What does a hospital do with a truck of liquid oxygen?

August 29, 2009 7:28 PM

What is the hospital doing with a truck of "oxygen refrigerated liquid"?

I live next door to a large hospital. Every Saturday evening, a large truck labeled "oxygen refrigerated liquid" pulls up, hooks up some tubes and makes a LOT of noise (a loud sort of rumbling noise). It appears that they are flooding a hallway with this stuff - it seeps out in clouds from the open door.

When they finish, you can hear them hitting the tubes to disconnect them, since they've frozen to... something. There's also a sound that could be described as a hissing or water running through pipes.

So all this leads my boyfriend and I to wonder: are they freezing bodies? Storing the oxygen? Preventing a zombie uprising?

Can anyone explain what exactly they are doing? Any guesses?

Here are some pictures of the mysterious operation taken from my apartment window:
One.
Two.

posted by Amanda B to grab bag (19 comments total)

MRI needs liquid nitrogen.
posted by sciencegeek at 7:32 PM on August 29

It's liquid oxygen, which is turned into oxygen gas and used to help patients breathe. For some reason the people who move around gases use weird terminology -- "oxygen refrigerated liquid" means "refrigerated liquid oxygen."

Your hospital also gets liquid nitrogen delivery trucks (as does practically every large bar or fast-food restaurant). It might get some liquid helium too, though I think that usually comes in much smaller amounts. Oxygen is the only one with flammable warning signs all over it.
posted by miyabo at 7:44 PM on August 29 [3 favorites]

Actually, NMR needs liquid nitrogen, I'm not sure that MRI does as well. But I'm pretty sure the liquid you're seeing being pumped into the building is liquid nitrogen. It is used to cool things - I've used liquid nitrogen freezers to keep cells frozen as well as quick freeze various protein samples.

Things I can think of in a hospital that need this kind of cooling: sperm, and tumor bank.

The weekly deliveries are likely to be to fill up a big tank in the hospital.
posted by sciencegeek at 7:44 PM on August 29

Actually, NMR needs liquid nitrogen, I'm not sure that MRI does as well.

According to Wikipedia, the most common type of MRI today uses liquid helium:

When a niobium-titanium or niobium-tin alloy is cooled by liquid helium to 4K (−269°C, −452°F) it becomes a superconductor, losing resistance to flow of electrical current. An electromagnet constructed with superconductors can have extremely high field strengths, with very high stability. The construction of such magnets is extremely costly, and the cryogenic helium is expensive and difficult to handle. However, despite their cost, helium cooled superconducting magnets are the most common type found in MRI scanners today.
posted by sbutler at 7:50 PM on August 29

There is a gap in the text on the truck, so it's more like "Oxygen. Refrigerated Liquid", which makes more sense. The truck probably carries liquid oxygen (and/or liquid air, which includes liquid oxygen), which is dangerous in those two distinct ways: it's a powerful oxidiser, and it's very cold.

Hospitals can use liquid oxygen as a compact source for gaseous oxygen. They also use liquid nitrogen to freeze things very deep and very fast, and that might well be delivered by the same company. Lets assume it's nitrogen.

The rumbling is due to the nitrogen boiling as it enters the initially warm pipes. The boiled off nitrogen lost this way has to be released, possibly causing a hissing sound, and as this very cold nitrogen gas mixes with and cools the warm water-vapour laden air in the building it forms the cloud you see.
posted by Canard de Vasco at 7:56 PM on August 29 [2 favorites]

Not an answer to your main question, but the stuff "seeping out in clouds" is not the oxygen itself, but water vapor from the air which condenses when the air is cooled.

Your hospital also gets liquid nitrogen delivery trucks (as does practically every large bar or fast-food restaurant).

Uh, what? OK, it's been 20 years since I worked in fast food, but I don't think things have changed that much since then. And we certainly didn't use liquid nitrogen for anything. And this was at a chain that specialized in frozen treats. All we used to keep things cold were a walk-in cooler and a walk-in freezer, which were no colder than your refrigerator and freezer at home, respectively, just much larger.
posted by DevilsAdvocate at 7:57 PM on August 29

My guess - refilling the oxygen supplies at the hospital. Hospitals use a LOT of oxygen.

On a side note - MRI uses liquid helium to get the superconducting magnets to do their thing... that's much colder than liquid nitrogen.
posted by TravellingDen at 7:58 PM on August 29

miyabo writes "Your hospital also gets liquid nitrogen delivery trucks (as does practically every large bar or fast-food restaurant)."

Bars and operations selling pre or post mix pop/soda get compressed gaseous CO₂ not liquid nitrogen. Or at least in Canada I've never seen a nitrogen dewar in a restaurant or bar. Middlin' big operations are starting to run CO₂ concentrators instead of bottled gas because it's cheaper in the medium long run and it is much safer (no potential rockets just waiting for a valve to get knocked off in the storage room).
posted by Mitheral at 8:10 PM on August 29 [1 favorite]

It's just a convenient way to deliver oxygen to the hospital. It comes in as a liquid, it evaporates and becomes gaseous oxygen, patients breathe it. If they delivered oxygen as a gas, it would take many trucks to deliver the same amount. Yeah, it's kinda spooky with the clouds, the clanking, and all, but it's really OK. Nothing to be concerned about.
posted by exphysicist345 at 8:10 PM on August 29

Devils -- I googled around and it looks like bars and restaurants get liquid CO2 delivered, not nitrogen. I didn't even know liquid CO2 existed. My bad!
posted by miyabo at 8:16 PM on August 29

Thanks everyone! Mystery solved!
posted by Amanda B at 8:18 PM on August 29

Yep, as others have noted, MRI and NMR both use superconducting magnets (which is why you should never, ever take metal anywhere near them—it can very quickly turn into shrapnel). Currently-known superconductors only retain this property at very cold temperatures. Thus, liquid helium is typically used to keep them cold. Most refrigeration equipment is not powerful enough to reach temperatures that low (−268 °C), but the nice thing about liquid-phase gases is that, as long as they’re under pressure, they'll stay a liquid regardless of temperature. Thus, it's more economical to have liquid-phase gases shipped on site than it would be to install hard-core refrigeration equipment around the MRI.

Liquid oxygen is not as cold as liquid helium (-223 °C). As others have noted, it’s most likely being used directly, to supply oxygen to patients with respiratory problems, and to mix with anesthetic gases during surgery. Gases take up a lot more space than liquids, so it's easier to ship them in liquid form.
posted by dephlogisticated at 8:26 PM on August 29 [1 favorite]

Bars may use compressed nitrogen to dispense some beers, like Guinness draft, but I seriously doubt they are getting it delivered as a liquid. CO2 on the other hand, turns liquid at room temperature at ~1000psi.

If the truck says liquid oxygen, I don't know why people would assume that it would be liquid nitrogen instead. The authorities are pretty picky about labeling hazardous materials, and while both are very cold, liquid oxygen presents dangers that liquid nitrogen doesn't.

Oh, also, liquid nitrogen is often used to help keep liquid helium cold because it is a hell of a lot cheaper.
posted by Good Brain at 8:27 PM on August 29 [2 favorites]

So all this leads my boyfriend and I to wonder: are they freezing bodies? Storing the oxygen? Preventing a zombie uprising?

They're giving it to patients. Nearly all patients who spend more than about twenty minutes in the hospital are given oxygen at some point. Ever had laughing gas at the dentist? They gave you oxygen as well (to prevent suffocation and to calm you).

I'm actually surprised you would have considered anything else. But, I guess not everybody has a doctor for a mother and a nurse for a wife.

If the truck says liquid oxygen, I don't know why people would assume that it would be liquid nitrogen instead. The authorities are pretty picky about labeling hazardous materials, and while both are very cold, liquid oxygen presents dangers that liquid nitrogen doesn't.

Seriously.

There is basically zero chance that a truck labeled "oxygen" is going to carry anything but oxygen. Just no way. The people who handle gas deliveries are utter and complete sticklers about this. Mainly because the federal government will fine your company into oblivion for mislabeled hazmat shipping. And liquid or compressed gasses, of any sort, are considered a hazmat for the cold and pressure issues.

On a side note - MRI uses liquid helium to get the superconducting magnets to do their thing... that's much colder than liquid nitrogen.

What's more, the helium in a modern MRI is constantly reused and recompressed. Losses are quite negligible. I've heard a figure like they top it off once a year. Instead, the heat is transferred to liquid nitrogen, which is allowed to boil off in a greater measure. Because nitrogen is really, really cheap as compared to helium--nitrogen is available from the air, helium is pretty much only available from oil wells.

Bars may use compressed nitrogen to dispense some beers, like Guinness draft, but I seriously doubt they are getting it delivered as a liquid. CO2 on the other hand, turns liquid at room temperature at ~1000psi.

I imagine that bars who're dispensing nitrogenated beers are receiving cylinders of compressed, but not liquid, nitrogen.

They're definitely receiving liquid CO₂, though.
posted by Netzapper at 9:12 PM on August 29 [3 favorites]

Yes, (larger) fast food restaurants receive liquid CO2. It's much more convenient and cost effective than trying to cart around bottles. As has been stated, it will exist in three phases if there is enough pressure. Fun fact- the instructions for the giant CO2 containers inside the restaurant have a procedure if you have to make a repair to the valve on the top of the tank, and you can't wait until the vessel is empty. You vent it outdoors as some fast rate, and the pressure drop will be fast enough that most of the liquid in the tank will turn solid. Then you can take the top off and make the repair. As soon as you put the top back on, pressure builds and it turns back into a liquid.
posted by gjc at 10:01 PM on August 29 [1 favorite]

This is liquid oxygen. As an in-home health worker, I've seen this delivered to houses on a much smaller scale. A van pulls up, hoses come out the back, hook to a liquid oxygen tank in the house, and make a lot of noise as the pressurized oxygen is pumped into the tank. There is some smoky-foggy stuff that occurs on the hooking and unhooking of the tank. This is condensation from the extremely low temperatures of the O2. When the O2 is released it is depressurized and instantly turns to its gaseous form. It is a way to condense O2 into a small space for storage.
posted by Bueller at 10:06 PM on August 29

@sbutler, the new Magnetom Trio in the Beckman Institute does indeed use helium.
posted by Eamon at 10:53 PM on August 29

gjc, that's more of a temperature effect than a pressure effect. Venting gas increases the evaporation rate of the liquid in the tank, cooling it. With enough evaporation, the liquid CO₂ freezes into dry ice. While you carry out your repairs, the dry ice sublimes directly into gas, keeping the mass cold. After the valve is repaired, the pressure in the tank increases, lowering the rate of sublimation. This stops the cooling effect, allowing the dry ice to warm up and melt into liquid CO₂.
posted by ryanrs at 1:39 AM on August 30

The reason the trucks say

OXYGEN

REFRIGERATED LIQUID


is that they're all painted with the "Refrigerated Liquid" part upon manufacture, and then the specific gas to be transported (oxygen, nitrogen, helium) is painted in later.
posted by Sidhedevil at 12:40 PM on August 30 [2 favorites]