This study continued the biomechanical investigations of forearm fractures caused by direct loading of steering wheel airbags during the early stages of deployment. Twenty-four static deployments of driver airbags were conducted into the forearms of unembalmed whole cadavers using a range of airbags, including airbags that are depowered as allowed by the new federal requirements for frontal impact testing. In general, the depowered airbags showed a reduction in incidence and severity of forearm fractures compared to the pre-depowered airbags tested. Data from these twenty-four tests were combined with results from previous studies to develop a refined empirical model for fracture occurrence based on Average Distal Forearm Speed (ADFS), and a revised value for fifty-percent probability of forearm-bone fracture of 10.5 m/s. Bone mineral content, which is directly related to forearm tolerance, was found to be linearly related to arm mass. The ADFS criterion was found to be effective in predicting forearm fracture, regardless of the airbag system, subject size, and age. Additional testing was conducted to examine the principles underlying the ADFS criterion. Specifically, static airbag-deployments were conducted into cylinders of different mass to study the relationships between forearm mass and forearm-to-airbag module distance relative to ADFS. ADFS was found to be linearly but inversely related to cylinder mass, and to the distance between the forearm and airbag module. The suitability of using existing surrogate arms to assess airbag aggressivity relative to forearm fractures using ADFS was explored as well.
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