A Scenario-Based Approach to Assess Exposure for ASIL Determination 2014-01-0211
Exposure in ISO 26262 is defined as the state of being in an operational situation that can be hazardous if coincident with the failure mode under analysis. An operational situation is defined as a scenario that can occur during a vehicle's life with examples given such as driving, parking, or maintenance. Accurately predicting exposure is one of the more difficult tasks in the ASIL determination. ISO 26262 Part 3 attempts to provide guidance in Annex B through tables of potential operational situations and associated exposure levels. However, the contents of these tables may not allow for an accurate prediction of exposure and may lead to an exposure value that is too high or too low.
In this paper, we describe a potential method for determining exposure that considers a potential mishap scenario as a composition of multiple coincident operational situations rather than considering a single operational situation as indicated in the tables in Annex B of Part 3. We purport that for a potentially hazardous situation to occur if the failure mode under analysis occurs, it typically requires multiple operational situations to be present at the same time, in addition to the failure mode. We believe that considering a mishap scenario with multiple coincident operational situations in the evaluation of exposure provides a more accurate determination of exposure.