A Liquid Nitrogen Cocktail Party

But at least, as you mention, you can be sure it was clean. There's no knowing what nasties a used dewar might have been contaminated with (heavy metals, scary organics, etc).

Yet my PhD adviser did not. Sometime after I graduated, one of my fellow grad students blew up a dewar!! (Luckily no one got hurt).

He obtained an old dewar from another lab, and went through the usual cool-down procedure - evacuate the Outer Vacuum Chamber, fill the LN2 shroud, then pre-cool the main bath with LN2. Stupidly he did not notice there were no pressure relief safety valves!!! (Not only should you verify these exist, but you should also verify they work by slightly pressurizing the dewar.) He put in a bunch of LN2, capped it, and left for the weekend. When he came back, the dewar had exploded, pretty much along the weld seams, strewing the metal body and super-insulation all over the lab.

The first professor I mentioned above made sure we understood all valves and release valves. And also noted that if opened for too long while full with LHe, it's possible ice could form in the dewar neck, below the safety relief valves. Always kept me on my toes while working with LHe (well, that and the fact that LHe burns way worse the LN2 if it makes accidental skin contact).

LN expands by 700x when it evaporates and warms up to room temperature. This makes thermoses inherently unsafe for storing LN, because they come with lids. Human experience, and the lid itself, through its design, say: Put this lid on top of the thermos! If you get carried away in the heat of the moment, you might give into this instinct and accidentally put the lid on the thermos. Or someone else who was late and missed the safety briefing. Proper lab equipment, by design, does not come with screw-on tops, for exactly this reason. If you are hosting an LN cocktail party, I propose that you hide, throw away, or destroy the lids for the thermoses. A few years ago a German hobby cook lost his right hand due to putting the lid on his thermos: https://translate.google.com/translate?sl=auto&tl=en&js=y&pr...

Don't ever swallow liquid nitrogen. Once you ingest it (which actually is possible) it will rapidly expand by 700x. If you swallow a tablespoong (15ml), you end up with 10 liters (2 gallons) of gas in your stomach, and it will rupture. Occasionally you'll see YouTube videos of people doing this, but they either don't ingest anything, or very small amounts. I would not ever recommend trying this. Here is an example of the feat going wrong - google "LN ingestion" for more: http://www.ncbi.nlm.nih.gov/pubmed/20065833

Don't put things that have been cooled to liquid nitrogen temperature in your mouth. This is more of a personal story: It was the birthday of one of our lab-members, and he had brought some warm beer. We naively decided to chill the bottles with liquid nitrogen. This made most bottles burst and created huge levels of steam, fun, and what we called "beer popcorn": Beer that had frozen into small nuggets by the violently boiling liquid nitrogen. Eventually the birthday-guy decided to try one of the beer nuggets. As he put it on his tongue, it froze to it. He tried to spit it out, but it froze to his cheek as well. He did not manage to rip it out in time and had nasty cold-burns in his mouth. Fortunately, he was not one to easily be bothered by such injuries, so the party did not end at that moment. But, looking back to it now, the feat very obviously was a bad idea.

Don't transport large amounts (more than a few liters) of LN in small enclosed spaces (a car with the windows rolled down, a small basement room). If the container tips and the gas rapidly boils away, it can dilute the oxygen in the room to dangerously low levels. Danger starts below 17% or so.

Small splashes of nitrogen won't hurt your hand, but they can hurt your eye. The cornea of the eye is quite sensitve and (since it has no blood vessels) heals quite poorly. Most people (not all) recommend safety googles.

LN easily soaks through fabrics - also pretty much all of the fancy "cryo"-gloves that you can buy in lab equipment stores. While they look like they might be the right protection for submerging your hands in LN to grab whatever stuff that fell into the dewar - they won't help.

Touching objects that have been cooled with LN can hurt. If the metals conduct heat well (metals, for example), they can hurt you more quickly than you would expect. You can get nasty cold-burns this way. It is good practice to wear protective gloves (although I sometimes leave them off if bulky gloves makes handling the ultracold equipment less safe.)

All in all, have fun playing with LN! But I recommend to start with some simpler experiments(freezing roses and smashing them, ...) first, and then work your way up to food, and then to alcohol. Be paranoid about pressure buildups and prevent them by design of the vessels that hold your LN.

http://show.aad.org/annual11/Data/EC/Event/Exhibitors/152/pr...