Further Remarks on Protective Measures, with Special Reference to High Voltage

Abstract

TO enumerate all the possible dangers associated with the operation of a modern high voltage X-ray plant would be difficult, and to safeguard oneself adequately against every conceivable danger in such an installation would be well-nigh impossible. Yet by a careful regard for electrical laws and with the assistance of intelligent electrical engineers, a practically safe high line X-ray laboratory can be successfully equipped and operated. Nearly all the accidents reported up to the present time have been due to carelessness upon the part of the operator or his assistants. More rarely, the patient receives an injury due either to an involuntary movement which brings him into electrical contact with the line, or else to the accidental breakage of tube terminal connection or a detached wire coming into the patient's circuit. While no one can provide for all possible contingencies, yet from the mechanical or physical aspect, there is no excuse for permitting faulty construction or installation of X-ray equipment in any office or institution. After being satisfied on this score, one of the first duties of the operator should be to inspect every part of the line before closing the circuit. This should not be an occasional function, but a routine act before every individual contact with the switch. With high voltage installation, the question of ground connection must be carefully considered. What constitutes a safe ground under all conditions is not easily comprehended by one who is not an expert electrical physicist. Yet there are a few fundamental principles which the average radiologist can understand and apply. If one could successfully ground everything in his whole plant, except the patient and operator, the question would solve itself, but as the success of operation of the tube carrying the high voltage line depends upon complete insulation, it is obviously impossible to have any sort of ground connection on this line, and extreme precaution must therefore be observed that the patient does not become the ground conductor. This is especially pertinent in view of the high peak surges which accompany the normal load pressure. Such surges can be made harmless to the individual in three practical ways: either by a quick-acting circuit breaker of the two or three pole variety; by complete insulation of the patient, or by properly placed leads which will arc to absolute ground in the event of surge or overload. A thoroughly equipped high voltage laboratory should be provided with these or equally good means of protection. In the writer's opinion, the best method to provide proper grounding facilities is to connect all metallic tube carriers, all leaded screens and walls together to one common, thoroughly adequate ground line, preferably a main water pipe. A metallic table for the patient should never be used with high voltage work; neither should a table upon which the patient reclines be grounded.