▁of ▁the ▁d ive . ▁These ▁dissol ved ▁g ases ▁must ▁be ▁released ▁slowly ▁from ▁body ▁t issues ▁by ▁cont rolling ▁the ▁as cent ▁rate ▁to ▁restrict ▁formation ▁and ▁growth ▁of ▁b ub bles . ▁This ▁is ▁usually ▁done ▁by ▁p aus ing ▁or ▁" do ing ▁stops " ▁at ▁various ▁depth s ▁during ▁the ▁as cent ▁to ▁the ▁surface . ▁Most ▁technical ▁divers ▁bre at he ▁o xygen ▁en rich ed ▁breath ing ▁gas ▁mi xt ures ▁such ▁as ▁nit ro x ▁and ▁pure ▁o xygen ▁during ▁long ▁duration ▁decom pression , ▁as ▁this ▁increases ▁the ▁rate ▁of ▁in ert ▁gas ▁elim ination . ▁El im ination ▁of ▁in ert ▁g ases ▁continues ▁during ▁the ▁surface ▁intervals ▁( time ▁spent ▁on ▁the ▁surface ▁between ▁div es ), ▁which ▁must ▁be ▁considered ▁when ▁planning ▁subsequent ▁div es . ▁A ▁decom pression ▁oblig ation ▁is ▁also ▁referred ▁to ▁as ▁a ▁" soft ", ▁or ▁" phys i ological " ▁ce iling . ▁ ▁Phys ical ▁ce iling ▁These ▁types ▁of ▁physical ▁overhead , ▁or ▁" hard " ▁or ▁" environment al " ▁ce iling ▁can ▁prevent ▁the ▁diver ▁sur f acing ▁directly : ▁ ▁C ave ▁div ing ▁– ▁div ing ▁into ▁a ▁cave ▁system . ▁ ▁Ice ▁div ing ▁– ▁div ing ▁under ▁ice . ▁ ▁W reck ▁div ing ▁– ▁div ing ▁inside ▁a ▁ship w reck . ▁In ▁all ▁three ▁of ▁these ▁situations , ▁a ▁guide ▁line ▁or ▁lif eline ▁from ▁the ▁exit ▁to ▁the ▁diver ▁is ▁the ▁standard ▁method ▁of