28 August 2009

Jarrah's Question No4

Jarrah said:On page 38 of The History Of Manned Space Flight, Dr. David Baker tells us: On Earth, atmosphere consists of a 760mmHg mixture of 21% oxygen and 79% nitrogen, plus several trace gases that can be ignored for temporary and artificial environments. Because the quantity of oxygen in the lungs regulates the amount entering the blood, any appreciable increase in partial oxygen pressure of 160mmHg will cause irritation of mucous membranes and could disturb the function of critical enzymes.

However, even a moderate fall below the normal partial pressure value quickly causes brain damages and severe side-effects.

The option available to Mercury engineers were that the capsule could contain either a two-gas mixture of oxygen and nitrogen at sea-level pressure (760mmHg) or a single gas atmosphere of pure oxygen at about 160mmHg. Tests revealed that the pure oxygen pressure limits were between 150mmHg and 345mmHg.

Oxygen pressure for a single gas atmosphere outside these limits would cause severe, if not permanent, damage."

150mmHg = 2.9psi
345mmHg = 6.67psi

Depending on whether you ask Michael Collins, Gordon Cooper or Frank Borman; Apollo 1s cabin pressure was either nearly 16psi or 16.7psi or 20.2psi. Either way, these pressures are outside the safe pressure limits for breathing pure oxygen.

Why did NASA not classify Apollo 1 as hazardous, when they knew since Mercury that breathing pure oxygen at those pressures alone was a hazard?

The reports I have read list slightly different tolerance (Po2=425mmHg) but not enought to make a difference to what you are saying.

So: is breathing 100% oxygen at 16 psi or greater (or at a Po2 of 425 mmHG or greater) hazardous? Yes, if it is done for anything other than short periods... but the astronauts were all in their A1C pressure suits, breathing oxygen at around 2.5-3.5 psi. If there were an emergency whereby they had to remove the helmets, they pressure would have been dumped and the short exposure to 100% oxygen at elevated pressures would have had little - if any - effect on the affected crewmember.

Even so, we once again come to the question as to why this test was not classified as hazardous... and once again the answer is they got complacent and just didn't think it was that hazardous. None of the astronauts did.

4 comments:

  1. So: is breathing 100% oxygen at 16 psi or greater (or at a Po2 of 425 mmHG or greater) hazardous? Yes, if it is done for anything other than short periods... but the astronauts were all in their A1C pressure suits, breathing oxygen at around 2.5-3.5 psi.

    No, they were breathing either 16 or 20psi. Because the air pressure around them was somewhere over 16psi, the pressure in their spacesuits would have contained that same pressure. Everyone knows spacesuits cannot contain a sea-level pressure in space, so they use 3-5psi during EVA. If the A1C suit was holding 3.5psi during the test, the surrounding cabin pressure of 20.2psi would have created an inward pressure difference of 16.7psi – which would obviously have crushed the suits around the astronaut’s bodies.

    Further, if you refer back to the audio communications you’ll note there were instances when the astronauts had their visors open during the test. So much for breathing 3.5psi!

    and once again the answer is they got complacent and just didn't think it was that hazardous.

    All the previous flights took those hazards into consideration and they obviously knew Apollo 1 was going to be hazardous, as a new hatch had already been redesigned to overcome the problems of the predecessor.

    None of the astronauts did.

    Young did.

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  2. So the point you are still making is that it was clear that this was hazardous, and the astronauts were almost sure to be killed.

    THEN WHY DID THEY ALLOW THEMSELVES TO CONDUCT THE TESTS?

    ARE YOU NOW CLAIMING THE ASTRONAUTS WERE SUICIDAL?

    No-one forced the astronauts into the capsule at gunpoint on multiple occasions. They knew there were risks, but they believed them to be acceptable risks.

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  3. "CERTIFICATION TEST SPECIFICATION (CTS) SID 65-1210 recognised that ground operations would involve short duration, high pressure exposure. It specified 14.7 pounds per square inch absolute (psia) of 95% oxygen for four hours, and 21 psia with 14.7 psia partial pressure oxygen for two hours."

    Source: report of Apollo 204 Review Board, appendix D-2, page D-2-4, para 2.

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  4. So the point you are still making is that it was clear that this was hazardous, and the astronauts were almost sure to be killed.

    The point I’m making is that obviously the test was going to be a hazard just from breathing the air in that vehicle, that should have given anyone all the more reason to class the test as hazardous. That’s just from breathing it, never mind the fire hazard. And, no offence, the fact that you can suggest the astronauts could breathe 3.5psi oxygen and sit in a 3.5psi suit whilst surrounded by 16.7 or 20.2 or whatever, signifies to me what can only be described as idiocy on your part. Are you gonna retract your ludicrous claim anytime soon?


    THEN WHY DID THEY ALLOW THEMSELVES TO CONDUCT THE TESTS?

    Maybe they were under the impression that the team in charge of opening the door should they become incapacitated was on duty, you know, as they did on all the previous tests.

    No-one forced the astronauts into the capsule at gunpoint on multiple occasions.

    Cooper claims that there was a lot of pressure from NASA to do that test.

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