Glossary · Stopping functions and safe states
Safe state
German: Sicherer Zustand
In machine safety and functional safety, a safe state is a condition in which risk has been reduced to an acceptable level for the relevant situation. What counts as safe depends on the machine, the hazard and the task being performed.
- Machine safety
- Risk assessment
In one sentence
A safe state is any condition in which risk is acceptable for the situation at hand, which is not always the same as “stopped” or “off”.
Example
For a press, the safe state for tool change is ram at bottom dead center, blocked and de-energized; for a ventilation system in a paint booth, the safe state after a fault may be running fans, not stopped ones.
How it applies
- Machine safety: The safe state follows from the risk assessment and acceptable risk, not from habit. Removing power is often safe, but not when it releases a load, stops cooling or opens a clamp.
- Integrated systems: Fail-safe behavior means that faults lead to the safe state. In a line, one machine’s safe state must not create an unsafe condition in the next.
- Technical documentation: Write the concrete defined safe state for each situation instead of the generic phrase “bring the machine into a safe state”, which users cannot act on.
- Evidence: Each safety function should reference the safe state it achieves, so validation can test against it.
Safe state vs. stopped state
A stopped machine can still hold stored energy, a raised load or hot surfaces. A safe state is judged by the remaining risk, not by the absence of motion.