Libyan rebels are rejoicing in Tripoli by firing their guns in the air. Little do they know, this is one of the dumbest ways they could celebrate.
It all comes down to our good friend gravity. When a bullet goes up, it must come down and you have little control where it's going to land. Though a falling bullet is estimated to have only 10% of its original muzzle velocity, it still has a good chance of injuring and possibly even killing you.
A 30-caliber bullet falls at 200 MPH, while a 50-caliber falls at almost 330 MPH. And that's why they kill people. A bullet falling at as little as 105 MPH can pierce the skin, while one falling at 135 MPH can travel through your skull and into your brain.
Even if the bullet falls at a rate somewhere between 100 and 135MPH , it still can knock you on the head and give you a traumatic brain injury. Of course the bullet can miss your head, but it could hit you in the arms, shoulders, and legs. Ouch. [Amazing Facts and The Straight Dope]