Korean fir is usually quite resilient in the landscape.  Since the damage appears to be mostly on one side, have there been any sprays used that could have drifted onto it, or is it facing a road that is salted in winter?  It that side more exposed to wind or sun?  When was the damage first apparent?  Also, I can't tell from the photo, but is this year's growth affected?

Fir trees do best in acidic, well-drained soil with consistent moisture.  They will not tolerate overly wet soil or prolonged drought.  One possibility is overly dry soil followed by sun and wind drawing moisture out of the tree, which it was unable to replace.  There are many other possibilities.  

If you can provide answers to these questions, and comment a bit more on irrigation, fertilization, and any changes that may have disturbed the tree, that would be helpful in ferreting out what may be happening here.