An air bag module (12) includes an inflator (18) that is actuatable to supply inflation fluid to inflate an inflatable vehicle occupant protection device (16). A housing (14) directs the inflation fluid from the inflator (18) toward the inflatable device (16). At least one vent opening (40) is formed in the housing (14) for selectively venting inflation fluid from the housing. A door panel (70) is movable between a closed position blocking venting of inflation fluid from the housing (14) and an open position enabling venting of inflation fluid from the housing. The door panel (70), when in the closed position, is biased toward the open position. In one embodiment, the door panel (70) is resiliently deformable. In another embodiment, a spring (71a) is connected with a door (70a) and biases the door toward the open position.