G-force

The amount of g-force the human body can handle actually depends on a couple of things:
1. How long the interaction is (how long the force is applied)
2. What direction the interaction is (horizontal or vertical)

Humans can withstain 100's of g's for example, for a mere second. However, over a sustained period of time (such as 20 g's for a minute) it can be deadly.

A typical person can sustain about 5g's in a vertical direction and about 17g in the horizontal direction.

The record for the most g force at an amusement park is 5.5g.

Fighter pilots can go between 6-9g, but may experience what is known as a "greyout" (temporary loss of vision, ability to speak, etc)

Formula One drivers typically experience 5g while breaking, 2g while accelerating, and 4-6 g when cornering.

Strongest g-forces survived by humans
Voluntarily: Colonel John Stapp in 1954 sustained 46.2 g in a rocket sled, while conducting research on the effects of human deceleration.
Involuntarily: Formula One racing car driver David Purley survived an estimated 179.8 g in 1977 when he decelerated from 173 km/h (108 mph) to 0 in a distance of 66 cm (26 inches) after his throttle got stuck wide open and he hit a wall.