In what sense can an object in outer space be "on fire"? The famous "Tears in rain" soliloquy in Blade Runner goes like this:

I've... seen things you people wouldn't believe... [contemptuous
  laugh] Attack ships on fire off the shoulder of Orion. I watched
  c-beams glitter in the dark near the Tannhäuser Gate. All those...
  moments... will be lost in time, like [small cough] tears... in...
  rain. Time... to die...

In what sense can attack ships be "on fire" in space? I would think that lack of oxygen would externally-visible keep combustion as we know it on Earth from going on more than momentarily, but perhaps I'm wrong. Or maybe there's some other phenomenon we would describe as "on fire." Could some sort of a nuclear reaction be described as "on fire"?
 A: Ok... ask yourself "what is fire?"  Check out Webster rather than Wikipedia:  http://www.merriam-webster.com/dictionary/fire
Fire is combustion, which is the rapid oxidation of a substance creating a plasma.  So, what you need to have a "fire in space" is you need to have oxygen, a material that can be oxidized and some initial energy to start the reaction going.
We humans have done this in real life on the ISS.  See http://www.theatlantic.com/video/index/276950/fire-in-space/ and http://www.smithsonianmag.com/science-nature/in-space-flames-behave-in-ways-nobody-thought-possible-132637810/?no-ist .  So the flames are real and the "explosions" can be real too.
In addition, it is possible to weld and "explode fireballs" underwater:  http://www.youtube.com/watch?v=mvBG_Ly-2I8 and http://www.aws.org/education/plunge.html.  Again, you need to supply your own oxygen.
Nuclear reactions are not "on fire".  They can be hot enough to cause a plasma and an explosion, but technically fire is oxygen combining with another substance chemically.  Since all chemical reactions (yes all) are the result of electron orbital interactions are do not include neutrons or the nucleus, fire cannot be a "nuclear reaction" by definition.
