Apollo 1

[Luke Pemberton]

I've posted this in this discussion section out of symbolism that the Apollo 1 accident was just that, an accident.

I understand the cause of the Apollo 1 fire and the recommendations that followed, but I have never really understood the hoax argument (other than Grissom et al. were going to whistleblow and needed removing).

The argument as I understand:

• Pure oxygen above atmospheric pressure was used test the CM.
• The use of pure oxygen was exploited in a 'tragic accident' to remove the astronauts.
• At the inquiry various people stated that they did not understand the dangers of pure oxygen.
• The CTs claim that NASA must have known about the dangers as it was obvious what oxygen does when it oxidises a fuel and there had been incidents with the USAF before.

Is this a correct interpretation of the CT argument? The natural connect would be that it was common practice to use pure oxygen and Apollo was a tragic accident.

Why was pure oxygen used, I have never properly understood the reason. I've read some arguments about N₂/0₂ mixes being better from the point of view of decompression, and that N₂/0₂ mixes are easier to scrub. I've also read that pure O₂ can be dangerous to the body when used at the pressures in the Apollo 1 CM test. I've tried to digest the information but it's a bit of a minefield with various people pitching in their view point.

Note: Sorry if this has been discussed somewhere else.

[Bob B.]

I've read some arguments about N₂/0₂ mixes being better from the point of view of decompression

That sounds backwards to me.  Decompression sickness occurs when dissolved nitrogen in the bloodstream comes out of solution and forms bubbles.  Breathing pure oxygen would purge the nitrogen from the bloodstream and prevent decompression sickness.  Apollo astronauts could easily decompress the cabin and lower the pressure in their spacesuits without worrying about decompression sickness.  The Space Shuttle, on the other hand, used a N₂/O₂ environment, which resulted in the astronauts having to go through a lengthy pre-EVA decompression process, including breathing pure oxygen for about an hour before starting a spacewalk.

[Luke Pemberton]

I've read some arguments about N₂/0₂ mixes being better from the point of view of decompression

That sounds backwards to me.  Decompression sickness occurs when dissolved nitrogen in the bloodstream comes out of solution and forms bubbles.  Breathing pure oxygen would purge the nitrogen from the bloodstream and prevent decompression sickness.

That is what I thought. When wading through the arguments and debates from both sides of the fence I was found I wasn't getting far. Scuba diving sprung to mind in this case.

The Space Shuttle, on the other hand, used a N₂/O₂ environment, which resulted in the astronauts having to go through a lengthy pre-EVA decompression process, including breathing pure oxygen for about an hour before starting a spacewalk.

That's an interesting snippet of information. A certain CT argues that the physiological dangers of breathing pure oxygen would have been known to NASA, and that filling the CM with a pure oxygen environment would have been harmful. Therefore, the use of pure oxygen in the test was part of the conspiracy to kill the astronauts. 

[Bryanpoprobson]

O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.

[Bryanpoprobson]

O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.

Ps this is what limits compressed air diving to 40meters, after that depth other gas mixes have to be used, at 40 meters the pressure of O2 reaches one bar

[Bob B.]

That's an interesting snippet of information.

A normal air mix can't be used in an EVA suit because the required pressure would result in the suit being too stiff.  To obtain the necessary mobility, the pressure inside the suit must be kept low.  This requires the use of pure oxygen because the partial pressure of oxygen in air wouldn't be enough to breath.  The Space Shuttle cabin used a mix of 21% O₂ and 79% N₂ at one atmosphere pressure.  However, starting about 24 hours prior to an EVA, the entire cabin underwent a pressure decrease of about 30% with a slight increase in O₂ percentage.  Starting about an hour before the EVA, the spacewalking astronauts would have to wear a mask and breath pure oxygen.

Apollo got around the decompression problem by using low-pressure 100% oxygen at all times in both the cabin and spacesuits.  The health and fire risks were lessened by the low pressure.  Of course, on the launch pad the cabin had to be pressurized to over one atmosphere to provide positive pressure inside the spacecraft.  Since Apollo used a single gas system, it was pressurized using pure oxygen (as had been done on both Mercury and Gemini).  This was a fire hazard that probably should have been recognized but wasn't, and it sadly resulted in the Apollo 1 tragedy.

After Apollo 1 the procedure was changed.  On the launch pad Apollo was pressurized using a mixture of 60% O₂ and 40% N₂.  During ascent the pressure was vented down to 5 psi, and, while in orbit, the atmosphere was eventually replaced with pure oxygen.  Although 60% O₂ was much higher than normal air, the introduction of N₂ greatly reduced the fire hazard.  60% O₂ was needed because as the pressure vented down to 5 psi, the partial pressure of oxygen remained high enough (3 psi) for the astronauts to breath normally after removing their helmets.

[Luke Pemberton]

After Apollo 1 the procedure was changed.  On the launch pad Apollo was pressurized using a mixture of 60% O₂ and 40% N₂.  During ascent the pressure was vented down to 5 psi, and, while in orbit, the atmosphere was eventually replaced with pure oxygen.  Although 60% O₂ was much higher than normal air, the introduction of N₂ greatly reduced the fire hazard.  60% O₂ was needed because as the pressure vented down to 5 psi, the partial pressure of oxygen remained high enough (3 psi) for the astronauts to breath normally after removing their helmets.

Thanks Bob. That has helped a lot. Sometimes a question can save a lot of digging to find the pertinent detail. Thanks for taking time to explain.

[Allan F]

Apollo on the launch pad - didn't they use ambient air until liftoff? Since the astronauts were in full spacesuits, hooked up to the lifesupport system inside the capsule, the capsule could be vented to space, plugged up, and then pressurized with oxygen.

[raven]

It was part of the test. It wasn't just pure oxygen at one bar, I believe, a terrifying enough idea in retrospect, it was oxygen at pressure  enough to simulate the internal stresses on the spacecraft as a pressure vessel equal to what it was in the vacuum of space, I am guessing part of it being a 'plug out test' to see how the spacecraft handled under full internal power.
Here's my problems with the whole 'whistleblower quash' claim.
For one, there are other ways to kill people that aren't nearly so public and damning. Other astronauts died in training as well, but do CT mention people like Clifton C. Williams or Edward G. Givens, Jr? Oh hell no, those people are, typical knowledgwise, non-entities in comparison. Two, as part of being very public, you are going to have a lot people not part of your organization crawling over everything. What if someone finds an invoice for several hundred tons of 'Lunar grey sifted sand'?
I know I am preaching to the choir here, but the whole thing is damn screwy, like CT claims generally are.

[Bob B.]

It wasn't just pure oxygen at one bar, I believe, a terrifying enough idea in retrospect, it was oxygen at pressure  enough to simulate the internal stresses on the spacecraft as a pressure vessel equal to what it was in the vacuum of space

From what I've read, it was pressurized to 16.7 psi, or 2 psi over atmospheric pressure.

[raven]

It wasn't just pure oxygen at one bar, I believe, a terrifying enough idea in retrospect, it was oxygen at pressure  enough to simulate the internal stresses on the spacecraft as a pressure vessel equal to what it was in the vacuum of space

From what I've read, it was pressurized to 16.7 psi, or 2 psi over atmospheric pressure.

If that's true, then I was wrong about it being over pressured enough to exactly test the strain, but it was still over pressured with *shudder* pure freaking oxygen. Valentin Bondarenko died from burns suffered during a fire in a test chamber. Some have speculated that if the former USSR had being more public about this failure, it might have awoken NASA to the dangers of pure oxygen.

[Luke Pemberton]

From what I've read, it was pressurized to 16.7 psi, or 2 psi over atmospheric pressure.

This much I did know. The positive cabin pressure sealed the plug door hatch cover and purged the cabin space of nitrogen containing air.

[Bob B.]

Apollo on the launch pad - didn't they use ambient air until liftoff? Since the astronauts were in full spacesuits, hooked up to the lifesupport system inside the capsule, the capsule could be vented to space, plugged up, and then pressurized with oxygen.

After the hatch was sealed, the CM was pressurized using a 60-40 oxygen-nitrogen mixture supply by equipment on the ground.  There were no hardware changes made to the spacecraft's single gas system.  Only the cabin used the 60-40 mixture, the spacesuit loop remained 100% oxygen.  During ascent the gas was vented down to 5 psi, which left a partial pressure of oxygen high enough to be breathable.  As the spacecraft experienced normal leakage during flight, the loss was replaced with oxygen.  Thus, by the end of the flight the atmosphere was nearly pure oxygen.

(ETA) Of course in cases where an EVA was done, the atmosphere would be completely evacuated and replaced with 100% oxygen.
 

[Luke Pemberton]

After the hatch was sealed, the CM was pressurized using a 60-40 oxygen-nitrogen mixture supply by equipment on the ground.  There were no hardware changes made to the spacecraft's single gas system.  Only the cabin used the 60-40 mixture, the spacesuit loop remained 100% oxygen.  During ascent the gas was vented down to 5 psi, which left a partial pressure of oxygen high enough to be breathable.  As the spacecraft experienced normal leakage during flight, the loss was replaced with oxygen.  Thus, by the end of the flight the atmosphere was nearly pure oxygen.

So during the Apollo 1 plugs out test, the astronauts were hooked up to the life support system and weren't breathing oxygen at 2 psi over atmosphere?

[Bob B.]

So during the Apollo 1 plugs out test, the astronauts were hooked up to the life support system and weren't breathing oxygen at 2 psi over atmosphere?

From what I've been able to gather, it appears they were breathing high-pressure oxygen.  Since the suits were flexible, they had to be pressurized to at least the 16.7 psi cabin pressure.  And everything I've read leads me to believe the suit circuit was using 100% oxygen.

Here's a basic description of the system:

The spacecraft used an oxygen only system.  The oxygen was supplied from tanks in the SM and passed through high-pressure regulators that lowered the pressure to 100 psi.  From there the system split, providing oxygen to the suit circuit demand regulator and the cabin pressure regulator.  Under normal operating conditions, the cabin pressure regulator maintained the cabin at a nominal pressure of 5 psi. 

The suit subsystem provided the crew with continuously conditioned atmosphere.  It automatically controlled suit oxygen circulation, pressure and temperature.  It removed debris, excess moisture, and carbon dioxide.  When a crew member's face mask was closed, the circuit was isolated from the cabin environment.  The suit regulator maintained a pressure of at least 3.5 psi pressure whenever the CM was depressurized.  During shirtsleeve operation, the suit system remained in operation, even though the crew was out of their suits, to remove carbon dioxide and moisture from the cabin.