Glossary · Hazards and harm
Bypass behavior
Also known as: guard defeat
In machine safety, bypass behavior is the intentional defeat or avoidance of a protective measure, such as bridging an interlock switch or reaching around a guard. It is often driven by poor usability, nuisance trips or production pressure.
- Machine safety
- Human factors
- Risk assessment
In one sentence
Bypass behavior means people deliberately defeat guards or interlocks, usually because the protective measure gets in the way of the task.
Example
On a packaging line whose interlocked door stops the machine for every jam, operators tape a spare actuator into the switch so they can clear jams without a restart.
How it applies
- Machine safety: Treat foreseeable bypassing as reasonably foreseeable misuse in the risk assessment. ISO 14119 asks designers to consider the motivation to defeat interlocking devices and to minimize it, for example by making every necessary task possible without defeat.
- Design: Remove the incentive first: provide safe modes for setting and jam clearing, reduce nuisance trips, and add tamper resistance where motivation remains.
- Technical documentation: Describe how each task that needs access is done safely. Missing procedures invite improvisation. A warning against bypassing is not a substitute for a design measure.
- Evidence: Field reports, maintenance records and observed workarounds are input for change control. A bypass found in operation shows that the design or the procedure does not fit the task.
Bypass behavior vs. human error
Human error is unintended. Bypass behavior is a deliberate choice, usually made to get the job done, which is why training and warnings alone rarely stop it.