July 1969 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
It should come as no surprise that in the pre-safety-ground
era which included the 1960s that electrical shocks of patients in hospitals was not
uncommon. If the jolt came intentionally from a cardiac defibrillator, then it would
be a good thing. However, these shocks, which were the subject of a Time magazine
story in the
April 18th, 1969 issue cited by Mac's technician, Barney, were being
administered unintentionally by patient monitoring and ancillary life-sustaining equipment.
Per the article, no Underwriter's Laboratory (UL) certification was required for hospital
equipment. Maybe it was felt that it wouldn't be so bad if someone got zapped in the
hospital since there would be a doctor on-hand to resuscitate the zapee. Since that time
medical equipment has been required to undergo stringent safety conformance requirements
that makes electrocution virtually impossible. Now, if we could just keep doctors from
cutting off the wrong limb or removing the wrong organ...
Mac's Service Shop: Safety in Medical Electronics
By John Frye
Increased use of electronic equipment in medicine
is creating a demand for meaningful safety standards.
"Mac," Barney said to his employer, "did you see that story a while back claiming
that some 1200 hospital patients were accidentally electrocuted every year?" "Yes," the
older man replied, taking a final swipe with the cleaning cloth at the face of the portable
TV he had just serviced.
"As I remember, the story first appeared in the January 27th issue of Electronic
News. The figure was given by John A. Hopps, Radio & Electrical Engineering
Division, National Research
Council, Canada, at the Reliability Symposium held in Chicago the week before. He
was quoting Dr. Carl W. Walter, surgeon at the
Peter Bent Brigham Hospital in Boston, who said he received the figures
from an actuary of an insurance company who had made a computer study of the situation."
"Ask for a slice of bread and you get a bakery!" Barney exclaimed. "You know more
about it than I do. I was talking about a
Time story that ran in the April 18th issue. Anyway, can you
believe that 'shocking' figure? A guy goes to the hospital to get well, not electrocuted."
"One more bad pun like that and you may go to the hospital yourself," Mac growled.
"I, of course, have no way of judging the validity of the figure, but the original story
concluded with the comment that throughout the survey conducted by the newspaper 'no
one denied the figure of 1200 deaths or made a lower estimate.' Dr. Walter, who is recognized
as a man of stature in the medical field, sticks with the figure and contends it would
be a lot higher if it included patients who suffered cardiac arrest from shock but were
"The Time story says a spokesman for the AMA claims the figure is exaggerated by about
1175 cases," Barney offered.
"On the other hand," Mac countered, "Richard Merris, sales manager for Dallons Instruments
is quoted as saying the figure sounds about right to him. As Dr. Walter points out, many
hospitals are unaware of the cause of death in these electrocution cases. Death is attributed
to other causes, and that is why it is difficult to get hard figures regarding these
"I got the idea most of the deaths were caused by incompatible grounding systems used
on different kinds of complex equipment and on such simple things as frayed cords or
broken plugs," Barney said.
"That's partly oversimplification," Mac answered. "Leakage of any sort between two
different pieces of electrical equipment with which the patient is in contact could produce
death, especially when the attachments of the instrument bypass the skin resistance by
being inserted in a vein or artery or deliberately reduce the skin resistance through
the use of moisture or conducting paste."
"Know what you mean," Barney offered. "I read an article in the September, 1968, issue
of QST written by Melville M. Zemek of the Associated Factory Mutual Fire Insurance Companies
in which he said the resistance of the human body varies from 100,000 ohms down to 1000
ohms or less, and most of this is made up of contact resistance. A value of approximately
500 ohms is usually accepted as the average resistance of the human body between the
"He went on to point out that while high voltage produces severe surface tissue destruction
at high resistance contact points, it's the current flowing through the body that kills
you. Danger of electrocution depends on the magnitude, duration, and path of this current
through the body.
"The most dangerous path is through the chest, for this is likely to cause the heart
to lose its life-sustaining rhythm and to go into a condition of ineffective quivering
called ventricular fibrillation in which the heart feels, in the almost-too-graphic words
of a surgeon, 'like a handful of worms, just squirmy.' Experiments on animals to determine
the amount of current through the chest to produce usually fatal fibrillation have been
projected into a theoretical criterion of danger for man in terms of current and time
duration. This data produces a straight line graph on log-log paper from 400 mA for 0.005
second down to 75 mA for 5.0 seconds."
"Electricity can produce death in other ways, can't it?"
"Oh sure. Shocks can cause respiratory inhibition, heart block, and severe damage
to the nervous system. These other mechanisms of death, however, ordinarily require a
lot more current than that needed to initiate the deadly ventricular fibrillation; and
that's why the latter is more likely to be cause of death in a hospital electrocution.
A current that only tickles the hands of a doctor or technician may be more than enough
to bring death to a weakened patient when the electrodes are applied in such a manner
as to bypass his protective skin resistance."
"Let's see if we can figure out for ourselves how some of these deaths might occur,"
Mac suggested. "In older hospitals or hospitals that have added wings at different periods,
there may not be a common ground for all outlets. If two pieces of equipment are plugged
into receptacles with different grounds, there may be a 'ground-loop current' flowing
from one instrument to the other through the patient."
"Yeah, and suppose the grounded lead in the line cord is broken loose from the plug
prong, leaving the case ungrounded. Suppose further that a capacitor from the hot side
of the line to the case is leaky or has been actually shorted by a lightning surge. Now
if the patient touches the case or anything connected to the case and also touches with
his other hand a grounded object such as a radiator, water pipe, or wall plate, the current
flows to ground right through his chest."
"These are pretty obvious examples," Mac admitted.
"Quite likely the more subtle leakages are the ones that cause the most trouble. We both
know that the primary or secondary of a power transformer can short to the core and thence
to the case. An arc-over can establish a carbonized path that can carry enough current
to produce fibrillation and still be high enough in resistance, especially when the instrument
is not operating, to be hard to detect by a casual examination.
"Dr. Leon Pordy, Assistant Professor of Medicine, Mount Sinai School of Medicine,
points out that patients in an operating room are often wired up for sixteen different
things. Every precaution is taken to avoid accidents, and the first consideration is
to make sure the patient is not grounded. Actually the patient is safer in the operating
room, even with all this equipment, because it is being used by experts. He is in more
danger from more ordinary equipment carelessly used by hospital personnel with no training
in electronics, equipment that is less rigorously examined. Few hospitals in the country
use expert electronics technicians to operate complicated instruments. They usually scout
around for some doctor with a smattering of electronics and turn the job over to him."
"Hey, that's about as smart as finding a janitor with a first aid course and turning
the emergency ward over to him!" Barney exclaimed. "As I get it, there is at present
no pre-marketing clearance of medical electronic equipment such as the UL tag on household
equipment. How come?"
"There are a couple of reasons. For one thing, the doctors and the equipment manufacturers
can't agree on what is necessary. The doctors want foolproof equipment that requires
a minimum of maintenance and that can be operated by untrained personnel. The equipment
manufacturers want the medical profession to set up some standards as to what constitutes
safe leakage currents. But no doctor is willing to stick out his neck and say this is
x number of microamperes. Doctors say the fibrillation level varies from individual to
individual. They would prefer, of course, an impossible leakage level of zero.
"The second reason for a lack of safety standards is that Congress will not pass same.
Starting in 1962, bills have been introduced every year requiring approval of electrical
medical equipment by some federal agency, and every year these bills have died in committee.
Two more bills were introduced in the House and Senate at the present session, but no
one will wager they will ever get out of committee. However, the chance that some sort
of legislation will be passed eventually is improving as a result of the present publicity
regarding the hospital electrocutions - especially since Ralph Nader brought this subject
up in testimony before the Product Safety Commission in Washington last February. The
pity is that several hundred - or perhaps thousand - patients will die of electrocution
while undergoing routine diagnostic tests or treatment before that takes place."
"That reminds me that Professor Paul E.Stanley, a Purdue University professor of aeronautical,
aerospace, and engineering sciences, has spent the last few years in researching the
causes and prevention of these hospital electrocutions. He has come up with both a long-range
and a short-range plan for correcting the condition. His long-range plan is a typical
engineering approach: 1. Define the problem and collect facts about the hazards of medical
instrumentation. 2. Do research to determine more precisely I the maximum nonfibrillibrating
current. 3. Expand the study to include such things as electrically operated beds, heating
pads, TV sets, etc. 4. Set up design standards and procedures that will reduce the accidental
electrocution rate in hospitals to zero.
"All this, he admits, will take time, precious time in which other lives will be lost
needlessly. To reduce this loss, he recommends that in the meantime all personnel using
electrically operated equipment in hospitals be trained in the fundamentals of safety,
that a positive earth ground and a single ground reference be used for all equipment
connected to one patient, that isolated and monitored ungrounded power be provided for
all hospital rooms where patient monitors are used or where cardiac catheterization is
performed, and that adequately trained personnel be employed to provide specifications
for the purchase of equipment and to provide preventive maintenance on same."
"Makes sense," Mac observed. "The important thing is to fix the responsibilities.
Dr. Pordy said it well: 'Suppliers of electronic equipment have the first responsibility
to make sure their equipment is safe. Doctors have the second responsibility to make
sure the equipment is properly used.' If both groups accept their responsibility, we
should be able to bring a halt to this needless loss of life."
Posted May 30, 2018
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive stories was the brainchild of none other than John T.
Frye, creator of the Carl and Jerry series that ran in
Popular Electronics for many years. Mac's Radio Service Shop began life
in Radio & Television News
magazine (which itself started as simply Radio News), and then changed
its name to Mac's Service Shop after the magazine became
World. 'Mac' is electronics repair shop owner Mac McGregor, and Barney
is his eager, if not somewhat naive, technician assistant. 'Lessons' are taught
in story format with dialogs between Mac and Barney.