Airbag/Ballute Instead of Parachute

If military para-drops have to occur at low altitude in order to
minimize the vulnerable parachuting phase where the parachutists are
vulnerably exposed while floating down, then what about an airbag
solution?

When you look at videos of automobile airbags inflating, they do so at
lightning speed, before your head can even hit the steering wheel or
wind****eld.

http://www.edinformatics.com/inventions_inventors/airbag.htm

What if you had a airbag that explosively inflated at the last moment,
to generate the drag+buoyancy to rapidly slow down your freefalling
skydiver nearer to the end of their descent? I'm picturing an airbag
that would explosively inflate with hydrogen gas for buoyancy and not
just drag. The "H-bag" would inflate below the skydiver, and not above
them, so that it could also act as a shock-absorber between the
skydiver and the ground, similar to the automobile airbag. It would
have to instantaneously inflate to a large enough size to 1)cause rapid
deceleration from buoyancy+drag and 2)create a large and safely
decelerative shock absorber between the skydiver and the ground.

I'm imagining the airbag would be stored in a device that would be
strapped on to the bottom of your feet, sort of like a snowboard. Or
else it might look like a pogo stick, and you would ride it that way.
I'm presuming that feet-first is the best way for the body to handle an
impact. I'm also presuming that the highest deceleration rate the body
can safely handle along its vertical axis is at 8 G's.

The H-bag would explosively inflate below the skydiver in the shape of
an elongated teardrop -- actually more like a clove of garlic with 4
bulging lobes. I'm imagining the extent to which each lobe is inflated
would be calibrated based on the trajectory/disposition of the
skydiver. Likewise, the altitude at which it triggers is based on the
speed of descent. As the H-bag contacts the ground, the skydiver would
plunge through the middle of it to contact the ground at reasonable
speed.

If you had to jump out of a tall building, Sept11-style, the H-bag
could work there too.

For the sake of discussion -- in a typical skydive, how large a size
would the H-bag have to inflate to, and what would be the best height
for it to trigger at, in order for you to safely reach the ground?

Any ideas?