▁of ▁ 2 . 5 ▁bar . ▁The ▁duration ▁of ▁the ▁ 5 0   f sw ▁stop ▁is ▁ 1 5 ▁minutes ▁for ▁the ▁Re vision ▁ 6 ▁tables . ▁The ▁chamber ▁is ▁then ▁decom pressed ▁to ▁ 4 0   f sw ▁( 1 2   ms w ) ▁for ▁the ▁next ▁stage ▁of ▁up ▁to ▁ 4 ▁periods ▁on ▁o xygen . ▁A ▁stop ▁may ▁also ▁be ▁done ▁at ▁ 3 0   f sw ▁( 9   ms w ), ▁for ▁further ▁periods ▁on ▁o xygen ▁according ▁to ▁the ▁schedule . ▁Air ▁breaks ▁of ▁ 5 ▁minutes ▁are ▁taken ▁at ▁the ▁end ▁of ▁each ▁ 3 0 ▁minutes ▁of ▁o xygen ▁breath ing . ▁ ▁Sur face ▁decom pression ▁procedures ▁have ▁been ▁described ▁as ▁" sem i - control led ▁acc idents ". ▁ ▁Data ▁collected ▁in ▁the ▁North ▁Sea ▁have ▁shown ▁that ▁the ▁overall ▁inc idence ▁of ▁decom pression ▁sick ness ▁for ▁in - water ▁and ▁surface ▁decom pression ▁is ▁similar , ▁but ▁surface ▁decom pression ▁tends ▁to ▁produce ▁ten ▁times ▁more ▁type ▁II ▁( ne uro log ical ) ▁D CS ▁than ▁in - water ▁decom pression . ▁A ▁possible ▁explanation ▁is ▁that ▁during ▁the ▁final ▁stage ▁of ▁as cent , ▁b ub bles ▁are ▁produced ▁that ▁are ▁stopped ▁in ▁the ▁lung ▁cap ill aries . ▁During ▁recom pression ▁of ▁the ▁diver ▁in ▁the ▁deck ▁chamber , ▁the ▁diameter ▁of ▁some ▁of ▁these ▁b ub bles ▁is ▁reduced ▁sufficiently ▁that ▁they ▁pass ▁through ▁the ▁pul mon ary