▁rivers . ▁. ▁ ▁P neum atic ▁bar riers ▁are ▁also ▁known ▁as ▁air ▁cur tain s . ▁The ▁p neum atic ▁bar rier ▁is ▁a ▁( non - pat ented ) ▁in vention ▁of ▁the ▁Dutch ▁engineer ▁Johan ▁van ▁Ve en ▁from ▁around ▁ 1 9 4 0 ▁ ▁. ▁ ▁A ▁p neum atic ▁bar rier ▁is ▁an ▁active ▁( as ▁opposed ▁to ▁pass ive ) ▁method ▁of ▁water way ▁oil ▁sp ill ▁control . ▁ ▁( An ▁example ▁of ▁a ▁pass ive ▁method ▁would ▁be ▁a ▁contain ment ▁bo om .) ▁ ▁Method ▁of ▁operation ▁ ▁The ▁p neum atic ▁bar rier ▁consists ▁of ▁a ▁per for ated ▁pipe ▁and ▁a ▁com pressed ▁air ▁source . ▁ ▁Air ▁esc aping ▁from ▁the ▁pipe ▁provides ▁a ▁" h ump " ▁of ▁rising ▁water ▁and ▁air ▁which ▁contains ▁the ▁oil ▁sp ill . ▁ ▁An ch ors ▁to ▁keep ▁the ▁pipe ▁in ▁a ▁particular ▁spot ▁are ▁helpful . ▁In ▁case ▁of ▁a ▁density ▁current ▁due ▁to ▁sal inity ▁differences ▁the ▁bar rier ▁mix es ▁the ▁salt ▁water , ▁but ▁also ▁slow s ▁down ▁the ▁speed ▁of ▁the ▁density ▁current . ▁ ▁Un ique ▁consider ations ▁ ▁At ▁water - current ▁spe eds ▁exceed ing ▁one ▁foot ▁per ▁second , ▁the ▁p neum atic ▁bar rier ▁no ▁longer ▁functions ▁effectively , ▁limit ing ▁deploy able ▁sites . ▁ ▁Environment al ▁issues ▁ ▁The ▁release ▁of ▁com pressed ▁air ▁in ▁the ▁water ▁adds ▁o xygen ▁to ▁the ▁local ▁environment . ▁ ▁This ▁may ▁be