Robert Green wrote:
So here's the question. Has anyone ever seen or even thought about
designing a home-brewed "safe" stairway? I've been thinking about a
collection of airbags (or one superlarge one) at the bottom of the
stairs, triggered by some sort of detector circuit that could detect
a human falling down the stairs faster than normal walking.

Rather than airbags, quickly deploying nets might be simpler. Imagine channels
on each side perpendicular to the slope of the stairs with wheels in it attached
to the net, which could be pulled from above with cables or pushed from below
with spring loaded rods. The net could be concealed in the stair risers.