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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. $\endgroup$ 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. $\endgroup$ 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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    $\begingroup$ You know that when discussing immersing carbon fiber in oxygen, you should discuss flammability and properties of epoxy resin, not carbon? Carbon fiber composite has the carbon fibers completely embedded in epoxy resin, providing extra structural durability, but completely isolated from the environment. $\endgroup$
    – SF.
    Jul 10 '18 at 9:36
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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. Compare with these two videos 4 and 5 showing hot and burning charcoal thrown into LOX.

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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    $\begingroup$ Why exactly do you say "...the piece of charcoal did not ignite on contact with LOX, it was ignited before and still glowing..." The video does say that the charcoal is hot, but I don't see any evidence that it was ignited before contact with the liquid oxygen. Remember also that's at least oxygen-rich air in the container. $\endgroup$
    – uhoh
    Dec 20 '19 at 6:42
  • $\begingroup$ @uhoh See these two videos youtube.com/watch?v=pix4_rZ9Aq4 and youtube.com/watch?v=y7uCBWkrAXo showing hot and burning charcoal thrown into LOX $\endgroup$
    – Uwe
    Sep 15 at 20:30
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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. $\endgroup$ Jul 10 '18 at 0:59
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    $\begingroup$ 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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As he says the charcoal in the experiment is very hot (plus charcoal has a lot of carbon dust all over it, which is really flammable stuff), even then the charcoal doesn't burn until after it bounces out of the liquid oxygen, having vaporised some oxygen. To summarise we have hot carbon dust in an almost pure oxygen atmosphere.

By contrast COPV's use carbon fibres which are bonded (and therefore far more stable) structures of carbon (their structures are actually somewhat similar to graphite which is used on some rocket nozzles). They are also in the middle of a tank full of LOX which is at -183C or lower. Furthermore oxygen isn't very flammable in it's liquid state, only when it's gaseous.

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  • $\begingroup$ "Furthermore oxygen isn't very flammable in its liquid state, only when it's gaseous" Oxygen is an oxidizer so it's never considered "flammable". $\endgroup$
    – uhoh
    Sep 15 at 13:06
  • $\begingroup$ Asphalt isn't very flammable in its solid state, but there have been unwanted ignitions when liquid oxygen was poured on an asphalt floor. $\endgroup$
    – Uwe
    Sep 15 at 13:27
  • $\begingroup$ Recommended reading about liquid oxygen; www1.grc.nasa.gov/wp-content/uploads/chapter_05.pdf $\endgroup$
    – Uwe
    Sep 15 at 14:19
  • $\begingroup$ See these two videos youtube.com/watch?v=pix4_rZ9Aq4 and youtube.com/watch?v=y7uCBWkrAXo showing hot and burning charcoal thrown into LOX $\endgroup$
    – Uwe
    Sep 15 at 20:31

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