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Post by banjomd on Sept 23, 2010 9:46:53 GMT -4
A while back someone (I can't remember who or what topic.) asked about post-Apollo 1 fire extinguishers. I came across this at KSC:   |
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Post by ka9q on Sept 26, 2010 17:32:26 GMT -4
What was in the fire extinguisher? I can't read the label. CO2 would have taxed the LiOH canisters, though in extreme cases the crew could don their suits and vent the cabin to get rid of smoke and toxic gases, and that would also conserve LiOH.
The CM and LM both provided water guns that could also be used for fire fighting as well as preparing food and for drinking. There were vents in the panels for injecting fire extinguishing agent.
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Post by banjomd on Sept 26, 2010 20:19:25 GMT -4
What was in the fire extinguisher? ... It didn't state. |
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Post by ka9q on Sept 26, 2010 21:55:42 GMT -4
Come to think of it, I think I read it was one of the Halons, i.e., hydrocarbons with the hydrogens substituted with multiple halogens (fluorine, chlorine, bromine). Most have low innate toxicity, and apparently they interfere with combustion without having to completely displace oxygen. That's important in a cramped spacecraft when the astronauts are not necessarily in their suits.
I've always wondered just how a fire would really behave in a 5psi atmosphere at 0g. It's not just the O2 partial pressure of O2 that matters; diluent gases like N2 interfere with a fire, probably by carrying heat away. Yet in 0 g, a fire would tend to suffocate itself. NASA must have conducted some post-Apollo-1 fire tests in 0 g airplane flights, no?
If NASA had been willing to keep the astronauts in their pressure suits for a while after launch, they could have launched with ordinary air in the cabin instead of the 60-40 O2/N2 mixture chosen after Apollo 1. Dump the cabin on the way to space and refill it with pure O2 after reaching orbit. But while ordinary air would improve fire safety on the ground, relying on the suits adds its own risk.
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Post by banjomd on Sept 27, 2010 6:00:44 GMT -4
... relying on the suits adds its own risk. Michael Collins (anecdotally and presumably) writes that he, even with prebreathing 100% O2, got the bends in his right knee, twice!  Actually, come to think of it, it wouldn't have mattered what the cabin atmosphere was for his knee!  |
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Post by PhantomWolf on Sept 27, 2010 7:22:52 GMT -4
If NASA had been willing to keep the astronauts in their pressure suits for a while after launch, they could have launched with ordinary air in the cabin instead of the 60-40 O2/N2 mixture chosen after Apollo 1. Dump the cabin on the way to space and refill it with pure O2 after reaching orbit. But while ordinary air would improve fire safety on the ground, relying on the suits adds its own risk. They pretty much did. The enviroment system had an external relief valve that was open above 0.9 psi external pressure. It allowed the initial 02/N2 mix to leak out as the craft launched, slowly being replaced by pure O2 which stablised at 6.0 psi before being lowered to 5.0 psi for nominal operation. Then as the CM rentered the valve would re-open letting in air, equalising the interior atmosphere with that outside the craft. During launch time the crew were in suits which stayed about 1-0.5 psi above the cabin pressure. They were connected to the pressure suit circuit system passing them pure O2 with any excess being dumped into the cabin. Once the pressure dropped enough to close the valve, the crew would open their suits allowing the O2 inside to further flow into the cabin before disconnecting. After the accident with Soyuz 11, the Apollo crews of 15, 16, and 17 all donned their suits and connected to the pressure suit circuit during re-entry as well. Again it was keep at slightly above the cabin pressure, but they remained on pure O2. |
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Post by banjomd on Sept 27, 2010 9:16:02 GMT -4
... After the accident with Soyuz 11, ... (Self-imposed thread drift;) I wonder if Wally Schirra ever commented on Soyuz 11 in regards to his refusal to don helmets for Apollo 7's re-entry. |
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Post by PhantomWolf on Sept 27, 2010 19:40:51 GMT -4
... After the accident with Soyuz 11, ... (Self-imposed thread drift;) I wonder if Wally Schirra ever commented on Soyuz 11 in regards to his refusal to don helmets for Apollo 7's re-entry. I'm betting Al Bean wishes that he'd worn his.  |
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Post by banjomd on Sept 27, 2010 20:19:33 GMT -4
or remembered to stow that camera! |
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Post by ka9q on Sept 28, 2010 4:02:15 GMT -4
They pretty much did. The enviroment system had an external relief valve that was open above 0.9 psi external pressure. It allowed the initial 02/N2 mix to leak out as the craft launched, slowly being replaced by pure O2 which stablised at 6.0 psi before being lowered to 5.0 psi for nominal operation. Right, but because the astronauts were to remove their helmets soon after reaching orbit it was necessary to boost the O2 concentration so that the partial pressure would be high enough to sustain life at 5 psi. 60% of 5 psi is 3 psi, about equal to the partial pressure of O2 at sea level. Had they launched with ordinary air in the cabin, the prelaunch fire hazard would have been substantially less, but there wouldn't have been enough ppO2 to sustain life when the cabin bled to 5 psi during ascent. The crew would have had to nearly dump the cabin to space to get rid of the residual N2 and then fill it up with O2 before removing their helmets for the first time. |
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