In my profession, I often observe manufacturers of active (electrical) medical devices making the mistake of implicitly assuming that safety-relevant aspects are already adequately addressed during development by circuit design, material selection, or individual component testing.

For IEC 60601-1 compliance, this is not enough.

These manufacturers are overlooking the explicit requirement to identify, justify, and document critical components as specified in the standard.

Even when recognized, uncertainty frequently arises as to which components must be classified as critical components. This uncertainty becomes particularly evident when assessments are not performed consistently on a risk-based basis.

Furthermore, manufacturers often lack clear understanding of which types of components that can fall into the category of critical components.

These are not limited to electrical parts; mechanical, thermal, or structural elements may also be safety-relevant and thus fall in this category

The result: incomplete evidence in accordance with IEC 60601-1 or follow-up questions during IEC 60601-1 testing, with serious consequences such as delayed market-access and unexpected extra costs.

The central challenge therefore lies in clearly identifying critical components and documenting compliance with the requirements of IEC 60601-1 in a traceable and comprehensible manner.

Here are the steps to solve this problem.

IEC 60601-1 defines critical components in Clause 4.8 as:

“All components, including wiring, the failure of which could result in a hazardous situation […].”

This implies that:

• Not every component is automatically considered critical.
• Criticality results from the function of the component within the ME equipment.
• A component is considered critical if its failure leads to an unacceptable risk.

The examples below illustrate identical components that may or may not be classified as critical depending on their intended use.

The identification of critical components is best performed as part of the risk management process described in Clause 4.2 of IEC 60601-1.

A structured approach to identify critical components includes the following activities:

1. Hazard identification
   Identification of potential hazards associated with the medical device (e.g., electrical, mechanical, acoustic, thermal hazards, data loss).
2. Risk evaluation
   Assessment of whether the identified risks are acceptable.
   If not, appropriate risk control measures must be implemented.
3. Risk control measures
   Measures implemented to reduce the severity and/or probability of a risk.
   → If a component forms part of such a measure, the component is classified as a critical component.
4. Evidence of effectiveness
   Demonstration of the protective function and compliance through:
   • Test reports
   • VDE certificates
   • UL numbers
   • UL Yellow Cards

The corresponding evidence must be referenced and added to the list of critical components.

Practical examples

Example 1: Fuse in the primary circuit

A fuse prevents overheating or fire in the event of a fault. Failure of the fuse may result in a fire hazard.

Assessment & documentation:

• Function: Overload protection or short-circuit protection. In the event of a fault: Operation at maximum current. Interruption of the mains voltage
• Risk: Fire hazard
• Standard: IEC 60127; IEC 60601-1: Clauses 8.11.5 & 15.4.3.5
• Evidence: Test report according to IEC 60127 or UL number
• Critical? Yes, or justification in the risk management analysis for omitting the fuse.

Example 2: Plastic material for a fire enclosure

The enclosure ensures that no fire resulting from an electrically initiated fire can escape from the enclosure.

Assessment & documentation:

• Function: Hazard to people, caused by fire
• Risk: Mechanical and thermal injury
• Standard: IEC 60695-11-10; IEC 60601-1: Clause 11.3 (constructional requirements for fire enclosures)
• Evidence: Test report according to IEC 60695-11-10 or Yellow Card (materials certified by UL)
• Critical? Yes, if a fire can occur within the medical device.

With the identification of the critical components completed, proceed to select or source implementations of the components where their protective functions can be demonstrated to be in compliance with applicable standards.

IEC 60601-1 clause 4.8 requires that critical components (unless a justified exception is documented, either in the standard or within the risk management process) are tested in accordance with relevant standards or evaluated against defined requirements of IEC 60601-1.

Appropriate forms of evidence may include:

• Test reports (e.g., CB reports, accredited test reports)
• Certificates (VDE, UL)
• UL Yellow Cards for plastic materials
• ASCA-accredited test reports (FDA context)

It is strongly recommended to obtain and secure quality assurance statements or agreements from suppliers of critical components that guarantee that the protective function remains unchanged over a defined period and that design or manufacturing changes are performed in a controlled manner.

For critical components without a direct technical standard reference, testing in accordance with IEC 60601-1 may be used to experimentally demonstrate the protective function. However, this approach involves increased uncertainty and should only be applied when no normative alternatives are available.

It is important to note that critical components are only to be replaced by components that meet the same requirements and provide equivalent documented evidence.

In this article, we have addressed three common problems manufacturers experience in conjunction with managing Critical Components:

• Understanding what critical components are and how they can be identified and thus avoiding that too few or no components are listed as „critical“
• The importance of identifying them as soon as possible, as assessments and evidence collection takes time
• Avoiding not having good enough evidence for critical components or not knowing where, or how to collect the evidence.

Critical components are not merely technical key elements but central elements of normative safety in accordance with IEC 60601-1. Their identification must be risk-based, traceable, and compliant with applicable standards. Failing to do so can put the medical device release-to-market in danger with high and unexpected costs as a consequence.

Best practices show that an early and well-structured selection and documentation of appropriate evidence reduce regulatory uncertainty, facilitates conformity assessment, and contributes significantly to the overall safety of the medical device.

Sarah Lippert is a test engineer at the DAkkS-accredited testing laboratory of KEYMKR GmbH. She studied Medical Engineering at South Westphalia University of Applied Sciences and Biomedical Engineering at Münster University of Applied Sciences. Since 2022, she has been testing active medical devices at the KEYMKR laboratory in accordance with the relevant safety standards, primarily the IEC 60601-1 and IEC 61010-1 series.