The Debris Bunker is a husk left behind by Russian buildings when they are destroyed. They hold Conscripts inside and will automatically collapse after a short period of time.
Russian buildings are composed of several layers, allowing them to operate even when the outer protection has been severely damaged. When a structure's integrity is fatally compromised, most of it will collapse but the inner area will remain intact. Now incapable of accomplishing whatever task the structure was built for, it uses the building's own rubble as protection and effectively becomes a stationary bunker, where the surviving personnel grab arms and prepare for a last stand against the enemy. Nonetheless, the bunkers are and remain largely rubble, so after a short time they will eventually collapse.