Safety Concepts – Functional safety, SOTIF

I want to capture Functional Safety concepts. This is an important topic given the number of vehicles and their increasing automation. It was a major topic at the recent ArmTechCon.

Airbags, seat-belts, ABS, and tire-pressure-monitoring-systems are some of the safety features in a car.

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

Safety Related Control Function (SRCF): This is the control mechanism by which the safety function is achieved. For example, collision above a certain impact threshold leads to airbag deployment by an airbag control module. Quote: “The airbag control module is installed inside the center console and contains a safety sensor, G sensor, ignition judgment circuit, and a backup power supply.”

Safety Integrity Level (SIL): The reliability of a safety-related-control-function is captured with a Safety Integrity Level or SIL. SIL level go from 1 to 4 (highest). SILs are derived from a risk estimation process and are used in estimating risk of a system built using pre-built components.

A safety standard is ISO26262. The V shaped functional safety process diagram describes the design steps flowing from OEM to supplier and verification steps flowing back from supplier to OEM (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 hazard and operability study ( HAZOP ) 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 – this has a table of typical safety issues when a person enters a robot safeguarded area. Industrial robots security was briefly discussed in this blog 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.

An Nvidia safe driving report is here.

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