Re: Independent study into collapse of World Trade Center Building 7
> 90% of what is below those 30 stories is air.
Yep. Highly compressed air can, and often does, behave much like a high explosive. There's a reason that pressure vessels are tested using incompressible fluids rather than air or inert gases. Even at 4 or 5 bar, containers can become fragmentation bombs. Compressed air can be fucking scary.
If we posit a large concrete slab, which to all intents and purposes can be considered airtight, being accelerated downwards at 9.81 m/s^2, and an interslab space of, let's say, 4m, there's something like 16,000 cubic metres of air that all have to go somewhere in around half a second. ure, a big chunk of that is gonna blow out the windows, but there's also a fuckload of it that is going to be massively, rapidly, compressed; that energy *will* go somewhere - lots will go outwards, more and more violently as pressures rise, and pretty much the rest of it will go to further accelerating the slab underneath it, quite possibly helping, if not directly causing, a chain reaction. The stuff that's going outside will get faster and faster until it reaches the speed of sound, at that point you have a shock wave that is effectively identical to that generated by high explosive. And you'll have air being forced down the stairwells and lift shafts, again, this will rapidly become a speed of sound shock wave running through the core of the building.