A colony ship was outfitted to set up operations in the "tiger stripe" ice caves of Enceladus. [sorry!] But its main drive was hacked during a course correction and the ship crashed on Saturn. Fortunately, a very flat graphene-containing organism was spotted for it to land on, using an aerofoil improvised from an origami habitation dome. The external temperature is a comfortable 300 K and there is a gentle, if pungent, rain falling.

Unfortunately the ship is now at about 15 atm of pressure and that pressure is about 75% hydrogen gas. The hull has multiple small breaches and the atmosphere is pouring in. The ship's normal air (and pressure) is similar to that of Earth. There is not enough reserve on hand to reach a full 15 atm internally, even if you wanted to. Postulating a large number of sensors to detect hydrogen levels accurately, and any reasonable fire control systems you can think of, and quick thinking by the crew ...

What would you do to minimize the damage, or at least keep it from exploding completely?

Response: bulkheads are a reasonable fire precaution, so these can be part of your response. The crew has the option to reduce the amount of crumpling on the way down by releasing more atmosphere or allowing the hydrogen influx to being before landing. This was the route I had originally chosen - allowing hydrogen to enter the topmost portions of the ship to "smoothly" replace air before any electrical system damage. However, hyperbaric oxygen on the lower level is also a bad thing...

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    $\begingroup$ Futurama addressed this question in Season 2, Episode 12 (2000): "How many atmospheres can the ship withstand?" "Well, it was built for space travel, so anywhere between zero and one." $\endgroup$
    – user535733
    Mar 16, 2021 at 2:45
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    $\begingroup$ hydrogen mixed with air is explosive in concentrations ranging from as little as 4% to as much as 74% $\endgroup$
    – John
    Mar 16, 2021 at 3:35
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    $\begingroup$ The ship was intended for space. I was tempted to add some wiggle room on the basis that it might somehow be heated and submerged on Callisto, but the whole idea seemed pretty absurd - you can't fly a submarine. The pressure seems like it has to balance one way or another - hydrogen, air, steam, something... And especially: Would halon be effective in this situation? $\endgroup$ Mar 16, 2021 at 4:21
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    $\begingroup$ To continue on what @John said, and please forgive me as I'm no chemist, but it seems like an atmosphere of 75% hydrogen would have solved itself by this point. Keep in mind, introducing a flame to a hydrogen environment will put out the fire, not make it explode. It's oxygen that's causing the big boom... the mix of hydrogen only helps at this point... and generally for every atom of oxygen, you need two hydrogen to produce this fire and the chemical byproduct of H2O. The fact that there has been no ignition source in this atmosphere until man arrived seems a bit far fetched to me. $\endgroup$
    – hszmv
    Mar 16, 2021 at 13:19
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    $\begingroup$ You lost my suspension of disbelief at something heading for Callisto at Jupiter and happening to make it to Saturn due to "hacked during a course correction"; then "crashed on Saturn"; again at aerobraking using an improvised aerofoil from an unplanned trajectory; again at "very flat graphene-containing organism" on which they "land" (where the organism is able to hold up the ship's mass, preventing further descent); again at 15 atm of pressure not doing more damage to a ship built for space than just "leaking"; etc. I honestly hope you have fun with your story, but ... issues. $\endgroup$
    – Makyen
    Mar 16, 2021 at 16:19

5 Answers 5


Withdraw to a smaller volume, and take your air with you.

I'm assuming two things:

  • Your colony ship is luxurious and large, with epic amenities to ensure that consists arrive with excellent morale and sanity.
  • The ship is also designed to land on the surface and function as the settlement for the first few years of a colony, so can survive descent and some pressure difference. 15atm is over it's safe pressure level hence the leaks, and its creaking a lot, but theres just enough safety margin so it stays in one piece as they descend.

As much as the colonists love the tennis courts, botanic garden, and simulated beach dome (with wave generator), they're not going to be able to use them any more now that hydrogen is seeping in. They're to be closed, all the air pumped into tanks, and then hydrogen atmosphere allowed in. This is done during the descent to help keep the hull in one piece.

The colony ships were constructed with radiation shelters - strongly shielded reinforced airtight regions to fall back to in case radiation exceeds what the hulls shielding can manage. Similar concepts exist in "the expanse" (bunkers on eros), "Battlestar galactica" (sickbay), and "ascension" (one per family in the suite). Your colonists fall back to these shielded smaller volumes with food, water, and the air (which they use to increase pressure to around 4atm - the max you can breathe normal air, but keeps the shelter walls under less stress), and wait it out.

A sensible ship design would allow a control room to exist in this shielded region allowing a mayday to be broadcast and someone to come rescue them.

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    $\begingroup$ They'll have spacesuits, too. There's nothing to stop them visiting and using the tennis courts and beach dome, though it might be tricky to keep the botanic garden looking nice for very long. $\endgroup$ Mar 16, 2021 at 9:50
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    $\begingroup$ Is it just me or does the 'reverse Hindenburg" sound like a wrestling maneuver? $\endgroup$
    – Mon
    Mar 16, 2021 at 10:08
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    $\begingroup$ @Mon: I was thinking you could use it to help a diner choke to death at a restaurant, but now I realize that's what you said. :) $\endgroup$ Mar 16, 2021 at 12:39

TL;DR: It isn't entirely beyond the realms of possibility that you could mix oxygen from the ships's supplies with ambient hydrogen or hydrogen propellant and get a breathable mixture at 15atm that isn't immediately flammable.

From this NASA article on hydrogen safety:

Hydrogen has a very broad flammability range—a 4 percent to 74 percent concentration in air and 4 percent to 94 percent in oxygen

This is clearly quite bad. However another NASA paper, Oxygen Partial Pressure and Oxygen Concentration Flammability:Can They Be Correlated? says

The findings presented in this paper suggest flammability is more dependent on oxygen concentration than equivalent partial pressure.

As breathing gas pressure increases, the absolute percentage of oxygen required in that gas to support human life drops, so long as the partial pressure of oxygen is high enough for gas exchange in the lungs to work.

At an ambient pressure of 15 atmospheres, oxygen concentration only needs to be about 1.5% in order to provide STP-equivalent ppO2... this might, in fact, be below the threshold of explodability. It might even be possible to drop the oxygen concentration further to a mere 1%, after all this is an emergency and the equivalent oxygen pressure of a 3000m mountain might not be pleasant, but it would be better than catching fire.

15atm is equivalent to ~150m of water, and commercial and experimental diving has certainly been performed at those depths on hydrox. It is pretty far from being considered routine, of course, but depending on how quickly a rescue mission could be put together, this might not be the worst possible idea. Maybe. I mean, it is better than a bunch of the alterntives, right?

Some effort will need to be made to scrub the inflowing gas of toxic components (and remember that the considerable pressure can make small percentages of noxious contaminants quite lethal).

Note that it isn't beyond the realms of possibility that the ship has its own supply of H2... it is a very useful low molecular weight propellant for a whole range of engines (including the sort of nuclear rockets which might take you to saturn). With a bit of clever plumbing, pure liquid H2 from the propellant tanks can be warmed and expanded in the atmosphere outside, then pumped back inside to displace the possibly-toxic local atmosphere.

Long term effects of living in a super-pressurised high-hydrogen atmosphere won't be detailed here, but you probably don't want to be staying there long term.

  • $\begingroup$ A "hydrox" breathing mixture is a longer term solution, so those long term side effects are relevant. ("Hydroheliox" is better, and not impossible since Saturn's atmosphere is at least 4% helium by volume) $\endgroup$ Mar 16, 2021 at 12:38
  • $\begingroup$ @MikeSerfas its kinda depends on the timescale of a rescue... you haven't specified in the question, but I feel like any answer at this point is going to be short term, "just don't die" rather than even medium term stabilisation. Saturation diving can involve multiple-week stays at pressure, but possibly not this much pressure. A helium blend may be useful for deeper dives (200-250+m), but for "just" 15atm plain hydrox might be just fine even for longer stays. (possibly useful reference from a COMEX EU grant blurb). $\endgroup$ Mar 16, 2021 at 12:50
  • $\begingroup$ I'd never heard of hydrox before -- but that is definitely what the scenario calls for. The people in this story have a unique opportunity to study the long term effects of hydrogen narcosis. $\endgroup$ Mar 16, 2021 at 13:17
  • $\begingroup$ As I recall, the reason for breathing hydrogen instead of helium is because at these high pressures the air is getting noticeably viscus. Hydrogen is less "thick" to get down your windpipe. (My classes and certification are for plain SCUBA. There was just a page and casual discussion of "technical" diving and how it overcomes the limits we were learning about) $\endgroup$
    – JDługosz
    Mar 16, 2021 at 17:34
  • $\begingroup$ @JDługosz I'm fairly certain that even at that depth helium viscosity isn't an issue, but a bit of hydrogen in your breathing gas helps avoid HPNS which you can get from using helium as your only diluent. There are various other good reasons to use it, but a comment thread isn't really the right place to go into the details ;-) $\endgroup$ Mar 16, 2021 at 18:18

Set fires!

Open flames will burn the hydrogen that passes through them as the air circulates, and prevent the hydrogen concentration from building up to 4%. Recall that gasses only "explode" (flash over) if the mixture is within a certain range.

reduce the oxygen

People can breathe with less oxygen than the "sea level" comfortable environment of the ship. Use a higher absolute pressure that you can maintain (we know you can't get high enough to prevent influx, but I suppose it helps) and reduce the partial pressure of oxygen to still-breathable levels.

I don't know what that does to the needed mixture ratio.

increase the oxygen??

I don't know for sure how it works, so look into the chemistry perhaps on the Chemistry Stack Exchange. But it it takes 4% hydrogen to explode, would adding more oxygen cause it to reduce the percentage that is hydrogen? Adding oxygen has the same effect as reducing hydrogen, percentage wise. Imagine the drama for convincing the Captain about that!

remove the oxygen

If people use small portable bottles with the little nose tubes, the atmosphere in the ship can have all the oxygen removed.

scrub the hydrogen

Other than open flame (the initial stop-gap effort), come up with chemical scrubbers that rapidly absorb the hydrogen or use catalysts to react it safely inside a container that air is being pumped through.

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    $\begingroup$ Increasing the oxygen is ruled out by the scenario -we don't have 15 atm to work with to maintain the pressure, and otherwise, I don't think the hydrogen can possibly be below 4%. "Removing the oxygen" is definitely an option for longer term - it has maximum convenience, with the sticky issue that there are probably many ways to blow yourself up. Also, the corneas of the eyes need external oxygen. A carefully designed mask mixing "hydrox" breathing mixture would be more prudent... but someone is bound to improvise with a bottle. $\endgroup$ Mar 16, 2021 at 15:58
  • $\begingroup$ hydrogen can easily be above 75% instead. Even at normal pressure you could still have a comfortable partial pressure of oxygen. $\endgroup$
    – JDługosz
    Mar 16, 2021 at 17:31

Start by getting most of your Oxygen into tanks, as much as possible. Then build a Sugar/Oxygen bomb to blow an Airlock and vent the whole ship before entering the atmosphere (saturnsphere?). Then set the airlocks and bulkheads to have 4 layers of pressure to prevent them from critical error. Outside you have 15 bar, first layer is 10 bar, second one is 5 bar, third is Vacuum, 4 layer is breathable Air. Put your Crew into the 4th layer. Then try to patch up as much leaks as possible, and continue to pump saturn-air back to the outside. If necessary you could also embrace Saturn, let the 15 bar fill the ship and live in your space suits.


MacGyver take 2!

/aerofoil improvised from an origami habitation dome/

Your MacGyver got this thing out already to bring you down easy. And it is big, and it is draped over the ship already because you used it as an aerofoil coming down.

Probably that thing laying against the ship is why they are doing as well as they are! The exteroir pressure has pushed the material of the aerofoil into multiple cracks, sealing them. Your people can notice that some cracks are not leaking and some powder blue stuff is poking thru them. It is the powder blue of the earth sky that this dome is painted, because Earth people were going to live in it. There are birds and clouds painted on there too.

Now tuck your ship in. Pull that dome aerofoil down so that it covers the other cracks. The pressure difference will suck it into place. If it is not big enough to wrap the whole ship get out another one.

The graphene you landed on offers longer term possibilities. That stuff comes in big sheets. Maybe you can peel some up and augment your aerofoil.


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