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Anne Marie Helmenstine, Ph.D.

Liquid Nitrogen Safety

By April 11, 2013

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Liquid nitrogen is great fun, but how careful do you have to be with it? Here's an email I received that asks a question you may be wondering about, too:
We recently had a teacher from another school visit us and pair his students with our students. At the end he made ice-cream using liquid nitrogen to freeze the milk, sugar, cream mixture.

He had a large container of liquid nitrogen. I was concerned about his treatment of the liquid nitrogen. After making the ice cream he started pouring cups and dishes of it on students hands. Later he threw cups of it up into the air over their heads. He let it splash all over students' bodies. The liquid quickly evaporated and no one got hurt but I thought it showed students very dangerous tactics.

Our students might do that with any chemical. They don't know the difference. And not respecting the danger of liquid nitrogen might lead students to put their fingers or hands into it.

We had about 40 students seeing all this. They were ages 14 to 20.

May I ask if I am being overly concerned?

Christine Upton
My response:

I think a 14-year-old knows chemicals are not equally safe. I don't believe seeing liquid nitrogen tossed into the air is going to lead to experimentation with airborne sulfuric acid, for example. However, I think you have well-founded concerns about cavalier treatment of liquid nitrogen.

Throwing nitrogen into the air where it could land on students is ill-advised. There is a good chance the nitrogen will vaporize before touching skin, but I don't think the effect is worth risking a student's vision, for example. Plus, I suspect that demonstration would lead to students tossing cupfuls of nitrogen toward each other.

I'm all for people having fun with liquid nitrogen. It's very safe when proper safety precautions are used. Those precautions should include eye protection and skin protection to minimize the risk of injury if a spill occurs. I recommend good air circulation, since adding nitrogen to the air diminishes the partial pressure of oxygen, especially near the ground if the nitrogen is a fog.

Making ice cream with liquid nitrogen is one of my favorite demonstrations, but another excellent demonstration is dipping a rose or hot dog into nitrogen and shattering it on a countertop. That demonstration illustrates how cold the nitrogen is. Ask a student what they think would happen to their finger in the nitrogen.

Make Liquid Nitrogen Ice Cream | Liquid Nitrogen Fog
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Comments

March 31, 2009 at 9:52 am
(1) Steve Hampson says:

Regarding the ice cream demonstration,I would reconsider the wisdom of pupils making food in a school chemistry laboratory utilizing hazardous materials.Furthermore, throwing liquid nitrogen over studentís heads is not “ill-advised”, it is absolutely ludicrous. I appreciate your faith in 14 years olds understanding of chemical safety, however,you do not have to look too far back (August of 2008), when a gifted 15 year old student in New Jersey, drank liquid nitrogen during the ‘ice cream’ lab. The liability issues are still being hammered out. A grad student at Worcester Polytechnic Institute ingested liquid nitrogen in 1999 during the ‘ice cream’ lab.If I have not rattled your faith in 14 year olds with hazardous chemicals, consider the grad student at Worcetser Polytechnic Institute who almost died after drinking liquid nitrogen during the same ‘ice cream’ lab. In 2005 a teacher in Mercer, PA was arrested for doing the ‘toss the liquid nitrogen’ trick that resulted in mutiple burn victims. I am all for making chemistry class fun, but not so big on making it stupid. Ann marie, what are you thinking.

March 31, 2009 at 6:38 pm
(2) chemistry says:

To be honest, I’m thinking you didn’t read what I wrote at all, just reacted to the reader’s question. I believe I said throwing nitrogen into the air over students was unsafe.

April 3, 2009 at 4:03 pm
(3) Steve Spangler says:

Anne Marie – I couldn’t agree more with you on your response. Safety starts with the demonstrator. When a trained professional (yes, a science teacher) uses liquid nitrogen correctly, it’s a safe and fun chemical that behaves nothing like any other chemical a child has ever seen. That said, training is the key. You have to “play” with the stuff in order to get comfortable with how to handle it. I just returned from the Oklahoma Science Center where they place LN2 in a soda bottle and make it explode in a special container on stage. The demonstration is amazing and dramatically demonstrates the incredible power of a liquid turning in to a gas. Keep pushing training and the quality of our science teachers will continue to rise.

July 28, 2009 at 3:07 pm
(4) Steve Hampson says:

I simply do not share your faith in 14 year olds knowledge of chemical safety particulary in an environment where adults are tossing hazardous chemicals over their heads. I absolutely do believe that pupils seeing liquid nitrogen tossed into the air actually could lead to experimentation with airborne sulfuric acid and what ever else is handy. I would caution against throwing any chemicals in the science lab regardless of the shock value, and regardless of the presence of ‘good air circulation’. I do appreciate that one of your favorite demonstations involves using hazardous materials to make ice cream in the science lab, however,I am simply pointing out the horrific track record of that demonstation even at the university level. Furthermore, I am hard pressed to fathom the value of using hazardous materials in the lab to prepare food, in the face of so much expert guidance against even eating in the lab. I appreciate your take on fun in the lab, but experience tells us a more professional approach may be the way to go. A review of the injuries and litigation resulting from lab fun gone wrong tells us that we are simply not ready for such antics and ill conceived demonstrations in chemistry class. A good rule of thumb is to post the most basic safety rules in the lab, and discontinue any of your own practices that violate those rules. (eating and throwing things in the lab) I recall where students at MIT did their version of the ‘sodium drop’ lab. The only problem is that they dropped it off of a bridge in Boston where it landed on a boat and set it on fire. We latter learned that this is an annual event (except for the part where the boat catches on fire) sponsered by the chemistry department. What’s next, shooting a cannon in the classroom during a lesson on the Civil War. Well I gotta get going, they are cooking up some burgers on a hot radiator in the auto shop. Gross negligence and professional misconduct may be entertaining, but still Anne-Marie…..what are you thinking.

April 6, 2011 at 7:25 am
(5) Lanthanum says:

It used to be mercury, now it’s liquid nitrogen… It’s hard to tell which one is more dangerous when misused.

April 7, 2011 at 5:42 pm
(6) Javier says:

Probably the reason the students weren’t hurt is because of the Leidenfrost effect, but the demonstrator’s actitude was indeed very reckless.

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