We humans can withstand very high G’s but it all depends for how long do we withstand them! People have survived high G’s in accidents and plane crashes (some times up to friction of second with 80 G’s). The human tolerances depend on the size of the g-force, its length, time, direction, and the person’s posture. In addition g-tolerance is often trainable; and there is also considerable variation in innate ability between individuals.
High G for long period are experienced by aviators (stunt pilots and so.) 10 – 12 G’s for a few seconds, and astronauts during liftoff (its lower G’s for longer periods)
And us during a cough (3.5 g) and during a sneeze (2.9 g)
Lethal car accidents are usually around 30 – 60 G’s