Experiments　on　explosion　venting　of　a　stoichiometric　hydrogen-air　mixture　ignited　near　the　top　vent　of　a　1-m(3)　rectangular　vessel　with　a　hinged　aluminum　vent　panel　were　performed　to　investigate　the　effect　of　the　panel　area　density　on　the　pressure　build-up　and　flame　behavior.　When　using　aluminum　panels,　three　pressure　peaks　could　be　distinguished　in　the　pressure-time　histories.　The　first　pressure　peak,　which　increases　with　the　panel　area　density,　is　the　dominant　one.　However,　the　second　and　the　third　pressure　peaks,　with　magnitudes　ranging　from　5　to　10　kPa,　are　independent　of　the　panel　area　density.　The　use　of　aluminum　panels　weakens　the　external　explosion　because　the　gas　mixtures　were　vented　laterally　shortly　after　the　vent　panel　was　opened.　Panel　inertia　has　a　negligible　effect　on　the　final　stage　of　the　downward　propagating　flame.　The　maximum　external　flame　length　decreases　with　the　increase　in　panel　area　density.　(C)　2019　Hydrogen　Energy　Publications　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.