squib

A squib is a small pyrotechnic initiator, typically a thin wire filament or bridge wire surrounded by a chemical primer compound, housed in a metal or ceramic body. In an airbag system, the squib receives an electrical pulse from the vehicle's crash sensor module and ignites almost instantly, generating a shock wave that detonates the sodium azide pellets in the inflator canister. This chain reaction creates the pressurized gas needed to fill the airbag in milliseconds. The squib itself is passive and inert until current flows through it; a typical automotive squib fires at currents between 1 and 3 amperes.

The electrical pulse that triggers a squib must be precise and reliable. The airbag control module sends a specially timed, high-current signal down a dedicated wire pair to the squib's terminals. Modern vehicles use dual-stage or multi-stage squibs in larger inflators, allowing the control module to modulate bag inflation by firing different squibs in sequence or varying the timing. This gives engineers control over deployment force and inflation rate, important for passenger safety across different seating positions and crash types.

Squib failures and reliability

Because a squib must function reliably on demand after years of dormancy, automotive squibs are engineered to tight tolerances. Corrosion of the bridge wire, degradation of the primer compound, or contamination can cause misfire or failure to ignite. Vehicle manufacturers and squib suppliers perform rigorous qualification testing, including thermal cycling, vibration, humidity exposure, and accelerated life testing. A single failed squib can render an entire airbag system non-functional, which is why recalls occasionally occur when manufacturing defects or design flaws emerge in squib batches.

The term squib comes from military and firearms tradition, where it originally referred to a small charge or flash-producing device. In automotive context, it remains unchanged despite the device's critical safety role. Unlike automotive fuses or relays, which are standardized and interchangeable, squibs are inflator-specific; they cannot be transferred between different airbag models or manufacturers without validation testing.

Squib integration into the inflator assembly is a specialized manufacturing process. The device must be crimped or press-fitted into the canister body under controlled conditions to ensure proper electrical contact and structural integrity. A loose squib connection creates an open circuit and prevents deployment; over-pressure during installation can damage the initiator chemistry. This assembly work is typically performed in dedicated facilities with ESD controls and explosive material handling protocols.