Altimetry and altitudes/levels
Couple of questions that hopefully aren't too ridiculous. Please correct me if I've got the wrong end of the stick here....
i) If 1 mb = 30 ft in terms of air pressure change related to altitude, whereby a drop of 1 mb eqautes to a gain in altitude of 30ft, how is it that there are not enough millibars in a QNH of say 1000 to accomodate an altitude past 30,000ft? For example, QNH 1000 = 0ft amsl, pressure 500 = 15,000ft amsl, pressure 0 = 30,000ft amsl. Obviously the air pressure at 30,000ft is not zero millibars, so how does this 1 mb = 30 ft yardstick work?
ii) If aircraft change to the standard setting 1013.2 mb through a transition altitude, is it possible that 1,000ft vertical separation would be compromised if there was an aircraft at say FL40 on 1013.2 and another at 3000ft on, for example, QNH 990?
I've spent a good deal of time trying to get my (relatively ATC-novice) head round these - if anyone can assist me in my quest to work them out, that would be much appreciated.