Shooting actually straight up is very safe, at least for people on the ground. The terminal velocity of a bullet is fast enough to make you say "ouch", but not much else.

Problems can arise if you're shooting up-ish, but shooting straight up means the bullet has zero velocity relative to its origin at the apex, so the only speed it has from that point forward is imparted by gravity and wind, pretty much.

The image is of a starter pistol, though.