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PV=nRT: It's not just a good idea....
August 18, 2006 9:20 AM   Subscribe

200 liters of condensed liquid nitrogen (LN2) were delivered to Berkeley’s Condensed Matter Lab this past Monday. Sent to retrieve the 400lb dewar from the loading dock but faced with a non-working elevator, an enterprising young lab student decided to carry it down the stairs. Gravity is a harsh mistress.

If things had turned out differently, they could have been scraping his remains off the walls with a spatula. At Texas A&M in January a lab was badly damaged when someone ignored the Ideal Gas Law, removed the pressure valve and rupture disk off an old (LN2) tank and filled the remaining holes with metal plugs. "How to Tell a True Lab Story" talks about a similar incident. LN2 is good for more than just blowing up a school (or, um a watermelon), though: Spanish Chef Ferran Adrià uses it to create dishes at his restaurant. Previously on MeFI: How to make LN2 ice cream (careful!) and unwise science experiments.
posted by zarq (27 comments total) 14 users marked this as a favorite

 
Law of Gravity 1
Law of Natural Selection 0
posted by weapons-grade pandemonium at 9:34 AM on August 18, 2006


Great. Now the airlines are going to prohibit dewars of liquid nitrogen on planes as well. Nice going, Berkeley student.
posted by QuietDesperation at 9:41 AM on August 18, 2006


Even more fun than confined LN2 is LOX. If droplets of liquid oxygen are scattered on a grease-stained floor, then a hapless fool who confines LOX + grease under his shoe can potentially look forward to an explosion, beyond a mere PV=nRT expansion. (Or so I've been told).
posted by gregor-e at 9:42 AM on August 18, 2006


Abide by the law, esp. the Ideal Gas Law...
posted by Mister_A at 10:03 AM on August 18, 2006


For some reason that story reminded me of this picture:


posted by clevershark at 10:09 AM on August 18, 2006


Stupid lab tricks. Had it ruptured the inner tank, I wonder if he (she? - I have to assume only a male would attempt such idiocy) would have been suffocated by the cloud of boiling nitrogen first, or been frozen to death by gallon after gallon of 77K liquid spilling on him? I guess it depends on whether he was on the same side or opposite side of the tank from the gash. Either would be a nasty way to go. Lucky for him they build those big dewars pretty strong.
posted by Joe Invisible at 10:18 AM on August 18, 2006


Amazing for a science student to do! I was just a poor humanities shlubb and I knew better. (On the other hand, I avidly read Gravity's Rainbow and Judith Butler, which arguably did more damage to me.)
posted by OmieWise at 10:27 AM on August 18, 2006


I wonder if he (she? - I have to assume only a male would attempt such idiocy) would have been suffocated by the cloud of boiling nitrogen first, or been frozen to death by gallon after gallon of 77K liquid spilling on him?

Frozen. The LN2 and very cold gaseous nitrogen would sink rapidly. The dewar is on a stairwell landing, so the N2 would drop below the landing level, thus, the air would be breathable.

Well, until 200L of LN2, at 77K, condense out enough oxygen (boiling point, 99K), then staying alive might be a problem. I'm guessing that frozen is going to be the real answer.

Of course, Dewars are built very tough. The most likely way of dying mishandling a dewar like this is to be crushed by it.
posted by eriko at 10:32 AM on August 18, 2006


Here's a link to a link to the 9MB accident report (with pictures!) on the Texas A&M explosion.
posted by iceberg273 at 12:11 PM on August 18, 2006


hey, i was just asking about this :)

the one time we made liquid nitrogen ice cream, i was amazed at how good it was. i expected the texture to be weird but it just tasted like really good ice cream. hopefully take 2 will be a success... if it lasts the trip.
posted by jcruelty at 12:41 PM on August 18, 2006


wow. hopefully, they'll also warn undergrads about liquid helium tanks...
posted by mhh5 at 12:57 PM on August 18, 2006


Gravity, not just a good idea...it's the LAW!

Line cracks me up...
posted by bullitt 5 at 1:19 PM on August 18, 2006


clevershark writes "For some reason that story reminded me of this picture:

""


This is the ordnance and residue return dock at Ft. Hood's ASP, isn't it?
posted by IronLizard at 2:14 PM on August 18, 2006


I just don't get it. The fact that it contained cryogenic fluid aside, did the student just not realize that this thing weighed 500+ pounds and that it couldn't just be carted down the stairs? I mean, did he think it was just all empty inside or something? How did he move it from the loading dock without realizing how heavy it was?
posted by Rhomboid at 2:40 PM on August 18, 2006


Aw yeah, I never expected to see the Ideal Gas Law on Metafilter. Can we get a little quadratic equation while we're at it?


posted by beatrice at 2:56 PM on August 18, 2006


Re the Texas A&M story:

The dewar was 20" in diameter, or 10" radius.

Area = pi * radius2 = 314 in2

The engineer estimated the dewar was at 1,200 lbs/in2 when it blew. That's 1,200 * 314 = 376,800 lbs of force.

Holy shit.
posted by ZenMasterThis at 3:11 PM on August 18, 2006


[Actually, the hole in the floor was 20" diameter, and was said to be "clean" or something like that. I assumed the dewar was 20" diameter.]
posted by ZenMasterThis at 4:47 PM on August 18, 2006


Well constructed post! Thanks.

Also, fun with LN2 and a swimming pool.
posted by jiawen at 5:22 PM on August 18, 2006


jiawen's link is to an event at last year's Penguicon. That was some of the leftovers from a weekend of making ice cream out of just about everything, including caffinated coffee flavouring syrup.

Unfortunately, I left for home only a few minutes before this happened.

I don't know if they'll have another tank of liquid nitrogen next year, but reg just opened, and Penguicon is a blast.
posted by QIbHom at 8:11 AM on August 19, 2006


Area = pi * radius2 = 314 in2

The engineer estimated the dewar was at 1,200 lbs/in2 when it blew. That's 1,200 * 314 = 376,800 lbs of force.


Area also includes sides: it was at 1200 lb/in2 before it exploded. You need the surface area of the entire flask (well, the inside bit, at any rate).
posted by five fresh fish at 9:08 PM on August 19, 2006


I like the story about the elevator from the first link:

"A second-hand tale: A physics department that shall remain nameless had a brand new elevator installed, making transferring equipment up from the loading dock to the upper floor much easier. A lab doing experiments involving radiation had a large quantity of lead bricks delivered to the loading dock. Enterprising students decide to take them up to the lab, and transfer them into the new elevator, a couple at a time. After all the bricks are in the elevator (they don't take up much space...) they hit the button. The elevator makes strange groaning noises and does not move. They sheepishly realize they might have overloaded it a bit (!) and move bricks out into hallway. Try elevator again and it still won't move.

"Elevator repairman is called, and is quite distressed. He's never seen an elevator shaft with bent guiderails before..."
posted by Monday at 2:21 AM on August 20, 2006


I once was doing field circus work at a Federal Reserve Bank, when the truck came in. They told me I had to stop working and stay visible, but I'd probably want to see this.

We watched as the truck pulled in. Four guards stood at the corners, other guards were about, and I know I didn't see them all. They opened the truck.

It was carrying gold bars. Lots of them -- but not as many as you think. My minder walked me around and said "look in the back".

There was a thin layer of gold bricks -- one brick high. Why? Gold is very dense, thus, very heavy, anything more would have overloaded the truck. He asked if I'd ever held pure gold, I said not in any real quantity -- my dad had done some jewelry work, but we're talking an ounce, tops.

He talked to a couple of people (this was in the 80s, before everyone was afraid of TEH TERRAR) and they said sure, and put a small bar, face down, on the plywood deck they'd laid down to walk the gold across. (I asked why -- if they drop the gold, the bar doesn't lose much mass to scraping.)

I picked it up, and it didn't want to move. I got a good hold on it, flipped it over, and this one bar, that fit into my hand (The size was roughly 8x4x2cm, or 5"x2.5"x1.25") massed (according to the Canadian mint marks) one kilogram.

I quickly estimated the size of the truck bed -- it was about 7'x5'. So, call it 250cm x 160cm, or 40,000 cm2. Each kilo bar took up 8cmx4cm= 32cm, so in a perfect fit, 1250 bars. Assume it's not perfect, still, 1100 bars wasn't unreasonable. 1100 bars = 1110 kilos, ~2500 pounds, or one and a quarter tons of gold.

I went to hand the gold back, they said "Carefully put it down -- handing betwen people is a good way to drop it." I did, we backed away.

1.25 tons -- and the layer of gold was barely over an inch thick. The suspension and tires would have failed long before they would have been able to fill the truck, had they tried.

Come to think of it, I never worked out how much money that represented. I knew gold was dense, but you don't grok how dense until you hold large amounts of it.

So, yeah, I can see eager student lining the floor of an elevator two-three deep and overloading it. Lead isn't as dense as gold (12g/cm3, as opposed to 19g/cm3 -- compare to iron, at 9g/cm3 or aluminum, at 3g/cm3.) but it is dense enough that your "my, that may be too much stuff for one elevator" sense really doesn't kick in.
posted by eriko at 7:21 AM on August 20, 2006 [6 favorites]


Intelligence ≠ wisdom.
posted by five fresh fish at 7:32 AM on August 20, 2006


Well constructed post! Thanks.

Thanks! :) That swimming pool experiment looked cool!
posted by zarq at 2:58 PM on August 20, 2006


Aw yeah, I never expected to see the Ideal Gas Law on Metafilter.

Happy to oblige. :)
posted by zarq at 2:59 PM on August 20, 2006


How did he move it from the loading dock without realizing how heavy it was?

My guess was that it was presented to him on a hand truck or some manner of dolly/rolling cart. He might have just tried rolling it down the stairs a step at a time and lost control.
posted by zarq at 3:03 PM on August 20, 2006


Here's a link to a link to the 9MB accident report (with pictures!) on the Texas A&M explosion.

Excellent! Thanks!
posted by zarq at 3:17 PM on August 20, 2006


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