Hazards of Electrical Apparatus

Abstract

Hazards of electrical apparatus arise from increased use of electricity and from new devices that make possible accidental as well as intentional application of electrical energy directly to the heart. The mode of death in electrocution by medical devices is ventricular fibrillation; this occurs if alternating currents in a range from 100 Ma to 3 amp are passed through the trunk and intact skin. When electrical energy is applied directly to the myocardium, currents as low as 20 Mamp may cause fibrillation. The major determinant of current flow is the resistance afforded by the current pathway. Electrical systems in the US are of the grounded type 1 of the conductors is at earth potential. Thus, contact between the ungrounded conductor and earth presents a hazard as great as simultaneous contact with the 2 wires of the circuit. Specific applications of grounding are discussed, including protection of personnel afforded by equipment grounding. Examples of electrical hazards are a.c.-d.c. [alternating current-direct current] devices and leakage currents. The latter are generally the result of voltage division, either accidental or as part of circuit design, playing a leading role in medical electrocution; the role of capacitance is not established. Improved electrical safety requires use of a 3 conductor plug and cable. Isolation by added transformers or by battery-operated equipment plays a minor role. Technical and engineering factors are considered, and emphasis is placed upon improved maintenance of fixtures and equipment. It is essential that the electrical environment of the operating room be under supervision of an informed authority. Improved labeling of medical electronic devices is imperative and must include complete circuit descriptions and diagrams.