The　effects　of　ignition　position　and　hydrogen　concentration　on　the　pressure　build-up　and　flame　evolution　during　H2/air　deflagrations　were　studied　in　a　1-m3　vessel　with　hinged　aluminum　vent　panel.　Three　ignition　positions　were　tested:　TI　(top　ignition),　CI　(central　ignition),　and　BI　(bottom　ignition),　with　hydrogen　concentrations　ranging　from　12　vol%　to　27　vol%.　Explosion　overpressure　was　simulated　using　the　CFD　software　FLACS　and　validated　against　experimental　data.　Results　revealed　that　Helmholtz　oscillations　occurred　only　for　12–18　vol%　H2/air　mixtures　at　TI.　Three　overpressure　peaks　inside　the　vessel　were　identified:　P1,　P2,　and　Pvib,　caused　by　the　opening　of　the　aluminum　panel,　interplay　between　the　external　explosion　and　the　venting　process,　and　flame-acoustic　oscillations,　respectively.　Compared　to　inertia-free　venting,　the　aluminum　panel　significantly　increased　P1　at　TI.　For　CI,　the　panel　enhances　the　external　explosion,　but　it　weakens　the　explosion　at　BI.　When　hydrogen　concentration　exceeded　18　vol%,　the　maximum　explosion　overpressure　(Pmax)　at　all　ignition　positions　increased　with　increasing　hydrogen　concentration.　An　external　overpressure　peak,　Pext,　was　observed　at　all　ignition　positions　for　hydrogen　concentration　above　18　vol%.　For　TI,　an　additional　overpressure　peak,　Popen,　caused　by　the　propagation　of　the　flame　wave　after　the　aluminum　panel　opening,　was　recorded.　The　maximum　external　overpressure　(Pe-max)　increased　with　hydrogen　concentration.　The　simulated　values　of　Pmax　and　Pe-max　closely　matched　the　experimental　data　for　CI.　However,　simulations　overestimated　the　experimental　results　for　hydrogen　concentration　above　18　vol%　at　TI　and　BI.　Additionally,　the　vent　panel　obstructed　external　flame　propagation.　©　2025　Elsevier　Ltd