The Hazard Analysis and Risk Assessment (HARA), required by Part 3 of the ISO 26262 standard, is used to identify malfunctions that could lead to hazards, to rate the relevant risks of hazards, and to formulate safety goals.
The HARA can easily become a tedious task to complete when the number of functions and scenarios increase. Below are a few common points to remember while approaching the HARA:
- Item definition: Preparing a HARA can be simplified by many levels if a good item definition is in hand. The HARA is based on the malfunctions at the vehicle level, so having a broad understanding of the working of a vehicle and its many sub systems is necessary.
- HAZOP: The HAZOP is a good starting point to identify the malfunctions that are potentially hazardous by using guide words such as wrong, reversed, too much, too little, too early, too late, etc.
- Scenario catalogs: Scenario catalogs with predefined ratings (usually exposure) may seem to reduce effort initially. However, predefined ratings must be revisited within each HARA based on an understanding of the malfunctions.
- Grouping scenarios: In order to reduce the complexity of HARAs, scenarios may be grouped relevantly or added as aggravating factors during other situations; making sure that the uniqueness of each of the grouped scenarios is preserved.
- Safety mechanisms: While preparing a HARA for a system, the internal safety mechanisms of that system are not considered. However, external safety mechanisms in other systems may be considered in the analysis.
- Duration or frequency: Exposure, as mentioned in the standard, can be based on duration or frequency. Duration is used when a malfunction causes a hazardous event during the situation. Frequency is considered when a pre-existing fault in combination with the occurrence of the given situation causes a hazardous event.
- Documentation of rationale: Lastly, recording the reasons for using a particular S, E or C rating is highly recommended to ensure consistency of ratings and will be helpful when revisiting the HARA.
A HARA is a complex and challenging exercise. There’s no way to make every HARA simple or easy, but with these simple tips you can successfully complete it in a reasonable time and be confident in the outcome.