Sound and Noise Distance

[nuke11]

And for those that want to figure out how far aware you can hear an explosion;

180dB - 1 POUND T.N.T. AT 15 FEET

[mmartin798]

There are other factors to consider if you want to dig deep enough. Lets say you have birds singing nearby (44dB). A firefight breaks out at the 11.3km, using the distance referenced above (30dB). If we add the two sounds together, we get 44.169 dB (The math is non-trivial, see here for a calculator http://www.sengpielaudio.com/calculator-spl.htm)

This change in sound is well below the 3dB threshold for hearing a change. So the bird will completely hide the firefight. The 1 pound of TNT might be heard.