Let's tackle this from several angles: Physical shock: depends on proximity to the ground zero and strength of the blast, as well as internal padding (none in the typical safe) and physical trauma suffered by impact. Heat: Again, proximity to ground zero and size of blast makes a difference here. Also, how well insulated the safe is from effects of thermal radiation (fire rating, if you will). Radiation: Two major kinds of radiation here to consider: Gamma: High energy gammas, plus X-ray (and a bunch of other electromagnatic energy) are the two biggest types of electromagnetic radiation to be concerned with. This also depends upon proximity to the blast and warhead size. The steel and concrete lining of the safe will provice SOME radiation shielding, perhaps as much as one tenth-thicknesses depending on the size of the safe. But that would be a d*mned hefty safe. A tenth thickness is the thickness of a shielding material which will reduce the incoming radiation levels to one tenth of it's original levels. Depending on the energy levels of the radiation, this could be 4 inches of steel and several feet of concrete. Which means the typical safe would provide you next to nothing in terms of shielding for this type of radiation. Neutron radiation: Neutrons don't really give a darn about steel, concrete, lead and so forth for shielding. Neutrons are extremely penetrating and essentially willpass right through the steel and concrete linings of a sturdy gun safe with no reduction in radiation levels. Now, if the safe were additinally shielded by damp earth, where lots of water would be present to slow down and absorb the neutrons, then maybe. But the safe alone? No luck here. Neutrons will pass right through. So all you're left with is distance from ground zero and the warhead blast. Now, if a neutron warhead were used, then blast and infrared heating effectes would be minimal. However, the neutrons, as discussed above, would not be affected by the steel and concrete of the safe. So; Is it possible to survive a nuclear explosion by locking yourself inside a safe? Yes, it is, especially if it's further shielded in a basement, behind heavy embankments, or far enough away from the blast. Getting out depends upon the internal design of the safe, how it lands, and whether or not you sruvived the initial physical shock and landing.