Appendix B

Steel and high speed impact

Could the falling block of 12 floors have shocked the structure to such a degree that the shock frees up the entire core of the building below the 98th floor and dropped it in front of the falling block? I don’t think so. We have to back up a bit to get a better handle on it. First there is the “highly unusual,” I’d say all but impossible, premise that the top block of 12 floors could have fallen due to uncontrolled kerosene (jet fuel) fires, straight down as if all the supporting columns remaining after the asymmetrical aircraft impact severed some columns and damaged some others in one off-center area suddenly collapsed simultaneously.

As can be seen in the strength vs temperature graph for steel (Appendix F) steel loses strength gradually, not suddenly, as it heats. In such a case, it’s highly unlikely that the heating is uniform, something that is hard to control at our scale and is usually only enabled in, for example, jet engines and carefully designed and built burners made specifically for kerosene, but never, in my experience, in open air on a surface like an open concrete floor that may or may not actually allow the fuel to spread across the floor to cover it evenly. And even if that could happen, that wouldn’t produce a uniform fire at these scales. We’ll also note that there were no fires outside the building, so the outer sides of the columns were unheated, all the fire there was inside the building.

To ask the initial question assumes that the upper block of 12 floors could be suddenly released from 12 feet above the lower structure. This seems astronomically unlikely to me. This should be fairly obvious to most people and certainly to anyone who has any experience with uncontrolled liquid-fuel, open-air fires.

I’d also point out that NIST’s premise is an unusual one and that the assertion must be defended or proved by the one making the assertion, showing that it is true, and not proven false by the one that person is trying to convince.

But let’s keep playing this game to see where it goes next. Assuming that the top block of 12 floors could have suddenly been released to fall absolutely straight down the 12 feet of the floor height onto the rest of the structure, the question is, could that action have hit the inner part (missing the outer part) of the lower structure have caused it to shatter or disassemble and fall ahead of the upper block? Already we are in a fairyland—another unusual premise the party making the assertion would be responsible for proving and not the responsibility of the questioner to disprove—but let’s take a look. The floor, if it fell the 12 feet absolutely freely, would have hit the structure below it at about 28 ft./sec. or 19 mph. Consider the path of inquiry into this just below:

How fast can someone swing a hammer? 10 m/s is rather fast – the speed of a sprinter or of a hammer dropped from 5 metres. It's hard to move your hand much faster than that without practice. To accelerate a 2 kg hammer to that speed over half a metre requires a force of 200 N. So I used 10 m/s. See: Smashing Bricks and the Ballistic Pendulum - Physclips

That’s about 33 f/sec. let’s say, then, that the block fell upon the lower one hitting it at about the speed of a hammer hitting a nail head. If such low speeds shattered steel, we couldn’t hammer nails into wood or concrete without them shattering. Also, consider the following:

Pneumatic Nail Guns | HowStuffWorks
Some nail guns can launch nails at 1,400 feet per second [427 m/s]. The most popular sort of nail gun is the pneumatic nailer.

1400 feet per second is over 70 times the speed of a hammer hitting a nail, and the nails still hold up. I had originally felt (guessed…but it’s a somewhat educated guess since I’ve worked with steel) that we wouldn’t run into problems with steel, any steel used in building construction, until we get to velocities somewhere around the speed of sound in steel where the steel can’t get out of the way easily at a molecular level. These speeds are around 6000 ft./sec. or 4100 mph. At speeds like that one might expect steel to exhibit different behavior provided we’re always at about room temperature as was the steel in the buildings of the structure and floors beneath the fire during the collapses.

If steel hitting steel caused steel to shatter (at normal temperatures such as they were on September 11 in a controlled environment…~72F) then automobile accidents, some with closing speeds in excess of 200 mph, would result not in bent fenders and automobile frames but shattered fragments of steel all over the place. This doesn’t happen.