The safe usability of occupant protection systems over their entire service life is a core concern in planning and procurement - especially of those devices that contain pyrotechnic formulations, such as airbag gas generators, seatbelt pretensioners and actuators. Artificial aging, as provided for in current standards, provides an estimate of product life. However, it often reaches its limits when it comes to predicting the safe life of pyrotechnic compositions. Complications in age prediction arise from the nontrivial chemical processes involved in the aging of propellant materials. The multitude of environmental influences and vehicle-dependent design differences require a variety of assumptions and simplifications that lead to discrepancies between prediction and reality.
More than two decades after the introduction of OEM standards for the procurement of airbag inflators (AK-LV, SAE) and more than a decade after the outbreak of incidents involving ammonium nitrate-based propellants, the state of science and technology has significantly advanced the specifications currently in use.
GWP can draw on a wealth of experience from
- Damage investigations
- Performance tests
- Qualification tests
- environmental simulations and
- field parts monitoring
projects and, with GWP Guideline 012 (GWP RL 012), has created a procedure by which the knowledge gained can be translated into specifications based on the current state of science and technology. During the development of GWP RL 012, a wide variety of approaches to the development and testing of specifications were evaluated, and the large number of sources evaluated for this purpose covers a wide range of applications. As a result, GWP RL 012 was created as an approach tailored to the challenges of pyrotechnic safety devices.
Based on a definition of the vehicle platform and airbag device, environmental influences are derived. Load duration and "strength" of the corresponding environmental influence are then approximated using prior knowledge or estimations based on failure modes and failure paths. Interconnections as well as synergistic interactions between individual environmental influences and equipment failures are revealed. Even at an early procurement stage, the results can influence further device development.
Environmental simulation and test procedures are then aligned with the relevant environmental factors and the underlying failure modes, respectively. In terms of test complexity, a distinction is made between product qualification, e.g. of a novel device, and input testing (lot size dependent). Each step of the process is documented and provides useful information on how scientific progress in testing and environmental simulation can improve the resulting specification. This serves as a guide for interpreting test results and their impact on the safe life of the device. A schedule of iterative updates to the specification will be established. The resulting document will be adjusted and improved over time. In this way, it will continually increase its usefulness in improving motor vehicle occupant safety.