If your using clamps and lifting heavy weights by yourself you are really asking for trouble. Your one saving grace is to have the weights slide right off the bar. I've seen many, many people nearly choke themselves to death because of clamps.
Its much better to be embarrassed and have the weights go crashing down then be dead.
But then again, its always wise to use a spotter. Even if your as cool as Steve's workout buddy.
QOTD:
I lost to a guy by one point in the arcades on NFL Blitz. It turned out that they guy was the #1 player at that arcade. He was sweating and cursing the whole game and I was just amazed it was so close. Sure I lost and it was Blitz but I must have only been about 13 years old.