How is it possible to have high voltage that is safe?
Safety standards are different for a taser from an ordinary electrical appliance.

The whole point of a taser is to have an adverse effect on the human body, and a small fraction of people who get tased do die from it. This risk is considered acceptable (by some people), since the alternative is for the taser user to use a gun or nightstick instead, either of which has risk of death.

However, if you are designing a kitchen appliance or a television set, if it has the same effect on its user as a taser, that would be a gross failure, and an unacceptable risk.