Kerosene Won't Melt Steel

Normally I don't spend a lot of time refuting conspiracy theories, mainly because most conspiracy theories have no impact on public policy or debate. What difference does it make to me if you believe that UFOs are abducting people, or if you think there is something in the Bermuda Triangle that eats ships and airplanes, or if you think the spirit of Lucille Ball is occupying your toaster? These theories simply don't matter. They don't impact me or my government, and thus are entirely harmless and frankly irrelevant.

But there's a new conspiracy theory going around that argues that the World Trade Center towers were brought down by "controlled demolition"and not by the airplane impacts. This theory does impact me, because it has the possibility of radically altering the nature of the national security debate going on in the United States. The real debate should be how we deal with the attack, and trying to turn it into a general-purpose anti-government conspiracy theory is a waste of time and effort.

Don't get me wrong - I'm not here to argue that we should implicitly trust the government, or any government. I've always believed that the press's role should be that of professional doubter, and the new habit of certain news networks to shill for certain political points of view strikes me as a pretty fundamental dereliction of duty.

But let's be honest with ourselves and admit that the airplane crashes were what brought down the Twin Towers. Let's just settle that factual matter up front and move on with the rest of the security debate. My personal belief is that Osama bin Laden carried out the attack to goad the United States into an asymmetrical and reflexive military reaction. I could be wrong, but we can't even have that debate until we finally accept that it was the airplane crashes that did the damage, not government agents in the employ of some shadowy Neocon elite.

The main argument of the conspiracy theorists seems to be that burning kerosene can't melt steel. Let's look at some numbers.

Jet-B, the kerosene-based fuel in airliners, burns at a temperature of 260 to 315 C in open air, and up to 980 C under ideal conditions. Generic steel melts at about 1370 C, and I imagine that the ASTM-36 structural steel used in the Twin Towers melts at about the same temperature.

So they're right in this respect: a kerosene-fueled fire can't melt steel. But they're massively wrong in this respect: you don't have to melt steel to bring down a steel building. All you have to do is soften the steel, and it turns out that steel softens at a much, much lower temperature - some engineering handbooks cite 350 C at the magic temperature at which steel becomes incompetent as a structural element.

When I was a kid, my dad took my brother and I on a camping trip to Lake Meade. The adults (read "men") had a big campfire where they could drink, talk about adult stuff, and tell extravagant fishing lies. My brother and I had a smaller campfire of our own, and we made an interesting discovery. If we left large nails in the coals for a while and then took them out with a pair of pliers, we could twist them into wild pretzel shapes with no difficulty whatsoever.

Not that this a new discovery. Blacksmiths have known since the dawn of the Iron Age that iron and steel, when heated, become soft and workable. Get a piece of steel red hot and you can bend it quite readily. But how hot is red hot? A campfire burns between about 400 C and 600 C, and will bring steel to a red heat where it has the structural strength of butter. (All objects that are red hot are at about the same temperature. A coal in a campfire that is red hot is at about the same temperature as a piece of red-hot steel.)

This is why farriers heat up horseshoes before bending them to shape. This is why the X-15 was built out of an exotic high-temperature alloy called Inconel-X - normal steel wasn't strong enough at the temperatures the X-15 was likely to encounter.

Now let's look at the Twin Towers for a moment. To increase available floor space, most of the steel columns in the Twin Towers were either in the central elevator shaft core, or on the outside walls. The floors were supported on long steel trusses that were attached to the outer walls and the central core. The trusses supported the floors and also kept the outer walls from buckling either inward or outward.

Now let's imagine a fire in the building, originally ignited by Jet-B from the airplanes and then going on to consume paper, furniture, carpet and other items. I don't know how hot the fire was, but it's reasonable to assume it was at least as hot as a campfire, and that in time the steel in the vicinity of the fire began to approach a red heat. The first damage would be where the trusses are bolted to the outer walls and the central core. The trusses there are mostly under tension, and under a lot of tension. They heat up and sag, increasing the tension on the upper sets of bolts. Soon the bolts on one or two trusses pull through the soft steel and that truss collapses, transferring its load to other trusses. A cacase failure of trusses ensues, leaving a section of the building without trusses and thus with nothing to keep the heat-softened outer wall from buckling outward.

Soon the outer wall buckles, and once that happens, impact loading of the upper part of the building falling onto the lower part dooms the whole thing to come down.

You don't have to melt the steel. All you have to do is heat up the trusses enough for the bolts to pull through the softened steel. And a campfire will do that, if it's big enough and is allowed to burn long enough. So can we please stop wasting time and energy on this silly argument?

I don't know why the conspiracy theorists like this particular theory so much, but I suspect the motivation is largely political. The Bush Administration has done some pretty high-handed things with complete ideological aplomb, and it perhaps suits the conspiracy theorists to imagine that the Bush Administration is sufficiently evil it would destroy the Twin Towers on purpose.

But this theory is clearly based on politics, not science, and at some point we have to let science, engineering and common sense override politically motivated conspiracy theories.