▁correct ▁gas ▁is ▁bre athed ▁for ▁the ▁depth ▁and ▁decom pression ▁management . ▁Bre ath ing ▁a ▁gas ▁with ▁in app ropri ate ▁o xygen ▁partial ▁pressure ▁ris ks ▁loss ▁of ▁conscious ness , ▁and ▁comprom ising ▁the ▁decom pression ▁plan . ▁When ▁switching , ▁the ▁diver ▁must ▁be ▁certain ▁of ▁the ▁composition ▁of ▁the ▁new ▁gas , ▁and ▁make ▁the ▁correct ▁adjust ments ▁to ▁decom pression ▁computer ▁settings . ▁Vari ous ▁systems ▁have ▁been ▁used ▁to ▁identify ▁the ▁gas , ▁the ▁demand ▁val ve , ▁and ▁the ▁source ▁cyl inder . ▁One ▁in ▁general ▁use ▁and ▁found ▁by ▁experience ▁to ▁be ▁reliable , ▁is ▁to ▁clearly ▁label ▁the ▁cyl inder ▁with ▁the ▁maximum ▁operating ▁depth ▁of ▁the ▁contents , ▁as ▁this ▁is ▁the ▁most ▁critical ▁information , ▁carry ▁the ▁demand ▁val ve ▁on ▁the ▁cyl inder , ▁and ▁leave ▁the ▁cyl inder ▁val ve ▁closed ▁when ▁the ▁cyl inder ▁is ▁not ▁in ▁use . ▁This ▁allows ▁the ▁diver ▁to ▁vis ually ▁identify ▁the ▁mix ▁as ▁suitable ▁for ▁the ▁current ▁depth , ▁select ▁the ▁demand ▁val ve ▁at ▁the ▁cyl inder , ▁and ▁confirm ▁that ▁it ▁is ▁the ▁demand ▁val ve ▁from ▁that ▁cyl inder ▁by ▁opening ▁the ▁cyl inder ▁val ve ▁to ▁release ▁the ▁gas . ▁After ▁the ▁mix ▁is ▁confirmed ▁the ▁diver ▁will ▁switch ▁over ▁the ▁computer ▁to ▁select ▁the ▁current ▁gas , ▁so ▁that ▁decom pression ▁computation ▁can ▁remain ▁correct . ▁ ▁It ▁is ▁not ▁unusual ▁for ▁deep ▁technical ▁div es ▁to ▁require ▁four ▁gas ▁mi xt ures ▁aside ▁from