Fundamental considerations concerning the detection of gross leaks in bridge-wire initiators

Bridge-wire initiators are small electro-explosive devices that use an electrical current to heat a fine wire which results in the ignition of a small pyrotechnic charge. Due to their critical role in inflatable restraint systems these devices are intended to be hermetic and therefore impervious to the surrounding environment. However, the small internal volumes characteristic of most modern bridge-wire initiators introduce difficulties in the detection of gross leaks when using conventional tracer gas leak detection methodologies. This paper is intended to illustrate the potential for gross leaks in bridge-wire initiators and address specific difficulties related to performing accurate and legitimate gross leak tests in these devices. Results from a simple viscous flow analysis indicate that the limited amount of free volume characteristic of modern initiators can impact the ability to perform a legitimate gross leak check using conventional tracer gas methods.