Change Room and Air Lock - Design & Layout

What is the difference between a ‘change room’ and an ‘air-lock’? When Michael requested for more clarification on change rooms design vis-à-vis pressure differentials and movement of air, I didn’t thought that our discussion will go in so detail. While a change room is generally required for change of outside attire before entering a clean zone, the applied air-pressure differentials makes it an air-lock keeping outside air out and not allowing contamination to fly inside. Thus an airlock divides two different zones or classes of clean areas.
As Michael impressed on our discussions, I thought to share some of the useful bullet points emerging out of it.
Air lock connects two different environments, usually at different pressures, that enable personnel to transfer from one environment to the other.
An air lock is required when the particles from adjacent area is less clean than the clean-room of concern, therefore, the infiltration of particles can be minimized by controlling the air flow direction so that air flows from the clean room to its adjacent space (less clean). This can be easily accomplished by supplying more air than return air (++ condition), thus slightly pressurizing the room.
Above picture gives the schematic view of change room with requirement of pressure differentials across different zones.
See carefully the blue arrows for direction of air –flow, direction in which doors are opening and ‘+’ sign for pressure differentials.