2 HARA and Safety Concept Assessment Stage

The Hazard Analysis and Risk Assessment (HARA) is a well accepted process for defining system-level safety goals. The first step in the HARA process is to identify all potential hazards in a system and then classify each of the hazards based on risk of harm. The criteria used to classify the hazards varies based on the standard used but typically includes factors such as how dangerous (severity), how likely to occur (exposure), and how controllable the hazard is (controllability). This paper focuses on the Safety Integrity Level (SIL) and Automotive Safety Integrity Level (ASIL) hazard classification techniques and levels.

After the system-level hazards are identified and assigned SIL or ASIL levels, safety goals can be defined to mitigate the hazards. To achieve the safety goals in the end system, safety concepts are required which are defined during the Safety Concept Assessment phase. It is during this phase that the individual components needed to support the safety concept are identified and assigned an appropriate SIL or ASIL level. For example in this phase the system integrator determines if the MCU or processor are critical to implementing the safety concept and if so, assign an appropriate SIL or ASIL rating. Decomposition techniques as per safety standards can be used to lower the safety integrity levels on certain components based on system architecture without lowering the final system safety-integrity levels.

Figure 2-1 shows a graphical representation of the HARA and Safety Concept stages.