An initiator assembly that includes an initiator and a containment shell. The initiator has an initiator housing, an initiator device mounted inside the initiator housing, and an input charge that is formed of an energetic material. The initiator device is configured to initiate at least one of a combustion event, a deflagration event and a detonation event in the input charge. The containment shell is coupled to the initiator housing and defines a space into which gas and/or particles are ejected from the initiator housing if the initiator device is not activated and the input charge is cooked off.