▁amount ▁of ▁self - ex periment ation ▁is ▁done ▁by ▁technical ▁divers , ▁but ▁conditions ▁are ▁generally ▁not ▁optim ally ▁recorded , ▁and ▁there ▁are ▁usually ▁several ▁unknown s , ▁and ▁no ▁control ▁group . ▁Several ▁practices ▁are ▁recommended ▁to ▁reduce ▁risk ▁based ▁on ▁theoretical ▁arguments , ▁but ▁the ▁value ▁of ▁many ▁of ▁these ▁practices ▁in ▁reducing ▁risk ▁is ▁uncertain , ▁particularly ▁in ▁combinations . ▁The ▁vast ▁majority ▁of ▁professional ▁and ▁recre ational ▁div ing ▁is ▁done ▁under ▁low ▁risk ▁conditions ▁and ▁without ▁recogn ised ▁sympt oms , ▁but ▁in ▁spite ▁of ▁this ▁there ▁are ▁occasionally ▁un exp la ined ▁inc id ences ▁of ▁decom pression ▁sick ness . ▁The ▁earlier ▁t endency ▁to ▁bl ame ▁the ▁diver ▁for ▁not ▁properly ▁following ▁the ▁procedures ▁has ▁been ▁shown ▁to ▁not ▁only ▁be ▁counter product ive , ▁but ▁sometimes ▁fact ually ▁wrong , ▁and ▁it ▁is ▁now ▁generally ▁recogn ised ▁that ▁there ▁is ▁statist ically ▁a ▁small ▁but ▁real ▁risk ▁of ▁sympt om atic ▁decom pression ▁sick ness ▁for ▁even ▁highly ▁conserv ative ▁profiles . ▁This ▁accept ance ▁by ▁the ▁div ing ▁community ▁that ▁sometimes ▁one ▁is ▁simply ▁un l ucky ▁encourag es ▁more ▁divers ▁to ▁report ▁border line ▁cases , ▁and ▁the ▁statistics ▁gathered ▁may ▁provide ▁more ▁complete ▁and ▁precise ▁indic ations ▁of ▁risk ▁as ▁they ▁are ▁anal ys ed . ▁ ▁Re comm ended ▁practices ▁Pract ices ▁for ▁which ▁there ▁is ▁some ▁evidence ▁or ▁theoretical ▁model ▁suggesting ▁that ▁they ▁may ▁reduce ▁risk ▁of ▁decom pression ▁sick ness : ▁ ▁Ext ended ▁decom pression