Frozen Groin? God Help Us.

I can’t believe that I’m writing this post, but I bring to you today a case where a teacher in Carpentersville, IL badly injured a student in his class by pouring liquid nitrogen on his chest and groin as he lay in the classroom. You can read more about this here.

Before I do anything else, I want to describe the things that went right after this occurred:

  • The teacher immediately voluntarily gave up his teaching position and resigned from the school as a result of what had happened.
  • The school quickly investigated the situation and took steps to make sure that this didn’t happen again.
  • The student who was injured was given prompt medical attention and is, as far as I can tell, in good health.

Of course, the best responses to an accident don’t make up for the fact that the accident happened in the first place, or that a student suffered an injury because of the negligence of a teacher. Because I have incredible powers of discernment and can read minds, I’ll describe from you what I believe probably happened in this case:

  • The teacher was teaching about phase changes and wanted to give the students something really cool to talk about. I think all of us chemistry teachers have the natural inclination to do flashy things to keep students’ attention, and by itself, this isn’t something that’s negative at all.
  • The teacher had read about the Leidenfrost effect, where pouring a liquid on a surface that’s much hotter than the liquid’s boiling point will cause it to instantly boil, putting an insulating layer of gas between the surface and the colder liquid. If you’ve ever seen water drops dancing on a hot cooktop, you’ve seen the Leidenfrost effect. What this teacher was trying to do is just a low temperature version of the same thing.
  • I’m sure this demonstration started with his pouring liquid nitrogen over his arm, which is completely harmless due to the Leidenfrost effect. He probably got a big response from the kids, who asked if they could do it.
  • He did the demo with the kids’ arms and it was a huge hit.
  • Knowing that the demonstration would be even more interesting if it lasted longer, he decided to pour the liquid nitrogen on somebody’s shirt. With the nitrogen gas trapped temporarily in the shirt, it probably led to a much cooler and much more interesting demonstration.
  • At some point, the teacher realized that this demonstration would not only be cool but also funny if he poured the liquid nitrogen on the student’s groin. The much thicker pants kept the very cold nitrogen gas in contact with the skin, causing the accident described above.
  • Why did he pour the liquid nitrogen on his student’s groin? I don’t know. The only thing I can think of is that he figured the students would find it amusing (?). This defies all rational explanation.

Let’s deconstruct this series of events and figure out what the teacher should have done:

  • Before doing anything the teacher should have checked to see if pouring liquid nitrogen anywhere on somebody is a good idea. I just did a quick search to see if I could find any good sources that says it’s a good idea and couldn’t find anything, but I won’t rule out the possibility that it’s up on the web somewhere.
  • If it did turn out to be an OK demonstration, he should have only done the demonstration on himself and not on a student. Though it’s always a bad idea to do something dangerous, it is of utmost importance that our students NEVER are in danger.
  • If he had found the demonstration to be safe and if he, for whatever reason, decided to do it on a student, he should never have poured it over their entire bodies. I’m pretty sure that’s not something that’s recommended by anybody, ever.
  • And finally, IF he had found the demonstration to be safe and IF he had performed it on a student and IF he poured it on their bodies, he should never have poured it over their groin. There are so many reasons this is a bad idea.

So, what have we learned from this debacle? First, we’ve learned that we should never perform a demonstration that we don’t know is harmless. Next, we’ve learned that we shouldn’t use students as subjects in demonstrations unless your demo is really, really harmless (baking soda and vinegar and the like). Most importantly, we’ve learned that teachers should stay away from doing demonstrations with anyone’s groin. Science education professors, please make sure to add this to your curriculum.

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