A metallic case for a pyrotechnical igniter of a gas generator for a vehicle safety device that includes a peripheral side wall, a closed end, and a weak zone in the peripheral side wall. The weak zone extends along a continuous trace having a first end portion, a second end portion, and an intermediate portion between the first and second end portions. The first and second end portions of the continuous trace both transition from a first point having a first side wall depth to a second point having a second side wall depth. The second side wall depth is greater than the first side wall depth. The weak zone is configured for opening a vent in the peripheral side wall in response to an increase of pressure within the metallic case.