Experiments　were　conducted　in　a　1-m(3)　rectangular　vessel　with　a　700　mm　x　400　mm　top　vent　to　investigate　the　effects　of　cylinders　placed　parallel　to　the　venting　direction　on　vented　hydrogen-air　deflagrations　and　the　structural　response　of　the　vessel　wall　to　an　explosion.　Three　pressure　peaks,　which　corresponded　to　the　opening　of　the　vent　cover,　venting　of　the　burnt　gas　mixtures,　and　the　occurrence　of　the　external　explosion,　respectively,　were　observed.　The　pressure　peak　corresponding　to　the　external　explosion　always　dominated　the　pressure-time　histories,　and　the　maximum　internal　overpressure　was　reached　at　the　bottom　of　the　vessel.　The　presence　of　cylinders　in　the　vessel　affected　the　explosion　venting　significantly.　When　more　cylinders　were　placed,　the　maximum　internal　and　external　overpressure　increased,　whereas　the　amplitude　of　pressure　oscillation　and　the　time　needed　to　reach　the　maximum　overpressure　decreased.　A　close　relation　between　the　pressure　oscillation　and　vessel　vibration　was　found.　Low　and　high　dominant　frequency　spectra　of　vessel　vibration　were　observed　in　all　tests.　The　former　resulted　from　the　acoustic　oscillation　of　the　internal　pressure,　and　the　latter　corresponded　to　the　resonance　of　the　vessel,　which　may　react　against　the　flame　and　result　in　pressure　oscillation　with　a　frequency　comparable　with　the　natural　frequency　of　the　vessel.　(C)　2019　Institution　of　Chemical　Engineers.　Published　by　Elsevier　B.V.　All　rights　reserved.