▁death ▁when ▁the ▁demand ▁val ve ▁mouth pie ce ▁falls ▁out ▁and ▁the ▁victim ▁d row ns . ▁Sometimes ▁the ▁diver ▁may ▁get ▁warning ▁sympt oms ▁prior ▁to ▁the ▁conv ulsion . ▁These ▁can ▁include ▁visual ▁and ▁aud itory ▁hall uc in ations , ▁n ause a , ▁tw itch ing ▁( es pecially ▁in ▁the ▁face ▁and ▁hands ), ▁ir rit ability ▁and ▁m ood ▁sw ings , ▁and ▁d izz iness . ▁ ▁These ▁gas ▁mix es ▁can ▁also ▁lower ▁the ▁level ▁of ▁o xygen ▁in ▁the ▁mix ▁to ▁reduce ▁the ▁danger ▁of ▁o xygen ▁to x icity . ▁Once ▁the ▁o xygen ▁is ▁reduced ▁below ▁about ▁ 1 8 % ▁the ▁mix ▁is ▁known ▁as ▁a ▁hy po xic ▁mix ▁as ▁it ▁does ▁not ▁contain ▁enough ▁o xygen ▁to ▁be ▁used ▁safely ▁at ▁the ▁surface . ▁ ▁Saf ety ▁ ▁Techn ical ▁div ing ▁en comp ass es ▁multiple ▁aspects ▁of ▁div ing , ▁that ▁typically ▁share ▁lack ▁of ▁direct ▁access ▁to ▁surface , ▁which ▁may ▁be ▁caused ▁by ▁physical ▁constraints , ▁like ▁an ▁overhead ▁environment , ▁or ▁phys i ological , ▁like ▁decom pression ▁oblig ation . ▁In ▁case ▁of ▁emer gency , ▁therefore , ▁the ▁diver ▁or ▁div ing ▁team ▁must ▁be ▁able ▁to ▁troubles ho ot ▁and ▁solve ▁the ▁problem ▁under water . ▁This ▁requires ▁planning , ▁situ ational ▁aw aren ess , ▁and ▁redund ancy ▁in ▁critical ▁equipment , ▁and ▁is ▁facil itated ▁by ▁skill ▁and ▁experience ▁in ▁appropriate ▁procedures ▁for ▁man aging ▁reason ably ▁for