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Comment by MaxScheiber | Hacker News Reader

Watching the videos on the CCTV America link reminded me of some basic (but apparently necessary) safety advice. If you're ever in a situation like this, don't stand by a window filming it! You only have seconds until the blast breaks yours windows (depending on your distance from the epicenter and the explosion strength). From what I understand, the biggest immediate danger is lacerations from flying glass.

Get away from the windows and duck behind something solid.

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The shockwave took about seven seconds to arrive, so they were about 1.5 miles away from the blast. It's not intuitive that the explosion can harm you at a distance like that -- as evidenced in more than one amateur video that came out of Iraq of EOD work.

I agree, which is why it's especially necessary advice. Your gut instinct upon seeing that blindingly bright flash should be to duck and cover, whether you're outdoors or indoors.

I wish this didn't have to be so important, since it feels like a Cold War relic, but that's just how things seem to be these days.

During the 2013 Chelyabinsk meteor kaboom, one 4th grade teacher remembered her Russian "Duck and Cover" lessons and her 44 charges avoided injury: http://www.nytimes.com/2013/02/17/world/europe/russians-seek...

By no means a "Cold War relic".

"Duck and cover" is a popular target for ridicule, which is weird because it's always been excellent advice, even for global thermonuclear war. The fact that it's good for more conventional explosions lends further emphasis to that fact.

It seems we (they) still have the right gut instinct, but the timespan before the blast hit their building is just long enough so curiosity wins back.

with volcano: https://www.youtube.com/watch?v=BUREX8aFbMs

and meteor: https://youtu.be/VPFSyokDrec?t=251

Amazing how you can actually see the volcano explosion's blast radius push the clouds away.

FYI, the clouds aren't pushed away, they are created by the difference in pressure the shockwave (temporarily) creates. Waves in general do not move matter (except for the temporary oscillation).

I am sure you are right about the apparent cloud movement in this case, but shockwaves can result from sudden displacement. I read somewhere that Fermi made a good estimate of the Trinity bomb yield by dribbling a stream of shredded paper from his hand. After the shockwave passed him, he paced out the displacement of those that were in the air at the time.

http://www.dannen.com/decision/fermi.html

Just to expand on this (pun intended), a sound wave is just a change in the local pressure of the fluid it's going through. The rapid and sudden pressure drop across the leading edge of the shock wave causes vapour in the air to condense and form clouds. This happens because lower pressure air has a lower temperature (in this case, because it cannot reach equilibrium fast enough) and lower temperature air holds less humidity. That humidity is the vapour that condenses.

You'll see this same effect on some jet fighters going transonic, contrails from wingtip vorticies on aircraft and other various natural phenomina.

Indeed. This occurs with rockets, too. One of my favorite pictures is one of a Saturn V going supersonic. See here:

https://en.wikipedia.org/wiki/Vapor_cone#Gallery

As that gallery shows, the same effect is in play with nuclear explosions (and any significantly large explosion, really)

It's a longitudinal "wave" impulse, so matter is not moved much, but energy is transferred outward by compression and decompression.

https://wikipedia.org/wiki/Longitudinal_wave

You called it. Video in tweet. https://twitter.com/XHNews/status/631562306854322176

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