The ventilation system in the works of the Vallo Alpino is more complicated than you would expect. In fact the works had a double system. The first is quite conventional. It take air in through armoured intakes and leads the air, if needed, through filters that absorb any toxic gas. It then expels the air into the barracks and into the breathing system of the casemates. However the second is very unusual. In fact is ressembles a system that the Germans later used in their midget submarines. It had several air intakes in the barracks. The air was lead through a filter where a special mixture absorbed the carbon from the CO2, leaving the oxygene.