An external containment device for an inflator of an inflatable cushion is provided, the external containment device having: an outlet plate having an outlet opening; a burst disk disposed over the outlet opening; an initiator having an initiator cap; a support pin having a shaft portion and a head portion, the shaft portion being supported by the initiator cap and the head portion contacts the burst disk when the outlet opening is sealed by the burst disk; and wherein activation of the initiator causes the initiator cap to move shearing a portion of the shaft portion from the support pin which allows the burst disk to rupture.