This paper reports on investigations of the previously unexplored initial front rise differences between real human body model (HBM), transmission line pulse and components level HBM tester wave shapes. The d V/d t of the HBM test pulse amplitude below 2% has been shown to affect the high current immunity of Snapback type ESD protection circuits, and should replace the present time specification for a high voltage HBM pulse to rise from 10% to 90% of the peak amplitude, commonly known as risetime.