Impact of Recent Developments in Biological Electrical Shock Safety Criteria

Abstract

New electrical shock safety criteria are being evolved in the International Electrotechnical Commission (IEC), largely by researchers in Western Europe. These new criteria are significantly different from the older biological safety criteria currently being used in North America for electrical equipment design standards. As a first step to address these discrepancies, an international symposium was held to provide the needed exchange of information. Some important findings of this symposium are summarized. In these new criteria, the maximum allowable body current or voltage as applied between both hands and feet to preclude ventricular fibrillation in adults for 0.01-sec shocks are respectively 1/2.5 or 1/5 of the respective values recommended by the older North American criteria. For other body current paths or shock durations, the new criteria indicate safe exposure limits ranging from 1/7 to more than three times the values in the older criteria. The reliability of much of the basic shock data is still open to question, as are the conclusions drawn from the data. If no further research is done to clarify the discrepancies, the new IEC (International Electrotechnical Committee) shock criteria, along with their implications for major design revisions, might well become the basis for the safe design of electrical equipment even though there exist no epidemiologic studies to indict the current design criteria. Research is needed in the areas of bodyweight scaling, body impedance and body-current pathway effects, let-go limits, asphyxia, and electrical burns to resolve crucial grounding system design issues.