Electric shock hazard

A long-standing expert on electric-shock hazards summarizes the studies that determined the effective body impedance under varying conditions. He describes perception currents, reaction currents, let-go currents, and fibrillating currents. Turning to means for reducing low-voltage (120-240-volt) hazards, double insulation, shock limitation, isolation transformers, and the use of either high frequency or direct current are discussed for various environments. Macroshock is always a hazard in the home, in industry, and in the hospital. But the extreme vulnerability to microshock of patients with cardiac catheters, for example, requires special precautions in intensive-care and coronary-care units. Equipment such as the ground-fault interrupter (GFI) and a special isolation transformer are cited.