We　experimentally　investigated　the　pressure　buildup　and　flame　behavior　during　the　vented　deflagration　of　hydrogen-air　mixtures　with　concentrations　ranging　from　13%　to　39%　that　were　centrally　ignited　in　a　1-m(3)　rectangular　vessel　with　a　500　mm　x　400　mm　top　vent.　The　performance　of　some　available　models　for　estimating　the　maximum　reduced　overpressure　was　experimentally　evaluated.　The　maximum　reduced　overpressure　increased　from　approximately　3　kPa　to　100　kPa　as　hydrogen　concentration　increased　from　13　to　39%.　Turbulent　pressure　oscillations　with　frequencies　of　200-300　Hz　triggered　by　external　explosions　were　observed　in　our　tests　with　22-39%　hydrogen-in-air　mixtures.　Molkov＇s　best　fit　and　conservative　models　predict　the　maximum　reduced　overpressure　well　for　lean　and　rich　hydrogen　mixtures,　respectively.　The　average　speed　of　the　external　flame　first　decreases　to　a　minimum　value　with　the　fireball　expanding　to　its　maximum　size　and　then　increases.　As　hydrogen　concentration　increases,　the　maximum　length　and　duration　of　the　external　flame　increases　＇and　decreases,　respectively.　2018　Hydrogen　Energy　Publications　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.