Creative Speculation

... but it's totally irrelevant, anyway: It's a simple, well-known fact that structural steel loses about half its strength at only 600°C, and a fire that size would certainly get at least that hot. Under load, it's also subject to "creep" deformation at only 300°C. With the plane damage and subsequent load redistribution, that's enough to explain the collapses -- no need for magical silent explosives or imaginary thermite devices, much less imaginary bullshit physics.