Had a friend killed by one. Weird situation:
Paul was welding under a semi trailer doing repairs. He was working in the summer, for the most part properly clothed and safety gear on. He had taken his gloves off to do something and then when done, grabbed a fresh electrode and clamped it up in the holder. At the same time his head was near the frame and his glasses were touching the frame. When the electrode contacted the holder, and with is sweaty hands and head, he completed the circuit and was killed.
RIP Paul O.
Weird situation
PS
I have been stung by both a mig and a tig. Like above, in the summer, when I am sweaty.