The　effects　of　vent　area　on　pressure　and　flame　evolution　in　a　1　m(3)　vessel　with　and　without　obstacles　were　investigated.　Five　pressure　peaks　of　P-open,　P-out,　P-ext,　P-hel,　and　P-vib,　which　correspond　to　vent　activation,　flame　venting,　external　explosion,　Helmholtz　oscillation,　and　the　coupling　of　acoustic　waves　and　flames,　respectively,　were　observed　without　obstacles　when　the　vent　coefficient　K-v　＜=　6.25.　However,　the　pressure　peaks　of　P-ext　and　P-out　from　the　external　explosion　and　flame　venting　disappeared　when　K-v　＞　6.25.　Moreover,　the　pressure　peaks　of　P-open　and　P-vib　produced　by　vent　activation　and　acoustically　enhanced　combustion　become　dominant　when　K-v　＞　12.5.　With　the　installation　of　obstacles,　the　pressure　peak　P-vib　induced　by　acoustically　enhanced　combustion　disappeared.　The　other　four　pressure　peaks　were　observed　when　K-v　＜　6.25.　The　pressure　peaks　induced　by　the　external　explosion　and　the　Helmholtz　oscillation　disappeared　when　K-v　＞　12.5.　Nevertheless,　the　pressure　peak　resulting　from　the　obstacles　was　observed　and　became　dominant　at　K-v　＞　12.5.　It　takes　less　time　for　the　external　flame　to　propagate　to　the　maximum　displacement　in　the　tests　with　obstacles　than　that　without　obstacles,　and　the　maximum　flame　length　for　the　former　is　smaller　than　the　latter.