The detonation of a nuclear warhead in deep space, where the gravitational field is extremely weak, would produce a spherical pressure wave that would expand outwards at great velocity. Every type of radiation given off by the fusion of atoms would cause the area affected to increase in volume very quickly, as the radiation would be traveling at the speed of light. The pressure wave would be very intense initially, but would decrease inversely with the distance from the detonation. So the farther away from the blast that you were, the degree of the effects that you would experience would be less. But, as there is very little in interstellar space to slow down the wave, you would have to get VERY far from the blast area before you were at a safe distance. There would be no fire typical of Earth conditions, as there is essentially no oxygen in space to sustain chemical burning. There would however be copious amounts of both visible light, and other forms of energetic radiation expelled--x-ray, ultraviolet, even gamma rays if the blast were powerful enough. Possibly even sound waves, but that's another story altogether. As to the premise of a nuclear detonation at the event horizon of a black hole, as stated previously, such an explosion would assume a fairly spherical volume. However, I am not sure what sort of dimension an event horizon takes, i.e. I don't know if it is one sided, so you can only see it/get to it from one direction (imagine a dark black circle drawn on a sheet of white paper--you can see the circle/event horizon from only one side of the paper), or if it can be seen/approached from both sides (imagine a donut, known as a torus--you can see both sides of it and go through it from either side). This would be important in the answer to your question, as this would impact how much of the radiation would be subsumed by the gravity of the black hole, and how much of it would be able to escape. The varying angles of a two-dimensional object versus a three-dimensional object would alter the vectors of the radiation/particulate matter expelled from the blast.