OK, since you all ask ...
I was working as a research assistant at a Large University doing low temperature tensile testing of various composite materials. Each test involved submerging an entire tensile test rig in a big bucket of LN2, and since the university was too bloody mean to buy me the LN2 recycling pump I wanted, I would typically use around 40 - 50 litres of the stuff per test. To ferry that around I had a great big dewar, about as tall as I was, which carried 200 litres at a time.

So when the hot weather struck it was^H^Hould have been easy to take the dewar to the main LN2 store fill it up and then leave it pumping slowly out over the office floor. It didn't break our ankles off because it boiled instantly, providing a pleasantly cool layer of gas near the floor. It didn't asphyxiate us because as has been pointed out, air is mostly LN2 anyway and we kept the place well ventilated. It didn't bankrupt the university because LN2 isn't that expensive - about the same price per litre as milk.

All happy now?

I must say that being called a lying fantasist by Blaireau is an interesting experience. I presume the late Cyril Smith will be along in due course to call me fat ...
(ubergeekian, Tue 20 Sep 2011, 23:02, 3 replies)

I called you no such thing, you cheeky, lying cunt.
In fact I didn't call you anything at all.
But I presume that you, in a backhanded way are calling me that?
If that's the case then fuck you.
( blaireau69 , the Cumbrian Travis Bickle., Tue 20 Sep 2011, 23:21, closed)

(Kazza , loathing myself so you don't have to, Tue 20 Sep 2011, 23:31, closed)

Strong words.
And if you are stating that opinion as fact then it's even funnier, cos that makes you one instead.
Edit: If it's nothing more than an opinion then that makes you a bandwagon jumping fool.
( blaireau69 , the Cumbrian Travis Bickle., Tue 20 Sep 2011, 23:33, closed)

(Kazza , loathing myself so you don't have to, Tue 20 Sep 2011, 23:43, closed)

Well it shows a complete lack of imagination and/or intelligence.
So yeah, I do consider bandwagon jumping a bad thing.
( blaireau69 , the Cumbrian Travis Bickle., Tue 20 Sep 2011, 23:47, closed)

(Kazza , loathing myself so you don't have to, Tue 20 Sep 2011, 23:52, closed)

LOL so funny. I'm not getting wrapped up in anything, just making a valid point.
And I certainly don't need you to remind me what I called some people on Saturday. It wasn't everybody, just a few of your fellow bj's.
You didn't imply that I'm a liar, you said it straight out. At least what you lack in other areas you make up for with bluntness. Or directness, if you'd rather.
( blaireau69 , the Cumbrian Travis Bickle., Tue 20 Sep 2011, 23:59, closed)

(Kazza , loathing myself so you don't have to, Wed 21 Sep 2011, 0:09, closed)

Yeah, LOL I called you a bj!
BjLOLs
( blaireau69 , the Cumbrian Travis Bickle., Wed 21 Sep 2011, 0:25, closed)

I'm terrified
Leave my radiators alone, you maniac.
(ubergeekian, Wed 21 Sep 2011, 12:09, closed)

That's veeeeeery interesting.
SO if you worked at Large University one summer you must have worked with my friend Hugh Jass. You did, you say?

PSYCH! Hugh Jass never worked there. I made him up MoFo!

Caught you out
(Kazza , loathing myself so you don't have to, Tue 20 Sep 2011, 23:29, closed)

Whilst I might accept that your improved explanation makes it more plausible
since I forgot to factor in the 200L/8 hours thing, you most certainly did not fail to asphixiate people because "air is mostly nitrogen". That's irrelevant. You still can't respire nitrogen. You failed to asphixiate people because you were extremely fucking lucky.

However, I'm confused about this still. Dewars don't pump liquid out. They allow a tiny proportion of the internal liquid to vapourise, then vent this gas slowly to allow themselves to self-cool because the latent heat necessary for vapourisation needs to be sucked from the surroundings. Leaving a dewar to stand around in your office might cool the office (although we'd be getting into a bit of a 1st/2nd law of thermo situation so it's probably not that simple) and will produce a cool gas layer on the floor, as cool gas sinks, but it's demonstrably not pumping LN2 anywhere. And it's still really dangerous unless your office is the size of a hanger.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 21 Sep 2011, 9:06, closed)

I think word dewar is often interchangeable (even though it shouldn't be)
Some of our lot call the 200L storage tanks dewars, when they're not. Our magnetism lab wasn't much bigger than an average sitting room, but with the windows open, we'd pump ~120 litres through the SQUID when cooling it down over 6 hours, all of which came pissing out the exhaust port. Still didn't manage to set the O2 alarm off.

Still, not as much fun as the time the techie was a lazy shit and forgot to fill the N2 dewar in the SQUID. When it boiled off, the vacuum jacket decided to desorb all of its contents and create a heat sink for the helium dewar, which resulted in a screaming jet of helium boiing off through the safety valve. Fun times.
( Colonel Boris "...a desperate Buzzfeed imitation...", Wed 21 Sep 2011, 10:55, closed)

Helium's a different matter
I used to use a lot of helium too - in fact "helium evaporator" was more or less my job title for a bit. Any significant disparity between the liquid I collected and the metered gas I returned brought a furious technician to my lab door with forthright suggestions about my gas seals and my parentage.
(ubergeekian, Wed 21 Sep 2011, 12:07, closed)

This reminds me
of helping fill a superconducting electromagnet with liquid helium.

I was on work experience (back when I was 16) at a university and they let me play with high intensity lasers, cray computers, superconductors, extreme vacuums and liquid helium.

Not at the same time, unfortunately, that WOULD have been fun...
(Imaginary Ed was dreamed up on, Wed 21 Sep 2011, 13:50, closed)

There's a 1 kW unshielded laser lying around in one of my labs
it's aimed at the door. as you do. Fun times.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 21 Sep 2011, 14:06, closed)

Liquid helium
is an awful good way of making high (if not very extreme) vacuums. Cryopumping, it's called. ah, happy days and great fun.
(ubergeekian, Wed 21 Sep 2011, 16:35, closed)

Dewars
There are lots of different designs. For fast filling of the test rig I had a small centrifugal LN2 pump which was lowered through the neck. We tried (sorry, would have tried) that for the air conditioning experiment, but it was (would have been) a bit noisy. So we tried (hell, I can't be bothered pretending) method two. You seal the neck with a rubber bung containing a dip tube which goes to the bottom of the flask. As heat leaks in the thing self-pressurises and drives liquid out, just like the LPG tank on a car. That's how LHe dewars work, by the way, though you sometimes have to encourage things with a bit of work on a gas-filled bladder.

Whether this works for LN2 depends on how good your dewar is. Too good and it doesn't push enough out: too bad and it empties too quickly.

You are quite right about the physiology. We weren't poisoned because nitrogen is not (at those pressures) poisonous, which is where the air-is-mostly-nitrogen comes in. We weren't asphyxiated because the room was well ventilated, we weren't putting that much more nitrogen into it, and because the nitrogen rich area would have been at the floor. Touch shit for the mice, possibly.
(ubergeekian, Wed 21 Sep 2011, 12:05, closed)

Interesting.
you'd need to watch it, though, - the N2 rich air is only at the floor because it's cooler. N2 is marginally less dense than air, all else being equal, so it's really the room vents that matter.

I'm surprised by the amount in both yours and Boris's posts though - I can trigger a full 02 alarm just by mis-filling a small storage dewar, although all our labs run odd sealed air handling systems to be fair.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 21 Sep 2011, 14:05, closed)

Sure
It was the coolth what done it. It was just a normal office, so no alarms of any sort. None in the helium labs either - you knew something was leaking when your voice went funny. Seriously.
(ubergeekian, Wed 21 Sep 2011, 16:36, closed)