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Comment by gonzo41 | Hacker News Reader

A nuclear weapon is a fairly precise instrument. Chances are it breaks apart on impact with water. At that points its really just a hot piece of metal sinking to the bottom of the ocean. Not great but not really a worry.

Though on the other hand farmers keep finding old shells from WW1 and WW2 all over Europe. But a artillery shells probably lives a harder life and are made more robustly

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I was reading about old WW1 shells in Europe recently. For instance, around the Belgian town Ypres, in 2000 they still found around 200 tons of munitions per year, tens of shells per day. They have several full time teams collecting them from farmers. 5% of the shells contain poison gas and need to be dismantled by an automatic process. Probably now in 2016 a bit less, but not much.

And that's only Ypres (of course not a random town but one of the largest WW1 battlefields).

Edit: turns out their automatic installation blew up in 2012, new one completed last september: http://www.willemen.be/en/project/ontmijningsinstallatie-lan... . For a war that happened a century ago.

A short jaunt through parts of Europe is almost guaranteed to turn up some WW1 vintage artifacts, the level of fighting was so intense, so insane, that there's still thousands of tons of munitions and other dangerous junk out there. Who knows how many artillery shells either failed to explode or were lost.

It could be worse, too. Someone might have deliberately built a gigantic explosive charge underneath your farm that was intended to blow up someone's trench line: http://www.telegraph.co.uk/news/worldnews/europe/belgium/145...

Some estimates peg WW1 cleanup efforts to continue for hundreds of years. If you feel particularly optimistic about our future, that war may continue continue killing people into the next millennium.

While true that they are fairly precise instruments, they were not always built with insensitive explosives and other physical failsafes against accidental detonation. I believe some models could produce a significant amount of fission just from some of the explosive lenses detonating on impact with the ground.

That kind of accidents are only possible for gun-type bombs. For an implosion-type bomb to initiate, the explosives really do need to all go off simultaneously, detonation from one side just causes the core to be sprayed out through the other side. Implosion bombs are designed to have the least possible amount of fissiles for weight/economics reasons, which means that even a sub-millisecond delay in the detonation of one of the slow explosives causes the core to completely fail to initiate.

Not necessarily true, as the effort to miniaturize the package size for use in ICBM warheads proceeded, they've successively reduced from the "soccerball" style of lenses in the trinity device down to only a handful (it is a design mandate that a bomb retains "one-point" safety in the event that it is detonated by an external source at a single point, but referencing Command and Control here, there have been flawed bomb designs that had a 15% chance of a 40kt yield in an accidental one-point detonation).

A nuclear weapon is a very precise instrument, but there's a huge amount of extremely high explosives involved in some designs, especially those using a plutonium core. Those alone are extremely dangerous, especially because a "fizzle", or incomplete detonation, will release scary amounts of highly radioactive material. Low yield, high fallout.

Conventional explosives are a lot more dangerous, it's true, because they can be set off by a variety of things. A nuclear weapon requires a very aggressive initiator perhaps by design, but it's not like a nuke sitting at the bottom of the ocean is entirely safe.

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