Emazingeni okushisa aphansi, i-CO2 inomfutho wegesi ophansi. Amathangi kumele enzelwe ukubekezelela ushintsho lokucindezela emazingeni okushisa aphansi ngenkathi uvimbela izinguquko ezibucayi phakathi koketshezi nogesi. Njengoba izinga lokushisa likhuphuka, ingcindezi yegesi ye-CO2 iyanda, eyakha umthwalo omkhulu wengcindezi ethangini. Imiklamo yamathangi wokushisa okuphezulu idinga ukucatshangelwa kwengcindezi yokuphepha komkhumbi, kufaka phakathi ama-valves okulawula izingcindezi kanye nama-valves okuphepha.