Thursday, October 13, 2016

Corpsman Chronicles XI: It's a gas

No, it's a liquid!

Sarge had an interesting post over at The Chant the other day. All about dermatology and ideal gas laws, more or less. Give it a read, it's great stuff.

His post, which featured warts and liquid nitrogen, reminded me, as everything does, of a navy story.

I have no idea how they do things in the navy these days, but BITD you couldn't operate tactical aircraft without LOX (liquid oxygen) for aircrew breathing and very pure nitrogen for tire inflation and pneumatics. I think liquefied gas was also required for Sidewinder and avionics cooling, but I disremember exact details. (A quick dash through googleland leads me to believe that early AIM-9 models were uncooled, followed by CO2, then LN2 cooled versions. Today's AIM-9X actually has an onboard Stirling engine to provide cooling. Which I have to admit is very cool (pun intended, sue me.)) At any rate, every carrier and air station had an O2/N2 shop BITD.

Here is a short video of activity in USS Saratoga (CV-60) in 1985. Brings a pang of longing to the old heart. You can see some gas servicing and work on LOX carts.

If you're interested, here are navy press corps stories from 2003 and 2015 regarding O2/N2 production.

Making LOX and LN2 (liquid nitrogen) is a fundamentally simple process. First, you liquefy plain ol'/reg'lar ol' atmospheric air by taking advantage of the Joule-Thomson effect, which is basically how your refrigerator-freezer works. You compress the air to about 150 psi, then flow it through an orifice into a container. As the compressed gas expands its temperature plunges, and if you do it right with the right setup the air becomes cold enough to liquefy.

The liquefied air, just like ambient atmospheric air, is about 78 percent nitrogen, 22 percent oxygen, and the remainder noble gasses, hydrogen and helium, and carbon dioxide. There will also be some quantity of water present, depending on the humidity of the air when it was collected.

Separating the molecular components is rather complex in execution but simple in theory and is called cryogenic fractional distillation. That's a mouthful, but you've probably done fractional distillation in junior high or high school science or chemistry lab. The process is the same and relies on the unique properties of the various components, or "fractions,"  each of which boils (shifts from liquid to gaseous phase) at a different temperature (CO2 -57C, O -183C, N -195.8C, H -252.9C, He -268.9C). By carefully warming the liquefied air in precise increments you can remove the pure "fractions" as they "boil off." For the purposes of making pure molecular fractions the water component is considered a contaminant. Water boils at 100C, but it's usually filtered out rather than boiled off.

With the right equipment and correct procedures in place, making LOX and LN2 is dead simple. As I recall the navy O2/N2 plants bitd were operated by a couple of E-2's under the supervision of an E-3.
Filling a LOX cart in CVN-72. Image wickamaedia commoners.

But I digress.

As Sarge alluded to in his post, LN2 is also used in medical cryotherapy, including the removal of superficial skin growths such as moles and warts.

Warts are caused by a virus, which takes up residence in the outer layers of the skin and cause formation of rough growths. Warts are, by definition, benign, self-limiting tumors. In most cases they can be safely ignored, however, they can be cosmetically unpleasing and/or physically irritating. In some rather rare cases they can lead to less benign forms of cancer. For these reasons people often seek to have warts removed, and one approach to this is cryotherapy.

Cryotherapy is a big word, but the idea is simple and straightforward. Warts -- including the HPV (human papilloma virus) which causes them -- are present in the outer layers of the skin. In cryotherapy a freezing agent such as LN2 is applied to the wart and a small portion of the surrounding healthy tissue. This freezing causes a thermal injury which is little different than a second degree burn. The frozen area blisters, which lifts and separates the outer layers of the skin. During the healing process the outer layers slough off, taking all or part of the wart with them. Small warts may be cured with a single treatment, larger warts usually require a series of treatments over time.

There's gonna be an amusing navy story at some point, right?

On the beach at Oceana, when I was an E-3 for the first and second time, I worked mostly in sick call. I stood duty back in the ER, but my regular daily job was sick call. As with most noobs I started at the check in desk, then advanced to vital signs, and finally to seeing patients and doing patient care. I wasn't the dumbest corpsman to come down the pike so I ended up in patient care pretty quickly. Which does not mean that I was in any way smart. I lacked the experience to be anything other than stupid.

Small digression here, I was reading a story from "We Were Crewdogs III" the other evening and I came across a superb line. "I was pretty stupid back then, and might still be, but that's for another book." J.J. Parker, USAF.

One day a week at sick call -- I want to say Tuesday but I'm probably wrong -- we held wart clinic. We dealt with all kinds of warts, and for each kind the treatment aim was quite similar, that is, to gradually take away the wart and a small bit of surrounding tissue a little at a time until the wart was gone. Treatment techniques varied. Most could be treated with LN2 and cryotherapy. Some required electrocautery. Still others relied on the application of a caustic or acidic compound, such as salicylic acid or podophyllin.

On wart clinic days, directly after morning quarters, a couple of the sick call E-3's would be sent to collect liquid nitrogen. When I was on the beach my number was usually chosen. So myself and another fellow would check out a vehicle, grab the LN2 containers, and head for the O2/N2 shack. The LN2 containers were Stanley stainless steel thermoses. They didn't have stoppers, which were air tight and would have turned the containers into bombs, but they did retain the screw-on cup, which wasn't air tight. Each thermos was housed in a clever, varnished wooden box with a wide base, designed to hold the thermos vertically and prevent it from tipping (or being knocked) over.

On the ship the process for collecting LN2 was pretty much the same, except you walked to the O2/N2 shop, rather than driving.

But this first one is about wart clinic on the beach, at Oceana.

We did all the usual stuff, freezing and smashing all manner of objects, from superballs to flowers to latex gloves to insects and amphibians. But that got boring pretty quick.

What was fun -- really fun -- was making LN2 bombs.

It's a simple process, really. Take an empty hydrogen peroxide container. You know, the small brown plastic bottles with white caps. They look like they hold between a pint and a quart of peroxide, but they actually hold a pound of the fizzy stuff. Well, that's how they were measured and labeled back in the day anyway.

So, to the empty H2O2 bottle add a few ounces of LN2. Screw the cap down tight, then place the container out of sight but in rather close proximity to some of your co-workers. It's best to do this after hours when just the duty section is in the building, for obvious reasons. Then it's just a matter of waiting.

The peroxide containers are perfect for this job because they are built to be tough enough to take quite a bit of internal pressure and the caps are designed to vent a certain quantity of gas. This is because H2O2 naturally decomposes over time, releasing gaseous molecular oxygen.

The important point is that a peroxide bottle is a lot tougher than a regular plastic bottle, and will therefore contain a lot more pressure before failing. When they do fail, well, more pressure equals bigger boom.
Potential boom of doom. Just add junior sailors. Stolen from the interwebs.

Few things are funnier than the reactions of your shipmates when the quiet of late evening is split by the roar of a reverberating LN2 explosion.

One thing that is funnier is when the explosion occurs at the moment an O-8 (Rear Admiral) is checking in to the emergency room to have a laceration on his hand treated.

I'll leave it to your imagination, but I will note that back in the olden days, not every Admiral was a pure martinet, and some of the lower ranked enlisted folks could think and explain with lightning speed and sincerity. 

I've saved the best (or worst) for last.

This happened on Nimitz on my first deployment. I was a reasonably bright lad and my head was absolutely crammed with knowledge. At that point in my life I had little or no experience to go with the knowledge, so while I thought I was pretty smart, I was in fact pretty stupid. From time to time dangerously stupid.

Anyway, one evening following wart clinic I was on duty and tasked with straightening up the treatment room at the end of the day. The LN2 thermos still contained a few pints of liquid nitrogen, which, being a clear liquid, looks rather like water. I was in straightening/cleaning mode and decided to dump the LN2 down the drain of the treatment room scrub sink. This produced a small cloud of water vapor, and as I turned on the taps to flush the nitrogen down the drain the cloud grew and grew until it filled the treatment room with fog.

That was cool!

Thereafter, whenever there was leftover LN2 available I repeated the exercise. What can I say? The days underway are long and tedious and can be crushingly boring. Little things like a cloud of vapor can provide a bright spot in the midst of the interminable blah sameness of being at sea. A real boost to morale, you might say.

After several weeks of this, however, the treatment room began to smell funny. Then the drains began to back up. Ruh-roh.

Bring on the turd chasers! Turd chaser was the common nickname for Hull Technicians, or HT's. Among other things, they were in charge of the ships plumbing system. Of course there are no more HT's in the navy these days. Everyone is now a sojer.

At any rate, the turd chasers quickly found and solved the problem. The drain piping beneath the deck plates had, of course, broken when the LN2 I poured down the sink froze the water in the p trap. Water expands when it freezes, as we all learned in Kindergarten. This was knowledge I'd long possessed, however, it didn't spring to the fore in my mind until we were all examining the broken fitting. Remarkably, no one in the immediate chain of command was able to connect the dots between wart clinic and a frozen pipe. And I wasn't about to give any hints.

You might recall that some time passed between the beginning of my magic fog show and the drains backing up. IIRC it was two months or so. Where did the water go?

Well, a Nimitz class carrier is a warship, built to soak up damage and still operate. The drain piping beneath medical was contained in an armored chase, about two feet by two feet by 150 feet. As it turns out, that chase can hold a hell of a lot of water.
Dewatering. Wickimaedia commoners.

It wasn't quite this bad.
And there you have it, a couple of Cold War cold air sea stories.

Foot report

Since my last post I've been quite ill. Fighting this kind of thing is not for sissies and takes a lot of energy. Right now it's looking like MRI time tomorrow followed most likely by the knife. I'm not dead yet, though on Tuesday I thought dead might be a desirable improvement. Felt a good bit better yesterday and today isn't too bad so far. I'll sure be glad to get this behind me.


  1. Remarkably, no one in the immediate chain of command was able to connect the dots between wart clinic and a frozen pipe. And I wasn't about to give any hints. - Yup, sprayed the monitor on that one.

    1. Heh. Fortunately for me, stupidity did not entirely counter the survival instinct. ;)