Another spacey question

Q: Watching footage of astronauts slurping up globules of water in zero-G always made me wonder: What does a flame look like in zero-G? Let's assume you can burn a candle safely in the ISS. Normally heat pulls the candle up into the familiar tear-drop shape, but in space, which way is up? Is it just a sphere?

A: Voila. The flame is, in fact, a sphere. An interesting side note is that, without gravity, the flame can't get rid of the CO2 generated in the combustion, so it snuffs itself out unless there is a breeze to carry away the CO2 and keep the the flame exposed to oxygen.

The irony is that astronauts have been killed by flames while on the ground. In 1961 cosmonaut Valentin Bondarenko, and later in 1967, the crew of Apollo 1, were killed by accidental fires that ignited the pure oxygen environments in their enclosures. Subsequent missions reduced the oxygen content of the air to 60% Oxygen and boosted Nitrogen to 40% to prevent fireballs like those in the future.

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