I. In Intro troduc ductio tion n to Bio Biomed medica icall Engin Engineeri eering ng
Electrical Safety
• Introduct Introduction ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 1 • Industry Industry Regulatio Regulation n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 3 • BMET Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page .pag e 4 • History History of Electrica Electricall Safety Safety . . . . . . . . . . . . . . . . . . . . . . . . . . .page 4
Made Easy II. Fund Fundament amental al Concept Conceptss of Electrical Electrical Safe Safety ty . . . .page 6 III.Physiological Effects of Electricity
Table Of Contents
• Introduct Introduction ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 7 • Macroshock Macroshock and and Microsho Microshock ck . . . . . . . . . . . . . . . . . . . . . . . . .page 7 • High Frequ Frequency ency Effects Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 8 • Potential Equipment Safety Safety Hazards . . . . . . . . . . . . . . . . . . .page 8 • Equipment Equipment Safety Safety Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 8 • Electrical Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 8 • The Electrical Power Power System System . . . . . . . . . . . . . . . . . . . . . . . . . .page 8 • Contact Contact with with a Ground Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 9 • Skin Skin Resistance Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 9 • Leakage Leakage Current Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 10 • Electrical safety Power System Devices . . . . . . . . . . . . . . . .page 10 • Ground Fault Fault Circuit Interrupter . . . . . . . . . . . . . . . . . . . . .page 10 • Isolation Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 10 • Equipotenti Equipotential al Grounding Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . .page 11 • Codes Codes and Standar Standards ds . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 11-12
IV.. The AAMI Standa IV Standard rd . . . . . . . . . . . . . . . . . . . . . . . . . .page 13-32 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 32 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 33
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he field of medical instrumentation is by no means new. Many instruments were developed as early as the nineteenth century – for example, the electrocardiograph,, first used by cardiograph Einthoven at the end of that century. Progress was rather slow, however, until after World War II when a surplus of electronic equipment such as amplifiers and recorders became available. At that time, many technicians and engineers, both within industry and on their own, started to experiment with and modify existing equipment for medical use. This process occurred during the 1950’s and the results were often disappointing. For the experimenters soon learned that physiological parameters are not measured in quite the same way as physical parameters. They also encountered a severe communication problem with the medical profession. During the next decade many instrument manufacturers entered the field of medical instrumentation, but development costs were high, and the medical profession and hospital staffs were suspicious of new equipment and often uncooperative.. Many developuncooperative ments with excellent potential seemed to have become lost causes. It was during this period that some progressive companies decided that rather than modify existing hardware, they would design medical instrumentation specifically designed for medical use. Although it is true that many of the same components were used, the philosophy was changed; equipment analysis and design were applied directly directly to medical problems. A large measure of help was provided by the U.S. government, in particular NASA (National Aeronautics and Space Administration). The Mercury, Mercury, Gemini and Apollo programs needed accurate physiological monitoring for the astronauts;
consequently, much research and development money went into this area. The aerospace medicine programs were expanded considerably,, both within NASA considerably facilities and through grants to Universities and Hospital research units. Some of the concepts ad features of patient monitoring systems presently in use in hospitals throughout the world evolved from the base of astronaut monitoring. The use of adjunct fields, such as biotelemetry biotelemetry,, also found some basis in the NASA programs. Also, in the 1960’s, 1960’s, an awareness of the need for engineers and technicians to work with the medical profession developed. All the major engineering technical societies recognized this need by forming "Engineering Medicine and Biology" subgroups and new societies were organized, such as the Biomedical Engineering Society.. Along with the medical Society research programs at the universities, a need developed for courses and curricula in biomedical engineering and today almost every major university has some type of biomedical engineering program. However, much of this effort is not concerned with biomedical instrumentation per se. One of the problems of "biomedical engineering" is defining it. The prefix bio- of course, denotes something connected with life. Biophysics and biochemistry are relatively old disciplines in which basic sciences have been applied to living things. One school of thought subdivides bioengineering into different engineering areas – for example, biomechanics, and bioelectronics bioelectronics.. These categories usually indicate the use of that area of engineering applied to living rather than to physical components. Bioinstrumentation implies measurement of biological variables, and this field of measurement is often referred to as biometrics, although the latter
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I. Introduction to Biomedical Engineering
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term is also used for mathematical and statistical methods applied to biology.
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Naturally, committees have been formed to define these terms; the professional societies have become involved. The latter includes the IEEE Engineering in medicine and biology group, the ASME Biomechanical and Human Factors division, the Instrument society of America and the American Institute of aeronautics and Astronautics. Many new cross-disciplinary societies have also been formed. Several years ago an engineering committee was formed to define bioengineering. This was subcommittee B (Instrumentation) of the Engineers Joint Council Committee on Engineering on engineering Interactions with biology and Medicine Medicine.. Their recommendation was that bioengineering be bioengineering be defined as application of the knowledge gained by a cross fertilization of engineering and the biological sciences so that both will be more fully utilized for the benefit of man. More recently, as new applications have emerged, the field has produced definitions describing the personnel who work in it. A tendency has risen to define the biomedical engineer as a person working in research research or development in the interface area of medicine and engineering, whereas the practitioner working with the physicians and patients is called a clinical engineer. engineer . One of the societies that has emerged in this interface area is the Association for the Advancement of medical Instrumentation (AAMI). This association consists of both engineers and physicians. In late 1974, they developed a definition that is widely accepted:
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"A clin ical engin eer is a professional who brings to health care facilities a level of education, experience and accomplishment which will enable him to
responsibly, responsibl y, effecti effectively vely,, and safely manage and interface with medical devices, instruments and systems and the use thereof during patient care,, and who can, becaus care becausee of this this level of competence, responsibly and directly serve the patient and physician, nurse and and other health care professionals relative to their use of and other contact with medical instrumentation." Most engineers go into the profession through the engineering degree route, but many start out as physicists or physiologists. They must have at least a B.S. degree and many of them have M.S. or Ph.D. degrees. Another popular term, also coined in recent years, the biomedical equipment maintenance technician (BMET) is defined as follows: "A biom edical equi equi pm ent m ain te tenan nan ce te technician chnician (BMET) is
an individual who is knowledgeable about the theory of operation, operation, the underlying physiologic principles and the practical, safe clinical application of biomedical equipment. equipmen t. His capabilities capabilities may include installation, calibration, inspection, preventive maintenance and repair of general biomedical and related technical equipment as well as operation or supervision of equipmentt cont equipmen control, rol, safety and maintenance programs and systems." This was also an AAMI definition. Typically, the BMET has two years of training at community college. This person is not to be confused with a medical technologist. technologist . The latter is usually used in an operative sense, for example in blood chemistry and in the taking of electrocardiograms. The level of sophistication of the BMET is usually higher than that of the technologist in terms of equipment, but possibly lower in terms of the life sciences. In addition, other titles have been used, such as hospital engineer
and medical engineer. engineer . In one hospital the title biophysicist is preferred for their biomedical engineers, for reasons best known to themselves. These definitions are all noteworthy,, but whatever the noteworthy name, this age of the marriage of engineering to medicine and biology is destined to benefit all concerned. Improved communication among engineers, technicians and doctors, better and more accurate instrumentation to measure vital physiological parameters and the development of interdisciplinary tools to help fight the effects of body malfunctions and diseases are all a part of this field. The name itself is actually not all too important; however, however, what the field can accomplish is important. With this point in mind, we will be using the term biomedical engineering for describing the field in general and biomedical instrumentation for the methods of measurement within the field.
INDUSTRY REGULATION In it’s infancy, biomedical equipment was best serviced and maintained by the original equipment manufacturer as there were few, few, if any, any, qualified technicians who could do so adequately. A lack of standards linking the technology, an absence of service literature, and the general feeling from hospital personnel that, unless trained by these OEMs, no one would be able to provide a suitable level of services. Thus the early BMET was relegated to maintain and repair only the simplest of clinical equipment such as centrifuges, suction pumps and other such equipment. Several factors soon arose to alter this conception. First, agencies such as the Food and Drug Administration (FDA) developed subdivisions under which fell the area of medical instrumentation. This brought about a set of standards and practices for manufacturing of
hospital equipment, as well as the maintenance and repair of such. Secondly,, other agencies, under Secondly which hospital equipment was monitored and controlled, invoked requirements such as the release of service literature on any new equipment purchased or manufactured to the hospital. This literature, the law stated, must contain the procedures for calibration and alignment of said equipment. Thirdly, the training of biomedical equipment technicians began to catch up with the advancing technology so that the level of competence was significantly improved. Finally, through the feeling that they provided the only service available, the OEMs began to charge significantly more for their service contracts each year. Surprisingly Surprisingly,, this was not a major issue to the hospital community until the middle of 1980 when the government, in an effort to control the rising cost of medical treatment, and the subsequent rise in medical insurance claims, imposed major restrictions upon hospitals. These restrictions, known as Diagnostic related Groups (DRGs) limited the amount that medical insurance groups would reimburse both hospitals and physicians for each type of illness for which a patient might enter the hospital. Without Without going into great detail about DRGs, suffice it to say that their introduction brought with it a need for hospitals to lower their operating costs. One area in which these costs could be lowered was in the area of biomedical instrumetation. Where once a hospital would make a major equipment expenditure, such as buying a new chemistry analyzer,, every five or so years, they analyzer began keeping sophisticated equipment such as this for longer periods. So doing, the rising OEM service contract prices suddenly became an issue and the responsibility for these equipment fell upon the BMET as a lower cost alternative. As more and more responsibility responsibility fell upon the BMET within the
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hospital for larger and more sophisticated instrumentation, new problems arose for the hospitals. In order for the equipment to be adequately maintained, more BMETs needed to be employed, each having sufficient training in the sophisticated equipment involved. Hospitals were faced with weighing the additional cost of salaries, benefits and the costs of attending additional manufacturers schools and seminars with the cost of the OEM contracts. In very large hospital facilities, this was not such a significant problem as it was with smaller facilities. In many smaller facilities, typically those under 200 patient beds, it was simply not feasible to consider an in-house BMET program and, thus, these facilities were forced to pay for the OEM contracts.
be employed on sensitive, lifesaving medical equipment.
Again, the government became involved. Federal and state agencies began to require all hospital facilities to comply with stringent safety guidelines for patient related equipment. This included a routine electrical safety program under which all hospital equipment would be tested, evaluated and forced to comply with. Typically ypically,, the BMET provides one or more of the following services to hospital facilities:
In an effort to satisfy applicable federal and state requirements as well as to insure that clinical equipment are utilized both safely and to their optimum, some BMET shops provide periodic in-service and education services. This often ranges from simple electrical safety lectures to the proper use of a newly acquired piece of equipment for which hospital personnel might not yet be familiar.
BMET RESPONSIBILITIES
This brings us to the main purpose of this document. Periodic testing of patient and non-patient hospital equipment to insure that they meet the safety requirements and guidelines as set fourth by applicable federal and state regulations. This This in no way measures the equipment ability to perform the task for which is was designed.
Corrective Maintenance
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Non-scheduled repair of hospital equipment other than during Preventive Maintenance inspections. These repairs range from replacement of minor parts or components to total equipment overhauls as may be required. In an effort to further provide a cost savings to the t he hospital facility, some BMETs attempt to repair equipment to the smallest component level, rather than simply replacing circuit boards or sub-assemblies which may be very costly. Other BMETs follow a philosophy that component-level repair entails far too many risks of repeated failure or improper component soldering techniques to
Preventative Maintenance Inspections Periodic testing and evaluation of patient and non-patient related equipment to insure that they operate within the guidelines set fourth by federal, state and manufacturer guidelines. This includes calibration and alignment of said equipment along with the repair and/or replacement of component parts in order to bring the equipment into compliance. It is the belief of most BMETs that good, quality preventive maintenance inspections further reduce hospital costs by reducing equipment down-time for repairs.
Inservice & Education
Electrical Safety Inspectio Inspections ns
HISTORY OF ELECTRICAL SAFETY The introduction of electricity into commerce at the close of the 19th century carried with it the need to know how to deal with it safely. For the hospital environment, much of the electrical safety programs started after World war II. Shortly thereafter,, federal funds via thereafter v ia the
Hill-Burton Act increased the number of hospital facilities. Grounding for electrical safety was implemented because most electrical accidents in the home and industry occurred because exposed metal was energized. The National Electrical Code stated that "non-current carrying" metal parts of the electrical apparatus could prevent such accidents. Unfortunately, by the end of the 1950’s, electrical power in the hospitals was supplied in a haphazard, eclectic fashion. In the hospital environment of the sixties, electricity came to be used more often on, in and around patients to a degree beyond conception only a few years previously. It was early in 1961 that there appeared the first news that "microshock" (small electric currents applied to a conductor near the heart) was happening in the medical field. In 1969, Carl Walter, M.D., who was at the time a well-known surgeon, stated that, "1,200 patients were being accidentally electrocuted in U.S. hospitals each year." Although many engineers and health care professionals believed that Dr Dr.. Walter’ Wa lter’ss estimates were unrealistically high, the concept of microshock suddenly became publicized. Then, on June 16th, 1970, Ralph Nader (a household word because of his 1965 book, Unsafe at Any Speed ) gave a speech in Detroit. In this speech, he stated that, "1200 annual electrocutions in US hospitals was a very least figure" and quoted other experts indicating that the real number might be significantly higher. higher. The event was picked up by a wire service and run under an arresting headline the next day: Hospital electrocutions cited Detroit (UPI) Detroit (UPI) – "Accidental electrocutions claim 5,000 lives in American Hospitals every year but seldom get reported due to the "close nature of
hospitals" consumer critic Ralph Nader said yesterday. During the 1970’s, several proposals and regulations were introduced to manage this suspected problem in hospitals. In 1971, the National Fire Protection Association published a recommended standard (76BM) to help hospital engineers understand the principles of electrical safety and coordinate a program of medical equipment electrical testing in their facilities. In the spring of 1972, Underwriters laboratories issued document UL544 Medical UL544 Medical and Dental Equipment , which was intended to serve as a guideline for medical equipment manufacturers manufacturers.. In 1970, AAMI (the Association for the Advancement of medical Instrumentation) published a firstdraft standard for electrical leakage current standards that was adopted as an American national standard in 1978.
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Probably the most dramatic proposal was the Joint Commission on the Accre Accreditation ditation of Hospitals (now the Joint Commission on the Accre Accreditation ditation of Healthcare Organizations – JCAHO) 1976 recommendation that hospitals maintain equipment control programs to provide for electrical safety training, create a documented preventive maintenance program, and perform semi-annual safety and performance equipment inspections and annual inspections of electrical receptacles. Today, health care institutions in the United States support clinical engineering programs that provide ongoing electrical safety and performance testing as well as preventive maintenance and repair of medical equipment. Typically, these programs use the most recent editions of NFPA 70, NFPA 99, NFPA 101, AAMI Recommended Standards, and Joint Commission accreditation manuals for their reference standards. -5-
S
Electrical Safety
ome of the most basic concepts of electricity must be understood in order to grasp the potential hazards of electrical devices as they are used in a clinical setting such as a hospital. Some of these important ideas concerning electrical safety in a medical environment are explained below.
Made Easy The Nature of Electricity
II. Fundamental Concepts Of Electrical Safety
Electrical current flowing through a conductor is the result of electrons moving from the outer shell of atoms induced by an electric field that is imposed on a conductor. This field can be caused by any voltage generating source, such as a local utility company, a battery, or a chemical reaction. In the hospital, this voltage source is provided by the local electrical company and is redirected through a series of transformers to 240, 208, or 120 volts alternating current (AC). The amount of current that flows through an electrical device is determined by the resistance that the device is designed to provide to the applied field. This relationship is called "Ohm’s Law" and is written as:
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Where "I" is the current in amperes that flows through a device or conductor,, "V" is the conductor t he magnitude in volts of the applied electric field, and "R" is the resistance that the device or conductor has, measured in Ohms. Thus, if an electromedical device such as an aspirator is plugged into a 120 volt receptacle and the unit requires 3.0 amperes, then the resistance that the aspirator provides to the voltage is:
120 volts = 40 Ohms 3 amperes a measure of the amount of power that an electrical device consumes during operation is defined as the product of voltage and current and is recorded in Watts. From the previous example:
Power (watts) = (V ) (I) = (120) (120) (3) = 360 Watts Watts
B
ecause the amount of electricity that will flow through any medium depends on the resistance that it encounters, current can flow through the human body and cause various effects. If direct current (polarized, nonchanging) or high frequency alternating current passes through the body body,, heating effects and ultimately burns will occur. It is this effect that is intentionally created when electrosurgical generators are used to cut tissue and coagulate fluids. If low frequency alternating current is applied to the body body,, muscular polarization and depolarization take place that can ultimately create a "circus movement" in the heart muscle, resulting in fibrillation and death. It is this effect that normally accounts for death due to electric shock. Unfortunately, the typical resistance of the human body in combination with the frequency of commercially generated electricity (60 hertz) can create a potentially hazardous situation in the hospital environment.
MACROSHOCK AND MICROSHOCK The effect of electric shock on the human body can be anything from barely perceptible tinges, to muscle spasms, to death. Each can occur from small or large currents, depending on how the currents are introduced into the body body.. Large currents (milliamperes or larger) that are introduced into the body from one external point to another (arm to leg, for example) can result in macroshock. If small currents (as low as 10 microamperes) are introduced into the body from an external source such as a catheter or cardiac pacing wires, the resistance to the heart muscle can be very low low,, and electrocution can occur from microshock. The chart below describes the effect of different levels of current that are introduced into the human body by creating a voltage across each arm. For microshock, the same effect can be produced with current levels that are only 1/10,000 as great as those listed.
CURRENT
EFFECT
.001 .00 1 Ampere Ampere (1 (1 Millia Milliampe mpere) re)
"Ting "T inglin ling", g", thre thresho shold ld of perc percept eption ion
.020 Amps (20Ma)
Muscle Spasms, hard to release grip
.050 amps (50 Ma)
Pain, possible fainting, transient interruption of respiration
.100 Amps (100 Ma)
Ventricular fibrillation
>5 Amps
Sustained myocardial contraction, possible burns, temporary respiratory paralysis
Electrical Safety Made Easy
III. Physiological Effects Of Electricity
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HIGH FREQUENCY EFFECTS
EQUIPMENT SAFETY TESTING
As mentioned previously, previously, the primary effect of high frequency current (500 kilohertz to 2 megahertz) is to heat tissue as it is concentrated in a certain area. The amount of heat that is generated depends on the amount of current applied and the area that the current passes through.
Tests to determine the electrical safety of medical devices include a measurement of the continuity as well as the leakage current between the chassis and the cord grounding conductor.. Equipment that has conductor been designed with patient leads or contact points is also measured for current leakage from these points. Figures 1 and 2 show typical circuits that may be used to measure this leakage current.
This relationship is :
Heat He at = I x I A
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Where "I" is the applied current and "A" is the area that the current flows through.
POTENTIAL EQUIPMENT SAFETY HAZARDS Because current flow through the body can be hazardous if it is of a certain amplitude and frequency, stray currents must be eliminated from medical equipment. The best method to prevent leakage currents is to ensure that all conductive parts of the equipment are connected to the hospital grounding system through the power plug. Also, to minimize patient patient contact with current leakage on ECG signal leads, electrically isolated amplifiers should be used.
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In theory, the use of line isolated power systems helps to minimize safety hazards by isolating the neutral power line from earth ground. A line isolation monitor is also installed with these systems to identify visually and aurally the presence of leakage current between the isolated power line and the grounded conductor. conductor. Other power system devices that help to identify or disconnect power sources when leakage currents are present include ground fault detectors (GFDs) and ground fault interruptors (GFIs).
ELECTRICAL SHOCK The three ingredients in the scenario of electrocution are : 1. contac contactt with with the liv live e conductor of a grounded electrical system 2. con contac tactt with with a groun ground d 3. dimin diminished ished skin resi resistanc stance e
THE ELECTRICAL POWER SYSTEM Domestic voltages in the United States are from 120V for lighting and small appliances, and 240V for electrical ranges and dryers. In the hospital, outlets are 120V while 277V and 208V are often used for fixed lighting and special receptacles. Typically, a voltage of 240V is provided by the service drop to the power meter of the hospital. This line consists of a bare cable plus two wires having black insulation. The bare cable is connected to "earth" ground via a water pipe or grounding rod. It is this connection that makes the electrical service a grounded system. NOTE : The national electric Code defines ground as "a conducting connection, whether intentional intentional or accidental, between between an electrical circuit or equipment and the earth, or to some conducting body which serves in place of the earth."
There are three reasons to ground electrical systems: 1. Grou Grounding nding of the the system protects against introduction into the structure, via the wiring, of high voltages (with respect to ground) such as might arise from lightning or insulation failure in a high voltage pole transformer transformer.. 2. Tying the circuit circuit to ground ground obviates the multiple problems that might ensue were the domestic circuits "floating" at some undefined but high voltage relative to ground. 3. To facilitate operation operation of over current protective devices (fuses) which are located in the "live" (ungrounded) side of each circuit.
CONTACT WITH A GROUND For purpose of illustration, we will use an electrocardiograph (ECG) as our example of a medical device. Back in the 1950s, the standard ECG was fitted with a two-prong plug. The patient was connected to the chassis ground via the right-leg electrode, and one wire of the power cord was connected to the chassis through a 200,000-Ohm resistor.. This connected the chassis resistor to ground via the natural conductor in the power system. If the plug was inserted with polarity reversed, then the patient was connected to the "hot" side of the power system. However, the 200KOhm built-in resistor limited the current to 0.6 milliamperes if the patient or bystander provided a pathway to ground. Added safety to the machine included a fivemilliamp fuse in series with the right-leg electrode. As it turns out this approach was not practical because the fuse kept blowing after the patient was defibrillated. The codes changed this practice and today’s ECG machines do not ground any of the electrodes to earth ground. In fact, the "front end" electronics on most medical
devices have an isolated power supply and grounding system. Plus, the manufacturers use plastic cases minimizing the exposed metal.
SKIN SKI N RESIST RESIS TANC ANCE E Water affects affects skin resistance, and for a given voltage, resistance determines current. When dry, skin has a resistance of upwards 100,000 ohms. If there is an accidental application of 120 volts between the two hands, only 1.2 milliamperes will flow. In a wet environment or on a hot and humid day, that same current path may come to have a resistance as low as 1,000 ohms, resulting in a current flow of 120 milliamperes milliamperes..
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If a patient is exposed to electrical current, it takes about 1 milliampere of 60 Hz AC for a threshold of sensation. The sensation becomes uncomfortable if 5 milliamperes is attained. Strong muscle spasms appear at currents of 10 to 20 milliamperes ("let-go" current before sustained muscular contraction). A current flow of 100 milliamperes or greater may induce ventricular fibrillation and death. These values are for currents introduced at the body surface. They are termed macroshocks and require two points of external body contact. There is a possibility of a direct electrical path to the heart via a needle or catheter in an artery or vain. This directly reduces the resistance and current threshold. Small amounts of current (100 microamperes) can be potentially lethal. Electrical shock in these circumstances is termed "microshock". The frequency of the current is also important when considering electrical shock. If the frequency is raised above 1 KHz, these current levels no longer produce such sensations or life-threatening phenomenon. High frequencies in the megahertz region will not cause shock at all.
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LEAKAGE CURRENT
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All electrically operated devices have some current that flows from the energized electrical portions of the device to the metal chassis. This current is referred to as leakage current and has two components, capacitive and resistive. Capacitive leakage current results from distributive capacitance between two wires or a wire and a metal chassis case. Components that cause capacitive leakage currents are RF filters, power transformers, power wires, and any device that has stray capacitance. Resistive leakage current arises from the resistance of the insulation surrounding the power wires and transformer primary windings.
ELECTRICAL SAFETY POWER SYSTEM DEVICES Several techniques are available to protect clinicians and patients from electrical shock. The most common ones are the ground fault circuit interrupter (GFCI), the isolation transformer and equipotential grounding.
GROUND FAULT CIRCUIT INTERRUPTER The GFCI acts like a circuit breaker when it senses an inequality of as little as 6-ma between the "hot" and neutral wires of the circuit. It is mandated by the national electric code where electrical outlets are so situated that simultaneous contact with a grounded surface is especially likely. "Wet locations" such as a whirlpool bath or bathroom are examples of GFCI usage.
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In the GFCI, current in the "hot" wire passes through one transformer coil on the same transformer core. From the design, the net flux is zero zero,, when the
currents are equal. If the current is unbalanced (i.e. current flowing through ground) a net flux is induced across the third coil. This current will trigger a switch opening the "hot" line. The GFCI affords economical protection against electrical shock. However, the GFCI depends upon an active system, and the integrity of it’s mechanical operation is crucial.
ISOLATION TRANSFORMER The Isolation transformer offers electrical safety by converting grounded power into ungrounded power. This is accomplished by grounding the primary winding of the transformer and not grounding g rounding the secondary winding. Isolation is not perfect for two reasons. First, the isolation transformer has some stray capacitance to ground. Second, every medical device that is attached to the transformer possesses stray capacitance which causes some degree of coupling between its power power-carrying -carrying wires and the grounded frame. To monitor the system isolation, a line isolation monitor (LIM) is employed. Its function is to analyze the entire isolated circuit and quantify its degree of isolation from ground. The LIM provides visual and audible alarm signals when the predicted ground-seeking current exceeds a specified magnitude. The LIM does not indicate an existing current flow, rather it predicts the current that would flow if a short circuit were to develop between isolated wire and ground. In the operating room, isolated power systems were first installed as a measure directed against sources of ignition rather than electrical shock. Flammable anesthetics such as diethyl ether and cyclo-propane were used. Today, most anesthesiologists use non-flammable anesthetics and isolated power is not requir required. ed.
EQUIPOTENTIAL GROUNDING Another technique that reduces electrical shock is equipotential grounding. This is accomplished by adding another grounding wire from each chassis to a central point that is in parallel with the third wire in the power cord. If the chassis of all equipment is at the same potential there will be no current leakage to the heart. This technique has its advantages and disadvantages and is not typically used in today’s health care environment.
CODES AND STANDARDS In the 1960s, all aspects of hospital activities involving fire and explosion hazards (including electrical shock and emergency electrical power) were were seen to be in need of some guidelines and/or standards. As it turns out, in the standards arena of the 1970s, patient safety was twice corrupted. First, standards were generated in ignorance (solutions were imposed before the problems were defined)
and second, safety was blatantly exploited for ego-serving, bureaucratic,, and commercial bureaucratic gains. Today, there are two standards that specify electrical safety: NFPA 99 and the AAMI Standard for Safe Current Limits. The 1996 edition of NFPA 99 includes numerous technical changes that relate to leakage current and it now more closely correlates to the international standards. Originally, NFPA 76B covered the electrical wiring system and electrical appliances. The summary of the standard as it relates to electrical safety is in the Table on the following page.
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One further comment about standards. On may 30, 1972, Underwriter’s laboratories (UL) released the first edition of UL-544, Standard for Safety for Medical and Dental Equipment . UL-544 deals with details regarding enclosure enclosure safety, mechanical stability, and integrity of insulation. It’s leakage current, isolation requiremen requirements, ts, and test methods are similar to but not identical with those of AAMI and NFPA.
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NFP FPA A - 99 1996 1996
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Chassis Source Current, Cord Connected (Portable)
Gro roun und d Open
Gro roun und d Intact
With Isolated Patient Connection Connection
300µa
300µa
300µa
100µa
With Nonisolated patient Connection Connection
300µa
300µa
300µa
100µa
Likely to Contact Patient
300µa
300µa
300µa
100µa
No patient Contact
300µa
300µa
300µa
100µa
Chassis Source Current, Permanently Connected
Gro roun und d Open
Gro roun und d Intact
Gro roun und d Gro roun und d Open Intact In
With Isolated Patient Connection Connection
5000µa
5000µa
5000µa
100µa
With Nonisolated patient Connection Connection
5000µa
5000µa
5000µa
100µa
Likely to Contact Patient
5000µa
5000µa
5000µa
100µa
No patient Contact
5000µa
5000µa
5000µa
100µa
Lead to Ground Current
Gro roun und d Open
Gro roun und d Intact
Gro roun und d G Gro roun und d Open Intact In
With Isolated Patient Connection Connection
50µa
10µa
50µa
10µa
With Nonisolated patient Connection Connection
100µa
100µa
100µa
50µa
Gro roun und d Open
Gro roun und d Intact
With Isolated Patient Connection Connection
50µa
10µa
n/a
n/a
With Nonisolated patient Connection Connection
50µa
50µa
n/a
n/a
Sink Current (Isolated Test)
Gro roun und d Open
Gro roun und d Intact
With Isolated Patient Connection Connection
n/a
20µa
n/a
n/a
50µa
50µa
n/a
n/a
Gro roun und d Open
Gro roun und d Intact
Gro roun und d G Gro roun und d Open Intact
Gro roun und d Intact
Gro roun und d G Gro roun und d Open Intact
Gro roun und d Open 4 Oz
Gro roun und d Intact
Gro roun und d Gro roun und d Open Intact
Gro roun und d Open
Gro roun und d Intact
Gro roun und d G Gro roun und d Open Intact
Lead to Lead Current
With Nonisolated patient Connection Connection
Ground Impedance
0.5 Ohms
Existing System
0.2 Ohms
New Construction
0.1 Ohms
Receptacle Indicators
Gro roun und d Open
Hospital Grade Emergency System Isolated Ground
Retention Force, Ground Blade
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AAM AA MI/ I/AA AAM MI ESI ESI 1993
GFCI Trip Trip Current
Gro roun und d Gro roun und d Open Intact
Gro roun und d G Gro roun und d Open Intact
Gro roun und d G Gro roun und d Open Intact
Listed Red Orange
6mA
T
he AAMI Electrical Safety Committee began deliberating the issue of safe risk current limits for electromedical apparatus in 1967 and first published recommended limits and test methods in 1971. The first edition of this American National Standard was approved by the American National Standards Institute (ANSI) in 1978, and a second edition was approved and published in 1985. Wo Work rk on this third edition involved the dedicated efforts of concerned health care professionals, industrial scientists, and government representatives.. AAMI expresses its representatives gratitude for the service of all persons involved in the development of this standard.
fault conditions and provides risk current levels for each of these states. Also included included in this standard are test methods for equipment with nonconductive enclosures and for doubleinsulated equipment as well as limits for earth leakage or earth risk currents.
In this third edition of the standard, the risk current limits have been raised to be compatible with, although not identical to, the limits set forth by the International Electrotechnical Electrotec hnical Commission (IEC) in its standard, st andard, Medical electrical equipment—Part 1: General requirements for safety (IEC 601-1-1988). As in the IEC standard, this edition of Safe current limits for electromedical apparatus (ANSI/AAMI ES1—1993) introduces the concepts of normal operating conditions and single
Suggestions for improving this standard are are invited. invited. Comments and suggested revisions should be sent to Technical Programs, AAMI, 3330 Washington Boulevard, Suite 400, Arlington, VA 22201-4598.
This standard is intended primarily for the testing of electromedical apparatus intended for use in or near the patient care area. This standard should be considered flexible and and dynamic. As technology advances and new data are brought forward, the standard will be reviewed and, if necessary necessary,, revised.
NOTE — This foreword does not contain provisions of the American National Standard, Safe current limits for electromedical apparatus (ANSI/AAMI ES1—1993), but does provide important information about its development and intended use.
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IV. The AAMI Standard Standar d For For Safe Current Limits For Electromedical Apparatus Appara tus
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Electrical Safety Made Easy
IV.
SAFE CURRENT LIMITS FOR ELECTROMED ELECTROMEDICAL ICAL APPARATUS APPARA TUS 1 SC SCOP OPE E 1.1 Inclusions This standard sets risk current limits and referee test methods for electromedical apparatus intended for use in the patient care vicinity and also sets limits for nonpatient-contact electromedical apparatus. The standard applies to line- and battery-powered battery-power ed apparatus and to apparatus used singly or with properly connected accessory equipment. When more than one electromedical apparatus is powered by a single power cord, the equipment assembly acts like a single apparatus in terms of risk current limit requirements, and shall be considered as such for t he purposes of this standard. The safety and performance criteria defined in this standard are intended for use in design qualification by the device manufacturer. NOTE — The referee test methods of Section 5 are intended to provide means by which conformance with the standard can be established. These tests are not intended for use in verifying the performance of individual devices in routine quality assurance inspections. Also, referee tests allow for the use of alternative methods for design qualification, provided provided that devices so qualified will also meet the requirements requiremen ts of this standard when tested in accordance with the referee methods.
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1.2 Exclusions This standard does not set limits for the composite risk current when several devices are performing different functions for the same patient and are independently connected to the utility power system. This standard standard does not apply to therapeutic t herapeutic currents.
In addition, this standard does not apply to apparatus designed primarily for nonmedical applications and used in conjunction with electromedical apparatus, but located outside of the patient care vicinity. NOTE — As indicated above, all devices cannot be readily covered by this standard. Equipment such as video cassette recorders or computing devices are now being used in health care care facilities. facilities. Such equipment is designed to other standards. If such equipment equipment is not located in the patient care vicinity, such devices are not considered to pose a risk as they are not likely to contact the patient.
2 DEF DEFINIT INITION IONS S For the purposes of this standard, the following definitions apply. 2.1 accessory Device produced or recommended by the manufacturer of an electromedical apparatus, and intended to be electrically connected to that apparatus in order to make the apparatus useful or to improve its efficacy or versatility, and not a modular part of that apparatus. 2.2 auxiliary apparatus Electromedical apparatus used in conjunction with other electromedical apparatus to achieve a common purpose. NOTE — Auxiliary apparatus includes both interconnected apparatus and noninterconnec noninterconnected ted apparatus. 2.3 composite risk current Total risk current derived from the risk currents of all the apparatus associated with the patient that can flow through the patient, medical staff, or bystander. NOTE — This definition is included for reference only. A method of derivation and limits for composite risk current are not covered in this standard.
2.4 electromedical apparatus Instrument, equipment, system, or device that directly or indirectly uses electricity for any medical purpose. NOTE — Also included are all parts that are connected to such equipment and are required for the normal use of the equipment, including associated patient wiring or cables. 2.5 enclosure Exterior surface of the electromedical apparatus, including all accessible parts, knobs, grips, and shafts. 2.6 exposed electrically conductive conduc tive surface External metal or otherwise electrically conductive surface that is connected to the internal circuits, mechanisms, or enclosure of an electromedical apparatus. 2.7 input part Part of the electromedical apparatus, other than a patientapplied part, that is intended to receive input signal voltages or currents from other equipment. 2.8 isolated i solated patient connection connection Connection between the patient and the electromedical apparatus that is isolated from power ground (earth)1), the utility power system, and other supporting circuitry to such a degree that the risk current flowing through the connection does not exceed the limits given in Table 1—Summary of risk current requirements requireme nts in rms microamperes (mA), provided in Section 4.2. 2.9 modular apparatus Electromedical apparatus that includes modules in its construction. 2.10 module Self-contained assembly that performs a function or class of functions in support of the major function of an electromedical apparatus. NOTE — Modules can generally be
removed or replaced without affecting the operation of other assemblies in the apparatus. 2.11 nonoperational environmental conditions Temperature, humidity, altitude, or acceleration limits specified by the manufacturer for storage or shipment. 2.12 normal condition (NC) (NC) Condition in which all means provided against safety hazards are intact and the device is operating as desired. 2.13 output part: Part of the electromedical apparatus, other than a patientapplied part, that is intended to deliver output signal voltages or currents to other equipment.
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2.14 patient-applied part Entirety of any part of the equipment that comes intentionally into contact with the patient via a patient connection. 2.15 patient-applied risk current Current flowing from the electromedical apparatus through the patient to power ground (earth) or between patient-applied parts. 2.16 patient care vicinity Space, within a location intended for the examination or treatment of patients, extending 6 feet (ft) (1.8 meters [m]) beyond normal location of the bed, chair, table, treadmill or other device that supports the patient during examination and treatment. treatment. The patient care vicinity extends vertically to 7 ft, 6 inches (in) (2.3 m) above the floor. 2.17 patient connec connection tion Deliberate connection that can carry current between an electromedical apparatus and a patient. This can be a surface contact (e.g., an ECG electrode), an invasive connection (e.g., an implanted wire or catheter), or an incidental longterm connection (e.g., connective tubing).
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NOTE — As used in this standard, "patient connection" is not intended to include adventitious or casual contacts, such as push buttons, bed surfaces, lamps, and hand-held appliances. 2.18 patient isolation risk current Current flowing flowing from the patient to power ground (earth) through a part applied to the patient due to the unintended introduction of a voltage from an external source on the patient. 2.19 risk current: Nontherapeutic Nontherape utic current that can flow through the patient, medical staff, or bystander as a result of the use of electromedical apparatus. 2.20 single fault condition (SFC) Condition in which a single means of protection against a safety hazard in equipment is defective, a component failure could increase the risk current, or a single external abnormal condition exists. 2.21 sink current: Current that flows into a device or any part thereof, when an external voltage is applied to it. 2.22 source current Electrical current that flows from any part of an electromedical apparatus to any other part or to power ground (earth), when no external voltages are applied. 2.23 therapeutic current: Current that is intentionally applied to the patient for treatment of disease or disorder.
3 CLASSIFICATION OF ELECTROMEDICAL APPARATUS APPARA TUS AND MEASUREMENT CONDITIONS
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The following Sections define specific classes of electromedical apparatus and measurement conditions and detail how these classifications are applied in this standard.
3.1 Classification of electromedical electromed ical apparatus For purposes of this standard, four categories of electromedical apparatus have been defined. For each category, risk currents are established. These four categories are listed below : a) Electrome Electromedical dical apparatu apparatuss with isolated patient connection: Electromedical apparatus intended to be connected to the patient with the patient circuit isolated from power ground (earth), utility power systems, and other circuitry. circuitry. b) Elec Electromed tromedical ical apparatus apparatus with nonisolated patient connection: Electromedical apparatus intended to be connected to the patient. c) Electromed Electromedical ical appara apparatus tus likely to contact the patient: Electromedical apparatus that does not have a patientapplied part, but that is intended for use in the patient care vicinity. NOTE — See Section 2 for definition of patient care vicinity. d) Elec Electrome tromedical dical apparatus apparatus with no patient contact: Electromedical apparatus that is intended for use outside the patient care vicinity and that has no patient connections. 3.2 Classification of measurement conditions The following Sections define normal and fault conditions. 3.2.1 Normal operating conditions Under normal operating conditions, a device is operating as designed with all means provided for protection against safety hazards intact, connected properly and securely to an approved power source and, if the device includes patient-applied parts, with such parts applied according to the manufacturer's instructions. The following followin g are considered normal operating conditions:
a) power switch switch on/power on/power switch off; b) power polarity normal/power normal/power polarity reversed (cordconnected apparatus only); c) patient grounded; grounded; patient patient not grounded. 3.2.2 Single fault condition A single failure of a device's protection mechanism against a safety hazard or the failure of a single device component can introduce a hazard condition or lead to the existence of an external hazardous condition. The following followi ng are considered to be single fault conditions : a) power ground (earth) conductor open; b) short circuit of either barrier barrier of double insulation; c) failure of a single single component that can produce a hazardous current; d) (for equipment that that is not intended to be grounded) the application of line voltage to an input or output part or to accessible conductive hardware of the enclosure; e) (for electromedical apparatus with isolated patient connections) the application of line voltage on a patientapplied part.
4 REQU REQUIREME IREMENT NTS S 4.1 Labeling and documentation requirements 4.1.1 Isolated patient connections connec tions (labeling) Patient connections that meet the requirements requireme nts of this standard for isolated patient connections shall be identified as being isolated at the connector of the apparatus.
NOTE — Labeling of isolated patient connections shall comply with symbol number 3 of table DII, page 329, in the t he International Electrotechnical Commission (IEC) standard 601-1, second edition (IEC, 1988). 4.1.2 Information manuals The manufacturer shall supply the user with operating and maintenance instructions specifying how the electromedical apparatus should be operated and maintained to prevent the device's risk current from increasing beyond the limits set by this standard for its particular category (refer to Section Section 3.1). In addition, the manufacturer shall disclose the risk current category for which the apparatus is designed and shall identify the specific limits defined by this standard for that category.
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4.2 Risk current requirements requirements (general) Electromedical apparatus shall meet the applicable risk current limits of this standard under normal conditions and under the single fault conditions specified in the test methods of Section 5. Table 1 (see next page) summarizes s ummarizes these requirements requirements.. 4.2.1 Apparatus interconnection interconnection Electromedical apparatus shall meet the risk current limits of this standard when manufacturer manufacturer-designated auxiliary apparatus, modular apparatus, or accessories are attached in the quantity and combinations stipulated by the manufacturer. The manufacturer shall supply the user (and shall label the apparatus) with limitations and with directions for the interconnection of modular apparatus, accessories, and auxiliary apparatus, and with directions for the use of convenience receptacles. 4.2.2 Cleaning and sterilization Electromedical apparatus shall meet the risk current limits of this standard after exposure to any disinfection or sterilization process specified by the manufacturer manufacturer..
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4.2.3 Environmental conditions Electromedical apparatus shall meet the risk current limits of this standard after exposure to the nonoperational environmental conditions (e.g., storage, transportation, etc.) and under the worst-case environmental operating conditions specified by the manufacturer. 4.3 Enclosure risk current 4.3.1 General Enclosure risk current, when measured with the AAMI standard test load, is that current that flows between power ground (earth) and
IV.
a) exposed exposed chassis chassis conductive conductive surfaces or hardware; or b) a 200 cm2 cm2 (centimete (centimeters rs squared) foil in contact with a nonconducting enclosure enclosure..
NOTES : 1) The frequenc frequency-w y-weighte eighted d network compensates for the allowable allowabl e increase in risk current limits with increasing frequency. For measurem measurement ent purposes with a voltmeter as shown, the limit remains constant at 1 mA/mV, independent of frequency. With the meter connected, the entire circuit is called the "risk current tester." 2) Refe Referr to Section 5.7.2 for component requirements and tolerances. 4.3.2 Risk current limits Limits for enclosure risk current for all categories of electromedical apparatus, whether batterypowered, cord-connected, or permanently connected, and under both normal and single fault conditions, are shown in Table 1 on next page.
10,000 Ω
0.015 µF INPUT
1,000
Ω
100 Ω
Figure 1 AAM AA M I standar d test test l oad .
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MILLI VOLTMETER VOLTMETER
Categor y
Normal Condition
PatientPatient CordApplied Risk Isolation General Other Connected/ Per maCur rent Risk Current CordCordPer maBatter ynent (source (s i n k connected connected)1 nent2) current) current) 1 0 0 mA
100 mA
10 mA
N/A
5 0 0 mA
2,500 mA 5,000 mA
ISOLATED Single Fault Condition
3 0 0 mA
5,000 mA
5 0 mA
5 0 mA
1,000 mA
5,000 mA 10,000 mA
Normal Condition
100 mA
100 mA
10 mA
N/A
500 mA
2,500 mA 5,000 mA
5,000 mA
1 0 0 mA
N/A
1,0 00 00 mA
5,0 00 00 mA 10,000 mA
100 mA
N/A
N/A
500 mA
2,500 mA 5,000 mA
N/A
N/A
1,0 00 00 mA
5,0 00 00 mA 10,000 mA
100 mA
N/A
N/A
500 mA
2,500 mA 5,000 mA
5,000 mA
N/A
N/A
1,0 00 00 mA
5,0 00 00 mA 10,000 mA
NON-ISOLATED Single Fault Condition 3 0 0 mA Normal Condition
100 mA
LIKELY TO CONTACT PATIENT Single Fault Condition 300 mA 5,000 mA Normal Condition
100 mA
NO PATIENT CONTACT Single Fault Condition 5 0 0 mA
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Table 1 Sum m ar y of risk risk cur re rent nt re requi qui re rem m ents in rm s m icroamp ere res s (dc to 1 kHz)
1) Equi Equipment pment that that has no protectively grounded (earthed) accessible parts and no means for protective grounding (earthing) of other medical equipment and which complies with the applicable requirements require ments for enclosure leakage current and patient leakage current; also mobile x-ray equipment and mobile equipment with mineral insulation.
2) Equipment specified specified to be permanently installed with a protective power ground (earth) that is electrically connected and secured at a specific location so that the connection can only be loosened or moved with the aid of a tool.
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4.4 Patient-applied risk current (source current)2)
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4.4.1 General Patient-applied risk current, when measured with the AAMI standard test load, is that t hat current that flows between any patient-applied part and : a) pow power er ground ground (earth) (earth);; b) expos exposed ed chassis chassis conductive conductive surfaces or hardware; c) a 200 cm2 foil foil in contac contactt with a nonconducting enclosure; or d) any other patientpatient-appli applied ed parts. Patient-applied risk current is also that current that flows between all patient connections tied together and (a), (b), (c), and (d) listed above when measured with the AAMI standard test load.
NOTE — The current shall be measured at the patient end of the cable when connected to the device. 4.6 Earth risk current 4.6.1 General Earth risk current, when measured with the AAMI standard test load, is that current that flows in the protective earth conductor (ground conductor). NOTE — Not applicable to double insulated devices using a two-wire power cord.
4.4.2 Risk current limits Limits for patient-applied risk current for all categories of electromedical apparatus, whether battery-powered, battery-power ed, cord-connected, or permanently connected, under both normal and single fault conditions, are shown in Table 1.
4.6.2 Risk current limits Limits for earth risk current for all categories of electromedical apparatus, whether cordconnected or permanently connected, and under both normal and single fault conditions, are shown in Table 1.
NOTES :
4.7 Risk current limits versus frequency The risk current limits specified in Table 1 are for frequencies from dc to 1 kilohertz (kHz). (kHz). Above 1 kHz, kHz, the limit is increased proportionally to a maximum value 100 times the limit at 1 kHz. Above 100 kHz, the limit limit is that which is determined for 100 kHz (see Figure 2). The use of the AAMI AAMI test load automatically compensates for frequency.
1) These limits limits are are not applicable applicable to electromedical apparatus without direct patient-applied connections. 2) The current current shall shall be measure measured d at the patient end of the cable when it is attached to the device. The cable is specified by the manufacturer. 4.5 Patient isolation risk current (sink current)
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4.5.2 Risk current limits Limits for patient isolation risk current for electromedical apparatus with isolated patientapplied part(s), whether cordconnected or permanently connected, are shown in Table 1.
4.5.1 General Patient isolation risk current, when measured with the AAMI standard test load, is that current that would flow into a patient-applied part if the patient came into direct contact with a potential of 120 volts (V), 60 hertz (Hz) with respect to power ground (earth).
5 Tests This Section contains referee tests and procedures by which compliance with the requireme requirements nts of Section 4 and Table 1 can be determined. WARNING — These tests can WARNING expose personnel to hazardous electric shock and must be carried out with caution.
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100 mA
N O R M A L I Z E D C U R R E N T
Made Easy 1 mA
500 Hz
1000 Hz
10 KHZ
100 K HZ
1 MHZ
10 MHZ
FREQUENCY (HZ) Figur e 2 — Norm ali ze zed d cur rent l im it s ve versus rsus frequency
5.1 Compliance with the labeling requirements Compliance with the labeling and documentation requirements of Section 4.1 shall be verified by inspection. 5.2 Compliance with the risk current requirements (general test proced procedures) ures) The risk currents of electromedical apparatus shall be measured by the methods described in this Section. 5.2.1 Test equipment and power system 5.2.1.1 Measuring instruments The risk current tester consists of the AAMI standard test load and a millivoltmeter as shown in Figure 1. The millivoltmeter shall measure true rms volts; however however,, it may be calibrated to true rms microamperes (mA) by employing a conversion factor of one microampere per millivolt millivolt (mV). The millivoltmeter shall have an input impedance of at least 1 megohm and have a bandwidth of dc to at least 1 megahertz (MHz) (–3 decibels). In the band from dc to 100 kilohertz (kHz), the indicated measurement shall not display an error of greater than 5 percent of reading, and shall resolve a signal as small as 1 mV.
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Instruments that indicate true rms microamperes and have internal frequency compensation identical to that shown in Figure 1 meet the requirements of this Section if the measurement indicated does not display an error of greater than 5 percent of reading and resolves a signal as small as 1 mA in the band from dc to 100 kHz. 5.2.1.2 Power source 5.2.1.2.1 For line voltage powered equipment, the tests shall be performed on a grounded power system at the rated line voltage plus 10 percent. percent. In the grounded grounded system, the potential between the neutral and grounding conductors at the receptacle selected for the test shall not exceed 3 V. 5.2.1.2.2 The power ground (earth) terminal used in these tests shall be the grounding terminal of the specific receptacle powering the instrument under test. 5.2.1.2.3 Battery-powered Battery-pow ered apparatus shall be tested while powered by the type of battery recommended by the manufacturer and, if applicable, while connected to line power. power. -21-
5.2.2 Test conditions
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5.2.2.1 General First, the apparatus shall be disconnected from all other apparatus except auxiliary apparatus, modular apparatus, or accessories, as defined in the normative definitions (see Section 2). A single- or multi-function multi-function apparatus in a cabinet or in multiple cabinets with a single power cord connection connection is tested as a single apparatus. apparatus. Each individual individual apparatus shall also be tested independently if described by the manufacturer as a stand-alone apparatus. Tests shall be conducted at the rated line voltage plus 10 percent. 5.2.2.2 Nonconducting enclosure The risk current shall be measured from an electrically conductive foil the size of the enclosure, but not to exceed 200 cm2, in immediate contact with the enclosure. The The foil shall be placed at a location— determined by experimentation— such that the current measured to power ground (earth) is a maximum. If exposed exposed chassis hardware is likely to be touched by personnel, then the hardware shall be treated as an exposed electrically conductive surface. Testing of nonconductive exposed surfaces of patient wiring and cables is not required.
delivers therapeutic energy to the patient (e.g., a pacemaker), the therapeutic energy shall be zero during the test. Otherwise, the instrument shall be in the active or operable mode; i.e., with output switches closed, with electrodes properly connected to dummy loads, and with final circuit stages properly functioning but without a physiological drive signal. 5.2.2.4 Operation During the test, the apparatus shall run through a normal cycle and activate all accessories and/or auxiliary apparatus.
5.3 Enclosure risk current 5.3.1 Application The enclosure risk current tests shall apply to cord-connected, linepowered apparatus, to batterypowered apparatus with the charger connected, and to permanently connected apparatus. 5.3.2 Cord-connected, normally grounded apparatus 5.3.2.1 Using the test circuit of Figure 3, the enclosure risk current shall be measured:
5.2.2.3 Controls During risk current tests, all operator-accessible operator-acc essible controls shall be adjusted to yield the largest risk current found by experiment. If the electromedical apparatus normally Reversing Switch S1
a) between between enclosure enclosure and and power ground (earth); b) betwe between en electrical electrically ly conductive surfaces and power ground (earth); c) betwe between en a 200 cm2 foil foil in contact with the nonconducting enclosure and power ground (earth).
200 cm 2 fail
Rated Line Voltage +10%
Apparatus Under Test
Select Per 5.3.2.1
Ground
M
Ground Switch S2
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Ground Wire
Exposed Conductive Surface
Risk Current Tester
Figure 3 — Enclos Enclosur ur e ri sk cur rent test test circui t (nor m all y grou grou nd ed)
NOTE — The 200 cm2 foil line leading from the "select" box to the apparatus under test refers to the connective mode with insulated apparatus. The line with an arrow leading from the "select" box to the apparatus under test refers to connections made with conductive enclosure. 5.3.2.2 Each measurement is performed when: a) the utility utility electricity supply polarity is normal and when the utility electricity supply polarity is reversed (by reversing S1). These are are normal conditions; b) the apparatus power power switch is on; the apparatus power switch is off. These are normal conditions; c) the ground switch (S2) is open; the ground switch is closed. The first is a single fault condition; the second is a normal condition; d) each barrier of double insulation is short circuited. circuited. These are single fault conditions. NOTE — The test methods for all measurement conditions are not supplied in this standard because they are device- and circuitspecific. 5.3.2.3 The power on/power off test also applies to apparatus with nonrechargeable nonrecha rgeable batteries.
Rated Line Voltage +10%
Reversing Switch S1
5.3.3 Cord-connected, Cord-connec ted, normally ungrounded apparatus 5.3.3.1 Using the test circuit of Figure 4 (see next page), the enclosure risk current shall be measured: a) between enclosure enclosure and power power ground (earth); b)between electrically conductive surfaces and power ground (earth); c) betwe between en a 200 cm2 foil foil in contact with the nonconducting enclosure and power ground (earth). 5.3.3.2 Each measurement is performed when:
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a) the utility electricity supply polarity is normal; the utility electricity supply polarity is reversed (by reversing S1). These are normal conditions; b)the apparatus power switch is on; the apparatus power switch is off. These are normal conditions; c) each barrier barrier of double double insulation is short-circuited. These are single fault conditions. NOTE — The test methods for all measurement conditions are not supplied in this standard because they are device- and circuitspecific.
200 cm2 fail Apparatus Under Test
Select Per 5.3.2.1
Risk Current Tester
Exposed Conductive Surface
Ground
Figur e 4 — Enclos Enclosur ur e ri sk cur rent test test circui t (nor m all y ungrou nd ed)
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e) all patien patientt connectio connections ns shorted together and power ground (earth); f) all patie patient nt connec connectio tions ns shorted together and any exposed, electrically conductive surface; g) all patien patientt connectio connections ns shorted together and a 200 cm2 foil in contact with the nonconducting enclosure; h) any patient connection and all other patient connections connected together.
5.3.3.3 The power on/power off test also applies to apparatus with nonrechargeable nonrechargea ble batteries.
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5.3.4 Permanently connected apparatus Before line-powered apparatus is permanently installed, the enclosure risk current shall be measured according to the procedures described in 5.3.2. 5.4 Patient-applied risk current (source current)
IV.
5.4.1 Application The patient-applied risk current tests of this Section shall apply to line-powered line-powe red and battery-power battery-powered ed electromedical apparatus that has a patient connection(s).
NOTE — The test methods for all measurement conditions are not supplied in this standard because they are device- and circuitspecific. 5.4.2.2 Each measurement is performed when:
5.4.2 Apparatus with isolated patient connection 5.4.2.1 Using the test circuit of Figure 5 (see next page), the patient-applied risk current (source current) shall be measured between: a) any patient patient connecti connection on and power ground (earth); b) any patient patient connection connection and and any exposed, electrically conductive surface; c) any patient patient connecti connection on and a 200 cm2 foil in contact with the nonconducting enclosure; d) any patient patient connection connection and and any other patient connection;
a) the utility utility switch switch (S1) (S1) is normal/the utility switch is reversed. These are are normal conditions; b) the apparatus apparatus power power switch is on/the apparatus power switch is off. These are normal conditions; c) the ground ground switch switch (S2) (S2) is open/the ground switch is closed. The first is is a single fault condition; the second is a normal condition;
120K
Select Per 6.4.2.2.d Reversing Switch S1 Rated Line Voltage +10%
Ground Switch S2
120V / 60Hz
Patient Connection Apparatus Under Test
200 cm 2 fail
Select Per 5.3.2.1
Select Per 5.3.2.1 Exposed Conductive Surface
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Figure 5 — Pati ent -ap pl ied ri sk cur rent test test circui t
Risk Current Tester
d) line voltage voltage is applied applied to an input or output part or to accessible conductive hard ware of the enclosure, if not grounded under normal conditions. These are single fault conditions; e) each barri barrier er of doubl double e insulation is short circuited. These are single fault conditions. NOTE — The 120 K resistance is intended to protect the test operator. 5.4.3 Apparatus with nonisolated patient connection The patient-applied risk current shall be measured by the procedures described in 5.4.2 5.4.2.. 5.5 Patient isolation risk current (sink current) The patient isolation risk current shall be measured in each individual patient connection that is labeled "isolated" when a potential of 120 V rms, 60 Hz, is applied through a series 120 kilohm resistance to the labeled patient connection, as shown in Figure 6. The patient isolation risk current is measured with respect to power ground (earth). For solely batterypowered power ed apparatus, the patient isolation risk current is measured with respect to an electrically conductive surface on which the apparatus is positioned, and with an exposed conductive surface or
other external electrical connection on the apparatus apparatus grounded. This test shall be performed with the apparatus both on and off and properly connected to its electrical supply.. The patient cable shall be supply placed 20 cm away from a grounded surface. NOTE — The 120 K resistance is intended to protect the test operator.
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5.6 5. 6 Ea Earth rth risk risk curr curren entt 5.6.1 Applicatio Application n The earth risk current test shall apply to cord-connec cord-connected ted apparatus, to battery-powered apparatus with the charger connected, and to permanently connected apparatus.
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5.6.2 Cord-connected, Cord-connec ted, normally grounded apparatus 5.6.2.1 Using the test circuit of Figure 7 (see next page), the earth risk current shall be measured in the protective power ground (earth). 5.6.2.2 Measurementt shall be performed Measuremen when: a) the utility electrical electrical supply is is normal/when the utility electrical supply is reversed (by reversing S1). These are normal conditions;
1:1
Rated Line +10%
Apparatus Under Test
120V 60Hz
Select Per 5.5 120K
Ground
Risk Current Tester
Figur e 6 — Pati ent iso isola la ti on r isk cur cur rent test test circui t
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b) the apparatus power power switch is on/the apparatus power switch is off. These are normal conditions; c) each supply supply conductor conductor is interrupted, one at a time (opening S2 and S3 in turn). This is a single fault condition; d) each barrier of double insulation is short-circuited. This is a single fault condition. 5.6.3 Permanently connec connected ted apparatus Before the line-power line-powered ed apparatus is permanently installed, the earth risk current shall be measured according to the procedures described in 5.6.2 5.6.2.. 5.7 Risk current limits versus frequenc frequency y 5.7.1 General When multiple risk currents of various frequency and phase relationships are present during a single test, the resultant risk current is related to the voltage across the AAMI standard test load. The risk current of an apparatus
shall be the largest current measured during any of the required tests and conditions. The apparatus must meet all applicable limits of Table 1. 5.7.2 AAMI standard test load As shown in Figure 1, the test load shall be constructed using metalfilm resistors with a tolerance of 1 percent or better, and a mica- or plastic-dielectric (extended foil) capacitor with a tolerance of 5 percent or better. The AAMI standard test load has an impedance frequency characteristic (Figure (Figure 8) which is the approximate inverse of the curve of Figure 2, which shows risk current versus frequency. 5.7.3 Risk current calculation Using the AAMI standard test load of Figure Figure 1 and a voltmeter calibrated to indicate rms millivolts, the weighted risk current is read directly from the meter, because: V(mV rms)
I(mA rms) =
Line Interruption Switches S2• Reversing Switch S1 Rated Line Voltage +10% S3•
Z(k ohms)
Apparatus Under Test
Protective Earth (Ground Conductor)
Risk Current Tester
Figure 7 — Eart h ri sk cur rent test test circui t
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) B d ( 0 e d u t i n g a -20 M e v i t a l e -40 R 10
Figure 8 — Relative frequency char acteri sti cs of millivoltmeter readi re adi ng in AAM AAM I stan dar d t est load of Figur e 1
10 1
10 2
10 3
10 4
10 5
A.1 General The rationale discusses the need for the standard and describes the basic underlying principles, empirical data, assumptions, and sources that support the requirements requireme nts and test methods adopted in the standard. A.2 Need for the standard st andard This standard seeks to reduce the risk of inadvertent electric shock from medical medical devices. devices. In particular,, it concerns itself with particular the risk of injury from the small currents that inevitably flow from or to electromedical apparatus. The intent of the AAMI Electrical Safety Committee was to develop a general baseline baseline standard. The extent to which the standard should be applied is to be determined by individual institutions, standards groups, and other authorities. A.3 Classificat Class ification ion of electromedical electrome dical apparatus and measurement conditions Changes from the second edition of the standard (AAMI, 1985) have been made in keeping with changes to the requirements given in Section 4. A.4 Rationa Rationale le for the t he specific provisions of the standard A.4.1 Labeling Label ing and an d documentation requirements A.4.1.1 Isolated pat ient connection connec tion (labeling) Fault conditions can contribute to patient risk due to source and sink currents. The greatest risk is is with direct cardiac applications; such applications should utilize isolated patient connections. connections. In order order to better manage patients requiring direct cardiac connection, the user should be able to readily identify electromedical apparatus with isolated patient connections. Therefore, Therefor e, labels should appear on
the electromedical apparatus itself. The standard does not require nonisolated patient connections to carry any special labeling.
A.4.1.2 Informa Information tion manuals ma nuals By identifying the risk current classification and risk current limits, the manufacturer is informing the user of the device's intended purpose as that purpose relates to the risk of electric shock. Any special user actions required to ensure that the risk current limits are maintained throughout the life of the equipment should be described in the operating instructions or maintenance manuals.
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A.4.2 Risk R isk current cu rrent requirements requ irements (general) The committee felt that grounding should not be the primary approach to limiting the risk of electric shock because it is possible to have a single fault failure in the grounding system. Redundant means of grounding are possible but are controlled by the user and not the manufacturer of the electromedical apparatus. If the grounding is lost or if other safety means fail, the risk current available from the enclosure should not represent a substantial hazard to the patient. The risk current limits were changed for certain categories as compared to the previous version of this standard (ANSI/AAMI ES1— 1985). These changes have been made in order to bring this document into closer harmonization with risk current limits specified in the International Electrotechnical Commission standard, Medical electrical equipment—Part 1: General requirements for safety (IEC 601-1, 1988).
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In its review of the allowable risk current levels, the committee considered the followi following: ng: a) Likel Likelihoo ihood d of stimulation stimulation of excitable tissue. The likelihood of stimulation of excitable tissue depends upon: 1) the location location of the sites at at which current enters and leaves the body; 2) the area area of contac contact; t; 3) the amount amount of curren currentt flowing; 4) the suscep susceptibil tibility ity to mechanical stimulation; 5) the presenc presence e of a fault fault condition; 6) the probabi probability lity of of the current having a given value. Medical devices have been classified into the risk categories described in Section 3 because of the different magnitudes of risk associated with these categories. b) Surve Survey y of published published data. data. During the several years since the publication of the previous version of this standard (ANSI/AAMI ES1—1985), experience has been gained with respect to the incidence of problems related to risk current and the probability of occurrence of the potential hazard. The available published data on currents causing ventricular fibrillation in humans have also been reexamined. The following have been noted: 1) The combina combination tion of an open power ground (earth) wire and a person touching both a conductive part of the enclosure and the patient is a low probability event. 2) The combina combination tion of an open power ground (earth) wire and a person touching both a conductive part of the chassis and the distal end of an invasive cardiac connection is a low probability event. 3) In one study study,, Raftery Raftery (1975) found that the smallest current that produced a
disturbance in rhythm in humans was 80 mA. In a second study, Watson (1973) found that the smallest current that produced ventricular fibrillation in humans was 15 mA. 4) Mec Mechani hanicall cally y induced induced ventricular fibrillation has been observed during cardiac catheterization at zero current. 5) The human human data data obtained obtained by Starmer (1973) and Watson Wa tson (1973) follow, follow, reasonably well, a normal distribution for currents to 300 mA. All patients are not equally susceptible to current-induced ventricular fibrillation. According to Figure A.1, there is approximately a 1 percent probability of fibrillation at 30 mA. 6) Cur Current rent perce perception ption is is a function of contact location, contact pressure, skin condition, moisture, and contact contact area. Experiments report a wide range of current perception. Dalziel (1968) reports that only approximately 1 percent of the population can perceive 500 mA passing from the fingers of one hand to the fingers of the other hand. Tan and Johnson (1990) report that 300 mA produces a strong sensation for electrodes placed 10 cm apart on the upper arm. Levin (1991) reports that nearly all the population will perceive 500 mA without any reaction for current passing from the finger on one hand to the underside of the wrist on the other hand. Levin further reports that, on the underside of the wrist, the stratum corneum (layer of dead material on the skin surface) is not as thick as that on the forefinger and, therefore, the
sensitivity to current perception might be higher higher.. Startle current is that level of perception current that, when first perceived, might result in a nurse or other clinician's involuntary reaction to the sudden sensation of perception current. This uncontrolled reaction is of great concern. 7) Worldw orldwide, ide, since since the the advent of risk current standards, concern about grounding, and use of better practices in handling catheters and invasive cardiac connections, there have been no reports of incidents involving risk current passing through the patient. NOTE — A minority of the AAMI Electrical Safety Committee were opposed to increasing risk current limits unless scientific studies supported higher limits. Also, in order to harmonize harmonize with IEC 601-1 and to allow for additional fault conditions as compared to the current standard, the test measurement classifications of "normal condition" (NC) and "single fault condition" (SFC) were introduced. Measuring risk current under SFC Measuring is important because: — compo components nents can can fail; — singl single e faults exist exist that are not now considered in the standard; — faul faults ts can occur in accessory accessory equipment. A.4.2.1 Apparatus interconnection i nterconnection The total risk current associated with a device can be a function of the modules, accessories, and interconnections interconnectio ns used with the t he device. Voltage differences can occur between different parts of a device, particularly if current flows in the grounding circuit. Thus, a remote accessory powered from the device or from a separate source is, for purposes of the standard, considered part of the device.
Auxiliary power power outlets may be provided for powering additional devices. The labeling requiremen requirements ts provide some assurance that the user has appropriate guidance about the limitations applying to equipment or accessories connected to an auxiliary power receptacle. A.4.2.2 Cleaning and sterilizat ster ilization ion The long-term effects of repeated disinfection or sterilization of a device on risk currents must be considered because of possible degradation of insulating materials. A.4.2.3 Environm Environmental ental conditions condi tions Temperature, humidity, atmospheric pressure, mechanical shock, and similar environmental constraints can have an effect upon the risk currents. To protect the patient, the risk current limits must also be met in the intended environment.
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A.4.3 Enclosure Encl osure risk ri sk current cur rent The 100 mA NC values were selected for cord-connected and permanently connected apparatus on theoretical grounds. For a typical ground resistance of 0.2 ohms, 100 mA of enclosure risk current, measured as in Figure 3, requires that 500 mA flow in the power ground (earth) wire. This would be a major fault condition. The 300 mA SFC values for isolated, nonisolated, or likely-to-co likely-to-contactntactpatient, cord-connected apparatus were selected on the basis of reaction current measurements by Levin and the low probability of risk current reaching the distal end of an invasive heart connection via another person. person. Levin reported reported that currents of 300 mA will not produce sensations leading to a "startle" reaction (Levin, 1991). The 500 mA limit for SFC for cordconnected, no-patient-contact equipment was selected because there is no concern about this current reaching the patient. The 5,000 mA limit for SFC for permanently connected equipment is basically a power ground (earth)
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wire current, because the apparatus is, by definition, permanently grounded. grounded. This is the current allowed from the enclosure of permanently connected equipment if the power ground (earth) wire were opened. opened. The permanently connected power ground (earth) wire is not expected to open.
that produced ventricular fibrillation in humans are considered, the probability is approximately zero. The 50 mA SFC limit for isolated equipment was selected because the probability of causing ventricular fibrillation is low if the data of Figure A.1 are extrapolated and is approximately zero if only observed values of currents producing ventricular fibrillation in humans are considered.
A.4.4 Patient-appli Pat ient-appli ed risk ris k current curren t (source current) The 10 mA NC limit was selected as the current that may flow directly into the heart continuously continuously.. Figure A.1 shows that the probability of inducing ventricular fibrillation is very small if the data on which the chart is based are extrapolated. extrapolated. If only observed values of currents
The 100 mA SFC limit was selected for nonisolated equipment, because if this current enters and exits the surface of the body, then only a fraction will reach the heart.
Starmer 60 Hz D = 1.25mm Watson 60 Hz D = 2.0mm 2 .0mm
99.9 99 95 t n e c r e P e v i t a l u m u C
+ +
90 50
+ + +
20
+
+ +
+ +
5 1
0.1 0
50
10 0 15 0 2 00 2 50 30 0 35 0 40 0 4 50 5 00 Microamperes
Figure A. A.1 1 — Norm al pr obabili ty plot
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A.4.5 Patient Pat ient isolation i solation risk current (sink current) The 50 mA SFC value for isolated equipment was allowed because of the low probability of line voltage appearing on a patient, and because of the low probability of 50 mA inducing ventricular fibrillation. For line voltage to appear on a patient, a power ground (earth) wire must be open and there must also be a fault in basic insulation. insulation. If the data data in Figure A.1 are extrapolated, then 50 mA has a low probability of inducing ventricular fibrillation. If only recorded human data are considered, the probability of inducing fibrillation at 50 mA is approximately zero. A.4.6 Ear th risk ri sk (ground risk) current The original standard of 1978 and the revised edition of 1985 did not include earth current as a potential risk current. current. This was not considered to be an issue as most medical devices of the era utilized conductive enclosures requiring grounding. Thus, earth current current was effectively measured as enclosure (chassis) current under the open ground condition. In the last 25 years, however, the change to nonconductive enclosures negated this equality. The enclosure current is now measured as the capacitivecoupled current to a 200 cm2 foil in contact with the enclosure. enclosure. This current bears little resemblance to the earth risk current due to the current-limiting current-limitin g characteristics of the capacitive coupling of the nonconductive enclosure. The earth risk current does not pose a direct risk to the patient or medical personne personnel. l. However, excessive earth risk current, either by design or internal breakdown, will raise the potential of the device's ground with respect to true power ground (earth) as represented by structural elements, modular wall units, cold water pipes, and other installed piping, or by an adjacent receptacle power
ground (earth). Contact with with such elements and a second device under test will result in current flow.. Thus, the committee felt that flow leaving the earth risk current unmeasured and unlimited constituted a potential hazard that should be avoided. The allowable values for earth risk current detailed in this standard are not thought to pose a direct hazard as the current is safely returned to earth. The values selected were chosen to avoid any significant increase in the current flowing through the protective grounding system of the installation and to be consistent with the limits of IEC 601-1 for power ground (earth) and nonconducting enclosures. Further, the 2.5 mA limit in normal mode is within the limit for isolation monitors set by the National Fire Protection Association (NFPA, (NFPA, 1993, Section 3.4.3.3), which specifies that isolation monitors should not alarm at 3.75 mA.
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A.4.7 Risk R isk current cu rrent limits li mits versus frequenc frequency y Figure 2 of the standard was derived from strength/freque strength/frequency ncy data for perceptible and lethal currents (Geddes and Baker Baker,, 1971). The flat portion between 100 kHz and 1 MHz does not reflect physiological data obtained with purely sinusoidal currents. Stimulation has been observed with complex waveforms at high frequencies, but little data are available. In the absence of data, it was deemed prudent not to extrapolate beyond 100 kHz. A.5 Tests Tests The test procedures documented in Section 5 of the standard s tandard provide referee test methods for verifying compliance with the requirements of Section 4. These referee referee tests are not necessarily intended for purposes of manufacturing or quality control (although these applications are not precluded), as equivalent measurements may be obtainable by other means.
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ASSOCIATION FOR THE ADVANCEMENT ASSOCIATION ADVANCEMENT OF MEDICAL INSTRUMENTATION. Safe current limits for electromedical apparatus. ANSI/AAMI ES1—1985. Arlington (Vir.): AAMI, 1985. ISBN 0-910275-50-5.
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DALZIEL, CF. CF. Reevaluatio Reevaluation n of lethal electric electr ic currents. IEEE Trans Indus Gen Appl, GA-4, 1968, vol. 1, no. 5, p. p. 467-476. GEDDES, LA. and BAKER, LE. Response to the passage of electric currents through the body. J Assn Adv Med Instrum, 1971, vol. 5, p. 13-18. INTERNATIONAL ELECTRO INTERNATIONAL ELECTROTECHNICAL TECHNICAL COMMISSION. Medical electrical equipment—Part 1: General requirements for safety, 2nd ed. IEC 601-1. Geneva: IEC, 1988. LEVIN, M. Perception of chassis leakage current. Biomed Instrumentation and Technolog Technology, y, 1991, vol. 25, no. 2, p.135-140.
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NATIONAL FIRE PROTECTION ASSOCIATION. Standard for health care facilities. NFPA NFPA 99-1993. Quincy (Mass.): NFPA, 1993. RAFTERY, EB., GREEN, HL., and YACOUB, MH. Disturbances of heart rhythm produced by 50 Hz leakage currents in human subjects. Cardiovascular Research, March 1975, vol. 9, no. 2, p. 263-265. STARMER, CF. and WHALEN, RE. Current density and electrically induced ventricular fibrillation. fibrillation. J Assn Adv Med Med Instrum, 1973, vol. vol. 7, no. no. 1, p. 3-6. TAN, KS. and JOHNSON, DL. Threshold of sensation for 60 Hz leakage TAN, current: Results of a survey. Biomed Instrumentation and Technology, 1990, vol. 24, no. 3, p. 207-211.
Bibliography
WATSON, AB., WRIGHT WATSON, WRIGHT,, JS., and LAUGHMAN, J. Electrical thresholds thresholds for ventricular fibrillation in man. Med J Australia, 1973, vol. 1, p.1179-1182.
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Glossary Of Ter Terms ms AMPACITY: AMPA CITY: Current-carrying capacity of electrical conductors expressed in amperes.
ANESTHETIZING LOCA LOCATION: TION: Any area area of the facility that has been designated for the administration of any flammable or nonflammable inhalation anesthetic agents in the course of examination or treatment, including the use of such agents for relative analgesia.
CONDUCTIVE: Materials, such as metals, that are commonly considered electrically conductive, and materials that, when tested, have a resistance not exceeding 1,000,000 ohms. Such materials are required wheree electrostatic wher electrostatic interconnecti interconnection on is necessary. necessary.
CRITICAL EQUIPMENT:
Equipment that is essential to the safety of the occupants in the facility.
CRITICAL SYSTEM: A system of of feeders and and branch circuits in nursing homes and custodial care facilities arranged for connection to the alternate power source to restore service to critical receptacles, task illumination, and equipment.
DIRECT ELECTRICAL PATHWAY TO THE HEART: An external external conductive conductive pathway pathway,, insulated insulated except at its ends, one end of which is in direct contact with the the heart muscle muscle and the the other outside outside the body body,, that is accessible for inadvertent or intentional contact with grounded grounded objects objects or energized energized,, ground-refer ground-referenced enced sources. Catheters filled with conductive fluids and electrodes, such as may be used for pacing of the heart, are examples of direct electrical pathways to the heart.
DOUBLE-INSULATED APPLIANCES: Appliances having Appliances having an insulatio insulation n system comprising comprising both both basic insulation necessary for the functioning of the appliance and for basic protection against electrical shock and supplementary insulation. The supplementary insulation is independent insulation provided in addition to the basic insulation to ensure protection against electric shock in case of failure to the basic insulation.
ELECTRODE: A device intended intended to probe probe an electrically conductive connection through a cable to a patient. There are several types: electrode intended intended to generate generate a Active Electrode: An electrode surgical effect at its point of application to the patient. electrode intended intended to comDispersive Electrode: An electrode plete the electrical path between patient and appliance, and at which no surgical effect is intended. It is often called the "indifferent electrode", the "return electrode", the "patient plate", or the "neutral electrode".
EXPOSED CONDUCTIVE SURFACES: Those surfaces that are capable of carrying electric current and that are unprotected, uninsulated, unenclosed, or unguarded, permitting personal contact.
FAULT CURRENT: A current current in an accidental accidental connection between an energized and a grounded or other conductive element resulting from a failure of insulation, spacing, or containment of conductors.
FREQUENCE: The number of oscillations, per unit of time, of a particular current or voltage waveform. The unit of frequency is the Hertz (Hz). (The unit of frequency used to be "cycles per second", a term no longer may consist of preferred). Note : The waveform may components having many different different frequencies , in which case it is called a complex or nonsinusoidal waveform.
to a patient, but may be conveyed from exposed metal parts of an appliance to ground or to other accessible parts of an appliance.
LINE ISOLATION MONITOR: An instrument instrument that continually checks the hazard current from an isolated surface to ground.
GROUND-FAULT CIRCUIT INTERRUPTER:
MACROSHOCK: The effect of large electric current
A device whose whose function function is to interrupt interrupt the electric electric circuit circuit to the load when a fault current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit.
(milliamperes or larger) on the body.
GROUNDING SYSTEM: a system of conductors
MICROSHOCK: The effect of small electric currents (as low as 10 microamperes) on the body. To be hazardous, such currents must be applied to a conductor inside or very near the heart.
that provides a low-impedance return path for leakage and fault currents. It coordinates with, but may be locally more extensive than, the grounding system described in Article 250 of NFPA NFPA 70, National National Electric Electric Code. Code.
mV:
Millivolt.
mA:
Milliampere.
HAZARD CURRENT: for a given set of connections
facility where patients are examined or treated. Note : Business offices, offices, corridors, lounges,day rooms, dining rooms, or similar areas are not classified as patient care areas.
in an isolated power system, the total current that would flow through a low-impedance if it were connected between either isolated conductor and ground. The various hazard currents are: Fault Hazard Current: The hazard current of a given isolated power system with all devices connected except the line isolation monitor. Monitor Hazard Current: The hazard current of the line isolation monitor alone. Total Hazard Current: The hazard current of a given isolated system with all devices, including the line isolation monitor, connected.
IMPEDANCE: Impedance is the ratio of the voltage drop across a circuit element to the current flowing through the same circuit element. The circuit element may consist of any combination of resistance, capacitance, or inductance. The unit of impedance is the Ohm.
INTRINSICALLY SAFE: As applied applied to equipment equipment and wiring, equipment and wiring that are incapable of releasing sufficient electrical energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture. Abnormal conditions may include accidental damage to any part of the equipment or wiring, insulation or other failure of electrical components, application of overvoltage, adjustment and maintenance operations, and other similar conditions.
ISOLATED PATIENT LEAD: A patient patient lead whose whose impedance to ground or to a power line is sufficiently high that connecting the lead to ground or to either conductor of the power line results in a current flow below a hazardous limit in the lead.
ISOLATED POWER SYSTEM: A system comprising an isolating transformer or its equivalent, a line isolation monitor, and ungrounded circuit conductors.
ISOLATION TRANSFORMER: A transformer transformer of the multiple-winding type, with the primary and secondary windings physically separated, that inductively couples its ungrounded secondary winding to the grounded feeder system that energizes its primary winding.. winding
LEAKAGE CURRENT: Any current, current, including including capacitively coupled current, not intended to be applied
PATIENT CARE AREA: Any portion portion of a health health care care
PATIENT PA TIENT-CARE-RELATED -CARE-RELATED ELECTRICAL APPLIANCE: An electrical electrical appliance appliance that that is intended intended to be used for diagnostic, therapeutic, or monitoring purposes in a patient care area.
PATIENT EQUIPMENT GROUNDING POINT: A jack or terminal terminal that that serves as a collectio collection n point for redundant grounding of electrical appliances serving a patient vicinity or for grounding other items in order to eliminate electromagnetic problems.
PATIENT LEAD: Any deliberate deliberate electrical electrical connection connection that may carry between an appliance and a patient. This may be a surface contact (such as an ECG electrode), an invasive connection (such as an implanted wire or catheter), or an incidental long-term connection (such as conductive tubing). Adventitious or casual contacts such as a push button, bed surface, lamp, hand-held appliance, and so fourth, are not considered patient leads.
PATIENT VICINITY: In an area in which patients are normally cared for, the patient vicinity is the space with surfaces likely to be touched by the patient or an attendant who can touch the patient. Typically in a patient room, this is a space within the room 6 ft. (1.8m) beyond the perimeter of the bed in its normal location and extending vertically within 7 ft. 6 in. (2.3m) of the floor.
REACTANCE: The component of impedance contributed by inductance or capacitance. The unit of reactance is the Ohm.
REFERENCE GROUNDING POINT: A terminal terminal bus that is the equipment grounding bus, or an extension of the equipment grounding bus, and is a convenient collection point for installed grounding wires or other bonding wires where used.
WET LOCAT LOCATIONS: IONS: Those patient care areas that are normally subject to wet conditions, including standing water on the the floor, floor, or routine dousing dousing or drenchi drenching ng of the work area. area. Routine Routine housekeepin housekeepingg procedures procedures and incidental spillage of liquids do not define a wet location.
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