When I started attending tech-school to become a mechanic, one of the first things they teach is (ironically enough) safety.
They do this by having you memorize the locations of fire extinguishers, chemical properties, etc.
But most important is putting a vehicle up in the air with a lift. These lifts use 4 arms, each on a large steel pin, to contact points on the four corners of a vehicle.
With the vehicle (an early 90's Ford Bronco, around 2 1/2 tons) in the air, the whole class (myself included) proceeded to wander around underneath.
I noticed that one arm was looking a little saggy. Lo and behold, the pin was itching to pop right the hell out, which would have dropped the truck on about 13 people (again, me included).
Other than that, I got hit (on foot) by a Cavalier that ran a stop sign.