In case of necessity -- for example in case of fire or contamination -- is it possible for any pressurized element of the ISS to be exposed to vacuum?

If all compartments and airlocks were to be depressurized, I assume it would be possible for astronauts to take refuge in the Soyuz until the station is pressurized again.

Is this something that is feasible without damages to the elements? if so:

  • Has it been anticipated for specific eventualities?
  • What would be the time required to repressurize the whole station?
  • Would that require an immediate re-supply for food, water, etc?

Edited. About Zvezda:

"Much of the equipment necessary for maintaining ISS on-orbit, in the SM, is air-cooled and/or not vacuum-compatible, and will therefore eventually fail after a depressurization"
(source: SpaceViews, 2000 - Citing Nasa ISS Safety Noncompliance Report)

Related information, but not duplicate questions:

  • $\begingroup$ All of it or any of the two (US and Russian) segments? $\endgroup$
    – TildalWave
    Jan 11, 2015 at 14:45
  • 3
    $\begingroup$ Well full depressurization is one of last resort options, compartmental depressurization would be preferable if it really needs to be done. Either case you're doing a lot of damage (e.g. some pressurized environment experiments won't survive it, including live animals) to suppress fire like that, but it would be possible. I ask because the segments can be isolated even remotely (has been done before), and are essentially docked to each other standalone units with own life support systems. Some systems are obviously shared (like solar power) but not necessarily in an emergency scenario. $\endgroup$
    – TildalWave
    Jan 11, 2015 at 16:07
  • 1
    $\begingroup$ @TildalWave: Thanks. I could open several reports by R. Friedman. Partial depressurization as low as 100 hPa is mentioned as a last resort method for fire suppression. Consequences are unfortunately not discussed. $\endgroup$
    – mins
    Jan 11, 2015 at 17:04
  • 1
    $\begingroup$ I restored this question, if you don't mind. It's a good one and while it might not have any factual answer yet, this might change soon enough. For example, in this video, about 18 minutes in, Robyn Gatens (Acting Deputy Director, ISS Program, NASA HQ HEOMD) mentions that they're going to test a large fire behavior (no idea yet what that entails) on the ISS once Cygnus gets there. I was actually looking for your question because I kept it in my mind waiting to stumble upon more conclusive data, so please reconsider keeping it. Thanks! $\endgroup$
    – TildalWave
    May 28, 2015 at 21:18
  • 1
    $\begingroup$ @TildalWave: My pleasure. Thanks for the great link too! $\endgroup$
    – mins
    May 29, 2015 at 21:54

1 Answer 1


'What could go wrong' questions are hard to answer, but I would like to attempt it.
The reason the depressuarization happened is important. If it was planned, they would likely focus on pressurizing it quietly, minimizing risk.
If it was an accident, the worst case scenario is evacuation. Then it would take months getting things back to normal if the problem can not be fixed remotely, and repairing must wait for a new crew of cosmonauts

Machines do not need air, but they need cooling. For instance the Elektron units of the Russian segment, a major component of the oxygen regenerating system, are known to be prone to overheating. A lot of systems must be shut down to avoid that. But electronics may also suffer due to too low temperatures, and must if not kept at room temperature by the air be kept warm with heaters. (The Chinese lunar rover finally failed due to the extremely cold temperatures during the lunar night.)
To protect everything from overheating or freezing is thus a careful balance of shutting down, cooling and warming.
The major components of the ISS are not air cooled. instead, they are cooled by pipes containing coolant. A depressuarization may not affect those pipelines, but again, that really depends on what happened to the station. Leaks draining the pipes will render them useless.
Vacuum is also a good insulator, thus heat is likely to travel through the walls instead of radiating. That may in turn cause unpredictable cold and hot spots. See for instance this launch failure due to unexpecteed freezing of propellant.
A lot of smaller electric and electronic equipment is entirely dependent on air cooling (laptops, portable monitors). The best way of protecting them is simply turning them off. Even if not, like during an emergency, they are lightweight and easy to replace on the next resupply mission.

The next big issue is air. According to this, the air system is capable of replacing the air. But because of the risk of leaks, the station would likely be slowly re-pressurized to detect them. Because even small leaks are a huge problem, they would need to monitor the station for quite a long time at a low pressure. So a re-pressurization would likely take a couple of days. If the station happens to be without air for more than a brief period of time, on-board experiments, especially living, might suffer. If the accident in addition to puncture the station also involves a shock or explosion, experiments not relying on air but otherwise sensitive, like crystal growth, are vulnerable too.
enter image description here

There might be a lot of parts not vacuum compatible, but it is difficult to find such data for all the systems. I assume equipment are placed in pressurized compartments because of that, otherwise, these areas would be used for habitation instead.

  • $\begingroup$ Is there actually anything in the ISS that requires air cooling assuming there's no live occupants in it? ECLSS is largely cooled with the external ammonia loop and it would be off, together with the Oxygen Generating System and Carbon Dioxide Removal Assembly (as well as Elektron and Vozdukh, their counterparts in the Russian segment). The rest is then some smaller equipment like laptops and such that are air cooled when active, but those would be also off or already suffer damage from whatever caused the need for depressurization (fire, air contamination maybe with ammonia or hydrazine,...). $\endgroup$
    – TildalWave
    Dec 14, 2015 at 17:38
  • $\begingroup$ @TildalWave♦ That is what I am trying to find out more about right now, as it is a good question deserving a good answer. I am looking forward to expand it. $\endgroup$ Dec 14, 2015 at 17:42

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