Analysis of design parameters in SIL-4 safety-critical computer

Nowadays, Safety-critical computers are extensively used in may civil domains like transportation including railways, avionics and automotive. We noticed that in design of some previous works, some critical safety design parameters like failure diagnostic coverage (DC) or common cause failure (CCF) ratio have not been seriously taken into account. Moreover, in some cases safety has not been compared with standard safety levels (IEC-61508 SIL1-SIL4) or even have not met them. Most often, it is not very clear that which part of the system is the Achilles' heel and how design can be improved to reach standard safety levels. Motivated by such design ambiguities, we aim to study the effect of various design parameters on safety in some prevalent safety configurations: 1oo2 and 2oo3. 1oo1 is also used as a reference. By employing Markov modeling, sensitivity of safety to each of the following critical design parameters is analyzed: failure rate of processing element, failure diagnostics coverage, common cause failures and repair rates. This study gives a deeper sense regarding influence of variation in design parameters over safety. Consequently, to meet appropriate safety integrity level, instead of improving some system parts blindly, it will be possible to make an informed decision on more relevant parameters.