Aircrew and Oxygen.

[Talk Wrench]

Despite the spurious thread title, this is actually a serious thread!

Fast Jet bods, medics, airframe guys/gals,in fact anyone who may be able to explain the use of oxygen during FJ flying may be able to help.


A colleague and I recently had a discussion about excessive oxygen in the cardio-vascular / pulmonary systems. Me being me, stated that as far as I was aware, Fast jet pilots select "100%" oxygen as a matter of course.

He being he and only ever having worked on helo's said that can't be possible because of the damaging physiological aspects of such exposure.

I told him about LOX, OBOGS/MSOCS etc and described the operation and delivery through various expansion networks, plenum chambers and PEC portions (as much knowledge as I have on the subject), but one question I could not answer was, "Do the pilot/nav/crew actually physically receive 100% oxygen at the mask?"

This brought other questions into play such as, If not, then what actually is meant by 100% Oxy. Is it mixed with Ram filtered air? If so at what ratio?

If a true 100% oxy flow is delivered, how is the pilot/crew monitored. What effects does it have on them? How long can they be exposed for?


Forgive my ignorance on the subject, please bear in mind I have spent all of my adult life as an Avionic and aircraft electrical engineer.(And oxygen thief according to my esteemed green suited, tent living friend!!!)


Thanks in advance,

Talk Wrench

[L J R]

I have had 'oxy ear' in a Jet (prolonged exposure at high cabin alt etc....) Also occasionally get it a little in Avmed Chamber - just like the lecture zzzzzzzzzz.

[D SQDRN 97th IOTC]

and 100% Oxygen can also be selected on the ground for a few puffs.
Apparently very useful if you been on the tiles the night before.
But no-one would do that these days, would they?

[VigilantPilot]

Interesting question - as I understood it, it would take an extremely prolonged and constant exposure to 100% oxygen to have any damaging effect. I think prolonged exposure causes the alveoli to shrink. I am not totally sure on this though and could have been crewroom discussion!

When exposed to 100% for a significant part of a sortie, I have noticed my ears feel like they 'pop' a bit during the rest of the day.

[FJJP]

VigilantPilot

'Oxygen ear' is a fairly common phenomenon amongst crews that used O2 for prolongued periods. This is because the inner ear collects 100% O2 via the eustacean tubes during flight. Although 'clearing your ears' during descent and recovery equalises the pressure across the eardrum [and thus easing any pain from a stretched drum] the inner ear could still have high levels of O2 concentration. After flight this O2 is absorbed into the surrounding tissues, reducing pressure in the chamber, causing the eardrum to stretch inwards causing mild pain - relieved by clearing the ears in the normal manner to equalise the pressure.

Phew!

[Where R We?]

Interesting question - as I understood it, it would take an extremely prolonged and constant exposure to 100% oxygen to have any damaging effect. I think prolonged exposure causes the alveoli to shrink. I am not totally sure on this though and could have been crewroom discussion!

Prolonged exposure indeed causes issues; pulmonary oxgygen toxicity caused by long exposure at low doses (0.6-1.0 bar for more than 6 hours at time) and central nervous system toxicity caused by high pressures for short periods of time (1.6+bar for anything less than 45mins). Not sure what the extra pressure induced by pressure breathing would be but I doubt it would take the pressure to above 1.0 bar.

The latter is more likely when operating at hyperbaric pressures such as diving but the former can occur in hospitals or recompression chambers when 100% O2 is used. Indeed in most cases patients in hospitals who are on 100% are unlikely to be on 100% due to Pulmonary O2 toxicity but more likely an enriched air mix.

The alevoli do get irritated by the pure O2 and the gas exchange is reduced. To counter this the partial pressure of O2 can be reduced, thereby increasing the 'dose' allowed for the same period, or completely removing the 100% and breathing normal air to allow the lungs to recover. Obviously the latter is not an option when operating in a hypoxic environment such as high altitude flight.

When operating at high altitiude the partial pressure of O2, even when breathing 100% O2, would be quite low compared to surface or sub-surface pressures and therefore the period can be extended probably beyond the endurance of the aircraft/platform.

HTH

[Monty77]

On some jets you select oxy supply to 100% on start up (to make the engine start up fire more spectacular). Due to the female liney you forget to select airmix on taxy and empty the tank pretty much for the next hour. Lucky it's not a high level transit.

100% doesn't sober you up, it's just a blast of what seems like cold air on your mush and makes you feel better for a moment.

[Talk Wrench]

Some good gen appearing here. Thanks.

My learned friend, the one who likes green too much, originally referred to lab rats which were exposed to a 100% oxygen environment and subsequently experienced cardiac arrest through oxygen saturation of the CP/V system.

As already highlighted by VP, prolonged exposure could possibly lead to early alveoli atrophy.

WRW

Superb explanation which goes some way to help (or not) to the unfortunate sufferers of asthma who wish to become aircrew. (I was diagnosed with asthma prior to my station board for aircrew in '97)

More feedback appreciated please.

Talk Wrench

[Where R We?]

Pulmonary oxygen toxicity ( Lorraine Smith effect) is a direct time /dose relationship on the lungs caused by a direct effect of O2 on the lungs, blockage of airways, increased CO2, pulmonary surfactant changes , enzyme interference and an inert as effect. The best treatment is prevention and removal of pure O2 at the first signs of toxicity.

If you want to do some research look up 'Lorraine Smith Effect', here is a link http://www.scubaboard.com/archive/index.php/t-108703.html which might give you some more links. The site is scuba orientated but look at the post 08-18-2005, 04:56 PM for lots of links.

[Pontius Navigator]

VigilantPilot

After flight this O2 is absorbed into the surrounding tissues, reducing pressure in the chamber, causing the eardrum to stretch inwards causing mild pain - relieved by clearing the ears in the normal manner to equalise the pressure.

The 'normal manner' was by frequent and rapid swallowing action for at least two hours after flight. Of course it was no use doing this immediately on landing. You had to wait at least an hour - debriefing, changing etc.

The oxygen clearing exercise was then usually supervised on a buddy buddy basis.













In the bar:}

[FJJP]

PN

Of course! To clear the ears [valsalver method] required the act of swallowing at the same time as moving one's jaw. How wonderful in those days to have such a considerate employer as to provide us with a suitable locale to carry out this medical procedure, thus preventing potential for injury. Of coarse, after an hours of couple, cared anyway who?

Duty of care? Don't know the meaning of the word these days!

[Brian Abraham]

Off thread a little but given the above I raise the question why then did they use 100% O2 in the early space days (3 died in a fire while on the pad)

[Gaz ED]

Quite common on a RAFG fast jet sqn to see lineys walking round with large clear poly bags on their heads, full of O2. No-one was smoking though! I must admit,:\ it appeared to clear your head after a shed-on.

[wiggy]

You are going to wish you hadn't asked...Stand by whilst I don anorak.........OK

The Americans chose to use 100% O2 on their Mercury, Gemini and Apollo spacecraft for a variety of reasons, mostly weight related.
1. One gas means a simpler, lighter Enviromental Control system than with a two gas system, and only one set of tanks to carry into orbit, no worries about metering the ratios of gas, etc etc.
2. Running one gas, O2, meant the cabin pressure could be reduced after launch to well below one atmosphere without reducing the partial pressure of Oxygen to hypoxia levels. The American spacecraft ran their cabins at about 5 psi 100% O2 when in orbit. Lower cabin pressure meant a lighter pressure hull...again weight reduction
3. Looking ahead to space or moonwalks lower pressures were essential - using a spacesuit filled with air at 15psi (1 bar) would be impossible - the thing would blow up like a balloon or would have to be made so rigid it would be inflexible. The suits were, I think, run as low as 3psi 100% O2 to aid mobility.
Further problem: If you use air at 1 bar in the cabin and low pressure O2 in the spacesuits you have the "bends" problem when you transition from one enviroment to the other, so your space walker has to pre breath O2 before the walk and perhaps exit via an airlock ( which is what the Russian did and the Shuttle astronauts do.....). In Gemini and Apollo the guys "simply" suited up, dumped the cabin pressure completely and opened the hatch
Rapid decompression? Well in all instances you need to suit up in a hurry but if you are also instantly going from 1 bar air to 5 psi O2 you've again got the "bends" problem.
Hence the reasons the Americans opted for 5psi O2 when in orbit

As to the Apollo fire (Jan '67)
Firstly O2 at low pressure was not regarded as particularly inflammable..however on the pad, for a pre launch test, the cabin was pressurised at 100 O2 but at around 16 psi (normal procedure on the ground, overpressurising the cabin was to stop toxic gases that vented from the launcher entering the cabin). It seems the flammable properties of that enviroment had not been fully considered. It is now known that Grissom, White and Chaffee were sitting in a bomb and when an ignition source got into the spacecraft ( and no-one was ever able to establish the exact source or sequence of events) a tragedy resulted.....

Pheww, anorak off.

BTW I think the record on 100% O2 stands at 14 days for the Gemini 7 crew ( now that was an epic) - I stand to be corrected but I think Skylab used oxygen/nitrogen at reduced pressure??

Regards

[Rocket2]

Gaz Ed - also common at Goose Bay in the "good old days" was to see the old hands stagger up into the cockpit of the mighty Vulcans & start breathing the 02 whilst the new boys frantically tried to top the bottles up at the back during a BF following another night in the "Dog":ok:

[Pontius Navigator]

Once, in Cyprus, it was a rac against sobriety.

When it was noticed that the RAF Plod guarding the might Vulcan was drunk the worst was suspected. In fact it was worse than that.

The aircraft was p*ss*d too. The aircraft had been designed with a 12 gallon alcohol tank for windscreen and bomb aimer's windscreen deicing. We didn't use the windscreen de-ice as we now had gold film heating and we didn't use the bomb aimer's one either. The window didn't ice up and if we did use it we got a load of cr*p across the glass. Anyway, the tank was leaking.

The aircraft was full of fumes but I didn't notice as I was in the appropriate seat trying to empty the oxygen bottles.

I recovered in 24 hours and the aircraft took 2 days.:)

[Busta]

Then of course there's "Hunter lung"

Nothing matters very much, most things don't matter at all

[Brian Abraham]

Wiggy, rest assured I'm glad I asked and gladder still for the fullsome answer. No need for the anorak - ever.

[Arthur Rowe]

As Busta points out 'Hunter lung' was a problem in the 1960s. The oxygen regulators fitted at the time had a potential problem in that if a failure occurred in the bellows the system would deliver insufficient oxygen at altitude, so 100% was selected as a matter of course throughout the sortie.

Some Hunter pilots reported experiencing sharp pains in the chest when pulling 'g' at low altitude and on investigation it was discovered that they were suffering partially collapsed lungs as a result of the excess of oxygen.

The explosive effects of oxygen on grease or wax are well documented, explaining why the trolleys are fitted with brass connections. A possibly apocryphal story tells of a fast jet pilot with a waxed handle-bar moustache was the worse for wear from the night before and decided to take a whiff of 100% oxygen to clear his head. Unfortunately it cleared his upper lip of said moustache in a burst of flame.

Oxygen ear could be cleared by some time spent eating and drinking after flight, so it was the perfect excuse to stay on late after night flying for a few jars in the crewroom. Those were the days.....