I heard, that for each nuclear explosion, there's a chance the WHOLE atmosphere will blow up. How big is it?

Question

I've heard, that for EACH nuclear explosion, there's a statistical chance the WHOLE atmosphere will blow up and thus eliminating mankind. It was estimated that the chance was once in a million or so. But i heard that number many years ago. What's the current view on this?
Maybe the chance is 1 in only 1000 or so?

Answer 1

That's a matter of history. Scientists used to believe that was a possibility. It is now known to be false. No such chain reaction will occur.