3 types of QM?

We were recently guiding the Software team of an organization, on writing Software Safety requirements (SSR). During a review, we asked them if they have written the Safety-relevant QM requirements in the SSR document. The Software team was surprised - "Should we write QM requirements in an SSR document? Shouldn't that not be done in a separate requirements document as per QM process?", they asked. "Yes and No" - we said. "Depends on which type of QM it is". "What do you mean by type of QM?" they raised their eyebrows, puzzled.

In this article, we will explain the many shades of QM Requirements, and what kind of "QM" requirements must be written in a Safety requirement document (be it a TSR, SSR or HSR). Please note that ISO 26262 never talks about different types of QM explicitly, and the ideas shared in this article is coming from our experience.

Broadly, QM Requirements can be classified as follows - 

1. Non-Safety-relevant (NSR) QM
2. QM that is safety-relevant
• Diagnostic QM requirements
• Decomposed QM requirements

The diagram below summarizes these 3 types of QM for an easier understanding.

Typically, the requirements for 2 and 3 must be covered while writing safety requirements at System, SW and HW level. However, these requirements need not be implemented as ASIL, it is still implemented as per QMS process.  The requirements for 1 are not relevant for Safety, so it is typically also written in a separate requirements document as per QMS process.

QM(B) requirements are also considered during the Safety analysis and dependent failure analysis to prove that the safety mechanism at ASIL level has achieved independence from the decomposed QM requirements.

We hope this article brings more clarity to those writing safety requirements. Please do drop us a note if you have further questions on this topic!