Broadly speaking the human tolerance with harness and lap belt are given as,
Longitudinal
45 G (0.1 second)
25 G (0.2 seconds)
Vertical
25 G (0.1 second)
Lateral
20 G (0.1 second)
Of interest the lap belt only figures are,
Longitudinal
15 G (0.002 second)
Vertical
4 G (injured)
Lateral
11 G (0.1 second)
The latest seat standards if I recall correctly, is 16 G Forward, 8 G Lateral, 20 G Downwards and 4 G Upwards.
For bedtime reading see
www.everyspec.com/MIL-STD/MIL-STD+(1100+-+1299)/download.php?spec=MIL_STD_1290A.860.pdf and
http://ntrs.nasa.gov/archive/nasa/ca...1998394351.pdf