Could burning debris keep burning in space?
To have a fire you need three things: oxygen, heat and flammable material, therefore the cold vacuum of space is the last place you would expect something to burn. I was, however, wondering if a very large damaged spaceship would change this.
Suppose for instance that an explosion has happened aboard a spaceship, which not only has damaged a fuel pipe inside the spaceship, such that anything close to the explosion has been soaked in flammable liquids and has caught fire, but which also has made a significant hole in the exterior hull of the ship.
If the hole is big enough, and if the ship has so much air that it will not be emptied too quickly, I assume that the pressure of the air inside the ship would be enough to blow several of the fuel-soaked and burning things near the hole out into space.
As these burning pieces of debris leave the damaged spaceship, I was, however, wondering if they would keep burning for a short period of time, or if the fire would die out as soon as they left the spaceship.
My first hypothesis was that the burning debris could keep burning, at least the first few seconds after leaving the spaceship, since oxygen needed for the burning debris to keep burning would be provided by the air flowing out of the spaceship, the temperature by the combined heat of the burning debris and the air "“ which would have been heated up by the fire inside the spaceship "“ (also keep in mind that since there are no matter in space, the only way for the air and debris to lose thermal energy is through radiation, which is not very efficient) and the flammable material by the leaked fuel in which the burning debris is assumed to be soaked.
My second hypothesis was however that the burning debris would stop burning the very second it flew through the hole in the spaceship "“ perhaps even before that because the expansion of the air leaving the ship would cause it to cool down very rapidly, such that the air surrounding the burning debris very quickly would absorb almost all the thermal energy of the debris, thus making the fire die out.
My question is, therefore, taking all this into account (and perhaps more factors that I have completely missed) is it likely that burning debris in the given situation, could keep burning for more than a few seconds in space -- at least long enough to justify using burning debris as a visual effect in games or animations -- or is burning debris in space simply unthinkable.
This post was sourced from https://worldbuilding.stackexchange.com/q/83072. It is licensed under CC BY-SA 3.0.
1 answer
First off, something that might seem like an inconsequential detail or perhaps even nitpicking, but really isn't in this case: You don't need oxygen for something to burn. What you need is an oxidizer, of which on Earth oxygen happens to be one of the most readily available. Thus the typical fire triangle says oxygen, but that is really a simplification.
The Fire triangle created by Gustavb. Self-published work by Gustavb, used under CC-BY-SA-3.0.
Fuel plus oxidizer plus heat equals (typically exothermic) chemical reaction A.K.A. fire.
There are quite a few materials that do not require an external source of oxidizer to burn. For example, lithium-based battery chemistries typically contain their own oxidizer, and as such can create very difficult-to-put-out fires. Compare for example Why is there so much fear surrounding LiPo batteries? on Electrical Engineering, perhaps particularly metacollin's answer which discusses this directly.
What's more, spacecraft typically contain lots of such compounds. Quite a few rocket fuels are hypergolic, which means that two components will spontaneously combust upon contact. This is used for a variety of reasons, not the least of which is the relative simplicity (hypergolics are nasty, but they are a known nasty; in return, you don't need to worry about e.g. ignition). Even those that aren't hypergolic are typically highly energetic, and of course being designed to operate in a vacuum, a rocket will be bringing its own oxidizer along with the fuel. One of the workhorses of rocket propellants is cryogenic liquid hydrogen as fuel and liquid oxygen as oxidizer, which combine in the well-known chemical reaction to form dihydrogen monoxide -- also known as water, typically in the form of water vapor due to the high temperatures involved.
If a fuel pipe has been ruptured aboard a spacecraft, there is a very good chance that a nearby oxidizer pipe has also been damaged. (Typical spacecraft use bipropellants, but monopropellants are also a thing.) Depending on the exact conditions and the specific propellant combination in use, the two may combust spontaneously (hypergolics) or not (non-hypergolics), but there's a good chance that whatever damaged the spacecraft might have caused a spark, providing a source of ignition. As long as the fuel and oxidizer flow is maintained, then, they will continue to react with each other.
Once a sufficiently hot fire comes into contact with flammable materials, those materials will also start to burn, but only so long as there is a suitable oxidizer present.
Also keep in mind that the ability of a material to burn is typically a function of the amount of oxidizer present. Apollo 1 illustrated this quite well, and one quote sticks in my mind from a Nova documentary on the US moon program: At 15 pounds per square inch of oxygen, aluminum burns. We don't typically think of metals as flammable, but they are. Even iron is flammable in the presence of typical amounts of oxygen, although at a very slow rate: we refer to it as rusting, but just like hydrogen and oxygen forms dihydrogen monoxide, iron and oxygen forms ferrite oxide.
All this to say that yes, depending on specific conditions, having things burning in outer space is absolutely possible. All you need is a suitable local concentration of both fuel and oxidizer, as well as something to get the chemical reaction started. Localized spacecraft damage can easily provide all three.
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