the utterly predictable truther refrain will go. Doesn't matter. Bazant showed that the collapse would go to completion once it started, meaning that the only steel components necessary to show that the Twin Tower collapses were not intentionally blown or melted were the ones in the collapse initiation zone. That's all that needed to be investigated. So if a truther disagrees with this and believes that explosives were needed in zones beyond the collapse initiation floors, then they need to disprove Bazant's work before moving on. And no, Gordon Ross's miscalculation doesn't cut it. And his was the only quantitative attempt; not other conspiracy peddlers' attempt even come close to his. So yes, explosives in the main towers were already ruled out. And the road to refuting that goes through Bazant before it can reasonably address NCSTAR 1-3C.

So enough with the claim that explosives or incendiaries were not ruled out. They were. That's why speculation about such is useless and inane.

 

[ElMondoHummus]

Somehow double posted. This is aggravating...

 

[triforcharity]

DavidJames,

"Claim is supported by evidence from NIST, 9/11 report etc. The NIST report has not been challenged with analysis and supporting evidence using any professionally recognized mechinism."

So? It is still just an unsubstantiated claim hence a conspiracy theory. The spokesperson for the FBI and Mueller both admitted that they did not have a prosecutable case against UBL in regard to 9/11 so it is a conspiracy theory.

NIST is not a detective agency. The 9/11 commission was not even an investigation according to Ben Veniste who told Robert McIlvaine to remember 'this is not an investigation it is an eposition.' Besides the 9/11 Commission was wrought with lies. Even the chairman and co chairman of the commission have admitted to having been lied to so much that they often considered legal action.

Yes, they did. People lied to them to cover their asses. This is common with people in high places. But, you will also note, that those on the 9/11 Comission also go on to state that they finally got the truth.

PS, I now you are new, but if you press the quote button on someone's post, it makes you life easier.

 

[CurtC]

Decibels are so called because 10 of them make one "Bel," or an order of magnitude difference in amplitude. Therefore, a 3 dB increase means a doubling of pressure amplitude. 10^3/10 = 2.0.

Where it gets confusing, however, is 6 dB is a doubling of RMS amplitude or of power. This is because power scales as the amplitude squared, and when you square inside a logarithm it's the same as multiplying by 2 outside the logarithm.

You got it backwards - the "amplitude" is what we use to refer to RMS pressure, or RMS voltage, or similar. The power of any of these is proportional to the square of the amplitude.

Increasing the amplitude by a factor of two will quadruple the power.

With a signal expressed in dB, doubling the amplitude is a 6 dB increase, while doubling the power is a 3 dB increase. I believe this is the reverse of what you were saying.

Hey, I don't often get the chance to correct Ryan on a point! But I work with dB's several times a day every day and have for 25 years.

 

[kookbreaker]

Yes, they did. People lied to them to cover their asses. This is common with people in high places. But, you will also note, that those on the 9/11 Comission also go on to state that they finally got the truth.

Indeed. One of the reasons we have such commissions is because people will lie about their role in the story. The purpose of a commission is to get to the bottom of the matter in spite of such lies by checking evidence, looking at other testimony, and so on. You know, a real investigation, unlike trootherhunts.

I don't know why truthers think we should be shocked that commissions don't change human nature.

 

[triforcharity]

Skeptic Guy,

"If 9/11 was truly a crime perpetrated by the US government (Israeli government, NWO, whatever) to justify a war in Iraq/Afghanistan, why did they go beyond flying planes into the buildings? Why did they need the explosives? I would think that the singular act of flying a plane into the WTC could be used to justify the same thing. It seems a lot of added risk to plant explosives on top of it."

Simple. No steel framed high rise building had ever collapsed due to fire and airplane damage in history so there was simply no guarantee that the towers would completely fail. The image of airplanes hitting the towers itself may not have incited enough outrage and international support to go to war. The reality is that people would have seen it on the news channels and said "my, how awful" and forgotten about it the next day. The image of those two towers cascading down was played over and over again by the media. This image was adequate to incite enough hatred to motivate congress, and some international support to launch wars of agression against two sovereign nations that had not attacked any other country or threatened to do so.

1-No airplane had ever been parked in the side of a building at ~500 MPH before.
2-Fire has however collapsed many steel framed structures.
http://www.fpemag.com/archives/article.asp?issue_id=27&i=153
http://forthardknox.com/2008/01/25/steel-buildings-that-collapsed-due-to-fire-before-9-11/
3-the death of hundreds that was caused by the plane impacts would not have been forgotten the next day. Do you remember the Pan Am plane crash? How about ValuJet? Oh, right. We all remember those.
How about OKC? Yepo, remember that too. Still talked about 15 years later.

Now, what were you saying?

 

[triforcharity]

It's funny how you conveniently leave out the other two, particularly Flight 93 which reportedly landed in such soft land that the majority of the 95% of the aircraft that was reportedly recovered was said to have been found underground. Guess those titanium and reinforced steel data recorders were much more delicate than the dna that was reportedly recovered.
(cue the eye rolls)

Those were found.

 

[Alferd_Packer]

So, was dommy boy another hit and run truther?

 

[R.Mackey]

You got it backwards - the "amplitude" is what we use to refer to RMS pressure, or RMS voltage, or similar. The power of any of these is proportional to the square of the amplitude.

Increasing the amplitude by a factor of two will quadruple the power.

With a signal expressed in dB, doubling the amplitude is a 6 dB increase, while doubling the power is a 3 dB increase. I believe this is the reverse of what you were saying.

Hey, I don't often get the chance to correct Ryan on a point! But I work with dB's several times a day every day and have for 25 years.

Yeah, I guess I didn't explain myself properly. Let me try again. Tell me if this works for you.

deciBels is a unitless measurement. It has to be because you cannot take the logarithm of a quantity with units. Think about it -- if you changed from meters to feet, it would change your answer.

Because deciBels is unitless, what it represents is not a physical quantity. We often refer to a reading in deciBels as "intensity," and this could refer to various things.

If by intensity we mean the relative amplitude of a wave, as I said before, you use the following definition -- borrowing the conventions from Wikipedia:

L_dB = 10 log₁₀ A₁ / A₀​

where A₁ is your measured signal, and A₀ is an established reference signal, typically a sine wave of specified amplitude. This formula technically works for any quantity, whether A is power, pressure amplitude, water wave height, information content -- anything.

Where it gets confusing is if what we measure is not the same thing as we calculate. Power, for instance, is difficult to sense. When we're interested in power we instead measure the amplitude, and derive power from it, which again scales as the amplitude squared. In this case, one uses a slightly different formula, as I noted before:

G_dB = 10 log₁₀ (A₁ / A₀)²
or

G_dB = 20 log₁₀ A₁ / A₀​

The square term appears inside the logarithm, which we then bring outside the logarithm as a multiple of 2, hence the leading 10 becomes 20. But here we've cheated a little. This is because it is more convenient for us to specify a reference amplitude than a reference power. Thus, we convert to power and take the logarithm all on one step. If it was easy to specify and measure a reference power, we would use the previous formula, and there would be no confusion at all.

In this latter case, a doubling in power is still an increase of 3 dB. This is because 2x the power means a factor of 2^1/2 increase in amplitude. So by this little trick, the power behaves more or less the same as the first equation.

So to be perfectly, 100% clear, whether or not you use the first equation or the second -- whether a doubling in intensity is 3 dB or 6 dB -- depends on whether you are directly sensing power, or whether you are deriving it from amplitude. This is where the confusion comes from.

Again, in the case of normal sound, one measures the actual wave amplitude -- easy, because it's a wave -- and one computes power indirectly from this amplitude, because power is easier to relate to. So in this case, the second equation is appropriate, and doubling in amplitude means it increases by 6 dB. This does not mean 6 dB is a larger scale, far from it. Indeed, 1 dB difference is a SMALLER change in power than it would be if we used the other scale. Doubling in power does still correspond to a 3 dB increase.

Again, for explosives, we are dealing with an overpressure wave, measured in Pa or PSI, and we compare that to a reference amplitude typically from a reference explosive. The aperiodic nature of the blast wave makes it very difficult to specify a reference amplitude. Also, here we are not deriving power at all -- we don't care about power, we're not using amplifiers and loudspeakers, so power is irrelevant to this discussion. The units we measure are the same units we're interested in. So the first equation is the correct one -- and 3 dB is the correct doubling of intensity.

This example is particularly confusing because we hear both sounds and the explosive shock. You and I use the same measurement device (our ear) to hear both, so it seems odd that we'd use different conventions. But the two really aren't the same. If it helps to clear up the confusion, think of the explosive sound as a shock wave, which really is a different animal than a sound wave. Loud sounds will make our ears hurt, while a reasonably strong explosive shock will just bust our eardrums entirely.

Cliff's Notes: Doubling in amplitude means either 3 dB or 6 dB increase. Which deciBel equation you use depends on what you mean by intensity. If you're interested in power, doubling in amplitude means 6 dB.

 

[Seymour Butz]

Some cool stuff here.

http://www.makeitlouder.com/Decibel Level Chart.txt

310 (N)KRAKATOA VOLCANO ERUPTION-1883 A.D., CRACKED ONE FOOT THICK CONCRETE
AT 300 MILES, CREATED A 3000 FOOT TIDAL WAVE, HEARD 3100 MILES AWAY,
SOUND PRESSURE CAUSED BAROMETERS TO FLUCTUATE WILDLY AT 100 MILES
INDICATING LEVELS OF AT LEAST 170-190 DB (P) AT THIS DISTANCE OF 100 MILES
EVEN WHEN SHOUTING IN SOMEONES EAR, COULD NOT BE HEARD AT 100 MILES
CAUSED FOG TO APPEAR AND DISAPPEAR INSTANTLY AT HUNDREDS OF MILES

 

[applecorped]

Oystein,



There is nothing childish about listening to the view of one of the firefighters who was there saving lives on that day. This man's opinion means a lot more than mine.

Just click the link in your last post. (The link works fine. I just tried it.) No need to run away from the testimony of this firefighter.

Nice avatar.....as to your opinion on this subject....no comment.

 

[CurtC]

Yeah, I guess I didn't explain myself properly. Let me try again. Tell me if this works for you.

[...]

If by intensity we mean the relative amplitude of a wave, as I said before, you use the following definition -- borrowing the conventions from Wikipedia:

L_dB = 10 log₁₀ A₁ / A₀​

No, I don't agree with that. Let me start off by saying that we can talk about a signal's amplitude or its power. The amplitude is a measure of voltage, sound pressure, or similar. The power of a signal, whether a radio wave or sound pressure, is always proportional to the square of the amplitude.

Human perception of lots of phenomena, such as sound and light, is approximately on a log scale, plus a log scale makes it easier to compare very large and very small quantities, plus it makes calculations of amplitude and attenuation change from multiplication and division, to simply adding or subtracting. For these reasons, dB's are the preferred method of stating levels in radio and sound.

I think we both agree on all of that. Where we diverge is in that equation that I just quoted from you. A dB is defined as 10 times the log of a power ratio. It's this formula:

L_dB = 10 log₁₀ P₁ / P₀

But as you say, what we directly measure is usually the amplitude. Therefore the dB scale is 10 times the log of the square of the ratio of the amplitudes, or 20 times the log of the ratio of the amplitudes:

L_dB = 20 log₁₀ A₁ / A₀

Cliff's Notes: Doubling in amplitude means either 3 dB or 6 dB increase. Which deciBel equation you use depends on what you mean by intensity. If you're interested in power, doubling in amplitude means 6 dB.

You lost me here. Doubling a signal's amplitude always is a change of 6 dB. Doubling the amplitude is four times the power, so a 6 dB difference is a quadrupling of power, therefore doubling the power corresponds to a 3 dB difference. Always.

I'm not sure what you mean with the word "intensity" - I never use that in a technical situation.

The only thing that gets confusing is when switching to or from dB's and linear units, because you have to remember to multiply the log of the ratio by either 10 or 20 depending on whether you were starting off with amplitude or power. But once you get to dB's and stay there, it's pretty easy. Level ratios in dB's don't depend on which you started off with.

 

[sheeplesnshills]

My name is Dom Shenher and I am very proud to belong to the group Scholars for 9/11 Truth and Justice.

Proud? Any fool can join that so why would pride be involved? What have you or that organization done to be proud off?

 

[ktesibios]

I'm not sure what you mean with the word "intensity" - I never use that in a technical situation.

Basically, intensity is a measure of the power that would be transferred to a perfectly absorptive intercepting surface oriented perpendicular to the direction of wave propagation. It's denominated in power per unit area.

For example, the 0 dB SPL reference pressure of 20 μPa RMS corresponds, for sound propagating in air at STP, to 10^-12 W/m².

 

[Sledge]

Proud? Any fool can join that so why would pride be involved? What have you or that organization done to be proud off?

Because he knows something that most people don't. That it's batsqueak insane is irrelevant, he feels very smug and superior because we're all so dumb.

 

[R.Mackey]

No, I don't agree with that. Let me start off by saying that we can talk about a signal's amplitude or its power. The amplitude is a measure of voltage, sound pressure, or similar. The power of a signal, whether a radio wave or sound pressure, is always proportional to the square of the amplitude.

All right, here's the thing: You can't talk about the explosive's shockwave in terms of power. That analysis only works for quasiperiodic signals.

The shockwave has an amplitude, yes, but it has no duration. It's a discontinuity, and it's nondispersive. It delivers its impulse in, effectively, an infinitessimal length of time. This would translate into an infinite power. And in this case, the total impulse -- the closest thing we have to power -- does not scale as the amplitude squared, but instead is linear in amplitude.

This is why I still think using the other expression is more accurate. We can measure its amplitude, and if we like we can compare this to the typical 0 dB SPL amplitude.

The alternative is to pretend the shock is an ordinary sound after all. If all we're discussing is human perception this might work out -- we will overestimate its effective impulse, but then again being a sharp sound it would be quite distinctive to the human ear, so an artificially high estimate of dB might be appropriate.

I've seen dB used in contexts that have nothing to do with power, but now that I talk it through in public, it feels more confusing than it's worth...

 

[I Ratant]

...
The shockwave has an amplitude, yes, but it has no duration. It's a discontinuity, and it's nondispersive. It delivers its impulse in, effectively, an infinitessimal length of time. This would translate into an infinite power. And in this case, the total impulse -- the closest thing we have to power -- does not scale as the amplitude squared, but instead is linear in amplitude.

...

.
The shock wave has a physical effect..
Blue Angel solo flight over San Francisco Bay... the plane drags the shock wave with it, disturbing the surface of the water.
http://www.youtube.com/watch?v=K7rAUu8djZ4
.
And the muzzle blast from the 16 inch rifles on a battleship definitely disturb the surface of the water.
.
But in the Blue Angels instance, there's no compressive/percussive effect like the explosion of the gunpowder in the battleship guns.

 

[R.Mackey]

Planes don't drag shock waves, per se. An oblique shock will disturb a liquid surface, but there is also a large contribution from the aircraft wake -- a different effect.

Likewise, the smoke plumes that USS Wisconsin, above, is throwing out there represent gas jets, totally apart from the concussion exiting its main battery, and that roils the water much more than the shock leading it.

ETA: Incidentally, I'm not convinced that F/A-18 is going supersonic. I don't see it in afterburner, it's awfully close to fragile objects, and if it was shedding a shock off its nose, that shock should be coming down at an apparent angle of ~ 45 degrees. It doesn't look like it. Do you have more information?

 

[Army of One]

Cool and approachable info for know-nothings like me

Just to clarify: The cross section area would apply to the net steel surface, right? So if we have a box-shaped column 10"x10", steel plates 1" across, that would be 36 square-inches (4 sides times 1x9), and not 100 (10x10)?

Yes, that's correct. You just need to multiply the thickness of the steel by the length of the planned cut.

How sensitive is that formula to the shape of the beam? Would 36 square inches box column need the same amount as 36 square inches T-bar?

As far as I can tell, the shape shouldn't matter in determining the required amount of explosives (though it could affect the placement of the explosives). The formula is designed to be a catch-all, applicable to just about all steel cutting scenarios. It can be used for beams, columns, girders, steel plates, bars, etc.

Anyway, I wonder if we are ever going to get an explanation from dommyboysinjapan on how thermite can be mixed with explosives to make them quieter?