1 . 4 ▁A TA , ▁which ▁occurs ▁at ▁about ▁. ▁Both ▁sides ▁of ▁the ▁community ▁tend ▁to ▁present ▁self - support ing ▁data . ▁D ivers ▁trained ▁and ▁experienced ▁in ▁deep ▁air ▁div ing ▁report ▁fewer ▁problems ▁with ▁nar cos is ▁than ▁those ▁trained ▁and ▁experienced ▁in ▁mixed ▁gas ▁div ing ▁trim ix / hel io x , ▁although ▁scientific ▁evidence ▁does ▁not ▁show ▁that ▁a ▁diver ▁can ▁train ▁to ▁overcome ▁any ▁measure ▁of ▁nar cos is ▁at ▁a ▁given ▁depth , ▁or ▁become ▁toler ant ▁of ▁it . ▁ ▁The ▁D ivers ▁Alert ▁Network ▁does ▁not ▁end or se ▁or ▁reject ▁deep ▁air ▁div ing , ▁but ▁indicates ▁the ▁additional ▁ris ks ▁involved . ▁ ▁Mi xt ures ▁to ▁reduce ▁decom pression ▁time ▁N it ro x ▁is ▁a ▁popular ▁div ing ▁gas ▁mix , ▁and ▁while ▁it ▁reduces ▁the ▁maximum ▁allow able ▁depth ▁as ▁compared ▁to ▁air , ▁it ▁also ▁allows ▁greater ▁bottom ▁time ▁by ▁reducing ▁the ▁bu il dup ▁of ▁nit ro gen ▁in ▁the ▁diver ' s ▁t issues ▁by ▁increasing ▁the ▁percentage ▁of ▁o xygen ▁in ▁the ▁breath ing ▁gas . ▁The ▁depth ▁limit ▁of ▁a ▁nit ro x ▁mixture ▁is ▁govern ed ▁by ▁the ▁partial ▁pressure ▁of ▁o xygen , ▁which ▁is ▁generally ▁limited ▁to ▁ 1 . 4 ▁to ▁ 1 . 6 ▁bar ▁depending ▁on ▁the ▁activity ▁of ▁the ▁diver ▁and ▁duration ▁of ▁expos ure . ▁ ▁N it ro x ▁and ▁pure ▁o xygen ▁are ▁also ▁used ▁for ▁acceler ated ▁decom pression .