A primary operating function (German: Hauptbedienfunktion) is a term that originates from earlier editions of the IEC 62366 series. It denotes a function of the product that involves user interaction and whose correct performance is relevant to the safety of the medical device.
In the current consolidated edition IEC 62366-1:2015+A1:2020 (as of October 2026), the primary operating function is no longer a standalone central process step. The safety-related analysis is instead carried out by identifying user interface characteristics related to safety, potential use errors and hazard-related use scenarios.
Role in the usability engineering process
Primary operating functions form a bridge between the context of use, risk management and the user interface. They help to determine which parts of the interaction between user and medical device are particularly safety-relevant. The use specification provides important inputs for this, such as user profiles, use environment and operating principle. The actual safety-related analysis of user interactions, however, takes place as a separate, subsequent process step and is then carried over into the use-related risk analysis and the derivation of risk control measures.
Distinction from critical tasks
A primary operating function is not the same as a critical task: One describes a product function, the other a user task. The primary operating function first describes a safety-relevant product function with user interaction. A task is critical when its incorrect performance or omission can lead to serious harm; what matters is the severity of the possible harm. Several critical tasks can be assigned to a single primary operating function; conversely, a primary operating function can exist without each of its subtasks being critical.
| Primary operating function | Critical task | |
|---|---|---|
| Subject | A product function | A user task |
| Characteristic | Safety-relevant product function with user interaction | Incorrect performance or omission can lead to serious harm. What matters is the severity of the possible harm |
| Relationship | Can exist without each of its subtasks being critical | Several critical tasks can be assigned to a single primary operating function |
Typical examples
Examples include programming the infusion rate on an infusion pump, activating or deactivating a therapy, setting energy doses on electrosurgical devices, acknowledging alarms on intensive care systems, or selecting a diagnostic or therapy modality. The actual function here is not the individual control but the system function triggered by the user: A “Start” button, for example, is not a primary operating function, whereas starting a therapy can be one.
Connection to the use-related risk analysis
For primary operating functions, possible use errors and foreseeable misuse are examined. The analysis considers user groups, use environments, use scenarios and the resulting hazardous situations. In practice, methods used include task analysis, FMEA (failure mode and effects analysis), use-related risk analyses and other human factors methods. Identifying potential use errors, hazardous situations and hazard-related use scenarios supports the risk-related activities under ISO 14971.
Importance for formative and summative evaluations
Primary operating functions have high priority in formative studies. These examine whether users can understand, correctly perform and safely use these functions. If critical tasks are derived from them, these must be adequately covered in the summative evaluation. Primary operating functions thus help to prioritize test tasks and use scenarios.
Common misinterpretations in practice
A widespread mistake is to equate controls with functions. A button, a menu item or a display element are components of the user interface but not functions in the actual sense. Another mistake is to automatically classify all frequently used functions as primary operating functions. Under more recent editions of IEC 62366, the focus is on the safety relevance of the function and not on its frequency of use alone.
Regulatory reference
The current consolidated IEC 62366-1:2015+A1:2020 does not require primary operating functions to be identified and documented separately as a standalone central process step (as of October 2026). Comparable safety-related questions are addressed by identifying user interface characteristics related to safety, potential use errors, hazards, hazardous situations and hazard-related use scenarios, which then feed into risk management under ISO 14971. In its human factors guidance, the FDA calls for the identification of safety-relevant user interactions and for taking them into account in risk analysis and summative evaluation. The term “primary operating function” is not a focus of the guidance, but the concept is covered functionally. In Annex I, the EU MDR (Medical Device Regulation) requires the minimization of risks arising from ergonomic features, use errors and conditions of use; analyzing primary operating functions supports meeting these requirements.
A primary operating function is not a button or a menu item but the safety-relevant system function behind it. Risk-based prioritization, however, no longer takes place through a standalone list of primary operating functions but through the current process steps of IEC 62366-1: the hazard-related use scenarios and the possible harms.
Frequently asked questions (FAQ)
Is every frequently used function automatically a primary operating function?
No. In current interpretations of IEC 62366, safety relevance takes precedence. A frequently used function without safety-relevant effects does not necessarily have to be treated as a primary operating function.
Is a primary operating function the same as a critical task?
No. The primary operating function describes a safety-relevant product function. A critical task describes a specific user task whose incorrect performance can lead to a relevant risk.
Do primary operating functions have to be tested summatively?
Not the function as such. What matters is not the designation as a primary operating function but whether it gives rise to hazard-related use scenarios or other safety-relevant user interactions that have to be considered in the summative evaluation.
Are controls primary operating functions?
No. Controls are components of the user interface. The primary operating function describes the system function triggered by user interaction, for example “start therapy” or “set dose”.
Do you want to systematically identify and prioritize the safety-relevant functions of your medical device? We support you throughout the usability engineering process according to IEC 62366-1.
More about our usability engineeringSources
- IEC 62366-1:2015+AMD1:2020, Medical devices, Part 1: Application of usability engineering to medical devices
- ISO 14971:2019, Medical devices, Application of risk management to medical devices
- Regulation (EU) 2017/745 on medical devices (MDR)