We recently acquired a house that has an elevator-like mechanism. The former owners call the thing a "dumb waiter", suggesting that it's not safe for human use. Although it's roomy enough for a human to stand in, and supposedly has a 300lb capacity, I certainly wouldn't ride in it. (Amusingly, one of our new neighbors, friend of the former owners, says he's ridden in it; but, he's a retired jockey :-) ).
I'm wondering if there's any possibility of upgrading the thing so that it is safe for human use. I don't think it'd be possible to install a braking mechanism, like the one on a real elevator. Absent any other ideas, I think the solution would have to be some sort of redundant suspension mechanism.
This is probably a situation where a picture is worth a thousand words, so here's a few. The "shaft" is composed of 6x6 timbers at each corner. The "car" is about 3-feet square and is made of metal; little plastic wheels keep it rolling along the timbers. It's suspended by a small electric motor and a length of 1/4" wire rope. The overall floor-to-floor height is 18 feet.