Safety Integrity Levels (SILs) are four discrete levels of safety performance of safety-related systems that use electrical and/or electronic and/or programmable electronic (E/E/PE) technologies as defined in IEC 61508.
To minimise dangerous failures of such systems, R2A typically uses the following process to determine the required safety allocation of E/E/PE SIL. The process involves the following tasks:
- Establish all credible, critical threat/hazard scenarios.
- Develop threat barrier sequences.
- Determine barrier SILs.
- Allocate and determine E/E/PE SILs (if required).
- Analyse E/E/PE SIL hazard control system failures.
- Review sign-off.
R2A’s experience is that such a process would satisfy safety case arguments for E/E/PE SIL allocation since, inter alia, it should be comprehensible to judges and juries as well as senior management, that is, satisfy the requirements of the WHS act and the common law and thereby demonstrate due diligence.