U2 pilot incapacitation and long term brain damage....

[Mojocvh]

From a PPRuNe thread...

Seems there are an increasing number of pilots suffering various disabilities post operational "surge" flights these last 10 or so years..

Ref. http://www.airspacemag.com/military-aviation/kille...
http://www.dsls.usra.edu/20100310.pdf‎
http://www.bmj.com/content/314/7082/701

Must be worrying for those who were exposed even to lesser pressure effects during their service.....

[Silent1]

Your first link goes to page 4 of the article, this is the first page:
http://www.airspacemag.com/military-aviation/kille...

[pherlopolus]

I cant believe the only pressurize the cabin to 29,000 foot, and are reducing it to 15,000 as a partial fix. That's the equivalent of spending a few hours at the top of Everest!

[Silent1]

pherlopolus said:

I cant believe the only pressurize the cabin to 29,000 foot, and are reducing it to 15,000 as a partial fix. That's the equivalent of spending a few hours at the top of Everest!

They are inside an old school astronaut outfit which is pressurised to a lower altitude.

[pherlopolus]

Silent1 said:

They are inside an old school astronaut outfit which is pressurised to a lower altitude.

I fail to see how pressurizing to a lower altitude will help then :S

[anonymous-user]

Isn't it a 100% oxygen atmosphere too? (to avoid partial pressure issues)

[scubadude]

The atmosphere and pressure are one issue, surely the other is how they manage the transition to and from lower pressure, do that wrong and you get DCS, do it repeatedly and brain lesions follow. Speak to an old commercial diver and you'll see what I mean, they're all insane.... some might have been to begin with ;-)

If they've raised the cabin pressure that possibly gives them less risk on their current ascent/descent profiles.

[Hooli]

pherlopolus said:

Silent1 said:

They are inside an old school astronaut outfit which is pressurised to a lower altitude.

I fail to see how pressurizing to a lower altitude will help then :S

Isn't the pressurisation the suit quoted against outside pressure? so it's 29,000ft above the cabin pressure?

[Ganglandboss]

pherlopolus said:

Silent1 said:

They are inside an old school astronaut outfit which is pressurised to a lower altitude.

I fail to see how pressurizing to a lower altitude will help then :S

If there were no technical issues to overcome, they would pressurise them to sea level. I am not an aircraft expert but I understand a bit about DCI from diving. If they could maintain the cabin pressure at sea level, there would never be an issue, however, at the sort of altitude the U2 flies at, pressurising the suit (plane geeks - is the aircraft pressurised too?) to a higher altitude (and therefore lower pressure) will mean less strain on the suit/aircrtaft as the difference between that and the outside ambient air pressure is lower.

With divers, it works the other way. We start at low pressure and descend to high pressure. Every 10 metres we go down, the ambient pressure increases by 1 bar, so at 40 metres, we are at an ambient pressure of 5 bar. This compresses all the nitrogen and pushes it into our tissues. As we ascend, the gas expands so now our tissues are under tension. We need this tension to begin off-gassing but doing this too quickly will cause a decompression injury, of which there are many types. We use computers and/or tables which have been developed from years of research, but they are still just theory and not guaranteed to stop us getting bent. Our ascent profile will follow a recommended ascent speed and may involve holding stops at a particular depth to bring our nitrogen loading slowly back down.

Another concern is partial pressures of gas, which are mentioned on this thread. Air is roughly made up of 21% oxygen and 79% nitrogen. There are a few trace gases in there too but we can ignore them at this moment. At sea level (1 bar), we are breathing oxygen at 0.21 bar. If we go down to 10 metres, we are breathing 0.42 bar of oxygen. Now in the words of 'The Sweet', 'Love is like oxygen - you get too much, you get too high, not enough and you're gonna die'. This isn't strictly true, however, 'you get too much, you start convulsing, spit out your reg and drown' just doesn't have that same ring to it. Most diver training agencies teach us that we should not breathe mixes with a greater partial pressure of oxygen (ppO2) than 1.4 bar on the bottom as we will suffer from oxygen toxicity or 'hyperoxia'.

For aviators and climbers, the O2 risk is the opposite (ignoring rebreather and hypoxic trimix divers). As they ascend, the atmosphere is still composed of 21% oxygen and 79% nitrogen. The issue now is the ppO2 is reduced and they are at a risk of hypoxia. A couple of websites I just found tell me the atmosphere is approximately 0.7 bar at 15,000 ft and 0.3 bar at 29,000 ft. My rebreather will sound a low O2 alarm at 0.16 bar (0.4 in dive mode), so obviously anything below this is not good. If the figures from the websites are correct, at 15,000 ft, the ppO2 of the atmosphere will be 0.147 bar, so this is clearly not good. At 29,000 ft it is 0.063 bar, which we can safely assume means they would be f**ked. By breathing pure oxygen at the same ambient pressures, the ppO2 will be 0.7 bar and 0.3, both of which are pretty good and the reasoning behind the 29,000ft as it provides a safe breathing medium but does not put excessive pressure on the suit (or cockpit if it is pressurised).

The DCI risk comes from the ascent. I expect these guys don't f**k about when they get up to altitude, so the risk of DCI is immense. Breathing pure oxygen before the flight will flush some of the nitrogen from the body, but it won't eliminate it completely as we need some tissue tension to off-gas, which will only take place once the ambient pressure drops. If the pilot takes a hit on the ascent, things are unlikely to get any better until they descend, and possibly get put in the recompression chamber.

Increasing the minimum ambient pressure (i.e. decreasing the altitude) will not totally eliminate the risk of a DCI, but as it means the pilots are subject to a reduced change in pressure. For that reason, the logic is reasonable to me.

Edited by Ganglandboss on Wednesday 12th February 11:36

[c7xlg]

but rememebt with diving you are going from 1 bar at the surface to many bars of pressure (ie by 20m you are already at 3 bar).

With a plane you are going from 1bar at sea level to 0.3 bar or so at 30,000 feet. So I think the issues are very different. Certainly I haven't heard of any pilots getting 'The Bends' after being at a high cabin alt and then ejecting into un-pressurised atmosphere. THey certainly don't explode like the badie in The Living Daylights. :-)

[Ganglandboss]

A rapid climb from 1.0 bar to 0.3 is a big change though, and at the lower end of the pressure range, the gas volume change is greater.

[anonymous-user]

c7xlg said:

Certainly I haven't heard of any pilots getting 'The Bends' after being at a high cabin alt and then ejecting into un-pressurised atmosphere. THey certainly don't explode like the badie in The Living Daylights. :-)

You fart a lot.

[Silent1]

el stovey said:

c7xlg said:

Certainly I haven't heard of any pilots getting 'The Bends' after being at a high cabin alt and then ejecting into un-pressurised atmosphere. THey certainly don't explode like the badie in The Living Daylights. :-)

You fart a lot.

That's not farting, that's the colour of fear!

[Mistrale]

I would expect them to pre-oxygenate by breathing 100% O2 before flying in order to prevent DCI by removing the nitrogen from their blood.

[scubadude]

Ganglandboss said:

My rebreather will sound a low O2 alarm at 0.16 bar, so obviously anything below this is not good.

Hi Ganglandboss, what unit do you dive, an Inspiration perhaps?

The 0.16 is because loss of consciousness is likely below that level, its not a concern for DCS, I believe the U2 has a pure O2 atmosphere, so the pressure shouldn't be an issue.

Ganglandboss said:

The DCI risk comes from the ascent. I expect these guys don't f**k about when they get up to altitude, so the risk of DCI is immense. Breathing pure oxygen before the flight will flush some of the nitrogen from the body, but it won't eliminate it completely as we need some tissue tension to off-gas, which will only take place once the ambient pressure drops. If the pilot takes a hit on the ascent, things are unlikely to get any better until they descend, and possibly get put in the recompression chamber.

Quite, it sounds like their issue is the build up of multiple ascents to a low pressure rather than each flight alone. Lots of Sub-clinical DCI compounding the lesions rather than one off "bends" as such.

[MartG]

I believe the suits they use are an evolution of those used by the Apollo and Shuttle astronauts, and are pressurised to 5psi with 100% oxygen.

In the case of Apollo, the astronauts were suited up and breathing pure oxygen for several hours before they even entered the spacecraft, then had the additional time spent waiting for launch too. The Apollo spacecraft had an automatic dump valve which reduced cabin pressure during ascent until it reached 5psi - when on the ground it was the sea level oxy/nitrogen mix to reduce the fire risk ( after the Apollo 1 disaster ) but shifted to pure oxygen during ascent. I don't think there were any reports of DCS during this programme, but of course they weren't doing frequent ascents like the U-2 pilots.

The Shuttle cabin on the other hand was pressurised to 10.2psi with 20% oxygen 80%nitrogen - which is why astronauts going on an EVA had to spend 12 hours or so shut in the airlock in 100% oxygen as the suits were still the 5psi models.

[Ganglandboss]

scubadude said:

Ganglandboss said:

My rebreather will sound a low O2 alarm at 0.16 bar, so obviously anything below this is not good.

Hi Ganglandboss, what unit do you dive, an Inspiration perhaps?

The 0.16 is because loss of consciousness is likely below that level, its not a concern for DCS, I believe the U2 has a pure O2 atmosphere, so the pressure shouldn't be an issue.

Ganglandboss said:

The DCI risk comes from the ascent. I expect these guys don't f**k about when they get up to altitude, so the risk of DCI is immense. Breathing pure oxygen before the flight will flush some of the nitrogen from the body, but it won't eliminate it completely as we need some tissue tension to off-gas, which will only take place once the ambient pressure drops. If the pilot takes a hit on the ascent, things are unlikely to get any better until they descend, and possibly get put in the recompression chamber.

Quite, it sounds like their issue is the build up of multiple ascents to a low pressure rather than each flight alone. Lots of Sub-clinical DCI compounding the lesions rather than one off "bends" as such.

Close - I have an Evolution+, but the electronics are the same. I was referring to hypoxia - not DCS in that part of my post, and the reason why the pilots need a much greater O2 content at low pressure.

[scubadude]

Ganglandboss said:

Close - I have an Evolution+, but the electronics are the same. I was referring to hypoxia - not DCS in that part of my post, and the reason why the pilots need a much greater O2 content at low pressure.

Nice, I have MCCR modded Classic.

Ah yes, I see what you mean wrt hypoxia.