This description of the narrator might suggest be seen as an injection dark humor to the story by indicating that the narrator was saved by his own clumsiness. It might be considered as situational irony to show the horrible death he is about to suffer.
I believe you are correct. That's what I would put.
Answer:
I've not read Farenheit 451, but from the quote I believe it's trying to say "it doesn't matter what you do, as long as you impact it enough to be remembered" or something similar, though again I may be wrong as I've not read the book.
The slope of line c would be 1