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.