Oxygen toxicity

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Everything kills just depends on the amount.

With regards to oxygen it's all about the FiO2 and exposure time. Higher partial pressures as seen with diving reduce the FiO2 required to cause toxicity though there is the element of nitrogen narcosis as well. Breathing 100% you can't safely dive beyond 10m/30ft or so due to the risk of toxicity. Results are similar to other toxic agents.


Oxygen toxicity - Wikipedia
 
Not helped by the human body's own defence and control systems going haywire in extremes, as I understand it too little CO2 causes hyperventilation (as if there is too much) like people suffering from extreme cold taking their clothes off just before they succumb to the cold.
 
pbehn said:
as I understand it too little CO2 causes hyperventilation
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My limited human physiology training says the opposite occurs, pbehn. It's an increasing PaCO2 that will produce a higher respiratory rate and depth.
Subjects here are breathing air or air containing 2%, 4% or 6% CO2....

 
Graeme said:
My limited human physiology training says the opposite occurs, pbehn. It's an increasing PaCO2 that will produce a higher respiratory rate and depth.
Subjects here are breathing air or air containing 2%, 4% or 6% CO2....

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I don't even have limited training in human physiology, just what I have read. That is that a very low level of CO2 in the blood tricks the body into thinking there is too much. This is nothing to do with the CO2 in the air being breathed in, just the level of CO2 in the blood.
 
This is a stretch for my memory of over 50 years but in flying the unpressurized T-37 the altitude limit was 25k where, I think, your breathing 100% oxygen through the mask. Above that and you start pressure breathing. In the pressurized C-141, when you were above 40k ft., we were required to have one pilot with a mask on, breathing 100% O2 at a cabin pressure of 8000 ft. The reason for that was, in the case of rapid decompression, a persons time of consciousness is only a few seconds.
 
Many years ago I experienced a "chamber ride" courtesy of the USAF. This was to familiarize us with the effects of too little oxygen. The chambers' oxygen content was slowly reduced until we got to the equivalent of 25,000 ft. During the ride "up" we worked puzzles, talked, took quizzes, made sketches, etc. A couple of folks had no immediate reaction, others had difficulty reading or talking or doing arithmetic problems. One person was ill and had to leave (via a double door arrangement). My reaction was loss of color vision. First reaction was not being able to tell the difference between green and blue. Then yellow and red seemed the same. Soon all colors were just various shades of grey. A headache came later.
After that experience I kept several color patches on the instrument panel.
 
Most people's breathing is trigger by pCO2 not pO2 measured by arterial baroreceptors in the carotid bifurcation. The only time this isn't the case is in chronic lung diseases with underlying hypercarboxaemia from poor ventilation then it's the hypoxia which triggers breathing.

This is why those people can go into type 2 respiratory failure when given too much oxygen and require positive pressure ventilation with addition end expiratory pressure to keep the airways open to prevent collapse and inefficiency. This is done with NIV or BiPAP (we do a bit of this with COVID as well for similar reasons).

The other respiratory failure in type 1 which is hypoxia with low/normal CO2 (type 2 is just high CO2, oxygen can be low, normal or high). The acidosis in type 2 is caused by increased pCO2 whilst in type 1 failure there is less likely to be acidosis.

People will hyperventilate to blow off excess CO2. This can continue even with very CO2 but this is usually due to the pathology of the hyperventilation rather than the physiology. A panic attack being the most common example. A low pCO2 in itself will not cause hyperventilation.

Respiratory Failure
 
I watched a show on PBS that dealt with people working at high altitude. Oxygen starvation was illustrated by one guy saying "I've cut this thing three times and it's still too short."
 
The death of golfer Payne Stewart, others, due to O2 depletion caused by aircraft loss of pressurization stunned me. Apparently, the aircraft pressurization system malfunctioned and the crew lost consciousness and the plane flew on with dead crew and passengers for hours before running out of fuel and crashing. How could this accident happen? The pilot was reported to be an ex Air Force pilot, surely trained in pressurization issues. The aircraft had a cabin altitude warning, which was beeping. Analysis indicated that the crew probably went to the checklist for loss of cabin pressurization. Review of the checklist had, if I remember correctly, showed that there were three steps to be performed before the donning of mask was stated. Altitude chamber testing indicated that, at the altitude being flown, the crew would not have made it to the fourth step before becoming incapacitated. In my C-151 training, if there was a low cabin pressure warning, we had two steps to be performed before reading the checklist, DON MASK and INITIATE EMERGENCY DESCENT. In the C-141 procedures would be to don mask, throttle to idle, spoilers deployed, nose down about 30 degrees. In this configuration the C-141 would descent at 6000 ft/min + (I did this once when ground control wanted us to descent rapidly). If your flying at 40,000 ft., lose pressurization and initiate an emergency descent, after one minute the aircraft is at 34k, all crew and passengers unable to get O2 on have passed out. Another two minutes and the aircraft is at 24k and all crew and passengers unable to get oxygen are probably dead. Why didn't a trained Air Force pilot react this way. The only thing I can think of is that the pilot had flown only aircraft that require face mask always to be on like fighters. This automatically adjust O2 levels to safe optimum levels, so there is no worry about dealing with decompression. The moral of this story is that, if the masks come down on a commercial airliner, don your mask quickly, you may not have but a few seconds to react and you health and life depend on it.
 
boeing299 said:
Humans do not breath elemental oxygen. They breath O2 which is one form of molecular oxygen and is two atoms of oxygen combined. O3 is ozone which is toxic, so in that sense oxygen can be toxic.
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If you'll read the thread, O2 is easily toxic, under the right conditions.
 
davparlr said:
That was the finding. Review was made of similar aircraft checklist and deficient checklist were corrected. First two steps should be put on mask, start emergency descent, both bold face.
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Which is correct for my aircraft (A320 / 319) as well.

Oxygen masks and regulator - On 100%
Crew Communications- Establish

Cheers,
Biff
 
The Payne Stewart situation was very bizarre. I didn't know they even had to put the oxygen mask on the checklist, I thought that was just the first thing you did before anything else so you don't wink out.
 
The main problem is with Hypoxia is that losing mental capability is one of the symptoms.

So you are not aware and losing the ability to perform mental tasks so flying an airplane becomes impossible.

Hyperoxia is obviously not something that happens on the street. But anyone who breathes in very high levels of pure oxygen is in for a shock.

This is counter intuitive as more oxygen equals more breathing but the body is not set up that way.

So we talking astronauts or divers or medicare or even them oxygen bars that sprang up.

If one of the pilot guys can inform on the emergency air supply on an airliner so that's what you breathing in and the pressure that's it's at.

An airliner is using pressure at 8000 feet so don't run marathons on your 737 to Magaluf.
 
BiffF15 said:
Which is correct for my aircraft (A320 / 319) as well.

Oxygen masks and regulator - On 100%
Crew Communications- Establish

Cheers,
Biff
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I have some concern regarding this checklist. If you climbing through 40k going to 43k and experience a rapid decompression, let's look at the timeline. 3 seconds for pilot to check warning light and don O2 mask (quick don mask available? At this altitude, we did). Note, at this altitude, a person is incapacitated in 7-10 seconds (per wikipedia). In the back there is chaos, confusion, panic. Flight Attendants are at different location and need to get to an O2 supply (O2 bottle) and get it on in 7 to 10 seconds, a couple will probably not make it before they become incapacitated (aisle blockage, hesitation etc, or they may not know the necessity of speed). Contact with the crew at this time is problematic, maybe taking several minutes. When are you told to descend? With 200+ souls on board there will be quite a few unable to don masks before they are unable to and need help. Mask doning is demonstrated but not practiced. Is the passenger O2 system functioning correctly? Have all the masks deploy? If O2 cannot be given within 3 to 5 minutes, people will start to die. In my opinion, step 2 should be Begin Emergency Descent to Safe Altitude as required.
 


Davparlr,

The checklist, and checklists at my airline are well vetted. When we do normal training or check rides if a checklist is disliked or misinterpreted there is a focus put on it. Also the changing of said checklists is a well known process.

The A320 / 319 at my company is limited to FL390 or below. It's in our Ops limits.

The masks drop automagically when the cabin goes above 11,500'. There are both walk around bottles and or masks at all seats. The flight attendants are taught to use closest available. You are also assuming a rather large hole has appeared. Most of the time it's the outflow valve failing.

The CRM tools and procedures require both pilots if able are moving the plane up / down or changing configuration. I believe that step three would be to initiate a rapid descent. We practice this in training.

When flying in high terrain, or ground level at or above 10k we build escape routes into the navigation system (off route) and is published by Jeppensen. These routes are designed to get down to 10k ASAP.

Cheers,
Biff
 

The FAA Rules require that the pilots already be on oxygen while above 35,000ft (41,000 if quick-don masks are available and two crew are at the controls).

The chaos in the back is secondary

91.211 Supplemental oxygen.
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