Again, covered in the
FAQs, specifically the designers commentary. You can't modify below a 1, so yes, a result of "0" would blow up because it's one.
A roll of 2 with -1 to hit will overheat, same as a roll of 2 or 3 with -2 to hit, and so forth.
That's why the meme of moving overheating plasma at night exists.