Pelican's Perch #13:
Getting High on Welder's Oxygen
Having problems finding Aviator's Breathing Oxygen to refill your bottle? Upset about the rip-off prices some FBOs charge for an O2 fill? Don't put up with it, says AVweb's John Deakin, who explains why it's perfectly safe — and perfectly legal — to use cheap welder's oxygen, and tells you exactly what you need to know to buy it in bulk and do your own refills.
Can't breathe welder's oxygen? Aw, horsefeathers, as my dad used to say! Show me the rule!
Oxygen is oxygen. It is the substance that matters, not the intended purpose. These days, welding, medical, and aviation oxygen are exactly the same. All three come from the same tank of liquid oxygen (LOX). The liquified form is the cleanest, purest, driest form of oxygen (or any substance) you'll find anywhere.
Oxygen, Oxygen, Who's Got the Oxygen?
For many general aviation pilots, oxygen is so difficult to find, so much trouble to buy, and so expensive that many pilots wind up flying at lower altitudes without oxygen, when higher (with it) would be safer, and more comfortable. I know. I used to be one of them. Before I set up my own filling system, I frequently flew multiple long legs without being able to get a refill, and usually had to make special stops for it. Either oxygen was not available at all, or there was no one available to do oxygen fills on weekends or after hours. Of course, any suggestion that I might do it myself was instantly met with looks of horror, tales of insurance requirements, and citation of "rules."
Without oxygen being readily at hand, many pilots will also "push" their own personal altitude limits, often not having the faintest idea what those limits really are. It's awfully easy to take the macho approach and think "I can handle it"— and go on up to 10,000 feet, 12,000 feet or higher without it. (Some need it above 5,000 or so!)
Unless you have been through a good altitude chamber course, or you carry one of the wonderful little Nonin Onyx pulse oximeters that monitor the actual oxygen saturation of your blood, it is very unlikely you will truly appreciate how quickly human performance degenerates, and the extent to which pilots are unable to detect any loss of ability. This means you, not the other guy!
NOTE: Other related articles on the subject include Respiration: What Pilots Need To know (But Aren't Taught) and Altitude Decompression Sickness: Tiny Bubbles, Big Troubles.
In my opinion, a cheap, readily-available source of this gas will make cross-country flying much safer, and often smoother and more pleasant. In my mind, this enhancement to safety would far outweigh the very remote risk of getting oxygen with harmful impurities in it . . . IF there were any more risk from using "welding" oxygen (which there isn't). In this column, I'd like to explore some of the issues involved in spending a few hundred bucks to set up a safe, cheap, and effective personal oxygen refilling system.
Those Blessed Rules
Readers should be aware some of this advice may violate various rules of your hangar landlord, your airport, the EPA or others. It is pretty clear to me that nothing here violates any FAA rules, but your FSDO may have a different interpretation (as FSDOs are inclined to do). So proceed at your own risk.
For all the OWTs (old wive's tales) surrounding oxygen, there is remarkably little in the FAA and DOT publications, or even the old CARs and CAMs (pre-FAA). I have searched extensively, and can only find a very few citations, most of them from very old publications that are well out of date today. None of those publications are "regulatory," only "advisory."
I found the following notation in Advisory Circular AC 43.13-1A (Acceptable Methods, Techniques, And Practices — Aircraft Inspection And Repair):
Use only aviation breathing oxygen when having the oxygen bottle charged. MIL-O-27210C specifies that the moisture content of aviation breathing oxygen must not exceed 0.005 milligrams of water vapor per liter of gas at a temperature of 70° F and a pressure of 760 millimeters of mercury.
Good rule. It is easily satisfied by the modern methods of oxygen production.
The real nub of the issue is found in AC 65-9A (Airframe And Powerplant Mechanics General Handbook) which is some 25 years old now, and this is as good a place as any to extract a few words of wisdom:
Cleaning compounds for use in the oxygen system are anhydrous (waterless) ethyl alcohol, isopropyl (anti-icing fluid) alcohol, or a mixture of freon and isopropyl alcohol. These may be used to clean accessible components of the oxygen system such as crew masks and lines. Fluids should not be put into tanks or regulators.
It is imperative that the highest standard of housekeeping be observed in handling oxygen and that only authorized persons be permitted to service aircraft.
Here's the biggie, in my opinion:
Only oxygen marked "Aviators Breathing Oxygen" which meets Federal Specification BB-0-925a Grade A or equivalent may be used in aircraft breathing oxygen systems.
I have underlined "or equivalent" in the above citation because in the final analysis it is the legal loophole that clears the muddy water as if by magic. Some really heavy-duty experts have scoured government documents, and queried many government agencies, trying to find out just what the heck "equivalent" means in this context. Its meaning appears to be nowhere specified, which leaves it up to the user in my opinion (and the opinions of those with whom I've consulted).
All that said, there are still a lot of "experts" out there — including medical doctors, gas suppliers, and others who have not researched the issue — who will parrot the old rules for three types of oxygen. When you are faced with these folks, a simple "Show me the reg, please?" will keep them busy for months while you go flying with your self-filled tank.
There is also the possibility that a "bad" FAA Inspector will choose to make a problem, and violate you for using "filthy welder's oxygen" instead of Aviators Breathing Oxygen (ABO). It's very doubtful the violation would be approved at higher levels, but it's better to just be discreet about it. Yes, it's legal, but some in the FAA won't know that.
This subject got beaten to death in CompuServe's AVSIG aviation forum some time ago, and a senior FAA Inspector in Washington took the bone in his teeth and ran with it, to satisfy his own personal curiosity. The following is a direct quote when he sort of tossed in the towel after a lot of research over many months:
Fm: Rick Cremer FAA HQ 72130,3305
To: George W. Braly [ADH] 72311,556
George, I talked and talked to all the "right" people in the FAA including the aircraft certification people in ICT and here in HDQ, the maintenance people, etc. And NO one can point to a regulation or AC that says "exactly" that you must service an oxygen system with a specific kind of oxygen. People always start the conversation with "you should use....". Then I say "should or must and what reg says that". Then....silence.
The bottom line is, until someone can show me something more specific than what I have seen and heard thus far, I would say that we have no regulation that requires that a specific kind of O2 be used to service an O2 system on a airplane. That is my position, someone in the FAA may disagree with that. If I were a field inspector (which I once was) I surely would not be taking enforcement actions on people for alleged O2 violations.
This may be one of those questions that should be sent on to the Chief Counsels office for a thorough review and answer. Would you like the address?
Best Regards, Rick Cremer
The reality is simply that it all comes from the same tank. It's all the same. Some folks just slap an ABO label on the tank and charge higher prices because there may be a greater liability, or simply because it's aviation-related.
Some Reasons ... and Dangers
Why is this stuff so hard to find, when it's in the very air we breathe? I think there are a lot of factors. Where there used to be multiple FBOs at some airports, now there is just one, and sometimes none at all. Without competition, there is little incentive to provide "services" for pilots unless they are very profitable. The FBO needs to sell something that almost everyone will need, with as little time, trouble, risk, and manpower expended as possible. (Can you spell "self-service fuel"?).
Commercial oxygen refilling systems are troublesome, take a fair amount of care and operator training, do not provide much profit margin, and incur a fair amount of liability on several fronts. There is some danger in just having oxygen cylinders present, much more danger to those using the system to replenish a customer's system, and all this creates liability that must be assumed or insured against. There is also the very real exposure of getting sued by the customer for some real or perceived fault of the fill or the gas. I suspect the quite-reasonable attitude of many FBO owners is, "Why bother for a couple fills a month, when folks will only bitch at the price anyway?"
For those FBOs who do supply the service, the price they charge must be high enough to at least help cover the costs.
The real cost of the gas itself is just a few pennies per fill, but the real cost to the FBO is much greater: perhaps $1,000 invested in the equipment, perhaps some additional liability insurance premiums, and the lost time of an employee (often an A&P mechanic). By the time a mechanic stops what he was doing, gets to the aircraft, removes the bottle or finds the filler port (some are incredibly hard to get at!), does the fill, reinstalls the bottle (if necessary) and returns to his work, it's easy to lose an hour of shop time. Either the customer needs to pay for that, or the FBO needs to "eat" it as a "customer service," hoping the customer spends enough money on fuel and other things to make up for the loss.
Oxygen cylinders and filling systems have the very real potential to cause injury or death if not handled and used properly. All the containers, from the big green cylinders to the smallest portable bottles, are quite literally very powerful bombs capable of creating an incredible blast, with damage for hundreds of yards. Fortunately, they don't explode very often, but when they do, it's ugly. The movie scene where the scuba tank exploded in the mouth of "JAWS" was not overdone in respect to the violence of a 2,000 PSI tank exploding! Even if it's just a hose blowing or breaking, great injury can occur.
I once watched from a distance as the main filler hose on a "cascade" system broke on the supply end, with the filler end connected, but the valve turned off, pressurizing only the filler line. As the broken hose expelled the 2,000 PSI oxygen in the line in a second or two, that hose was a lethal weapon, flailing around much too fast for the eye to follow. Fortunately, the mechanic had walked away for some reason, and no one was hurt. Had it been the filler end that broke, or had the fill valve been open, the flailing hose would have made it impossible to approach the system until the tank ran out.
How It's Made
Ok, warnings out of the way, just what is this stuff, anyway? I'm not going to get into the dull chemistry of it, but there are some interesting tidbits. First called "dephlogisticated air" (love that word!), oxygen was first "discovered" in 1774 by Joseph Priestley, an English clergyman, who extracted it by heating mercury. Just what the heck he was trying to do heating mercury is unclear, but the gas that boiled off sure did make fire burn a lot better, and he later discovered it would support respiration. (Hmmm, just how did he "discover" that? Sounds like a modern doper looking for a new high!)
In 1895, Carl von Linde perfected the current method by which all oxygen is produced commercially. Plain air is filtered, then alternately compressed (and thus heated) and cooled in several stages, until it is at about 2,000 PSI and 70º F. Water is drained at each step as it condenses out, leaving the moisture content at near-zero.
Then the long, complex process of cooling the air begins, with several different systems used to bring the stuff to -275º F, and partly by dropping the pressure to about 90 PSI, where everything except the oxygen and nitrogen is frozen, and filtered out. By playing with the temperatures, the oxygen vapor is boiled off, captured, cooled again to the liquid state, and stored in special double-walled containers for transport.
Key point, here. That 90 PSI oxygen must then be re-compressed, and this is the point that led to all the hang-ups over "welding, medical, and aviator's" oxygen. In years gone by, there were several ways to do this. Breathing oxygen (medical and aviator's) was compressed by water-sealed compressors to reduce impurities added, and that nasty old welder's oxygen might have been compressed by machinery using oil for lubrication. This is what led to the old "Welders," "Medical," and "ABO" differences of decades past.
But modern industrial processes demand gases that are at least as pure as breathing gases, so the old ways died out, and compression is now universally done by the same compressor, using dry lubricants and the same standards of purity and cleanliness for all oxygen.
When the LOX truck pulls up to your local supplier, that oxygen is, by definition, the good stuff. It is 99.6% pure, with the remaining 0.4% being mostly Argon, a harmless gas, and it is utterly clean and dry. The by-product, liquid nitrogen, is 99.96% pure, but most of it is simply discarded as harmless waste. We humans use a lot more oxygen than nitrogen.
I have to laugh at some folks who insist that ABO is somehow "cleaner" than other oxygen, when they live in the Los Angeles basin, or in some of the other big cities, and the pollution level is broadcast hourly. Please, give me some of that "polluted oxygen" that is only 99.6% pure!
There are a couple other processes that can be used to get oxygen in the lab, but they are too troublesome, and too expensive when producing large quantities, so all industrial and breathing oxygen is now produced by this method, making the old terms obsolete.
As a side note, have you ever noticed in the hospital, when patients need oxygen, they must bubble it through a jar of water? This is because the absolutely dry stuff, as it comes from the supply tanks, is harmful (or at least uncomfortable) to human tissues when breathed for long periods, and must be humidified first. So much for the OWT about moisture in ABO (Aviator's Breathing Oxygen).
Truth be told, we pilots would probably be better off doing the same, as breathing oxygen can be dehydrating, at altitude. But classically, ABO has had a maximum limit of 0.5% moisture, ostensibly to keep it from freezing at altitude. Note that many systems are kept inside the cabin, where freezing temps will not occur. Some airplanes have bottles in non-pressurized, or non-heated areas, of course, but with modern oxygen, it's simply a non-issue.
Some people express concern about the drop in temperature caused by the drop in pressure when the oxygen flows through the needle valves and regulators. This is also a non-issue, because the flow is so slow that there is very little cooling of the metal taking place. If you simply open the valve and let the bottle exhaust itself into the open air, then you will see chilling, and perhaps a bit of frost on the outside of the hardware, but this is from the cold metal condensing moisture in the ambient air, not moisture from the oxygen coming from the tank. The tank temperature will also drop with the rapid pressure loss. However, this is not the way we use the system, unless you're trying to cure a hangover, in which case you should refill the bottle on the ground, anyway.
Fire in the Hole!
Oxygen itself doesn't burn, but a blast of it, combined with fire, is spectacular. Daredevils might take a couple of breaths of oxygen, then blow through a lit cigarette, and produce a violent flame several feet long. (Don't try this at home, and if you do, don't inhale!) Much of the literature cautions against mixing oil and grease with oxygen, which is a very bad thing. At normal atmospheric pressure it might not hurt, but there are many hydrocarbons that will burst into a violent fire spontaneously when exposed to oxygen under even low pressures. Oil and grease are the worst at doing this. If in a contained space, the sudden over-pressure may cause an explosion and an intense fire, as three astronauts found out during a simulation in a pure oxygen environment.
So it can be very dangerous stuff, which leads us right back to the dangers, concerns, and liabilities incurred by FBOs who do provide oxygen filling service. It is also my intention here to give pause to those considering setting up their own refilling systems. You must understand fully what you are doing and be careful, otherwise you might get hurt. Of course, that's equally true of many other aspects of the flying machines we love, so we need to understand the tradeoffs.
Rolling Your Own Oxygen
Your first step is to get at least a pair of the big, heavy tanks of oxygen. They're painted a dark green for easy identification, and contain somewhere between 220 and 250 cubic feet of the gas at 2,000 PSI. They're about four to five feet long, nine inches in diameter, and heavy (about 150 pounds when full). Two of them allow "cascading," where you first fill your airplane tank from one, then "top it off" from the other. The tank you use first drops in pressure much faster. After many dozens of refills of my small bottle, one of my tanks is down to about 1,000 PSI, the other one is at about 1,500 PSI which is now the highest "charge" I can get. It is time for me to swap the low-pressure tank for a new one, which will become the "topoff" tank. By the way, this will be my first tank change in over three years!
Any local industrial gas supplier can help you with getting these big tanks, and will usually have a variety of plans. (Look under "welding supplies" in the Yellow Pages.) You can lease the cylinders with some sort of plan to exchange, you can rent, or, as I did, you can purchase them outright. I paid about $175 each for two of them, with the agreement that I can just swap an empty tank for a full one any time I want for less than $20. That's not a typo, for you folks used to paying up to $50 for a refill of a small, portable bottle! You may do even better in price if you work your way up the food chain to the central distributor for the area.
I strongly recommend that you not get into a conversation with the supplier about why you need oxygen, and that you definitely do not mention you intend any aviation use! That is an instant red flag, and many will balk at the liability, or not understanding the situation, will insist "sorry, we can't do ABO." Just be very matter-of-fact and, if pressed, tell 'em it's for your home welding shop and let it go at that.
When you transport those tanks, be careful! If one falls over and happens to break the valve assembly off, the tank can turn into a rocket-powered missile and do great damage. Put the bottom of the tanks forward in your vehicle, and secure them so that even if you have an accident, they'll be as safe as you can make them. Try not to hit anything on your drive from the gas supply house to your hangar. The thought of having an accident, with smoking metal, and then having a whole tank of oxygen spraying all over the place is worse than a horror movie.
For similar reasons, give some thought to where you store the big tanks in your garage, or hangar. I prefer to lay 'em down flat, so they can't fall over, and chock them, so they can't roll around. Put them where nothing can fall on them.
Any discussion of using oxygen and flying would be incomplete without mentioning several fine vendors of oxygen supplies.
|Mountain High Equipment & Supply, Inc.
Salt Lake City, UT 84103
c/o Precise Flight, Inc.
63120 Powell Butte Road
Bend, Oregon 97701
|AEROX Aviation Oxygen Systems
200 Dillon Road
Hilton Head, SC 29962-3742
These outfits are run by excellent, truly helpful people, who will spend copious amounts of time on the phone, and who will go far beyond the call of duty to satisfy even the most difficult customer.
Mountain High sells the key to the personal oxygen filler system, a "Transfiller." This is the device that hooks between the big supply tank, and your little one. There are several models available, priced from well under $100 to about $250. All are very well-made from the very best material; the difference in price is solely due to the difference in features, not quality.
Don't stint on the cost of this device, or settle for less than the very best! It really needs to be made to the highest industrial standards, as this is the part that will most likely hurt you if it fails. The hose must be as short as possible, to keep it from flailing too much if it does fail. The Mountain High Transfiller hose is about 18" long, just enough to work with easily, yet short enough to be safe.
The least expensive Transfiller is simply a hose with an appropriate fitting at each end, one with an o-ring, one with a nipple that fits metal-to-metal. You hook it up between one big tank and your small one, turn on the valves one at a time (slowly, please), wait for the pressure to equalize, and turn off both valves. I don't like to blast the gas in, but if you take about ten seconds for the equalization, you'll be fine. Little or no heating takes place, as the gas is already at pressure in the big tank, and you're just equalizing it with the small tank. Whatever gas is already in the small tank gets compressed, and this may warm it very slightly to the touch. At this point, with both valves closed, you must be careful to loosen the end without the o-ring first, because there is high pressure still trapped in the line, and if you loosen the end with the o-ring first, you'll destroy the o-ring, and have to replace it. Crack the fitting, and let the pressure vent. The hose is then hooked to the next big tank in the "cascade" and the process is repeated. It works, but it's a little clumsy.
The best Transfiller (naturally, the one I like the best, at about $250) comes with o-rings in each fitting, and a hand-wheel to tighten the end on the big tank. Since you'll have to use an open-end wrench to get the usual fittings (and usually the regulator) off your small tank, obviously there will be a wrench available for the job. It also has a pressure gauge (very handy) so that you can tell what the pressures are in the big tanks as you work. Finally, it has a three-way valve that will 1) send oxygen through to the small tank, 2) trap the oxygen in the hose, or 3) vent the hose to the air. By thoughtful use of this valve, oxygen loss from venting the hose each time can be avoided. You really need to think about what you're doing, because if you err, you'll start removing one of the fittings with pressure still on it, and there goes your o-ring. Not dangerous, but annoying, especially if you don't have a spare!
Mountain High also has Transfillers with special fittings to fit other types of oxygen tanks, and interconnects to tie two or more big tanks together. I didn't bother with these.
With the top-of-the-line Transfiller, the filling procedure is as follows:
Remove the regulator and fittings from your small tank. Mount the Transfiller with the hand-wheel end on the big tank, and the other end on your small tank. Place the Transfiller valve so it points along the hose to the big tank. Open the valve on your small tank fully. You may hear the residual oxygen in your small tank hiss a little as it pressurizes the Transfiller hose. Next, gently and slowly crack the valve on the top of the big tank, listening for the hiss as oxygen begins to flow. By listening, and by watching the pressure gauge, you can "gently" let the pressure equalize. I really don't think there's any harm in just opening the valve and letting the pressure equalize quickly, but old habits die hard.
Once the pressure has equalized, close the valve on the big tank, and rotate the three-way valve on the Transfiller to dump the tiny bit of oxygen trapped between those two valves (keeping the bulk of the hose under pressure). Move the "big-tank end" to the next big tank, open the Transfiller valve, then use the big tank's valve to add more oxygen as before. When done, close all valves, vent the Transfiller at the big tank end, take the Transfiller off the big tank, vent the hose to the open air, remove the Transfiller from your small tank, and you're done.
If you think about each step before you do it, it's pretty simple. Otherwise, you may want to use a checklist. Blowing an o-ring is not dangerous, but it can be scary when you get a huge blast of oxygen after failing to turn off a valve! It's wasteful, too, and you may have to start all over.
I carry the Transfiller in the airplane with me, just in case I run out, and can find a big tank, perhaps even in a welder's setup. It will take some plain and fancy talking to convince the FBO to let you do it, though, and the best way is to just ask them to look the other way, perhaps in return for a little "consideration."
Other Tricks and Gadgets
What about carrying your oxygen in the liquid form (LOX)? Great idea, you can carry a lot of it in a very small space, but so sorry, it's just not practical, even though the military does it. To keep it in liquid form, the temperature must be kept below about -96º F, which implies either special equipment or servicing insulated tanks just before flight. There must also be special equipment to warm the stuff before humans can breathe it.
I use and like the ubiquitous "Oxymiser" (or "Oxysaver") system sold by all three outfits. These consist of a special conserving cannula that contains small reservoirs and check valves, plus a little in-line flowmeter with a floating ball to indicate oxygen flow and a vernier needle valve to adjust the flow to the desired rate. The conserving cannulas come in two flavors — "moustache" and "pendant" — but both have two small nozzles that stick into the nostrils, with thin plastic supply tubes draped over the ears. Once in place, I'm not even aware of it, and often find myself at the end of a flight sitting at the gas pump still breathing oxygen!
The cannulas are officially approved up to 18,000 feet, and if you're going higher than
that, a full-face mask is recommended. However, with the little pulse oximeter, it should
be easy to determine the individual need for oxygen, and with that, the "rules"
can be adjusted safely.
There are basically three types of oxygen tanks for in-aircraft use. The old conventional steel tanks are cheap, very heavy, and must be hydro-tested every five years. Aluminum tanks are less than half the weight, a bit more expensive, must be hydro-tested every three years and most are life-limited to 25 years. Finally, there are the new Kevlar tanks, which are very light and very expensive ($1,400 and up), must be hydro-tested every three years and discarded after 12 years. The rules about recurrent hydro-testing and life limitations come from the DOT, not the FAA, and there are rumors the DOT will be changing all these rules soon.
Mountain High also sells the very neat (and costly) EDS (Electronic pulse-demand Delivery System), which I would love to have, but have been too cheap to buy. This is mostly because my refills are now so cheap, and normally I go "out and back" and my portable bottle is sufficient for a high-altitude flight each way (to FL210 in a normally-aspirated Bonanza).
Anyway, the EDS (about $600) is a small, battery-powered black box that replaces the normal flow regulator, monitors the faint pressure fluctuations in the oxygen line from normal breathing, and delivers a small puff of oxygen only during inhalation. Since we usually spend about one-third the time inhaling and two-thirds exhaling, this dramatically decreases the wasted oxygen by up to 90%, or so they say. Of course, the EDS also regulates the flow for the altitude automatically, and can be set for day or night requirements.
A very nice feature of the EDS is an audible alarm signal that warns of "no flow" for any reason. If you're doing serious high-altitude work, this alone is worth the cost of the EDS, in my opinion. Without a warning system, it is all too easy to kink a line, run out, or get the regulator misadjusted, and any of these can be deadly if not detected. Of course, using a pulse oximeter to monitor your blood O2 saturation is also an excellent way to avoid such problems.
Full Bladders and Headaches
Some report having these problems, and they are related to the rest of this column. I am indebted to my good friend George Braly (of GAMIjector™ fame) for coming up with these suggestions.
For the headaches, simply take an aspirin before takeoff.
Solving the bladder problem is slightly more complex, but makes a lot of sense. We know that high-altitude flight and the continuous use of oxygen dehydrates the body, so we can take advantage of this to some degree, and "regulate" our need for a bathroom. But don't overdo it, as dehydration impairs human performance, just as lack of oxygen does.
Go light on the liquids for a couple hours before your flight, and make sure you make that last-minute pre-departure bathroom visit. Climb to an altitude where you use oxygen, and put it on. From that point, you can either sip liquids to keep from getting too dehydrated, or drink the liquid of your choice, up to about 16 ounces every couple of hours. More at higher altitudes, less at lower altitudes. Higher altitudes (and more oxygen use) will permit longer flights without discomfort, even for us older folks! You will probably find no pressing need after landing, even on very long nonstop flights. Some also find it useful to munch on potato chips, pretzels, or other salty snacks during the flight, as it seems to soak up fluid, rather than allowing it to go to the bladder.
Mike Busch, who does a good deal of flight-level flying in his unpressurized Cessna T310R, suggests carrying a small sack of seedless grapes, preferably de-stemmed before flight. The grapes provide an excellent source of moisture and sugar in a convenient form, and they won't spill if you get into turbulence!
If you use supplemental oxygen (and you should), think about setting up your own filling system. The $600 price tag (cylinders, Transfiller, etc.) may seem high until you figure that 10 or 15 refills at your (mostly unwilling) FBO is the "break-even" point. After that, you can play cheap airline pilot, and chortle to yourself as you load up on "nearly free" oxygen. Hey, it makes my day!
Once you do this, you'll find yourself just putting on that cannula from 10,000 feet on up (or sometimes lower), without regard for the trivial cost, or the fear of running out before you can find a refill. Just top off your bottle before or after every flight, and you'll always have plenty of O2 available.
This, in turn, will lead you to doing more high-altitude flying, where the engines are more efficient, the weather tends to be better and smoother, and where you have many more options to avoid ice and other unpleasantness. With the better fuel (and bladder) specifics, you'll be able to go longer distances and make fewer stops, reducing the wear and tear on your airplane.
Be careful up there!