Characteristics related to safety, often shortened to safety-related characteristics, are qualitative or quantitative characteristics of a medical device that can affect its safety. In usability engineering, the more specific term user interface characteristics related to safety must be distinguished from them.
Where necessary, limits must be defined for these characteristics. They are identified and documented as part of the risk analysis according to ISO 14971, taking into account the intended purpose (intended use), the reasonably foreseeable misuse, the intended users and the use environment. IEC 62366-1 requires identifying such user interface characteristics as well as the associated potential use errors. User characteristics and environmental conditions are important inputs from the use specification, but they are not automatically characteristics of the medical device or of the user interface themselves.
Role in risk analysis
Identifying the characteristics of the medical device that relate to its safety is one of the early steps of risk analysis according to ISO 14971. The goal is to determine qualitative and quantitative product characteristics that can be relevant for the subsequent identification of hazards and hazardous situations. Where necessary, the associated limits must also be defined.
Product characteristics to be considered can include, for example, energy output, temperature, pressure, dosing ranges, materials, software functions, data connections, alarms, controls and labeling. The intended purpose (intended use), the reasonably foreseeable misuse, the intended users and the use environment are important framework conditions for identifying and assessing these characteristics. They are, however, not readily characteristics of the medical device themselves.
Incomplete identification can mean that relevant hazards, foreseeable sequences of events or hazardous situations are not considered in the risk analysis. This can impair the completeness and traceability of the risk management file.
Connection to usability engineering
In usability engineering, the focus is on the user interface characteristics that are related to safety. IEC 62366-1 requires identifying such UI characteristics as well as the associated potential use errors.
The use specification provides essential inputs for this. Among other things, it describes:
- the intended medical indication,
- the intended patient population,
- the intended part of the body or type of tissue,
- the intended user profiles,
- the intended use environment, and
- the operating principle or mode of operation of the medical device.
User groups and contexts of use are thus important framework conditions of the analysis. They must, however, be distinguished from safety-related product or UI characteristics. A safety-related UI characteristic can be, for example, the legibility of a display, the distinguishability of two connectors, the design of an alarm message, or the feedback after a safety-relevant input.
Critical tasks are also not user interface characteristics. They describe user tasks whose incorrect performance or omission can lead to serious harm or cause or enable such harm.
Typical categories and framework conditions
For a traceable analysis, safety-related product characteristics and the framework conditions of their identification should be considered separately.
Safety-related characteristics of the medical device
- Physical properties, for example temperature, pressure, speed or energy output
- Mechanical and electrical properties
- Biological and chemical properties, for example materials, release of substances, or type and duration of body contact
- Measurement, control and software functions
- Automation functions and system states
- Data, communication and network functions
- Displays, controls, alarms, connectors and system feedback
- Labeling, packaging and accompanying documentation.
Framework conditions for identification
- Intended purpose (intended use) and intended medical application
- Reasonably foreseeable misuse
- Knowledge, training, experience, and physical and cognitive abilities of the intended users
- Lighting, noise, temperature and other conditions of the intended use environment
- Clinical and organizational workflows
- Operating, transport and storage conditions
- Foreseeable stress, time pressure or distractions during use.
Especially with complex medical devices, safety often results from the interplay of several product characteristics and framework conditions. For example, an acoustic alarm can work correctly from a technical standpoint and still be inadequate if it cannot be reliably perceived in the loud use environment for which it is intended.
Distinction from risk control measures
Identifying safety-related characteristics must be distinguished from selecting and implementing risk control measures. Safety-related characteristics support hazard identification and risk analysis. Risk control measures, by contrast, are defined to reduce identified risks.
A characteristic can, however, be introduced or changed by a risk control measure. It is therefore not always possible to consider a product or UI characteristic completely independently of risk control.
In an infusion pump, for example, the entry and display of a dose, including value range, unit, decimal representation and confirmation logic, can be safety-related characteristics of the user interface. A software check of the entered dose against defined dosing limits can be implemented as a risk control measure. The resulting warning or alarm is then both part of the user interface and part of the risk control.
This differentiated view is essential for traceability between product characteristics, hazards, hazardous situations, risk control measures, design inputs, verification and validation.
| Safety-related characteristics | Risk control measures | |
|---|---|---|
| Function | Support hazard identification and risk analysis | Are defined to reduce identified risks |
| Example: infusion pump | Entry and display of a dose, including value range, unit, decimal representation and confirmation logic | Software check of the entered dose against defined dosing limits |
Importance for the use-related risk analysis
When analyzing use-related risks, safety-related characteristics of the user interface and possible use errors are important starting points. These can include, for example, the following aspects:
- Perceptibility and prioritization of alarms
- Design and arrangement of safety-relevant controls
- Display of operating and system states
- Comprehensibility of values, units and symbols
- Distinguishability of connectors and components
- Feedback after inputs or operating actions
- Error tolerance of the user interface.
The identified UI characteristics and potential use errors feed into the description of hazard-related use scenarios. A traceable link should be established between the following elements:
- User task
- User interface characteristic
- Potential use error
- Foreseeable sequence of events
- Hazard
- Hazardous situation
- Possible harm
- Risk control measure, where required.
The results support the planning of formative evaluations and the selection of the hazard-related use scenarios to be examined in the summative evaluation, with particular attention to scenarios involving critical tasks or relevant possible harms. Critical tasks are not derived solely from individual UI characteristics but are assessed on the basis of the possible consequences of incorrect performance or omission.
Typical weaknesses in regulatory audits
In audits and reviews, the following weaknesses, among others, are found:
- Safety-related product characteristics were not systematically identified or documented
- Required quantitative or qualitative limits were not defined
- Product characteristics, user characteristics and environmental conditions were not clearly separated from one another
- The link between the use specification and the risk analysis is not traceable
- Potential use errors and hazard-related use scenarios were considered only superficially
- Software and UI characteristics were not recognized as safety-relevant
- Critical tasks were selected without a recognizable link to possible harms
- Traceability between characteristic, hazard, hazardous situation, harm and risk control measure is incomplete.
These aspects are particularly relevant for software-based medical devices, networked medical devices and products with a high degree of automation. In addition to the user interface, possible effects of data errors, connection losses, automated decisions and insufficiently recognizable system states must also be considered.
Regulatory reference
ISO 14971:2019 requires, as part of risk analysis, the identification and documentation of qualitative and quantitative characteristics of the medical device that can affect its safety. Where necessary, the associated limits must be defined. ISO/TR 24971:2020 contains supplementary explanations and examples for identifying and using such characteristics in hazard identification.
IEC 62366-1:2015 including Amendment 1:2020 specifically addresses the usability engineering process for medical devices. The standard first requires a use specification to be created. Building on it, user interface characteristics related to safety and the associated potential use errors must be identified. Known or foreseeable hazards and hazardous situations as well as hazard-related use scenarios are then considered.
The FDA also follows a risk-based human factors approach but in part uses different terminology. In particular, user interface characteristics must be distinguished from critical tasks. A critical task is a user task whose incorrect performance or omission could lead to serious harm. UI characteristics, possible use errors and critical tasks are linked with one another in the use-related risk analysis but are not synonymous terms.
In Annex I, the EU MDR (Medical Device Regulation) calls for risk management that is documented and maintained throughout the entire product lifecycle. In addition, risks related to ergonomic features, the intended use environment and the characteristics of the intended users must be reduced as far as possible. The MDR does not define the term safety-related characteristics on its own; for operational implementation, ISO 14971 and IEC 62366-1 are regularly used.
Safety-related characteristics are the starting point of risk analysis, not its result: They describe where hazards can arise, not how they are controlled. In usability engineering, a further distinction must be made between user interface characteristics related to safety, user and environmental characteristics, and critical tasks, since these terms are often mixed up in audits and reviews.
Frequently asked questions (FAQ)
Are safety-related characteristics identical to hazards?
No. A safety-related characteristic is a qualitative or quantitative property of the medical device that can affect its safety. A hazard, by contrast, is a potential source of harm. The characteristic can be relevant for identifying a hazard, a foreseeable sequence of events or a hazardous situation.
Are user characteristics part of the safety-related characteristics?
Not in the narrower sense of the ISO 14971 term, which refers to characteristics of the medical device. User characteristics such as training, experience, language skills and physical or cognitive abilities are, however, essential framework conditions of the risk analysis and components of the use specification. They can decisively determine which product or UI characteristics are safety-related.
Are UI elements safety-related characteristics?
UI elements can be safety-related characteristics of the user interface if their perception, interpretation or operation can affect safe use. Not every UI element is automatically safety-related. The classification is based on possible use errors and the resulting hazardous situations and harms.
Are safety-related characteristics risk control measures?
Not necessarily. Identifying safety-related characteristics is first of all part of risk analysis. A characteristic can, however, be introduced or changed by a risk control measure. For example, an alarm can be both a characteristic of the user interface and part of a risk control measure. Whether it is to be classified as a protective measure, information for safety or part of a combined risk control depends on its specific function and implementation.
Do safety-related characteristics have to be documented?
Yes. ISO 14971 requires identifying and documenting the qualitative and quantitative characteristics of the medical device that can affect its safety. Where necessary, the associated limits must also be defined. IEC 62366-1 additionally requires identifying user interface characteristics related to safety and the associated potential use errors.
Do you want to systematically identify the safety-related characteristics of your medical device and embed them traceably in your risk analysis? 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
- ISO/TR 24971:2020, Medical devices, Guidance on the application of ISO 14971
- Regulation (EU) 2017/745 on medical devices (MDR)