The fallout from a dirty bomb would be relatively easily cleaned up with showers and a few hoses on streets and buildings. The people close to the blast would a

The fallout from a dirty bomb would be relatively easily cleaned up with showers and a few hoses on streets and buildings. The people close to the blast would also inhale some radioactive dust which will be a much bigger problem, but most of them will probably just die because of the conventional explosion itself. The radioactive dust is definitely far less problematic than shrapnel from a fragmentation bomb. Overall dirty bombs are really not a problem bigger than any other kind of bomb.