Any electric tool with a trigger lock combined with someone not thinking everything through.
Saw two guys (temp workers) belt sanding a piece of Douglas fir, probably 20 feet long, to be used in a timber frame structure. The timber gets moved around the shop either by overhead crane or on roller conveyor belts, the kind with the steel rollers. This piece was on rollers, both guys locked the trigger on the belt sander, and started sanding, and watched as the beam flew down the rollers and fell off onto the floor. Then, to a man, put down the belt sanders to go get the beam, and watched as the belt sanders flew off down the floor.
Another guy, actually a lead hand for the company, standing on the top step of a 12 foot stepladder, you know the one that says "This is not a step!", had to drill a hole in something overhead. The trigger locked on at some point, then the drill bit snagged and stuck, and proceeded to whip around and keep smacking him in the chin till someone could quit laughing hard enough to pull the cord.
Same guy, you know how they say in safety lectures to make sure you are clipped in when running a Skyjack/scissorlift? And also how you should always turn around and back down the ladder, facing the Skyjack? Well, he was tied in alright....but he just went to jump down off the Skyjack, and was hanging there till someone went to go get him.
I've learned sometimes co-workers/friends/neighbours are the most dangerous, and most people need a 10 foot safety zone around them
