This question is actually a three part question.

In the doctor who episode The Poison Sky

  1. When the doctor activates the device that burns all the gas, why did it only burn the gas in the atmosphere if the gas had higher concentrations closer to the ground?

  2. Why when he burnt all the gas did the cars not keep producing more?

  3. If the gas in the atmosphere was the only gas to burn, why did the other gas on the ground disappear (not only that but it went away quickly).

Seems to me that if this were to ever happen really, either the gas would ignite over the whole planet and kill everything (or at the very least burn all the oxygen and everyone would suffocate), or the gas would linger and everyone would still suffocate.

  • 2
    As with many Doctor Who episodes, I thought this was silly too. Decided it was one of those 'suspend disbelief' moments.
    – B. Elliott
    Jan 26, 2013 at 17:43
  • 1
    Yep. Too many questions, like why would the atmosphere need to be poisonous to serve as a infirmary for Sontarans, while Sontarans are perfectly capable of breathing normal air?
    – Mr Lister
    Jan 26, 2013 at 17:46
  • And the obvious question: if fire uses oxygen to burn why didn't it suffocate the entire planet?
    – KutuluMike
    Jan 26, 2013 at 18:45
  • Glad to see I'm not the only one with a big question mark above my head at the end of this episode. I think this question is probably going to have to be closed with no answer other than "it just happened that way because that's how they wrote it." Thanks all for the comments! If anyone sees fit to answer it in the future, thanks in advance. :)
    – Dragus
    Jan 26, 2013 at 19:43
  • Also @MrLister, it is stated that the gas is "Clone Food" which probably means the cloning process needed something to sustain them before they could breath on their own. This probably has something to do with the reason they need a planet instead of being able to use a ship.
    – Dragus
    Jan 27, 2013 at 3:58

2 Answers 2


well my best guess would be that the gas was rising to make a sort of gas shell for the clone world that the santarins(probly miss spelled the name) were tying to make

that or the doctor set the machine to only burn the gass in the uper level of the atmosphere and the cras probly stoped when the ship went BOOOOM

  • 1
    cras i ment gas sorry
    – bleachert
    Mar 8, 2013 at 3:23

The Doctor had set the device to specifically burn off that gas only. When the higher concentration in the upper atmosphere was burnt out, the gas near to the ground started dissipating in the air above, and reached non-lethal concentrations. The cars didn't continue producing the gas because maybe the Sontarans turned that system OFF after the initial release.

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