Probability Surface Distributions for Application in Grounding Safety Assessment

The safety criteria of national and international grounding standards do not compare well due to a variety of adopted values for permissible safety voltages. These differences stem from disparities in assumed worst-case conditions which result from the adoption of discrete probabilistic assumptions of safety parameters embedded within an overall deterministic safety assessment. Harmonization of grounding design standards, however, could be achieved through the adoption of a probabilistic safety assessment which will lead to a quantification of the risk of ventricular fibrillation to an individual. Fundamental principles and criteria for such an approach are developed in this paper, and are based on a statistical analysis of the IEC published curves of ventricular fibrillation. The developed numerical approach also takes into account the effect of current path on fibrillation sensitivity and body impedance. Using this approach, probability surfaces of ventricular fibrillation are then calculated as a function of applied voltage and shock duration. This statistical approach to the characterization of the human body under various electric shock scenarios forms a platform for a full probabilistic approach which can be extended to take into account other statistical parameters, and may lead to a more objective measure for making investment decisions in hazard mitigation.