unclassified skid adjacent to a class 1 div 2 skid, pressurized?

[scha0786]

i am consulting on existing oil and gas facilities. i have a skid/module that is unclassified. within this unclassified skid is a pressurized ier room. now adjacent to the whole module is a classified area that has an air lock between them. do i need to maintain +0.1 " wc between the whole modules? the classification sheets usually indicate pressurized areas with a p and a circle around it. this particular module is unclass with the ier pressurized. by code can i just maintain a slight positive in the unclass mod relative to the class mod? like +0.05?

thanks for the help

 

[stookeyfpe]

See API RP 500 and explain what an IER room is.