My main job is to review all kinds of functional safety documents. Although I don’t know much detail of products, I can help engineers to make our products more safer.
Identifying safety requirement is a 2nd step of functional safety activity. Of course, 1st step is safety planning, and it is very important but many people don’t realize its importance.
Anyway, when I review requirements that regards as ‘safety’, I always ask this question to engineers;
“If this requirement doesn’t meet, it directly leads to violate safety goal?”
If it is safety requirement, it shall be always “yes”, but I experienced to get an answer “no” in many cases. Then it is not real safety requirement.
Engineers seem to have a custom to identify them as ‘safety requirement’ which look ‘critical’.
For system which control vehicle, it is critical not to ‘sleep’. But not always for system which report to system which has a responsibility to control.
For control system, detecting who is liar is very important because it directly leads to incorrect decision, which results to control unsafely. Of course ‘not to sleep for a long time’ is also important.
But these principles are not always applicable to “reporters”. To tell a lie is worst. To tell nothing is better.
So, “to be honest” is a very important characteristic for “Subordinates”
To summarize, ask this question always. Do Not determine it with your custom.
the question is “If this requirement doesn’t meet, it directly leads to violate safety goal?”