Safety Concepts

I have kept coming across functional safety discussions, most recently at ArmTechCon, and wanted to capture some of the terminology and concepts. To orient the discussion, think of airbags, seat-belts, and tire-pressure-monitoring-systems as safety features in a car.

Safety Function or Safety Instrumented Function: A function to take a system to a safe outcome when certain prerequisites on system inputs are not met. E.g. turn on a warning indicator when seat-belt is not used, or tire-pressure is below safe level, or deploy airbags when a collision is detected.

Safety Related Control Function: This is the control mechanism by which the safety function is achieved.

Safety Integrity Level: The reliability of a safety-related-control-function is captured with a Safety Integrity Level or SIL.

A standard is ISO26262. The V shaped functional safety process diagram is here. This process is used to achieve a Safety Integrity Level (SIL) where the SIL1, SIL2, SIL3, SIL4 reduce risk by a progressive factor of 10, i.e. by 10x, 100x, 1000x and 10000x. A HAZOP study is undertaken to understand the risks of the mechanism behaving incorrectly.

A good reference, from SIMATIC is here. Software aspects of safety function are discussed in in this whitepaper.

Safety systems for robotics are discussed here – it has a table of typical safety issues when a person enters a robot safeguarded area. Industrial robots security was briefly discussed here.

Another concept is SOTIF or Safety of the Intended Function, which comes up in functional safety discussions of AI-controlled vehicles. More links on it here.

Nvidia safe driving report here.

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