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Sir Martyn Poliakoff, also CBE FRS and his team produce a fascinating series of Periodic Videos.

In this one they team up with Smarter Every Day's Destin Sandlin to do high speed video of a piece of coal dropped into liquid oxygen.

The coal spontaneously combusts on contact.

Please watch the video first, then explain why immersing carbon fiber over-wrapped helium tanks into tanks of liquid oxygen in the presence of additional sources of energy (e.g. expansion, contraction, friction, vibration) is not likely to catch fire, and is likely to be safe and reliable for human-rated spaceflight.


edit: I'll also reproduce part of the block quote from this answer where the idea of putting a combustible material in direct contact with LOX is roundly balked-at:

Finally, for completeness, page 146 of Clark's book contains a rather disturbing mention of LOX + liquid methane as a proposed monopropellant:

"If Tannenbaum's mixtures were bad, that proposed at a monopropellant conference in October 1957 by an optimist from Air Products, Inc., was enough to raise the hair on the head of anybody in the propellant business. He suggested that a mixture of liquid oxygen and liquid methane would be an extra high-energy monopropellant, and had even worked out the phase diagrams of the system.* How he avoided suicide (the first rule in handling liquid oxygen is that you never, never let it come in contact with a potential fuel) is an interesting question, particularly as JPL later demonstrated that you could make the mixture detonate merely by shining a bright light on it. Nevertheless, ten years later I read an article seriously proposing an oxygen-methane monopropellant! Apparently junior engineers are allergic to the history of their own business."

I think we can see why this one never took off.

John D. Clark's famous book Ignition! (1972, online)

my bold

Related: Final conclusion/description of the cause of the SpaceX Sept. 1, 2016 anomaly.

“When you think about it boys”, he said brokenly, “that’s what holds us together more than anything else, except maybe gravity. We few, we happy few, we band of brothers - joined in the serious business of keeping our food, shelter, clothing and loved ones from combining with oxygen.”

--Kurt Vonnegut, God Bless You, Mr. Rosewater (1965)

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    $\begingroup$ Are you asking why the COPVs don't actually burst into flame? "Okay" seems... super, super loaded in this context. $\endgroup$ – Russell Borogove Jun 13 '18 at 1:16
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    $\begingroup$ @RussellBorogove I do not think "okay" seems "super, super loaded". I think that's a mischaracterization. But I have found a more mundane phrasing to accomodate you. $\endgroup$ – uhoh Jun 13 '18 at 1:19
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    $\begingroup$ Carbon fibers aren't very useful unless they're potted in some binder like an epoxy. There may also be other protective coatings or covers. And the form of carbon itself could be less reactive - consider the difference between a chunk of aluminum and fine aluminum powder, or a steel bar vs. steel wool. $\endgroup$ – Chris Stratton Jun 13 '18 at 2:21
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    $\begingroup$ It was a piece of hot burning charcoal thrown into liquid oxygen. No need for an ignition source. But a small arc from static charge may be enough to start a reaction between liquid oxygen and hydrocarbons. $\endgroup$ – Uwe Jun 13 '18 at 10:39
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    $\begingroup$ A nice old paper about using liquid oxygen as an explosive together with some form of carbon. $\endgroup$ – Uwe Jun 14 '18 at 10:37
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Liquid oxygen mixed with carbon powder has been used as an explosive for mining, see 1, 2. But there has been an explosion in a helium purifier 3.

The use for mining required safe explosives, the rate of spontaneus self-ignitions should be very, very low. The charges should explode only when triggered by a detonator, but not when handling them or by static discharges. They were used for decades. The accident rate was lower than with conventional explosives. The charges were explosive only when soaked with liquid oxygen. If unused, after some hours when the oxygen was evaporated, the carbon powder was not explosive anymore.

In the experiment video shown, the piece of charcoal did not ignite on contact with LOX, it was ignited before and still glowing. Throwing it into a container filled with gaseous oxygen would intensify the reaction too.

The surface of carbon powder is greater than that of carbon fibers, therefore the risk of self ignition should be smaller. But hydrocarbons are known to be a risk in contact with pure oxygen. The binder used with the carbon fibers contains hydrogen and carbon too. A contamination with other hydrocarbons may be possible if the procedure of cleaning it before contact with oxygen was not followed strictly.

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  • $\begingroup$ To the question Why doesn't carbon fiber overwrapping in LOX catch fire? can you add a tldr single answer of the form "It doesn't catch fire because..." Thanks! $\endgroup$ – uhoh Jul 14 '18 at 10:12
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In all cases I know of, fiber reinforced tanks consist of a thin metal inner tank called a "liner" wrapped with the supporting composite material. Hence, the oxidizer and fiber are never in contact. This is also important because the composite is porous and would not hold it's contents for long.

One source: (sorry, I don't have time to type the relevant passage right now)

https://books.google.co.jp/books?id=5LBx4EmBix8C&lpg=PA309&ots=yNiJNo8XLb&hl=de&pg=PA309#v=onepage&

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  • $\begingroup$ In this case, the liner contains helium, not oxygen. The carbon fiber overwrap is immersed directly in liquid oxygen. $\endgroup$ – Tristan Jul 9 '18 at 15:35
  • $\begingroup$ These are tanks that contain helium, which are then submerged within the LOX tanks. I'm pretty sure this puts the carbon fiber and LOX in direct contact. Answers to this and this go into more detail. Am I misunderstanding your answer? $\endgroup$ – uhoh Jul 9 '18 at 15:38
  • $\begingroup$ @uhoh No where in the question does it say specifically what tank you mean, so I can't really research it, but I would say that there is probably a barrier material in place. If not metallic, then maybe PTFE. $\endgroup$ – Rikki-Tikki-Tavi Jul 10 '18 at 0:59
  • $\begingroup$ The title says "...carbon fiber overwrapping in LOX..." and the body says "... immersing carbon fiber over-wrapped helium tanks into tanks of liquid oxygen..." and that's precisely what I mean. These have been there continuously, from the initial posting onwards. $\endgroup$ – uhoh Jul 10 '18 at 1:39
  • $\begingroup$ The link to the question Final conclusion/description of the cause of the SpaceX Sept. 1, 2016 anomaly. has been there from the beginning as well. That explains "Investigators concluded that super chilled LOX can pool in these buckles under the overwrap. When pressurized, oxygen pooled in this buckle can become trapped; in turn, breaking fibers or friction can ignite the oxygen in the overwrap, causing the COPV to fail." $\endgroup$ – uhoh Jul 10 '18 at 1:47

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