Abnormal use (German: abnormale Benutzung) denotes, in the sense of usability and human factors standards, a conscious, intentional act or omission that is contrary to the intended use and lies outside further reasonable user interface-related risk control measures by the manufacturer. It therefore differs fundamentally from use errors, which occur unintentionally, and from reasonably foreseeable misuse.
Not every deliberate deviation is automatically abnormal use. What matters is whether the behavior is reasonably foreseeable.
Distinction from use error and reasonably foreseeable misuse
One of the most common misinterpretations is to equate abnormal use with use errors. A use error occurs during normal use, that is, use that basically follows the instructions for use or common practice, and can often be traced back to errors of perception, comprehension, memory, or action. Abnormal use, by contrast, requires a conscious decision to deviate from the intended conditions of use.
There is also an important difference from reasonably foreseeable misuse: It can be intentional or unintentional, but it is regarded as realistically expected human behavior and must therefore be considered in risk management and product development. Abnormal use, by contrast, lies outside what can reasonably be controlled through further measures at the user interface.
| Term | Characteristics |
|---|---|
| Use error | Occurs during normal use, that is, use that basically follows the instructions for use or common practice. Often attributable to errors of perception, comprehension, memory, or action |
| Reasonably foreseeable misuse | Can be intentional or unintentional. Regarded as realistically expected human behavior and must be considered in risk management and product development |
| Abnormal use | Requires a conscious decision to deviate from the intended conditions of use. Lies outside what can reasonably be controlled through further measures at the user interface |
Role in the usability engineering process
IEC 62366-1 focuses on risks arising from normal use and the resulting use errors. Abnormal use is explicitly not treated as a subject of the usability engineering process itself. The manufacturer therefore does not have to prevent every conceivable deliberate misaction through design measures. At the same time, the distinction is difficult in practice: Many actions that initially look "intentional" turn out on closer analysis to be reasonably foreseeable misuse, for example skipping a work step because of time pressure or workflow problems. Such cases must not be prematurely classified as abnormal use.
Typical examples
Typical examples of abnormal use in the sense of IEC 62366-1 include:
- Sabotage of a medical device
- Tampering with software functions
- Removal or deactivation of protective devices
- Deliberate disregard of contraindications
- Use of a medical device for a clearly unrelated purpose
A frequently cited example is the deliberate deactivation of the alarm functions of a ventilator even though their safety function is known.
Challenges in risk analysis
In practice projects, there is a risk of prematurely declaring critical use scenarios as abnormal use in order to exclude them from the risk assessment. From a regulatory perspective this is problematic, because authorities and notified bodies (independent conformity assessment bodies under the EU MDR) regularly question whether the use in question actually lies outside foreseeable behavior. Especially for home-use products, digital health applications, or complex hospital environments, people bypassing processes is often foreseeable. Such behaviors should therefore first be considered as potential misuse and assessed systematically.
Influence on formative and summative evaluations
Formative studies can indicate that supposedly "intentional" rule violations are actually attributable to poor usability or unsuitable workflows. Such findings should flow directly into the use-related risk analysis. In summative evaluations, scenarios involving abnormal use are usually not defined as the subject of testing. Instead, normal use and reasonably foreseeable misuse scenarios are tested, provided they can lead to safety-relevant risks.
Documentation in the usability file
Manufacturers should document in a traceable way why a particular scenario was classified as abnormal use. The reasoning should be based on user analysis, context of use, known misuse, post-market data, and risk assessments. A blanket classification without justification is often viewed critically. A clear separation between use error, reasonably foreseeable misuse, and abnormal use is especially important.
Regulatory reference
IEC 62366-1 defines abnormal use as a conscious act or conscious omission contrary to the intended use that lies outside further reasonable user interface-related risk control measures; the usability engineering process addresses normal use including use errors, but not abnormal use. ISO 14971 requires that reasonably foreseeable misuse be considered and documented in risk management. The distinction from abnormal use is essential for risk assessment. In its human factors guidance, the FDA requires consideration of foreseeable use errors and use-related risks; an explicit regulatory focus on deliberate sabotage in the sense of abnormal use is not expressly evident.
Abnormal use lies outside what a manufacturer reasonably has to control through design, but the boundary to reasonably foreseeable misuse is narrow and must be justified in documentation, not merely asserted.
Frequently asked questions (FAQ)
Does abnormal use have to be tested in a summative usability study?
No. Summative studies address use as intended as well as relevant reasonably foreseeable misuse scenarios. Abnormal use is in principle not part of the intended subject of testing.
Is deliberately bypassing a process step automatically abnormal use?
No. If such behavior is foreseeable because of time pressure, workflows, or known usage patterns, it is often reasonably foreseeable misuse rather than abnormal use.
Can a use error be intentional?
No. By definition, a use error is an unintentional error in the course of use. Deliberate violations fall more into the categories of misuse or abnormal use.
May a manufacturer exclude risks from the analysis by referring to "abnormal use"?
Not without a sound justification. Manufacturers should be able to document why a behavior is not reasonably foreseeable and cannot be addressed by appropriate design measures.
Do you want to delineate reliably which use scenarios belong in your risk analysis and which do not? 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