California failure analysis expert witness analyzes a failed tempered glass toaster oven door to determine the cause of failure. The glass door remained intact, and this allowed the failure analysis to be performed. The origin is found to be in the center of a “butterfly” shaped region. There is a crush point that is the origin. The glass failure started at the crush region on the glass door surface and progressed inward till the residual stresses of the thermally tempered glass took over and caused the entire door to break into very small cubes. Upper left is an overview of the failed oven door. Upper right is a photomicrograph of the fracture surface at the origin.