Explosion　venting　and　inerting　are　two　commonly　used　explosion　protective　measures　in　hydrogen-based　industries,　both　of　them　are　effective　in　reducing　the　maximum　explosion　overpressure　when　used　alone.　However,　the　coupling　effects　of　venting　and　inerting　on　hydrogen　deflagrations　have　not　been　well　understood.　To　this　end,　experiments　were　carried　out　in　a　1　m　high　top-vented　vessel　with　a　cross-section　area　of　0.3　m×0.3　m　to　investigate　the　effects　of　nitrogen　volume　fraction　(φ)　in　the　range　of　0　to　50%　by　volume　on　vented　hydrogen-air　explosions　with　a　fixed　equivalence　ratio.　The　premixed　hydrogen-nitrogen-air　mixtures　obtained　according　to　Dolton’s　law　of　partial　pressure　were　ignited　in　the　center　of　the　vented　container　by　an　electric　spark　with　an　energy　of　about　500　mJ.　A　0.75-m　long　transparent　window　was　installed　in　the　center　of　the　vented　container,　through　which　the　flame　images　in　the　container　were　recorded　by　a　high-speed　camera　at　2　000　frames　per　second.　The　pressure-time　histories　within　and　outside　the　vented　container　were　measured　by　four　piezoresistive　pressure　sensors　with　a　measuring　range　of　0–150　kPa.　The　experimental　results　reveal　that　φ　significantly　affects　the　vented　deflagration　of　hydrogen-air　mixtures.　The　pressure　peak　owing　to　the　external　explosion　dominates　the　internal　pressure-time　histories　when　φ≤40%　and　that　resulting　from　the　rupture　of　vent　cover　becomes　dominant　for　higher　values　of　φ.　Under　the　current　experimental　conditions,　Helmholtz-type　oscillations　with　a　frequency　decreasing　with　φ　are　always　observed,　and　acoustic　oscillations　appear　in　the　tests　only　for　φ=25%,　30%.　The　maximum　internal　explosion　overpressures　(pmax)　near　the　vent,　at　the　center　of　the　vessel,　and　near　the　bottom　of　the　vessel　decrease　with　increasing　φ.　Moreover,　the　highest　overall　pmax　is　obtained　always　near　the　bottom　of　the　vessel.　However,　the　difference　of　pmax　between　the　three　measuring　points　is　negligible　when　φ　is　larger　than　40%.　The　maximum　external　explosion　overpressure　decreases　with　increasing　φ.　In　addition,　significant　effects　of　the　external　explosion　on　the　internal　pressure-time　histories　are　observed　in　all　tests,　regardless　of　its　explosion　overpressure.　©　2022　Explosion　and　Shock　Waves.　All　rights　reserved.