▁decom pression , ▁but ▁are ▁unlikely ▁to ▁use ▁a ▁dedicated ▁decom pression ▁gas , ▁as ▁they ▁are ▁usually ▁not ▁more ▁than ▁two ▁to ▁three ▁minutes ▁long . ▁ ▁A ▁study ▁by ▁D ivers ▁Alert ▁Network ▁in ▁ 2 0 0 4 ▁suggests ▁that ▁addition ▁of ▁a ▁deep ▁( c . ▁ 1 5   m ) ▁as ▁well ▁as ▁a ▁shall ow ▁( c . ▁ 6   m ) ▁safety ▁stop ▁to ▁a ▁theoret ically ▁no - stop ▁as cent ▁will ▁significantly ▁reduce ▁decom pression ▁stress ▁indicated ▁by ▁prec ord ial ▁do pp ler ▁detected ▁b ubble ▁( PD DB ) ▁levels . ▁The ▁authors ▁associate ▁this ▁with ▁gas ▁exchange ▁in ▁fast ▁t issues ▁such ▁as ▁the ▁sp inal ▁cord ▁and ▁consider ▁that ▁an ▁additional ▁deep ▁safety ▁stop ▁may ▁reduce ▁the ▁risk ▁of ▁sp inal ▁cord ▁decom pression ▁sick ness ▁in ▁recre ational ▁div ing . ▁A ▁follow - up ▁study ▁found ▁that ▁the ▁optim um ▁duration ▁for ▁the ▁deep ▁safety ▁stop ▁under ▁the ▁experimental ▁conditions ▁was ▁ 2 . 5 ▁minutes , ▁with ▁a ▁shall ow ▁safety ▁stop ▁of ▁ 3 ▁to ▁ 5 ▁minutes . ▁Long er ▁safety ▁stops ▁at ▁either ▁depth ▁did ▁not ▁further ▁reduce ▁P D DB . ▁ ▁In ▁contrast , ▁experimental ▁work ▁comparing ▁the ▁effect ▁of ▁deep ▁stops ▁observed ▁a ▁significant ▁decrease ▁in ▁v asc ular ▁b ub bles ▁following ▁a ▁deep ▁stop ▁after ▁longer ▁shall ower ▁div es , ▁and ▁an ▁increase ▁in ▁b ubble ▁formation ▁after ▁the ▁deep ▁stop ▁on ▁shorter ▁deeper ▁div es