Project engineering functional safety assessment

All engineering activities follow a predefined overall project work process. The development of a SIS has its own process. Individual steps are mapped into the overall process. Functional safety assessment is carried out at the appropriate stages. 

The project engineering activities have to be formally defined and managed as part of the drive to achieve conformance with functional safety standards. Clause 8 of the lEC standard spells out the requirements for functional safety assessment by independent auditors as was outlined in Chapter 1. 

In this paper the word limitation has been used as a general term to describe any difference fi om the ideal state of the evidence. Counter-evidence is defined in Defence Standard 00-56 as evidence with the potential to undermine safety claims. As Defence Standard 00-56 requires a pro-active search for counterevidence, a limitation needs to be considered as possible counter-evidence unless or until it can be shown that the safety claims are not undermined by that limitation. Suppose for example that a test has failed, and as a result a fault has been found in the software, this limitation (in the correctness of the software) might be counter-evidence. On the other hand if the fault is in some functionality that is not safety related, then it is likely that, fi om a safety perspective, the existence of tire fault is acceptable, and so this limitation is not counter-evidence. Any member of the project who is competent in a particular process area coidd record limitations and assess their impact in relation to the scope of that process. However, counterevidence is wholly related to flie safety of the product and must be assessed by a competent safety professional. Hence it is important that limitations are accurately and transparently recorded in the evidence generated by all of flie project processes and identified in the summary process documents, so that they can be assessed by a safety engineer. 

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