▁consumption ▁log istics ▁specific ▁to ▁the ▁planned ▁d ive ▁profile . ▁▁ ▁During ▁as cent , ▁there ▁will ▁be ▁a ▁depth ▁at ▁which ▁the ▁diver ▁must ▁switch ▁to ▁a ▁gas ▁with ▁a ▁higher ▁o xygen ▁fraction , ▁which ▁will ▁also ▁acceler ate ▁decom pression . ▁If ▁the ▁travel ▁gas ▁is ▁suitable , ▁it ▁can ▁be ▁used ▁for ▁decom pression ▁too . ▁Add itional ▁o xygen ▁rich ▁decom pression ▁gas ▁mi xt ures ▁may ▁be ▁selected ▁to ▁optim ise ▁decom pression ▁times ▁at ▁shall ower ▁depth s . ▁These ▁will ▁usually ▁be ▁selected ▁as ▁soon ▁as ▁the ▁partial ▁pressure ▁of ▁o xygen ▁is ▁acceptable , ▁to ▁minim ise ▁required ▁decom pression , ▁and ▁there ▁may ▁be ▁more ▁than ▁one ▁such ▁mixture ▁depending ▁on ▁the ▁planned ▁decom pression ▁schedule . ▁The ▁shall ow est ▁stops ▁may ▁be ▁done ▁breath ing ▁pure ▁o xygen . ▁During ▁prolong ed ▁decom pression ▁at ▁high ▁o xygen ▁partial ▁press ures , ▁it ▁may ▁be ▁advis able ▁to ▁take ▁what ▁is ▁known ▁as ▁air ▁breaks , ▁where ▁the ▁diver ▁switch es ▁back ▁to ▁a ▁low ▁o xygen ▁fraction ▁gas ▁( us ually ▁bottom ▁gas ▁or ▁travel ▁gas ) ▁for ▁a ▁short ▁period ▁( us ually ▁about ▁ 5 ▁minutes ) ▁to ▁reduce ▁the ▁risk ▁of ▁developing ▁o xygen ▁to x icity ▁sympt oms , ▁before ▁continu ing ▁with ▁the ▁high ▁o xygen ▁fraction ▁acceler ated ▁decom pression . ▁These ▁multiple ▁gas ▁switch es ▁require ▁the ▁diver ▁to ▁select ▁and ▁use ▁the ▁correct ▁demand ▁val ve ▁and ▁cyl inder ▁for ▁each