Did some people theorize that testing a nuclear weapon could cause the entire atmosphere of the earth to ignite?
I only know about this because as a kid I read a lot of pre-space-age sci-fi, and there was a story either by Heinlein or Asimov where the solution to this "danger" was to put nuclear fusion plants in orbit.
That gives you, a.o. https://fas.org/sgp/othergov/doe/lanl/docs1/00329010.pdf
Safety factor to get some nitrogen ignition is a worrying 1.5 when using fusion bombs of a thousand cubic meters, but even then, the reaction will fizzle out (at least, that's what I get from the abstract)