▁divers ▁may ▁work ▁in ▁the ▁range ▁of ▁ 1 7 0   ft ▁to ▁ 3 5 0   ft , ▁sometimes ▁even ▁deeper . ▁Techn ical ▁div ing ▁almost ▁always ▁requires ▁one ▁or ▁more ▁mand atory ▁decom pression ▁' st ops ' ▁upon ▁as cent , ▁during ▁which ▁the ▁diver ▁may ▁change ▁breath ing ▁gas ▁mix es ▁at ▁least ▁once ." ▁NO AA ▁does ▁not ▁address ▁issues ▁rel ating ▁to ▁overhead ▁environments ▁or ▁specify ▁the ▁recre ational ▁div ing ▁limits ▁in ▁its ▁definition , ▁and ▁the ▁use ▁of ▁single ▁mixture ▁nit ro x ▁is ▁well ▁established ▁in ▁main s ream ▁recre ational ▁div ing . ▁ ▁P AD I ▁defines ▁technical ▁div ing ▁as ▁" d iving ▁other ▁than ▁conventional ▁commercial ▁or ▁recre ational ▁div ing ▁that ▁takes ▁divers ▁beyond ▁recre ational ▁div ing ▁limits ▁( ). ▁It ▁is ▁further ▁defined ▁as ▁an ▁activity ▁that ▁includes ▁one ▁or ▁more ▁of ▁the ▁following : ▁div ing ▁beyond ▁ 4 0 ▁meters / 1 3 0 ▁feet , ▁required ▁stage ▁decom pression , ▁div ing ▁in ▁an ▁overhead ▁environment ▁beyond ▁ 1 3 0 ▁linear ▁feet ▁from ▁the ▁surface , ▁acceler ated ▁stage ▁decom pression ▁and / or ▁the ▁use ▁of ▁multiple ▁gas ▁mi xt ures ▁in ▁a ▁single ▁d ive ." ▁ ▁T DI ▁defines ▁a ▁technical ▁d ive ▁as ▁any ▁d ive ▁involving ▁decom pression , ▁additional ▁cyl ind ers , ▁alternative ▁breath ing ▁g ases , ▁re bre athers , ▁or ▁overhead ▁environments ▁such ▁as ▁w re cks , ▁c aves