[KineticLensman]

I used to regularly use these at the Uni of Leeds in the Roger Stevens lecture theatre building. Never saw an accident. Freshers were told that they turned upside down when going over the top but in fact they just slid sideways to the next shaft (we used to ride over the top sometimes to beat a queue going down) but they could apparently jam if too many people tried it so it was frowned upon by the porters.