Glossary · Risk estimation methods
Avoidability
In machine safety, avoidability is the possibility that a person can avoid or limit harm once a hazardous event begins. It is one of the elements that determine the probability of harm in risk estimation.
- Machine safety
- Risk assessment
- Human factors
In one sentence
Avoidability rates whether a person can still escape or limit harm once a hazardous event starts, based on speed, warning, awareness and skill.
Example
A slowly moving AGV that signals its approach offers a real chance of stepping aside, whereas a fast-closing press tool gives the operator practically no chance to withdraw a hand.
How it applies
- Risk estimation: ISO 12100 names factors such as who is exposed (skilled or unskilled), the speed at which the hazardous event develops, awareness of the risk, human ability to avoid harm and practical experience.
- Functional safety: In the ISO 13849-1 risk graph, parameter P distinguishes whether avoiding or limiting harm is possible under specific conditions (P1) or scarcely possible (P2). It influences the required Performance Level. IEC 62061 uses a comparable avoidance parameter.
- Human factors: Be cautious with optimistic assumptions. Reaction times, distraction and unfamiliar operating modes reduce avoidability in practice.
- Technical documentation: Record why a hazard was rated avoidable, for example low speed or clear warning signals, so that the assumption can be verified and revisited.
Avoidability vs. exposure
Exposure describes how often and how long people are near the hazard. Avoidability describes what they can do once something goes wrong.