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In Hungarian, there is a new-ish folk-song sung by school-children who dislike school whenever it snows to the tune of Twinkle, twinkle, little star:

Hull a pelyhes dinamit,

Robbantsuk fel a sulit!

Minden gyerek várva vár,

Hogy repüljön a tanár.

[irrelevant verses removed]

It would roughly translate to the following:

The fluffy dynamite is falling,

let us blow up the school.

Every child can hardly wait

for the teacher(s) to go flying.

Now this raises a few questions, like what is wrong with these children, but we aren't talking about that.

What explosive could potentially end up falling from the sky in a snow-like form? The less human intervention needed, the better (I mean, you could fly a plane over and dump it, but that's cheating).

It should be powerful enough to blow up a small school with less than a cubic meter of the stuff (a rough estimate of how much a schoolyard full of kids can collect and smuggle in without being apprehended).

Bonus points if you can make "snow"men or "snow"balls out of it. Extra bonus points if the snowballs explode. Even more bonus points if you can go skiing in it without blowing up.

This phenomenon is happening on a planet that looks like Earth, and has humans. So, blue sky, 1G gravity, and inhabitable by humans. If you want, you can put it on another planet, but the teachers need to be taken by surprise, so this is not a regular occurrence.

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  • $\begingroup$ On Earth? Or anywhere else? $\endgroup$ – L.Dutch - Reinstate Monica Jan 17 at 7:57
  • $\begingroup$ @L.Dutch-ReinstateMonica preferably earth, but any human-inhabitable planet would be ok. I'll add it. $\endgroup$ – Mark Gardner Jan 17 at 8:00
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    $\begingroup$ There is some nitroglycerin derivatives wich are very similar to snow. They have melting point quite high to be "snow" at room temperatures. But they are highly expolsive, toxic, illegal and hard to synthesize. So no bonus points and no humans on surface. But this compounds are known "homebrew anarchists explosives". $\endgroup$ – ksbes Jan 17 at 8:27
  • $\begingroup$ @ksbes if it looks white and fluffy, it goes. feel free to make it an answer. $\endgroup$ – Mark Gardner Jan 17 at 8:28
  • $\begingroup$ like ball lightning... $\endgroup$ – user6760 Jan 17 at 8:54
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DISCLAIMER: DON'T TRY THIS AT HOME, SCHOOL OR WHEREVER YOUR YOUNG AGE TAKES YOU

You are looking for a dust explosions, which can be caused by

grain, flour, starch, sugar, powdered milk, cocoa, coffee, and pollen. Powdered metals (such as aluminum, magnesium, and titanium) can form explosive suspensions in air, if finely divided.

But about dust explosions:

A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or other oxidizing gaseous medium, such as pure oxygen. In cases when fuel plays the role of a combustible material, the explosion is known as a fuel-air explosion. Dust explosions are a frequent hazard in coal mines, grain elevators, and other industrial environments.

There are five necessary conditions for a dust explosion:

  • A combustible dust
  • The dust is suspended in the air at a sufficiently high concentration
  • There is an oxidant (typically atmospheric oxygen)
  • There is an ignition source
  • The area is confined—a building can be considered an enclosure

Someone dusting a room with a bag of flour and putting a spark/flame (a candle?) in it sounds like the perfect occurrence of the five conditions above.

And any white dust can be confused with snow...

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    $\begingroup$ Good idea, but I'm not sure anyone would mistake flour for snow. $\endgroup$ – Mark Gardner Jan 17 at 8:06
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    $\begingroup$ @MarkGardner, I used flour or powdered sugar to mimic snow on my dioramas... $\endgroup$ – L.Dutch - Reinstate Monica Jan 17 at 8:07
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    $\begingroup$ In 1981, there was a dust explosion at the Bird’s Custard Factory in Banbury. A hopper became overfilled, creating a dust cloud of corn flour that ignited due to nearby electrical equipment. The explosion blew the roof off the building and 9 workers were injured. As custard is made when heat and water are added to custard powder, the water from the fire engines that came to put the fire out created gallons of custard inside the building, which then came pouring out. -- amalgamate-safety.com/2018/06/26/… $\endgroup$ – Kramii Jan 17 at 12:16
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    $\begingroup$ My favorite use of dust explosions: Monstrous Regiment by Terry Pratchett. Used once on-screen and suggested to have been used in the epilogue. $\endgroup$ – Gloweye Jan 17 at 22:39
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    $\begingroup$ Sometimes I really wonder how our species has managed to survive this long. $\endgroup$ – Shadur Jan 18 at 10:50
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The most popular explosives are already crystallized like snowflakes.

Example:

  • Nitroglycerin - has melting point at 14C, but can easily overcool to negative numbers. It needs shaking to crystallize, but crystallization is not the most probable outcome of shaking nitroglycerin. But if it crystallizes it produces something snow-like, especially if it was sprayed beforehand.

  • EGDN - has much lower melting point (-22C ). Highly explosive and extremely toxic (skin contact is enough to get lethal or almost lethal dose). Much more chemically stable than nitroglycerin (but easier to explode) and is produced by exactly same somewhat simple technology. Thus it is one of the most favorite terrorist explosions (or bomb igniters). If produced "at home" it is also snow-like (dirty-snow like actually). Mix with nitroglycerin is more stable than pure nitroglycerin, less explosive than pure EGDN and freeze at about 0C at some proportion.

So the right mix of this two at near zero temperatures can be (extremely cautiously!) formed into a snowball (with rubber gloves) and thrown. You may also try to ski on it. If you are slow enough (about snail pace) you might survive (friction is one of ignition factors).

Disclaimers:

  1. Do not do it at home, at school, etc. - anywhere!
  2. I am not a professional chemist, and can be wrong with all this. Correct me if this is the case.
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    $\begingroup$ "but crystalization is not the most probabale outcome of shaking nitroglycerin." - hilarious $\endgroup$ – Julian Egner Jan 17 at 11:17
  • $\begingroup$ But how would you get it to synthesize in the air? $\endgroup$ – Spencer Jan 18 at 14:48
  • $\begingroup$ @Spencer, you may just (gently!) spray it in the cold air - exactly like "artificial snow" is made. $\endgroup$ – ksbes Jan 20 at 7:09
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Guncotton is a form of nitrocellulose made from cotton wool. It looks white and fluffy. It's historically been used as a propellant rather than a high explosive, but was used for blasting and I think as a teacher-launching substance that's close enough. Jules Verne was a fan, using it in many stories; it was invented around the time he was writing.

Nitrocellulose Picture from Wikipedia, user Fabexplosive. This was the best image I could find with a suitable licence; other images look more snow-like

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  • $\begingroup$ Hm, that's exactly what "pelyhes" looks like. :D $\endgroup$ – Martha Jan 20 at 16:14
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Triacetone Triperoxide (aka TATP) was made famous several years ago by the "shoe bomber" -- who tried to light his shoes to blow up the plane he was flying in after filling them with this material before boarding. It's very easy to make (three easily obtained ingredients), and forms as a snow-like precipitate in the solution. It's a primary explosive -- that is, it doesn't require a detonation to initiate (the way, for instance, ammonium nitrate explosives do), but can be set off by simple ignition, impact, or friction.

It is too sensitive for commercial applications (there are other primary explosives that work as well to initiate a blast and are much safer to handle and store), but has long been a favorite of Internet chat rooms and newsgroups where the inexperienced gather to talk about blowing stuff up.

For this material to form "naturally" and fall from the sky as snow would take a very unusual confluence of conditions -- but I could almost see it happening in the old Soviet Union or late 20th century China.

You'd need an industrial ventilator, like a fume hood, blowing acetone into the air -- air already containing a suitable catalyst (perhaps another industrial pollutant from somewhere that isn't usually upwind) to replace the peroxide and acid catalyst usually used, and prompt the acetone to form is peroxide from atmospheric oxygen (solar UV would probably help here). And you'd need a LOT of both chemicals, to form vapor concentrations high enough to react and produce visible fall of the end product.

Worth noting that the kids are far more likely to blow their own hands or faces off (doing things like packing snowballs), or simply blow up the entire schoolyard with this stuff than to smuggle it inside and blow up the school -- but it wouldn't take anything like a cubic meter to do the job; a few kilograms -- one small snowman -- would be sufficient to level the school I attended from 2nd through 8th grades (concrete block construction, three classrooms and a gym/auditorium).

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    $\begingroup$ Wait, so this stuff could, in theory, actually fall like snow on earth?? $\endgroup$ – Mark Gardner Jan 17 at 22:51
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    $\begingroup$ I think it's very unlikely; the catalyst I mentioned that causes acetone to form a peroxide from atmospheric oxygen is very much handwavium. On the other hand, diethyl ether does spontaneously form explosive peroxides (very slowly), so I won't say it's impossible for acetone to do so under the right conditions. $\endgroup$ – Zeiss Ikon Jan 19 at 3:02
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Well, there's napthalene. AKA mothballs, napthalene is pretty widely available as an insect repellent. It's also explosive, especially when you shave the stuff into flakes. Napthalene bombs are used as pyrotechnics in movies to provide that nice big satisfying fireball.

Only problem is, it's used in the movie biz because it's a lot safer and less damaging than other pyrotechnics, so you can use it around structures you can't actually demolish as part of filming, and closer to people than a propane or gasoline pyrotechnic. So using it to blow up a school, especially one made of reinforced cinder block, might be a bit iffy.

It's also not something that occurs naturally in enough bulk to snow in any universe that also contains humans.

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    $\begingroup$ Perhaps a local factory had their napthalene supply get into the air, and the wind carried it into the school? That could make it seem like it was snowing moth balls $\endgroup$ – user43712 Jan 17 at 16:15
  • $\begingroup$ If it's enough to make the teachers fly (to escape the smell, if nothing else), damaging the school might not be necessary. :) $\endgroup$ – Martha Jan 20 at 16:22
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L.Dutch came close with dust explosions. However, none of the materials that typically cause dust explosions could be mistaken for snow.

Lets add a plant. We already have examples of wind-dispersed seeds, this plant takes that to the extreme--the seeds are encased in a very lightweight structure to increase their surface area so the wind blows them better. Furthermore, the plant wants to maximize the dispersion--the seeds are encased until the plant is subjected to winds above a certain speed--the threshold being a major storm.

Hence when a big storm comes through every plant releases their seeds--if you have enough plants you have bazillions of seeds all at once and brought by a storm at that. While the support structures aren't dust per se they have the very high surface area to mass that's required, and they're fluffy enough that the oxygen is already there, no need for them to be puffed into the air.

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  • $\begingroup$ Wow. I just imagined one of these seed-storms going over a bush-fire. Not a pretty sight. $\endgroup$ – Mark Gardner Jan 21 at 19:01
  • $\begingroup$ @MarkGardner I don't think it would do anything while the seeds are airborne. They'll be too dispersed to explode, they'll just add a bit to the fire. $\endgroup$ – Loren Pechtel Jan 22 at 3:56

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