ENTC 4350,Electrical Safety,Hospital electrical safety begins with the principles that we have discussed. An electrical shock is always unpleasant, but it can be lethal in the intensive care unit.,It is extremely important that all hospital personnel be constantly on the watch for manufacturing defects or wear and tear of critical parts. There are documented cases where equipment from reputable manufacturers was delivered with ground wires disconnected, cords broken, and improperly installed plugs. In the meantime, there is still the patient; it is your patient and your responsibility. You are the one who must be suspicious and check the equipment when it comes from the factory.,Even if equipment is in perfect condition when it arrives from the manufacturer, it is subject to the normal wear and tear of daily hospital use. This type of deterioration may be very severe if the equipment is dragged around, in a great rush, from one room to another in response to emergencies. Once again, the part of the system that is most likely to be damaged is the cord and plug assembly.,Quite often, the damage is not visible on a mere surface examination; you have to get out your VOM or continuity tester and test it. Connect the continuity tester or VOM between the ground plug on the end of the cord and the metal case of the instrument. If the test light goes out when you wiggle or pull on the wire, or If the resistance measured by the VOM is erratic when you move the cord, then the appliance is defective.,If your hospital has a red tag service that allows defective equipment to be marked for immediate pickup and repair, all is well. However, if there is any danger that the equipment might be used in patient service before the repair is done, the best thing to do is take your handy bandage scissors and cut the plug off. That may sound like a drastic measure (surgery is always drastic), but in this case, it is quite justified.,Another thing to watch for is someone elses home repair.” This is particularly apparent in hospitals where one sees cracked cords or broken plugs repaired with adhesive tape. That cord or plug cracked for a reason: either age or misuse is usually to blame.,If the insulation is cracked, most of the conducting wires may be broken, too. Just suppose that the last strand of ground wire broke when it was being used on your patient, and reflect upon the results of our computations with the current divider equations previously.,In this regard, you have to watch the other staff membersi.e., the orderlies, aides, and so onsince the natural human tendency is to put the broken item back on the shelf and take one that looks all right. Quite often, an aide will hesitate to report defective equipment for fear of being thought to be a troublemaker. Only endless repetition, and possibly a cash prize for reporting defects, will alleviate this situation.,It should he clear to everyone that if any defective equipment is noted, or if a tingle is sometimes felt when using a piece of equipment, this is a signal to stop using the equipment and report it.,The patient is truly at your mercy, and equipment that comes near to him or her must be in proper condition. At this point, you might be wondering just what proper condition is and how leakage occurs. The specifications on electrical leakage are complex and subject to change; however, two good points to keep in mind are the leakage to the chassis of hospital equipment and the leakage through any patient-connected leads.,With the ground wire disconnected, the chassis leakage is limited to 100 mA, and the patient-lead leakage must not exceed 50 mA. There are many causes for leakage: defective insulators, damaged wire, dirt, water, and the radiation leakage.,Figure 14.3 Let-go current versus frequency Percentile values indicate variability of let-go current among individuals. Let-go currents for women are about two-thirds the values for men. (Reproduced, with permission, from C. F. Dalziel, “Electric Shock,“ Advances in Biomedical Engineering, edited by J. H. U. Brown and J. F. Dickson IIII, 1973, 3, 223-248.),Figure 14.1 Physiological effects of electricity Threshold or estimated mean values are given for each effect in a 70 kg human for a 1 to 3 s exposure to 60 Hz current applied via copper wires grasped by the hands.,They all add up to a problem for the hospital.,The danger of having a single hospital appliance with a defective three-wire cord is illustrated below. Here we show a patient in an electrical bed with a three-wire cord that is good.,This means that when the patient puts his hand on the bed rail, he is grounded. too. There is nothing wrong with that until someone brings over a second appliance, like an ECG or an apnea monitor, which has a defective three-wire cord. The manufacturer designed the appliance with the idea that the three-wire cord would be operational and that stray leakage in his unit would be grounded off to the case and removed by