Knowing the ins, outs, ups, and downs of the standards that apply to your product is paramount.
I have worked as a safety engineer in the medical device industry for two years. With prior experience as a design engineer, I felt I was in a good position to navigate the world of medical safety product compliance. As it turns out, learning the ropes of compliance has been one of the most challenging experiences of my career.
One of the toughest concepts to grasp was how the meaning of terms differs between the design and safety product fields. Take, for example, the term “essential performance.” In design, essential performance refers to what is required to make the equipment work” (e.g., Does it need a fully charged battery? Does it need a certain rated power supply?). However, in the AAMI ES60601-1:2005/(R)2012 medical standard, essential performance refers to the performance of a clinical function where loss or degradation beyond the limits specified by the manufacturer results in an unacceptable risk. In one context, essential performance could refer to what makes the equipment work, while the other poses a question: If the equipment does not work as specified by the manufacturer, could there be an unacceptable risk to the operator or patient? That has caused much confusion when it comes to understanding the intent of the standard and having products comply with it.
As a safety engineer, there are many different and complex concepts you must keep in mind. They can range from the simplest concept—the scope of the standard—to the most difficult—leakage current. The simplest concept is making sure you are using the right standard. This involves determining if the scope of the standard addresses all the equipment’s potential hazards and, if not, considering if there could be another standard that addresses the equipment’s hazards more in-depth. Although this is a simple notion, it should never be overlooked, as this could lead to a complete waste of your time as well as your company’s time.
The challenge in evaluating the product to the correct standard is realizing there are many different standards for different types of equipment, and they do not all come in a neat and easily identifiable package. For example, part of determining if you have the correct standard involves making sure you cover not just the general standard (60601-1), but the collaterals and particulars of that standard’s series as well. Collateral standards (60601-1-xx) cover broad equipment categories, whereas particular standards (60601-2-xx) cover specific requirements. All of these collateral and particular standards can amend the compliance criteria and requirements of the general standard.
Where can you find these collateral and particular standards? The friendly IEC Webstore Web site is your best option. Say, for instance, your medical product has a defibrillator function. You have determined that the scope of 60601-1, the general standard, addresses the potential hazards as much as possible. Go to the Webstore and separately search for the 60601-1 and 60601-2 standards. Each search will populate a list of collaterals, better known as Part 1s, and particulars, better known as Part 2s. Read through the scopes of all the parts and determine if they fit any or all of your product’s application. Even if the defibrillator function is a small part of the application of your medical product, you still must consider “IEC 60601-2-4: Particular requirements for the basic safety and essential performance of cardiac defibrillators.”
Furthermore, do not stop investigating when you find one particular. Infant incubators have at least two particulars. Hence, it is good practice to read through the scopes of all the collateral and particular standards to determine applicability. (Important note: There are 80601-2 particular standards that are part of the 60601-1 series, which were developed as a joint venture between the ISO and IEC. The 80601-2 particulars are overlooked quite a bit, so keep them in mind as well.)
For the more challenging concepts, I learned to rely heavily on the “terminology and definitions” section. It has become one of my favorite and most referenced sections. As I had alluded to previously, you can see why. Terminology can be a tricky concept. One person can believe the sky is blue while another person believes the sky has multiple colors. Who should you believe? You need to figure that out on your own. So before attempting any type of evaluation or taking a product to a “third-party” certifier, refer to the “terminology and definitions” section in the standard as a start. Get on the same page as the safety engineer who will be evaluating your product. This will lessen the confusion and save you time and money. And let’s face it, we all like that idea.
One of the essential terms that I became familiar with before dealing with the complex concept of leakage current is the “applied part.” An applied part, according to AAMI ES60601-1:2005/(R)2012, is a part of the equipment that necessarily comes into contact with the patient for the equipment to perform its function. The AAMI ES60601-1 medical standard Annex A: General guidance and rationale, subclause 3.8 explains why defining an applied part is necessary. This subclause indicates that because the patient can come into contact with these parts and may not need to come into contact with the enclosure, they are subject to more stringent requirements than the normal enclosure’s leakage. In my opinion, the term “applied part” is the most important term used throughout the medical standard series.
And do not forget the manufacturer’s defined applied parts term—parts that are not considered “applied parts” according to the standard definition but rather have been defined by the manufacturer to be considered, treated, and held to the same compliance criteria as an applied part. This concept is not hard to understand but is often overlooked when it comes to addressing all potential hazards of the equipment. For example, imagine getting an x-ray for a potential broken bone. Sadly, most of us have been there. The table on which you lie is considered an applied part; it has direct contact with the patient. Do you remember wanting to reach out to touch the overhead equipment? (Maybe that was just me.) As a manufacturer, you need to consider if the parts the patient can reach and touch should be held to the same requirements as the table. Thankfully, the standard has given manufacturers a way to address this important potential hazard, and you need to consider all the possibilities.
As I was adjusting to the leakage current concept, I familiarized myself with the standard’s definition of it. The 60601-1 standard specifies it as a current that is not functional and says there are different types: earth leakage current, touch current, patient auxiliary leakage current, and patient leakage current. Because there are different types, I’ll focus on the particular patient leakage current, which flows through the patient connections of an applied part to earth. The language in the standard offers insight as to the particular patient leakage current compliance criteria, and I find this useful; however, I find that figure 15 in the 60601-1 standard pulls all that language and information for patient leakage current together in a neat package using visual guidelines. When you look at it, notice how the figure indicates the power source as mains. If your product does not connect to mains or you have a different type of mains than what is indicated in figure 15, you will have to consider this figure along with the appropriate figures F.1 to F.5 in 60601-1 for more information.
I’ll concentrate on this figure as an example. There are six switches used in the test setup to simulate various conditions that your equipment may or may not have. For instance, the S10 switch that comes from ground to the functional earth terminal. If your product does not have a functional earth terminal, then you omit this from the number of switch combinations you need to measure. Also, notice the figure MD that is electrically connected between earth and the applied part (see 60601-1: table 5 – Legends of symbols). MD stands for measuring device and has to meet certain requirements according to 60601-1.
If you are interested in knowing more about these requirements, seek out more information in the standard; it is there to help you. I have found using the “key” in the figures has helped me determine possible combinations and single fault conditions that are necessary according to the equipment’s specifications. As I had indicated before, this is a complex topic that could be written at length in order to fully dive into the compliance criteria; however, I hope this gives you a starting line to a brand new outlook on this multifaceted and confusing compliance concept. Please keep in mind that whatever level of experience you have, understanding the product safety compliance world is not as simple as one would think—experience with applying the standard is necessary.
In conclusion, throughout my last two years as a safety engineer, I have realized that familiarizing yourself with the standard before evaluating or having your product third-party evaluated is the best bet for success. This is why the product safety compliance world always encourages manufacturers to purchase the applicable standards and read them prior to the design phase, so they can successfully design to comply. Furthermore, success with purchasing the applicable standards includes determining if the standard’s scope, including any Part 1 and/or Part 2 scopes, effectively addresses the potential and foreseeable hazards of your product. Understand that assuming the meanings of terms is not the most effective way to approach safety compliance. Lastly, the compliance world is challenging and sometimes frustrating. Hence, use the standard to its fullest potential. Case in point: Seek out the Annex A subclause section in 60601-1 for any term or clause that has an asterisk in order to appreciate the full intent of the standard. If in doubt, ask. It is better to be informed than to assume; otherwise, you might find yourself in a lot of trouble.
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