I would agree with the others.
Using blanks is not adviseable. IF the situation deteriorates to the points that firearms are necassary, it is too late for blanks. If you want to frighten/intimidate without bullets, get a good Surefire or Streamlight flashlight, and a can of pepper spray or taser. Yell, loudly, that you are aware of their presence and are prepared to contact law enforcement, then resort to your weapons if necassary. I beleive that, if you are carrying a gun with a blank, you are much more likely to use it in an unnecessary situation. This is not a personal accusation, but a factual statement based on years of military training with both blanks and live ammo.
Seriously consider all possibilities and maybe talk to law enforcement/district attorney before taking this route.
"I won't be wronged, I won't be insulted, and I won't be laid a hand on. I don't do these things to others and I expect the same from them." - John Wayne