A 9/11 documentary showed up in my YouTube recommendations so I decided to watch it. As I was doing so, I realized that there were no shock waves when the planes hit the towers. You can hear the sound of the explosion travelling, but no massive window smashing/shattering like in the Oklahoma bombing or the Beirut explosion or even the [Black Tom explosion](https://en.wikipedia.org/wiki/Black_Tom_explosion#Explosion).
Why weren’t windows in New York blown out en masse that day? Was it due to the nature of the explosion? Thank you in advance!
In: Physics
The planes hitting the towers didn’t cause an explosion in the strictest sense. Instead, the impact of the planes hitting the towers caused a lot of fuel to be vaporized and spread away from the plane, which *then* ignited and created a fireball. However, because the fuel was already dispersed, the fireball didn’t produce a rapid change in air pressure, and without such a pressure difference you won’t get a shockwave.
The breakup of the Space Shuttle Challenger is a similar situation; despite people typically referring to it as an “explosion,” it wasn’t actually an explosion in the strictest sense. The shuttle broke apart first, which produced a cloud of fuel, which in turn ignited and burned without resulting in a significant pressure change.
In both cases, the use of the word “explosion” is a bit of a misnomer; the average person thinks of an explosion as any big ball of fire that suddenly comes into existence, but from an engineering perspective we see a difference between a true explosion/detonation (which has a shockwave) vs. a rapid deflagration/really rapid combustion (which does *not* necessarily have a shockwave).
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