Safety isn't a huge concern, IMO (as least as far as discharging the blank goes). A blank doesn't have a bore-sized lead plug containing the pressure, and as we all know a cartridge will expend most of its energy to the atmosphere if the pressure isn't contained and directed to accelerate something (e.g. bursting rounds outside a chamber are relatively harmless).
The issue is that extra 3mm. 9mm headspaces on the cartridge mouth, so even with a roll crimp (which, btw, wouldn't matter since headspacing primarily affects the leade, which is meaningless without a projectile) the case is going to be too long to allow the breech to go fully into battery.
To get what you want, you'll need to buy some blank dies for your reloading press. And for god's sake don't pull a Brandon Lee.
Also, a "standard semi-auto pistol" won't cycle blanks, of course. The standard approach is to install a bore restrictor, so as to somewhat increase the backpressure, and lighten the springs. Most pistols (especially 1911s) often need further work, such as a throwaway barrel with the locking lugs filed off.
ETA: These guys sell blanks in standard cartridge sizes:
http://www.atlanticwallblanks.com/