On May 19, 11:29 am, Bill wrote:

This way if you are loading a couple
of hundred pounds on it it can't suddenly drop taking your arms, legs or
feet with it,

Bill

If slicing off you arms is all you are worried about, how about
putting a hinged door on the box that swings out over the second floor
so the box can't go down unless the hinges shear off, then use beefy
hinges? or how about having a cam or some sort of linkage on a door to
the shaft that locks the box in place when the door is open?
Or how about a variation of Elisha Otis' design where the pressure of
the lifting mechanism keeps the pawls disengaged? though a slow leak
would be like a normal decent and could still trap an arm so maybe
that isn't really what you want.
While it might seem that a double acting cylinder isn't needed on a
dumbwaiter, If you do use a double acting cyl, and lock valves at the
cylinder ports (at least for down) it will take a pretty catastrophic
failure to be a big problem, you know, you could use a variation on
that idea, with a sequencing valve and a small cylinder to disengage
the pawl.