▁indicates ▁that ▁ 9 . 8 % ▁of ▁all ▁cases ▁of ▁decom pression ▁ill ness ▁and ▁ 2 0 % ▁of ▁div ing ▁fatal ities ▁in ▁the ▁USA ▁happened ▁to ▁technical ▁divers . ▁It ▁is ▁not ▁known ▁how ▁many ▁technical ▁div es ▁this ▁was ▁spread ▁over , ▁but ▁it ▁was ▁considered ▁likely ▁that ▁technical ▁divers ▁are ▁at ▁greater ▁risk . ▁ ▁The ▁techniques ▁and ▁associated ▁equipment ▁that ▁have ▁been ▁developed ▁to ▁overcome ▁the ▁limitations ▁of ▁conventional ▁single ▁cyl inder , ▁open ▁circuit ▁sc uba ▁div ing ▁are ▁necessarily ▁more ▁complex ▁and ▁subject ▁to ▁error , ▁and ▁technical ▁div es ▁are ▁often ▁done ▁in ▁more ▁dangerous ▁environments , ▁so ▁the ▁consequences ▁of ▁an ▁error ▁or ▁mal function ▁are ▁greater . ▁Although ▁skill ▁levels ▁and ▁training ▁of ▁technical ▁divers ▁are ▁generally ▁significantly ▁higher ▁than ▁those ▁of ▁recre ational ▁divers , ▁there ▁are ▁indic ations ▁that ▁technical ▁divers , ▁in ▁general , ▁are ▁at ▁higher ▁risk , ▁and ▁that ▁closed ▁circuit ▁re bre ather ▁div ing ▁may ▁be ▁particularly ▁dangerous . ▁ ▁Oper ations ▁Rel atively ▁complex ▁technical ▁div ing ▁operations ▁may ▁be ▁planned ▁and ▁run ▁like ▁an ▁expedition , ▁or ▁professional ▁div ing ▁operation , ▁with ▁surface ▁and ▁in - water ▁support ▁personnel ▁providing ▁direct ▁assistance ▁or ▁on ▁stand - by ▁to ▁assist ▁the ▁expedition ▁divers . ▁Sur face ▁support ▁might ▁include ▁surface ▁stand - by ▁divers , ▁boat ▁crew , ▁por ters , ▁emer gency ▁medical ▁personnel , ▁and ▁gas ▁bl enders . ▁In - water ▁support ▁may ▁provide ▁supp lement ary ▁breath ing