Awful Idea: Liquid Nitrogen at a Pool Party

June 18th, 2013

There is video circulating tonight of a summer party in Mexico where organizers poured liquid nitrogen into the swimming pool. They weren’t messing around, either—you can see a number of ~10 L dewars being upended into the water.


Of course, this is a very, very bad idea. Under these conditions, the nitrogen (b.p. = −196 °C) quickly boils and displaces all of the oxygen present, causing people in the area to asphyxiate. Remember, it only takes 28 g of liquid nitrogen to displace 22.4 L of air at standard temperature and pressure. The fact that you are asphyxiating is masked by your ability to exhale carbon dioxide normally, so the burning sensation you experience when holding your breath or drowning is absent. Furthermore, the thick fog produced upon mixing the liquid nitrogen and water conceals any distress.

It looks like multiple people were hurt at the party and needed to be rescued.

News reports, updated 21 June 2013: Daily Mail (corrected most of the wrong chemistry, but a caption referencing a reaction with chlorine remains), Latin Rapper Blog (corrected to get the chemistry right; gives ChemBark a shout out, see comments), International Science Times (gets it right, credits ChemBark), Excelsior (gets the chemistry wrong), Fox News (gets the chemistry wrong), MSN Now (gets the chemistry wrong), Huffington Post UK (gets chemistry mostly right, credits ChemBark, but still needs to correct photo captions), NY Daily News (gets the chemistry wrong), The Sun (gets the chemistry wrong), The Telegraph (gets the chemistry wrong in the headline), Popular Science (gets the chemistry right, includes interview and link to ChemBark), Slate (corrected the story to get the chemistry right).

Deborah Blum covered the misreports by the media of the chemistry at play on the Knight Science Journalism (KSJ) site. The post links to ChemBark.

Updated note to media: Many outlets have reported that liquid nitrogen will react with chemicals in swimming pools to generate a poisonous gas. This is almost certainly incorrect. Molecular nitrogen is relatively inert and should not react with anything present in the pool, like “chlorine” (mostly, NaOCl) or water. The danger of adding liquid nitrogen to the pool stems simply from the nitrogen’s boiling and pushing away all of the oxygen around, leaving none for the swimmers to breathe. The cloud that is present has nothing to do with poison gas. Rather, it is the same thing as fog. The liquid nitrogen is cold and cools the air close to the pool to the point that water vapor in the air condenses into very tiny droplets that stay suspended. The cloud is fog, generated from the same effect responsible for your being able to “see your breath” when you exhale on a cold day. The visible cloud is not nitrogen and it is not smoke; it is droplets of water suspended in an atmosphere of air that is heavily enriched in nitrogen.

47 Responses to “Awful Idea: Liquid Nitrogen at a Pool Party”

  1. Chad Jones Says:

    Watching this I realized something. You see people jumping up to get their head above the condensation, supposedly to take a breath of fresh air. The problem with that is it’s deceiving – you’re still going to have dangerously low oxygen levels above the condensation. You might get a deep breath of nitrogen in and think that you’re fine, when in reality you still haven’t gotten any oxygen. I’m sure people associate the condensation as nitrogen which means if you’re not breathing that in you’re fine, but that’s not true.

  2. Bob Sacamano Says:

    Courtesy of the chemists at the Daily Mail (via supplied link):

    Liquid nitrogen dumped into the pool reacted with chlorine, forming a toxic cloud

  3. berg Says:

    Just make up your own rules as you go along.

  4. Paul Says:

    @Bob: I skipped over that bit about nitrogen reacting with chlorine. Ugh, the stupidity…

    To visitors who stumble here looking for more info about the tragedy, nitrogen *does not* react with the chlorine in pools. In fact, nitrogen gas reacts with very few things. The danger comes purely from the fact that nitrogen gas can displace oxygen gas, which you need to breathe to survive.

  5. Chad Jones Says:

    @Bob – I believe that’s called “Nitrochloric acid”, right. :)

  6. Paul Says:

    And look at this stupidity:

    Event staff poured liquid nitrogen into the pool to create a smoke effect, not realizing its combination with chlorine would cause an unhealthy chemical reaction. According to OSHA, exposure to Nitrogen Trichloride can lead to difficulty breathing.

    No, no, no. Not even close!

  7. John Says:

    @Chad Jones
    I though N2 gas is less dense than air/oxygen?

  8. bad wolf Says:

    John–Well, the cold vapor will be denser than air, and that’s going to be highly enriched in N2, so… the lower you are, the more danger you’re in.

    Am i the only one who gets annoyed/concerned when lab folks dump a lot of dry ice in the sink, or leave it to evaporate in a small room? The amount of breathable air displaced, as Paul’s calculations show for liquid N2, is significant.

  9. Dante Says:

    One of the Mexican news sources stated that they were sick because of the chemical reaction. I’ve since changed that and attributed ChemBark for the correct info.

  10. Mark Says:

    A website called “latinrapper” gets the chemistry wrong? Who’d a thunk it.

  11. Dante Says:

    That was based on what a major news outlet stated. I have a degree, just not in chemistry, no need to be snide.

  12. @SuperScienceGrl Says:

    That’s brilliant that a news story was corrected as a result of this post. Thanks! Proof to scientists that sometimes highlighting misinformation does work.

  13. bad wolf Says:

    You should go look and see if “whiterapper” got it right. #notsubtleracism

  14. qvxb Says:

    It would have been safer to use all-natural organic nitrogen instead of the synthetic stuff. :)

  15. Paul Says:

    @Dante: Great! Thanks for correcting the story.

  16. Dr. Mel Says:

    Weird parallel don’t you think?

  17. Paul Says:

    Updated post to cover media coverage. Most outlets have gotten the chemistry wrong, probably confusing nitrogen gas with ammonia.

  18. wolfie Says:

    There is a simple chemical expiriement that my childs want to hear all day long. It’s the ammonia fountain. Have you ever made water-free ammonia yourself from a mixture of some salts, blew it into an empty round flask at the age of 17, stuck a pipet through a hole at the bottom, and then watched the ammonia fountain go ?

    Do you know what I mean ? This is the real facscination of chemistry, why this is possible.

  19. anon Says:

    there are night clubs that use liquid nitrogen to spray cold nitrogen gas onto clubgoers, and i suspect this pool variation has been done before as well. under the right conditions i’m sure it’s fun

    these conditions were horrible

  20. Howard Peters Says:

    Some would say that this event should be nominated now for a Darwin Award..?
    What do you think?

  21. Hap Says:

    No. The people who were dumb enough to pour LN2 into a pool weren’t the same ones who consented to be in the pool. If you’re dumb and kill someone else, that’s not a Darwin Award, that’s just negligent homicide or reckless endangerment. Even if the people were told LN2 was coming, they might have assumed the people using it were competent – maybe unwarranted, but nowhere near dumb enough for a Darwin.

  22. Leebeater Says:

    I used to make real snow artificially using liquid nitrogen. The golden rule was always be aware of the fact that the LN2 displaces oxygen.
    Accidents do happen despite all our knowledge

  23. Paul Says:

    This is from someone who should know better:


  24. Bob Sacamano Says:

    @Paul 11:03–

    This is what the ‘someone who should know better’ says about chemistry:

    “Chemistry is part of everyone’s life, from cooking and cleaning to the latest computer chip technology and vaccine development. It doesn’t have to be intimidating and it doesn’t have to be hard to understand.”

    The author demonstrates that the bar for understanding might need to be raised, perhaps just a bit. They ably demonstrate that it is certainly *not* hard to propagate chemical misinformation.

  25. BRateProf Says:

    This looks like a prime case of the dangers of partial knowledge. The party people may have known that nitrogen is inert and wouldn’t react with the water or the chlorine and therefore thought it was safe to throw in the pool.

    Sometimes in doing demos we spill liquid N2 onto the ground and act like it’s no big deal. It really isn’t, but perhaps we’re sending the wrong message.

  26. BobbyV Says:

    Slate gets it wrong too:

    Notice that the wording from the incorrect news sources is all similar… are these reporters even bothering to take a step back to realize how dumb this sounds? If this were true, nitrogen from the air would react with the “chlorine” in any pool, thereby making it toxic!

  27. Ben Yancey Says:

    There is also the obvious expansion when a liquid becomes a gas. Taking 40 L of LN2 it will actually expand to 25,800 L of gaseous N2 at room temperature. So even though the effect is cool, it is the amount of LN2 they added to the pool. I would also like to point out that the vast majority of “Air” is N2 (~70%) followed by Oxygen (~20%) but the density of N2 is higher at lower temperatures so the just boiled N2 is much denser than the air and will displace the air.

  28. dumbass Says:

    in a related story, the long awaited liquid nitrogen bong fails…

  29. Robert Slaven Says:

    Now, if they’d poured in at least a quarter as much LOX as LN2 (so as to match the roughly 20:80 ratio they exhibit in regular air), it would’ve been both a neat effect AND relatively safe (as long as they spread the LOX around, and didn’t just pour it all in in one place). Better living through chemistry, my friends!

  30. Daily Fail Says:

    The Daily Mail has now changed most of the inaccuracies in the their article [maybe after I contacted them and pointed out the inaccuracies and sent them a link to this page...although, after changing the article they still credit as the source of the information, despite that website (in Spanish) having the original "Nitrogen reacting with Chlorine" explanation!...but that's the Daily Mail for you!]

  31. Paul Says:

    @Daily Fail: Thanks for taking the time to do that.

  32. Paul Says:

    I was interviewed by Popular Science about the nitrogen pool story. The reporter’s query dealt mostly with the cryogenic danger of liquid nitrogen. Here was my full explanation:

    There is certainly a danger of liquid nitrogen freezing the swimmers’ skin because the material is so cold. These burns would be quite painful initially, and I expect would cause any affected swimmers to immediately exit the pool (assuming they were not already under respiratory distress).

    The way in which the swimmers reacted leads me to believe that the nitrogen was being added to the pool slowly enough such that it boiled before it came into contact with anyone’s skin for a prolonged enough period to cause burns. Due to the Leidenfrost Effect, the skin does not burn immediately when it comes into contact with the nitrogen because a layer of freshly vaporized molecules can serve as a thermal insulator (for about a second or so). Finally, the water present should also help conduct heat to dissipate the chill, though to what extent I can only speculate.

    It is important to remember that liquid nitrogen boils quickly when out in the open at room temperature, and it doesn’t take much liquid to produce a big volume of gas. One half-liter soda bottle of liquid nitrogen will expand to fill over 300 liters of atmosphere!

  33. Hap Says:

    I wouldn’t think anyone would want to play with that much LOX if they could avoid it, though – if they premixed it, it would probably still be a good enough oxidant to set fire to combustibles (which probably includes swimmers and their pool leavings), and if not premixed, it would definitely be a good enough oxidant to set fire to those things (because of the higher concentration in liquid than gas).

  34. Jim Says:

    One detail that I don’t think has been mentioned. Any nontoxic gas that displaces Oxygen in the air that you breathe reduces the partial pressure of oxygen (at sea level, normally about 3 psia or 200 mBar). The oxygen in your blood is in a pressure equilibrium with that partial pressure. So the net result is that with every breath, oxygen moves from your blood to the air you breathe until it is equalized again!
    And as was stated in the article above, carbon dioxide still can move from your blood to the air. So there is no sense of suffocation since you brain keys off the concentration of CO2 in your blood. You just pass out like you would in a jet plane depressurization accident at high altitude without supplemental oxygen.
    So at least in theory, if you are going to try pulling someone out of a oxygen deficient area, you would be better off holding your breath to conserve the oxygen in your blood.

  35. Greg Says:

    ” Any nontoxic gas that displaces Oxygen in the air that you breathe reduces the partial pressure of oxygen (at sea level, normally about 3 psia or 200 mBar). The oxygen in your blood is in a pressure equilibrium with that partial pressure. So the net result is that with every breath, oxygen moves from your blood to the air you breathe until it is equalized again!”

    Yes, and it is the build up in CO2 that causes you to feel like you aren’t getting enough air. In the case of breathing inert gases, you just pass out. I remember reading about people dying cleaning out industrial pipes that had nitrogen gas in them.

  36. having fun? Says:

    Hey guys. Mind If you build me sandwich chemically? Im hungry lol

  37. Phillip Toone Says:

    Why didn’t they just use liquid air to avoid asphyxiation?

  38. Bob Sacamano is a Dummy Says:

    Bob, you’re a dummy. The Daily Mail is not real news.

  39. KBOB Says:

    I have worked and played with all the cryo liquids for decades in clouds so dense you can not see your hand in front of your face. Many times in a closed shop. I am STILL here to tell ya, I have never seen it happen. It is too hard to get a rich enough Nitrogen atmosphere unless you stuck your head over a bucket of it. Quit worrying about nothing. Now the burns, that’s a different story. Just don’t allow skin submersion and all will be well. Signed Daily user

  40. Chris Says:

    I am pretty sure you are correct when you say the concentration levels have never gotten high enough to harm you, but in this case, the heads of the swimmers are at the low point where the heavy gasses will settle and displace O2.
    And become a real danger.

  41. elcabron Says:

    mexicanas drug dealers b like fuck it i got money lets try something new jjaja

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