mmmm, now that I think about it a little more. I dont believe unless your within blast range of ground zero the electro-magnet solenoid in an electronic safe door would be effected. Its sheilded by something like 1/16" to 1/8" steel that would defuse the pulse. Government EMP safe laptops rely on a foil layer .007" - .009" thick to defuse EMP... The keypad may fry, I'd be surprised if it got to the solenoid down at the handle in the middle of the door though. Those little things often only need 3VDC to actuate. Beter be ready to turn that handle as soon as you hook up your 9 volt, it'll likely fry the solenoid in a second or two, but once you turn the handle past the keyway its all good. EMP works something similar to ultrasonic welding, melting and fusing together circuitry.
It's feasable that North Korea will give us all the oportunity to learn more first hand very soon!
Combination safes are as easy to defeat as electronic. Pry or pull off the dial, chisel through the plate behind, and you'll find tumblers just like a key lock.
A human mind made it, a human mind can defeat it. Big price tags on safes are to buy cool looks, and cool features like recessed mood lighting. I've seen one with a mirrored ceiling! Perverts!