Glass bars and plates were subjected to impact loading. Failure waves were observed to propagate behind the compression waves. Material traversed by the failure wave suffers total loss of tensile strength and substantial drop in shear strength. Failure wave propagation velocities exceed the maximum crack propagation speed, but are not constant. In bars, failure wave speed range from 2.3 to 5.2 mm/&mgr;s, increasing with increasing impact velocity; in plates, the wave speed is about 2 mm/&mgr;s. The failure is ‘‘explosive’’ in nature, leading to radial expansion in bars and an increase in mean stress in plates.