That suggests a longer escape tunnel for this purpose that remained undisclosed even when the tunnels were used to store food which is a natural usage. We really need these systems to be properly mapped as well.
The Bronze age used a blow torch system to drive tunnels. This was as efficient as blasting today and wonderfully safe as no fractures are propagated through the rock. Thus miles of safe tunnel would be no trick to drive. The technology would be known through the Atlantean world.
Critical ventilation can be provided by driving raises to surface every one to two hundred yards or even much further as the air was blown though a large flexible skin tube from the surface.