Unug kala soocida hawada (ASU) waa aalad hawada u adeegsata sida quudinta, isku-buufinta iyo qaboojinta heerkulbeegga, ka hor inta aan la kala saarin oksijiinta, nitrogen, argon, ama alaabada kale ee dareeraha ah ee hawada dareeraha ah iyada oo loo marayo hagaajin. Iyada oo ku xidhan baahida isticmaalaha, alaabta ASU waxay noqon kartaa mid kali ah (tusaale, nitrogen) ama dhawr (tusaale, nitrogen, oxygen, argon). Nidaamku wuxuu soo saari karaa alaab dareere ama gaas ah si uu u buuxiyo shuruudaha kala duwan ee macaamiisha.