In a healthcare setting, medical equipment must be electrically safe for patients and users. The safety of clinicians, visitors, and patients who may come into contact with electrical devices is ensured by safety testing. It's always included in preventative maintenance operations, and it's designed to keep people safe from electric shock. IEC 60601-1 is an international standard that specifies the safety standards for medical device manufacturers, but it has also been adopted for routine testing of medical equipment. In-service, troubleshooting, and post-repair standards, such as IEC 62353, have been created expressly for a unified approach to periodic testing. Watch the webinar on Everything You Want to Know About Electrical Testing but Were Afraid to Ask
Additional protection for medical devices is essential to ensure proper electrical separation from any attached parts. Patient protection is categorized as:
All medical devices must be labeled with one of these classifications.
According to international regulations, medical device electrical safety is divided into:
Electrical shock can cause interruptions during health care procedures and result in injury or death. Physiological effects range from a tingling feeling to severe burns and electrocution. Excitable human tissue is susceptible to current in the frequency range of electrical power systems worldwide (50-60 Hertz). Figure 1 shows the effects of current ﬂowing from one skin contact point to another. Electrical shock can cause delays in medical treatments and even result in harm or death. Physiological effects range from a burning feeling to severe burns and electrical shocks. Excitable human tissue is susceptible to current in the frequency range of electrical power systems (50-60 Hertz). The effects of electricity flowing from one skin contact point to another are depicted in Figure 1.
Figure 1: Effects of current ﬂowing from one skin contact point to another.
Electrical safety takes on added significance in electrically susceptible patients. For cardiac procedures, electrically conductive catheters may be placed into the heart while the patient is connected to medical equipment. The skin exhibits a high electrical resistance, but internal body components such as blood and muscle have low electrical resistance.
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Varying electrical safety standards have been established in the United States, European countries, and other parts of the world. The measures differ in standards, measurements, and protocol. The International Electrotechnical Commission (IEC) and International Organization for Standardization (ISO) based in Europe provide standards worldwide incorporation with the World Trade Organization. These include standards for electromedical equipment. There are general and exact standards for medical device electrical safety.
The key standard for medical devices is IEC 60601. General necessities for protection against electric shock hazards are covered in IEC 60601.1, Section 3.
The terminology used in IEC 60601.1 3rd edition includes
• Protective earth resistance
• Earth leakage current
• Touch current (formerly enclosure leakage current)
• Patient leakage current
• Patient auxiliary current
• Mains on applied part (MAP)
Additional essential points regarding IEC 60601.1 include: the use of up to 25 amperes ac for protective earth testing, leakage current is measured at 100 percent of mains voltage, and performance of dielectric strength/insulation testing is estimated at 110 percent of the mains voltage. A new IEC standard, IEC 62353, is used for health device testing in hospitals. IEC 62353 was established because IEC 60601.1 is a type-testing standard with no risk administration criteria and is unusable for testing in the hospital setting.
IEC 62353 tests are performed on equipment before patient use, during periodic testing, and after restoration. Thus, this standard is for field hospital testing and does not report equipment design. In Annex E of the article, the manufacturer is requested to provide testing intervals and procedures based on risk, typical practice, and device history. The minimum testing requirement for life provision and other critical equipment is 24 months.
Only a measurement device that meets IEC 61010-1 should be used. The arrangement outlined in Figure 2 should be maintained. For example, protective earth resistance should be measured before leakage current measurements.
Figure 2: Testing requirements and sequence according to IEC 62353 Annex C.
Overall connections to an electrical safety analyzer (ESA) are shown in Figure 3. Documentation requirements for IEC 62353 include:
Figure 3: General connections to an electrical safety analyzer
Under IEC 62353, the electrical leakage current testing methodology requires expert decision-making. The following test procedures are recommended to ensure testing accuracy. The illustration depicts a decision tree that should be followed (Class I medical device—accessible ground, power cord with plug-connection to mains and Class II medical device—no reachable ground, typically double-insulated) to appropriately choose the Direct, Differential, or Alternative method of electrical leak current testing based on the design of the medical device to be tested.
Figure 4: Testing accuracy procedure
Every test should be performed with the device OFF and ON. The maximum reading should be documented or used for exception reporting.