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x87678r

here is an amazing view of the explosion. https://youtu.be/hp-n-ghagok

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The same photographer posted a very slow motion version of the same video: https://youtu.be/0tQ80Sj3QUs?t=122

Also note that you can hit "." on a paused video on youtube to go frame-by-frame.

Some observations:

* The camera vibrates long before the pressure wave reaches it. I assume this is due to energy traveling through the ground (i.e. an earthquake).

* On the third building from the bottom left there is some light reflected from another building's windows. Once the camera stops moving, these seem to still be moving.

* As the camera falls, two frames show a Nikon camera strap and a separate camera. It appears as if the photographer is taking stills. I haven't been able to find that these photographs were published, perhaps none were taken of the blast.

> * The camera vibrates long before the pressure wave reaches it. I assume this is due to energy traveling through the ground (i.e. an earthquake).

Had to check it out, earthquake p-waves travel really fast!

"Typical values for P-wave velocity in earthquakes are in the range 5 to 8 km/s."

https://en.m.wikipedia.org/wiki/P-wave

I live about 9km away from the site of the blast(as the crow flies). I can definitely confirm that the order of events was:

1 - Earthquake

2 - Sound (sounded like rolling thunder or a jet breaking the sound barrier)

3 - Pressure wave (felt as a sudden, short-lived, strong wind at that distance)

I am curious about 2 and 3. Since sounds is also just a pressure wave, those two should have been the same speed as well. I guess the sounds must have travelled through the ground as well.

The speed of sound in pretty much any solid (or liquid) body is much faster than in the air. That's why the earthquake came first, and it was probably the earthquake that caused the 2. noises.

This is explained in the article. It describes the pressure wave as moving slower than the speed of sound. It was not a shockwave which would be generated by high-explosives which would travel at the speed of sound and be much more deadly.

I calculated ~400m/s for the pressure wave (judging by destruction, not the white condensation wave).

I guess it makes it a proper shock wave, rather than just sound.

(Explosion at 7:30)

That's an amazing view. Terrifying. CGI people will be basing Hollywood explosions on this for years to come.

I'd imagine this is approximately what Hiroshima and Nagasaki would have looked like, but the direction of the pressure wave would be different as they were both air bursts.

You wouldn't have seen them...if you were looking in the direction you'd be blinded instantly.

But really this isn't especially similar.

There are plenty of videos of actual nuclear explosions.. e.g. https://www.youtube.com/watch?v=mP3bcPvgIG8

> You wouldn't have seen them...if you were looking in the direction you'd be blinded instantly.

Feynman disagrees: https://www.realclearscience.com/blog/2016/04/what_its_like_...

I don't think his statement "bright light can never hurt your eyes" is correct, and I think "I got behind a truck windshield, because the ultraviolet can't go through glass, so that would be safe" is pretty questionable: glass filters ultraviolet, but I don't think it blocks it completely.

But fact is: Feynman looked at an atomic explosion and he wasn't blinded.

This is absolutely nothing like a nuclear detonation. The energy released was less than 10% of Hiroshima, but besides that, the detonation velocity of ammonium nitrate can’t even hold a candle to the near instantaneous energy release of a nuclear weapon. It’s the difference between a pile of gunpowder and a block of TNT, and even that comparison doesn’t do it justice.

Thanks for writing this.

There’s been some strange tendency of late to conflate the weapons effects of nuclear or thermonuclear explosions with those of “really big amounts of conventional high explosive”. While that may even hold true at a sufficiently great radius, the proximate effects due to the near-instantaneous radiated energy is something that has no comparable analogue in the conventional world.

These effects are not really militarily useful, which is why even in the realm of small tactical nuclear weapons there has been a tendency towards minimising or not emphasising them, but...

The power of a nuclear weapon, intended properly as energy released per unit time, is in a league of it’s own.

Aside: for all the horror, at least this happened at the quayside and half the explosive force radiated away almost harmlessly over the sea. That basically halved the actual destruction at the outset. If it had been in the middle of the city, there would have been twice the damage.

EDIT: A startlingly worse case would have been if the explosives had been slightly interred, coupling the blast more closely to the ground and enhancing amplitude of the p-waves and providing plenty of really substantial debris raining down after basically ‘earth-quaking’ the buildings.

NOTE: Took the last paragraphs and placed them into their own comment, with logical conclusion. Apologies for the duplication.

> There’s been some strange tendency of late to conflate the weapons effects of nuclear or thermonuclear explosions with those of “really big amounts of conventional high explosive”.

Haven't people been using kilotons and megatons of TNT equivalent as a measure of nuclear bomb energy since the 1950s?

Yes, but that doesn’t mean that X tonnes of a random substance blowing up will be as destructive as the instantaneous release of equivalent energy that a nuke delivers

Yes, for the overall energy. But a nuclear bomb releases the energy faster than TNT, which makes a huge difference.

Nukes are different class of beast, being heavy metals nuclear materials don’t generate huge amount of gas mass that deliver destructive force in case with chemical explosives

Atomic/nuclear survivors account often starts with a blinding flash then move to a mushroom cloud and scorched world, also consider that the wreck of the building directly under Hiroshima nuke still stands to this day

I'm not a physicist but as I understand it, the shockwave of a nuclear blast can account for 50% or more of a nuclear blast's energy. This shockwave, as well as the fireball and thermal emission are all linked insofar as they're all caused by a massive amount of X-rays vaporizing the bomb and rapidly superheating the atmosphere near the bomb. These X-rays predominantly come from the energetic collisions of fission products and the fission itself.

AFAIK that building survived not because nuclear blasts produce weak shockwaves, but rather because it was a very strong earthquake resistant building in the first place, and because it handled being loaded from above well (concrete and brick generally handle compression well.) If it had been a bit further to the side, I think it might not have remained standing.

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