The　explosion　venting　of　hydrogen-air　mixtures　with　equivalence　ratios　ranging　from　0.4　to　6.0　was　investigated　in　a　small　vented　cylindrical　vessel.　The　experimental　results　show　that　the　maximum　internal　overpressure　initially　increases　with　an　increase　in　hydrogen　equivalence　ratio　up　to　approximately　1.6　and　subsequently　decreases.　The　discrepancy　between　the　maximum　internal　overpressure　and　the　vent　burst　pressure　is　significantly　high　for　equivalence　ratios　ranging　from　1.0　to　2.0　but　low　for　very　lean　or　very　rich　mixtures.　Buoyancy　has　a　significant　effect　on　the　evolution　of　the　internal　flame　bubble　for　very　lean　hydrogen-air　mixtures　only.　The　speed　of　the　external　flame　oscillates　violently　and　its　maximum　value　is　achieved　at　a　distance　downstream　from　the　vent.　The　maximum　length　of　the　flame　ejected　from　the　vent,　which　depends　on　the　hydrogen　equivalence　ratio,　may　be　underestimated　by　engineering　models.　©　2017　Elsevier　Ltd