Oxygen questions

[ghazanhaider]

Planning for an aircraft upgrade, my future Bonanza will have a service ceiling between 17000 and 21000.

This makes me wonder about oxygen systems. As a diver, I know it can't be as simple as strap on a mask with 95% oxygen (up from 21%) and everything is fine.

Too much oxygen can make your head spin, give you euphoria and induce seizures (please educate me if this problem is only specific to diving and is not an issue in high alt).

What are the rules of thumb higher altitude pilots use in unpressurized aircraft abouve 12500?

Do you slowly add oxygen until you're not lethargic? Is there a certain adjustable rate for a given pressure altitude to use?

And are there dangers to avoid and reasons to not go above 12500 for longer distance cruise?

G

[photofly]

I know it can't be as simple as strap on a mask with 95% oxygen (up from 21%) and everything is fine.

Actually, it pretty much Is that simple. It’s 100% O2 in the tank though, not 95%.

You can get various kinds of regulators, and most aviation systems ($$$$$!) come with a flow gauge calibrated for altitude. Either way, Use a pulse oxymeter ($30 on eBay) that clips on your finger and adjust the flow rate to keep your peripheral blood oxygen saturation (SpO2) at 90% or higher. You don’t lose consciousness until way below that, but your peripheral and night vision can suffer. And speaking for myself I start to get a really bad headache.)

The higher you go the more critical your oxygen system becomes because the less time you have to fix things. The cheap and easy cannulas (the oxymiser type saves a whole lot of oxygen flow rate) are only good up to 18,000 feet. Above that you need a mask.

I’ve also been experimenting with one of these
https://www.home-med-equip.com/catalog/ ... drive.html
But I don’t know how well it works above 18000 feet, that’s not what it’s designed for.

If you fly alone the cheapest setup is to piggy back off the medical industry: get your bottles and cannulas online, and use a low flow paediatric regulator that has more low flow settings. And the most economical oxygen fills are from welding suppliers. Take no notice of any guff about “impure” supplies. Welding stuff is the best you’ll get below lab grade.

[Heliian]

Take no notice of any guff about “impure” supplies. Welding stuff is the best you’ll get below lab grade.

The Oxygen is essentially the same except for Aviators breathing oxygen is meant to be dry to prevent Ice buildup. I feel better about using abox than just some dirty old welding tank oxygen. I never needed to use so much that I was worried about saving a few dollars by using a product not recommended for breathing.

[tbaylx]

Planning for an aircraft upgrade, my future Bonanza will have a service ceiling between 17000 and 21000.

This makes me wonder about oxygen systems. As a diver, I know it can't be as simple as strap on a mask with 95% oxygen (up from 21%) and everything is fine.

Too much oxygen can make your head spin, give you euphoria and induce seizures (please educate me if this problem is only specific to diving and is not an issue in high alt).

What are the rules of thumb higher altitude pilots use in unpressurized aircraft abouve 12500?

Do you slowly add oxygen until you're not lethargic? Is there a certain adjustable rate for a given pressure altitude to use?

And are there dangers to avoid and reasons to not go above 12500 for longer distance cruise?

G

You're confusing partial pressure of oxygen, oxygen percentage, nitrogen narcosis and oxygen toxicity from diving.

100% oxygen is completely safe to breathe up to approximately 1.2 partial pressure active, or as high as 1.6 PP resting. At sea level pressure breathing air oxygen has a PP of .21 (21% O2 and roughly 79% Nitrogen). If you breathe 100% O2 then the PP rises to 1.0. When you're diving the PP doubles for every 10M you descend below the surface. So if you dive to 10M then the PP of 100% O2 is 2.0 and above safe levels. Therefore about 6M down is about the maximum you want to breathe 100% O2 to remain below 1.6PP O2. Above that you risk oxygen toxicity which can induce seizures. Euphoria or drunkenness generally is not associated with O2 toxicity but comes from higher PP of nitrogen (nitrogen narcosis). You'd have zero risk of that with a 100% O2 mix since there is no nitrogen in your gas mix. This is how Nitrox works in diving. Higher O2 percentages reduces the amount of nitrogen in the mix so you have less nitrogen in your bloodstream to offgas on your surface intervals.

In an aircraft however you have the opposite effect. As you climb the PP pressure of a 100% O2 mix would drop with altitude so you'd never be at risk of O2 toxicity (for the relatively short duration of an aircraft flight) or nitrogen narcosis. Since air is less dense than water you have to climb about 16 000' to drop sea level pressure by half (vs 10M in water). The suggested lowest PP of oxygen to maintain normal function is .14 PP O2 (effects on vision and breathing occur below .19 PP 02) which occurs around 10 000' - hence why O2 is needed above that altitude.

If you're breathing 100% oxygen you could climb to around 43 000' before the PP O2 drops below .14, so even breathing 100% O2 isn't sufficient above those altitudes to avoid hypoxia. Above those altitudes you'd require pressurization to keep O2 PP high enough.

To sum it up you never need to worry about O2 toxicity and Nitrogen narcosis effects in an aircraft because the pressure is dropping as you climb vs diving where it increases. You do need to worry about hypoxia which can be prevented by breathing 100% O2 all the way up to 43 000'. At lower levels you could breathe a mix with less than 100% O2 as long as you keep your PP O2 above .14 but you'd always be safe breathing 100%

[TailwheelPilot]

Another option is an oxygen concentrator. There is at least one offered specifically for aviation plus the medical ones although not all may be suitable for use at altitude. They last quite awhile and no need to deal with oxygen cylinders or filling them up. The one I tried provided plenty of oxygen at 15,000’ (SpO2 at 95%) at low-medium settings. The aviation-specific one I have seen says it automatically adjusts for altitude - just plug it in and go.

[photofly]

Take no notice of any guff about “impure” supplies. Welding stuff is the best you’ll get below lab grade.

The Oxygen is essentially the same except for Aviators breathing oxygen is meant to be dry to prevent Ice buildup. I feel better about using abox than just some dirty old welding tank oxygen. I never needed to use so much that I was worried about saving a few dollars by using a product not recommended for breathing.

There’s absolutely no water in welding oxygen. It’s about a million times purer than what you need to breathe safely, because impurities in welds are very bad.

All oxygen for every purpose is now manufactured by distillation of liquified air; medical oxygen use has a humidifier applied at the point of use as it comes out of the cylinder.

For in aircraft use, the regulator never gets below freezing, and there’s no water in the oxygen anyway. As a matter of fact adding a humidifier is probably a good idea because dry nasal passages are quite an unpleasant side effect of a long flight using a cannula.

The only actual difference between medical and welding oxygen is the paperwork: medical oxygen is considered a pharmacological product and comes with traceability. One has the choice of course, if paperwork is important to you.