There is an awful lotof guess work in determining how shielded/hardened a piece of electronic equipment may be. Size of blast, distance from blast, etc. Every explosion, conventional or not produces an EMP field. Best defense is a steel re-enforced concrete enclosure, with some form of copper or metal mesh curtains to cover window openings, all of which are shunted to ground. Think of it as a large Faraday cage. Dissipation and grounding to kill the EMP are the main goals. For general electronics in civilian hands, electronics stored in a trash can and placed in an underground bunker, or concrete basement should be adequate. Automobiles are another story. Todays cars and trucks have many computers controling among other things fuel delivery, spark and timing, and the transmission. Short of keeping spares and being able to access the area where the computers are, you are basically screwed when it comes to protecting your transportation from EMP. The only other real option is to have a pre 1968 car or truck without the computers.