Experiments　were　conducted　in　an　obstructed　3-m-long　duct　to　investigate　the　effects　of　equivalence　ratio,　thickness　of　rupture　membrane,　and　vent　area　on　vented　hydrogen–air　deflagrations.　Shockwave-induced　pressure　peaks　were　observed　inside　and　outside　the　duct　in　some　tests.　In　the　tests　with　one　end　of　the　duct　totally　opened,　the　location　at　which　the　overall　maximum　internal　overpressure　is　achieved　depends　on　the　thickness　of　the　rupture　membrane　for　a　given　equivalence　ratio;　however,　it　is　independent　of　equivalence　ratio　for　a　given　thickness　of　rupture　membrane.　The　pressure　peak　resulting　from　an　external　explosion　always　dominates　the　pressure–time　histories　1.5　m　downstream　of　the　duct　exit.　The　maximum　internal　and　external　overpressures　first　increase　and　then　decrease　as　the　equivalence　ratio　increases　from　0.26　to　3.57,　unexpectedly;　none　of　these　increase　monotonically　with　an　increase　in　the　thickness　of　the　rupture　membrane.　Two　explosion　venting　regimes,　namely　sonic　and　subsonic,　are　observed.　During　sonic　venting,　the　maximum　internal　overpressure　increases　exponentially　with　a　decrease　in　vent　area;　it　is　nearly　independent　of　the　vent　area　during　subsonic　venting　when　the　vent　area　is　larger　than　approximately　19%　of　the　cross-sectional　area　of　the　duct.　©　2019　Hydrogen　Energy　Publications　LLC