Safe yes, but not fool-proof. The firing pin is shorter than the block around it. The spring holds it to the rear which allows the hammer impart sufficient energy to send the pin forward through the bolt face to fire the round.
When the hammer is down the firing pin is pushed forward to allow the hammer to rest on the slide. But the front of the pin is still behind the bolt face.
This is old-timer stuff (I'm 72 and have been shooting for 60 or so years). I learned it from an old timer in my early days. One younger shooter I know ha learned the same thing.
You must be sober and thoughtful while putting the hammer down.
Then I'm OK with putting it in a pocket holster for carry.
