Metaphorically speaking, one could argue that all of the choices you list can be considered relevant to the man who has been gassed. I would suggest, however, that the most striking image is one not alluded to in your question: that of "fire." The soldier is "flound'ring like a man in fire or lime." Owen is suggesting that when one is subjected to poison gas, it is similar to being burnt to death. But, paradoxically, it's also as if one's lungs are filled with water:
As under a green sea, I saw him drowning.
The multiple images of fire, lime, and water give the impression that all the elements of man and of nature have been arrayed against the helpless soldier—or rather, against all the men unlucky enough to be in combat. The irrationality of war and the powerlessness of ordinary men are emphasized by the central word "floundering," regardless of the specific elements in which each man has become trapped and helpless.