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Jet fuel doesn’t melt steel, but it does dramatically weaken it December 17, 2015

Posted by Tantumblogo in Admin, Basics, catachesis, foolishness, fun, huh?, non squitur, scandals, sickness, silliness, Society, technology.

A corollary to the below.  Aircraft aluminum melts at about 1150-1200 Fahrenheit.  But aluminum structure in aircraft is limited to speeds below Mach 2.3 continuous, or 2.5-6 for short bursts of time.  At those speeds, aircraft skin reaches temperatures around 350-400 F.  That is the maximum temperature that aluminum can be used without significant weakening.  All metals weaken greatly at temps well below their melting point.  That is why the SR-71, to travel at Mach 3.5 or so, had to be made almost entirely of titanium and exotic steels, to handle the 500-800 degree temps experienced.  Likewise, the X-15 rocket plane, to travel at Mach 6 and endure temps up to about 12oo F (or about 650 C) had to be constructed from exotic steels like Inconel X.  Regular steel would have softened too much even at those low temps to be used effectively in aircraft design.

Now, a building is not an aircraft, but the same basic principles do apply.  Aircraft, to save weight, are typically designed with safety factors of about 1.5 (that is for commercial aircraft, military aircraft, to obtain more performance, generally have lower safety factors).  This means the structural design is set to withstand 50% more load than the aircraft is ever expected to experience in even the most severe service.  Buildings generally have safety factors of more like 2.  This means there is more redundant structural strength, so that more structure can be lost, fail, or severely damaged before the overall design is compromised.

It is estimated that the jet fuel conflagration in the Twin Towers burnt at about 1500 F.  While it is true that steel does not melt until much higher – 2500~2800 F – at 1500 F low carbon steel of the type used in building construction will be structurally useless.  That’s the point of the video below. I, too, don’t want to get into the endless back and forth over 911 truthferism – I exhaust myself arguing one set of religious beliefs already, thank you –  but it’s a quite valuable demonstration all the same.

Another factor not mentioned is creep.  Creep is the (relatively) slow stretching out of a substance – typically member of some kind under load.  Creep is directly related to operating temperature.  The higher the temp, the larger the creep. A steel beam that doesn’t creep a micron at 200 F creeps like crazy at 1200 F.  That can also cause structural collapse, as members creep in a fashion that causes things like rivets to pop as holes no longer align, or welded joints to give way.  That can also precipitate structural collapse.

Creep also occurs when structural loading suddenly increases.  A beam that normally operates at 50% design stress that suddenly goes to 110% – say, because other members were caused to fail by impact – will start to elongate.  Over time, say, 12 hours or so, that could cause a structure to collapse even without the impact of heat.

I designed some plastic parts that worked like champs up to about 155 F.  But go to 160, and over 24 hours they would creep into frankenstein shapes.  And that was under no other load but gravity.  I know plastic is not steel, but the same principle definitely applies.




1. JorgeElCurioso - December 17, 2015

Not wishing to argue either, but assuming this might account for Buildings I and II, what might we say about Building VII?

Tantumblogo - December 17, 2015

My understanding is that WTC7 experienced severe structural damage, and some ancillary fires, due to the collapse of WTC1 and 2. That’s actually why I mentioned creep as specifically as I did. Structural damage could, over time and without repair, lead to structural collapse.

2. c matt - December 17, 2015

Do not attribute to malice what can be explained by incompetence. At the same time, I don’t see some elaborate scheme needed to be planned – 9/11 strikes me at most as the government taking advantage of a situation. The tried and true don’t let a crisis go to waste.

Is it possible that the gov’t was behind it all? Possible, but also not very likely.

3. c matt - December 17, 2015

The only thing that seems odd, and I am in no way knowledgeable on the matter, is that the buildings fell flat rather then toppling over. You would think the impact from the side would have made it keel over, or at least unbalanced enough that it would fall unevenly. But then, there could be some perfectly good explanation (building designed to absorb the impact like a car bumper crumple zone, impact force not really enough given the relative masses of the building vs plane?).

4. JorgeElCurioso - December 17, 2015

My view is that it is all far more complicated than “was or was not the government involved.” And the fact that I may be of the opinion that something is or is not likely means very little. My greatest doubts revolve around Building VII, for which the “structural damage” argument cannot be applied. Failure to adequately explain the collapse of Building VII provides some justification for people’s doubts regarding the other two buildings. I’m trying to figure out how incompetence explains the fall of Building VII.

5. JorgeElCurioso - December 17, 2015

Well, I actually watched the video. Not very helpful. To reduce the arguments to the one issue of the melting point of steel is to vastly oversimplify the objections to the argument that those buildings collapsed simply as a result of the damage they suffered as a result of impact from jetliners. Not much more to say. Hope that guy does not quit his day-job as a metalworker. And the question regarding Building VII remains.

c matt - December 18, 2015

Well, if the steel loses its structural integrity well within the jet fuel temperature range, and given the amount of forces involved with the mass of the building above the point of impact, it certainly puts a big dent in the conspiracy argument. I don’t know what other support systems were involved (concrete columns as well?) and if that could have supported the weight without the steel. Regardless, the gov’t reaction to the aftermath is the same and just as unsettling.

6. Indiana Bob - December 17, 2015

Does that temperature also pulverize the entire structure and turn it to dust? How did those buildings collapse in their own imprint? By this guy’s theory, the metal would have bent and the area above the impact would have tipped over and fell. Also, name one other steel structure building that has ever collapsed due to fire.

7. Peterk - December 18, 2015

if you don’t think steel will become misshapened at lower temperatures than you’ve never seen what happens to steel railroad tracks on a hot summer day

8. dymphna - December 18, 2015

I remember hearing Rosie O’Donnell asking how fire could just melt the steel in buildings and I laughed. Half my family lives in Pittsburgh. The ones who weren’t in the coal mine melted steel for a living.

9. JorgeElCurioso - December 19, 2015

Any comments on Building VII?

10. JorgeElCurioso - December 20, 2015

Didn’t think so.

11. Candace - December 21, 2015
JorgeElCurioso - December 21, 2015

I plan to read that. At quick glance I notice the author does not mention Building VII. Very important.

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