If you are at 1% HP, the only thing that can kill you are attacks/spells/effects that exceed 100% of your maximum HP.
Same goes for enemies.
Also, the trait states it doesn’t stack, but it DOES work with other damage reduction traits. If you have another trait that reduces damage by 25%, you need to hit for 400% of maximum life if the target is at 1%.
Maybe a cap for [Hell’s Protection] at 50% reduction is in order?