Acceleration trivia

3-4 g - a well-designed roller coaster
4-6 g - most people black out after a couple seconds (military pilots capable of 6-8 g)
8-15 g - maximum acceleration in human centrifuges, for astronaut training only; sustainable for a few seconds.
30-40 g - maximum sustainable acceleration for a fraction of a second in a car crash, if wearing a seatbelt.