How much heat can a Fire Pokemon withstand?

I am kind of new here, and what I am about to ask is out of pure curiosity. I have read a few posts about the types of questions that I should and should not ask, and I do believe that this question is valid.

Say that a Fire Pokemon (like a Charizard) is placed inside a box which begins to heat until it reaches a theoretical infinity. At what point does it 1.) feel pain 2.) burn 3.) die. If anyone has any canonical feats that would answer this, that would be great.