I'm talking about DC and/or AC. I've read about people surviving extremely high voltage shock(300kV) but that could be explained by extremely high resistance in the circuit that resulted insufficient current to cause death.
The main driver for the effect of electricity on the human body is current, not Voltage or Power (Watts).
The interaction is complicated, so you can't easily apply a single number to "safe" or "deadly". Effects are can be neurological, chemical and thermal. See https://en.wikipedia.org/wiki/Electrical_injury