From the article: The thing is, in that particular explosion, those guys would have been in a pretty safe position. The bomb itself was a small one (by nuclear standards — 2 kilotons) and it was way, way above their heads. They weren't in a zone to be too affected by the immediate radiation. The bomb was small enough and high enough that it wouldn't have sucked up dust to produce much fallout. The remaining cloud would have been full of (nasty) fission products, but it would have been extremely hot and most of it would have stayed aloft until it cooled down, by which point it probably would have been spread more diffusely.