Not clear why you think that. 30km is quite far. [1] is a pretty good site to play around and get an idea how far the nuclear blast reaches. For example the Rus

Not clear why you think that. 30km is quite far. [1] is a pretty good site to play around and get an idea how far the nuclear blast reaches. For example the Russian Topol SS-25 (800 kT TNT) has an air blast radius (5psi) of 6.5 km. This is quite a large bomb. For comparison, most US warheads are W76, with a 100kT yield and a blast radius of 1km. The largest currently deployed warhead is the Chinese Dong-Feng-5, which at 5MT has a blast radius of 12 km. [1] https://nuclearsecrecy.com/nukemap/ https://nuclearsecrecy.com/nukemap/