Accidentally rupturing a tank of mercury doesn't usually kill a worker and injure a dozen. A tank of very nasty mercury compound might.
Actually, to steer back to topic which is (laudably tolerated here) dislike of rationalists, this argument can make good tiny pet example of 'rationalist' vs 'experts' debates.
Rationalists believe by special powers of rationality they are unusually less prone to for example nuclear = scary bias, and say that uranium wrapped in paper safe as lead etc etc. (By the way, also false, uranium is a serious fire hazard). There's a lot of such 'rationalists' around, not just here but everywhere, that's where people get misconceptions like yours from.
Experts actually know the matters to conclude something. (Not that I am a nuclear expert, of course, I only know overall overview of the process, and would defer to experts)
Frankly, rupturing any tank of just about any hexafluoride compound would be expected to be pretty dangerous.
I'm by no means a nuclear expert, I was just a nuke plant mechanic. The reason I am unafraid of radiation isn't because the fearmongering is baseless, it's because I'm enough of a lay expert to know the magnitude of the actual risks.
How is elemental uranium a fire hazard? Does flame spread across it faster that it spreads across wood paneling? I never considered that kind of hazard to be important, because uranium-as-she-is-used is safe enough from fire.
My friend, hearing me recount tales of LessWrong, recently asked me if I thought it was simply a coincidence that so many LessWrong rationality nerds cared so much about creating Friendly AI. "If Eliezer had simply been obsessed by saving the world from asteroids, would they all be focused on that?"
Obviously one possibility (the inside view) is simply that rationality compels you to focus on FAI. But if we take the outside view for a second, it does seem like FAI has a special attraction for armchair rationalists: it's the rare heroic act that can be accomplished without ever confronting reality.
After all, if you want to save the planet from an asteroid, you have to do a lot of work! You have to build stuff and test it and just generally solve a lot of gritty engineering problems. But if you want to save the planet from AI, you can conveniently do the whole thing without getting out of bed.
Indeed, as the Tool AI debate as shown, SIAI types have withdrawn from reality even further. There are a lot of AI researchers who spend a lot of time building models, analyzing data, and generally solving a lot of gritty engineering problems all day. But the SIAI view conveniently says this is all very dangerous and that one shouldn't even begin to try implementing anything like an AI until one has perfectly solved all of the theoretical problems first.
Obviously this isn't any sort of proof that working on FAI is irrational, but it does seem awfully suspicious that people who really like to spend their time thinking about ideas have managed to persuade themselves that they can save the entire species from certain doom just by thinking about ideas.