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Date: 29 Jan 86 18:36:26 GMT
From: ulysses!burl!clyde!watmath!utzoo!  (Henry Spencer)
Subject: Challenger

"If we die, we want people to accept it.  We're in a risky business, and we
hope if anything happens to us, it will not delay the program.  The conquest
of space is worth the risk of life."
					Virgil I. Grissom
					commander, Apollo 1
					speaking a few weeks before his
					death in the Apollo fire
				Henry Spencer @ U of Toronto Zoology

Date: 12 Nov 92 17:52:59 GMT
From: Henry Spencer <>
Subject: Apollo fire

In article <> (Bill Collins) writes:
>One of the main reasons that the fire was so devastating was the fact
>that at the time Apollo capsules had 100% oxygen atmospheres at normal
>atmospheric pressure (14.7 lbs./sq.inch).  That's a lot of oxidizing
>agent to help with combustion!  After Apollo was allowed to fly subsequent
>to the Apollo1 fire the pressure was dropped to 5.3 lbs/sq. inch (am I
>right, Henry?).

Not really.  Having checked some references...

The Apollo spacecraft, like Mercury and Gemini spacecraft, ran on about
5psi of pure oxygen in space; it was designed that way from the start and
this was not changed after the fire.  The fire hazard in that atmosphere
is not significantly worse than in 14.7psi air, and in any case, the lack
of convection in free fall greatly reduces fire risk (which is nice of it,
since it also reduces the effectiveness of fire extinguishers).  A one-gas
life-support system is a good deal simpler and lighter than a two-gas
system, the lower pressure reduces structural loads, and prebreathing for
spacewalks would have been very awkward for Apollo.

The problem was that the capsule had to be pressurized to 14.7psi, or
preferably slightly more, while on the ground; it was not built to stand
external pressure exceeding internal pressure.

Now, that pressurization didn't have to use pure oxygen.  In fact, Mercury
used normal air for ground pressurization, although I believe the astronaut
breathed pure oxygen at all times.  However, it turned out that there were
risks in this approach:  a technician was killed in an accident which would
not have happened with pure oxygen.  (I don't have details, but I would
guess a pressure-chamber test went awry and he ended up breathing air at
low pressure.)  It was decided to use pure oxygen for ground pressurization
as a result.  Nobody noticed that this greatly increased the fire hazard,
partly because the fire-prevention philosophy at the time was to ensure
that there were no ignition sources to start a fire.

In the wake of the Apollo fire, this was all re-assessed.  It became clear
that there had been many potential ignition sources in the capsule, to the
point where there was no possibility of determining which caused the fire.
While a lot of this was due to sloppy manufacturing, it was decided that
the basic philosophy would have to change:  presence of ignition sources
would henceforth be taken for granted, so fires would have to be contained
rather than prevented.  A much more determined effort was made to exclude
flammable materials from the cabin, but it proved impossible to make it
fireproof for 14.7psi+ of pure oxygen.  Max Faget suggested using a mix
containing some nitrogen, as a compromise between avoiding the bends and
reducing fire hazard, and the final ground atmosphere was 60% oxygen and
40% nitrogen.
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  utzoo!henry

From: Henry Spencer <>
Subject: Re: Helium as a diluent
Date: Tue, 30 Apr 1996 19:13:19 GMT

In article <4lpigb$> (Kossowski Craig D) writes:
>: In his talk, he said that there is no significant increase in fire
>: risk for a 5psi 100% O2 atmosphere, and that the Apollo 1 fire was
>: caused by the fact that when Apollo was on the ground, it had a 14 psi
>: 100% O2 atmosphere...
>I doubt it very much.  14 psi pure oxygen is toxic, considerably so...

The specific cause of the Apollo fire was indeed the use of pure oxygen at
14.7 psi (actually, I think it was a notch higher) on the pad.  Some chance
of toxicity was accepted -- as in hospital oxygen tents -- due to overriding
practical issues.

However, it is a common misconception that low-pressure pure oxygen does
not increase the fire hazard.  Not true.  It doesn't increase it to nearly
the horrible level of 14.7psi oxygen, but it does increase it quite a bit.
The increase due to low-pressure oxygen was considered manageable, but it
was not zero.
Americans proved to be more bureaucratic           |       Henry Spencer
than I ever thought.  --Valery Ryumin, RKK Energia |

From: Henry Spencer <>
Subject: Re: Helium as a diluent
Date: Tue, 30 Apr 1996 19:08:55 GMT

In article <4ldm5l$> () writes:
>> ...want to reduce the fire hazard to roughly that found on Earth, you
>> need about 70% buffer gas.  Smaller amounts do reduce the hazard, compared
>> to pure oxygen, but not all the way.
>The question is how much are you worried about fire and are there better
>ways to reduce fire danger...
>I believe that if you quantified the trade offs and used scientific critria
>you would reduce the presure more than if you used emotional critieria 
>because of fear of a repeat of the Apollo 1 fire.

How about legal criteria because of fear of lawsuits after an accident?
That's definitely relevant in the US. :-)

Realistically, it will eventually be necessary for space systems to observe
safety criteria similar to those used on Earth.  In particular, any scheme
for really large-scale space operations is going to have to have *very*
good reasons for making exceptions to well-established industrial safety 
codes.  Every such exception is potential grounds for a lawsuit.

The industrial fire-safety people have studied non-standard atmospheres
with some care -- this is *not* a new and unexplored topic, folks -- and
have a specific definition of "atmosphere of increased burning rate".  I
don't have the formula on hand right now, but the bottom line is that if
you want Earth-surface oxygen concentrations at the lung wall (which is
not quite the same as having Earth-surface oxygen concentration in the
atmosphere), *and* you don't want an a.o.i.b.r., the lowest you can go is
about 12psi. 
Americans proved to be more bureaucratic           |       Henry Spencer
than I ever thought.  --Valery Ryumin, RKK Energia |

From: Henry Spencer <>
Subject: spacecraft fires (was Re: SHOCK! Gagarin was NOT first...)
Date: Wed, 24 Jul 1996 14:54:04 GMT

In article <4sof7p$> writes:
>Didn't the Russians then switch from 100 percent oxygen in their space
>capsules?  As I recall the report, because the Russians kept their
>accident secret (until the Soviet Union fell), the Americans didn't
>switch to the nitrogen mix until after the American accident.

The Americans would not have switched even if they'd known about the
Soviet accident.  ("Ho ho, those incompetent Russians -- that would never
happen here".)  The US philosophy, at the time, was that the best way to
prevent spacecraft fires was to eliminate ignition sources, which made
flammability issues very much secondary.

Furthermore, there were safety reasons to *use* pure oxygen for ground
operations, because it was breathable at all pressures.  Mercury
originally used ordinary air for ground tests, until a technician died
when a test capsule was taken down to 5psi without replacing the air with

After the fire, when people woke up to how poorly controlled the hardware
really was, the conclusion was that absence of ignition sources could not
be guaranteed, and the spacecraft had to be safe against fire even in the
presence of an ignition source.  That put much more attention on the
flammability issues, and of course the fire also alerted everyone to the
difference between 5psi and 16psi for flammability.

Even so, the mixed ground atmosphere was not adopted until it became clear
that there was just no hope of achieving fire safety in 16psi oxygen. 
They didn't want to complicate the hardware unnecessarily, and there was
still the issue of breathability for ground operations.  When the
materials people reported that flammability was an unsolvable problem in
16psi oxygen, the designers added the minimum amount of nitrogen needed to
bring flammability under control, yielding a mix that was still breathable
at 5psi. 
 ...the truly fundamental discoveries seldom       |       Henry Spencer
occur where we have decided to look.  --B. Forman  |

From: (Henry Spencer)
Subject: Re: Apollo 1 questions
Date: Tue, 15 Feb 2000 03:29:03 GMT

In article <>,
Ctrot  <> wrote:
>> Some burns, but those would not have been fatal -- the fire did not last
>> very long and the suits provided considerable protection.  What killed
>> them was smoke inhalation, after their suit hoses burned through.
>...a question I have had for some time: Could Grissom, White and Chaffee
>have survived the fire if the hoses were made of a material that would not
>have burned through? It seems to me that the answer would be yes.

Not sure, but I'd be doubtful.  The suits did take some damage, and some
of the metal plumbing in the life-support system was melted by the fire.
The space program reminds me        |  Henry Spencer
of a government agency.  -Jim Baen  |      (aka

From: (Henry Spencer)
Subject: Re: Apollo 1 questions
Date: Tue, 15 Feb 2000 15:08:46 GMT

In article <vs5q4.843$>,
J. David Bryan <> wrote:
>>Some burns, but those would not have been fatal...
>What is your source reference?  Baker says, "Their burns were indescribable"
>("The History of Manned Spaceflight", p.277) and "All three suits had been
>extensively burned" (ibid, p.278).  Slayton says, "The suits had protected
>them from the flames. None of them had any physical burns of any consequence"
>("Moon Shot", p.207).

Chariots For Apollo (NASA SP-4205), Men From Earth (Aldrin & McConnell),
Apollo (Murray & Cox), and Deke! (Slayton & Cassutt) all agree:  serious
but survivable burns, death by asphyxiation.

>Given some of the other stuff in Moon Shot, I'd tend to believe the former ;-)

If you want Slayton's opinion on something, read Deke!, not Moon Shot.
The space program reminds me        |  Henry Spencer
of a government agency.  -Jim Baen  |      (aka

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