I still think it depends on the strength of the bomb.
You'd still face cancer and other problems, but the bombs dropped on Japan did offer some real world examples of people being near the incident and being partially shielded not having some of the skin problems.
And bomb shelters were also known as fallout shelters. Not designed to withstand a hit so much as the later contamination (and you'd probably still evacuate the area afterwards when possible).
What would a dirty bomb do?
An hour later those same troops walked through ground zero inspecting the damage.