An apparatus (10) for inflating an inflatable vehicle occupant protection device includes a container (18) defining a chamber (16) containing fluid (14) under pressure. The container (18) has a first opening (34). A frangible portion (40) of the container (18) covers the first opening (34) and blocks fluid flow from the chamber (16). The apparatus (10) includes a second opening (50), spaced apart from the first opening (34), through which fluid can flow from the first opening to the inflatable device to inflate the inflatable device. A cutter (90) is movable in a first direction for cutting the frangible portion (40) to release fluid to flow from the chamber (16) through the first opening (34) to the second opening (50). The cutter (90) is movable in a second direction opposite the first direction for allowing an increasing flow of fluid through the second opening (50) as the cutter moves in the second direction.