Assuming any (optimal) body orientation/position relative to the direction of force and mechanism of death.
I'd be interested in a rough estimate of threshold force and a suggested mechanism of death. A person experiencing a force just below this threshold should be able to survive for a few minutes.
To give more context the question derives from: 'How much centripetal acceleration is fatal?', or 'How fast and tight must a rollercoaster go to kill you?'.
I realise there may be some biological considerations for this question, but giving bounds on these seems within the remit of back-of-the-envelope physics.