Liquid nitrogen?! On the floor?! Who's going to clean that mess up?!
See what really happens when one of the world's most beloved cryogenic liquids comes into contact with a room temperature floor.
Announcer: Frostbite Theater presents... Cold Cuts! No baloney!
Joanna and Steve: Just science!
Joanna: Hi! I'm Joanna!
Steve: And I'm Steve!
Joanna: From time to time, we spill a little liquid nitrogen! The reaction we sometimes get is....
Shannon: Did they just pour LIQUID NITROGEN on the FLOOR?!?!
Joanna: Yes. Yes we did.
Steve: One thing people seem to have a problem with is the mess that liquid nitrogen makes. Happily, there is no mess!
Joanna: Liquid nitrogen boils at 77 Kelvin. That's 196 degrees below zero Celcius or 321 degrees below zero Fahrenheit. The room is way hotter. When the nitrogen touches the rug, it boils and changes to a gas! So, no mess!
Steve: The rug is also useful in that it keeps the liquid nitrogen in one spot. If we pour the liquid nitrogen on a smooth surface, it skitters all over the place and could cause trouble elsewhere. It does this because the liquid ends up floating on a little layer of gas due to the Leidenfrost effect.
Joanna: Another concern some people raise is what we call ODH, or Oxygen Deficiency Hazard. When the liquid nitrogen boils, the gas that's made takes up a lot more space. The gas then mixes with the air, lowering the concentration of oxygen that's available. Reduce it too much and we're going to have problems. Air normally has 21% oxygen. The Lab's ODH alarm will sound if it falls to 19.5%.
Steve: If you take a look around, you'll see that we're in a fairly big space. We know how much nitrogen expands when it changes from a liquid to a gas and we know the volume of the room, so we can calculate how much nitrogen we can bring in here. For this room, it works out to 30 liters. Typically, we don't have more than 10. If we were to spill all the nitrogen we brought in here all at one time, we'd still be well above the ODH alarm threshold.
Joanna: Thanks for watching! I hope you'll join us again!
Steve: So, what's next?
Joanna: Well, I was thinking we could do something with lasers!
Steve: Oooh! That'll be fun!
Steve: So, aah, we don't need liquid nitrogen any more?
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