In rare cases, and I came across one the other day, you can achieve a SIL 3 with a single instrument. In this case it was a Durag flame detector, with a SFF > 99%, due to the extensive self testing and diagnostics built in.First of all, SIL 2 certified equipment means that the probability of failure on low demand (In other words, the safety function fails to do its job when called upon) is ≥〖10〗^(-3)<〖10〗^(-2) according to IEC 61508.
Based on that if you are having a Simplex FACP panel but certified with the above it can be a SIL2 otherwise it is not.
Generally redundancy (Dual and above) provides the hardware fault tolerance feature which helps to achieve SIL3 levels or even SIL4.
The highest achievable SIL with an non HFT system is SIL 2.
yes supplier do like to stretch the truth about their products, I've been involved with safety rated systems....most of them a tissue box of liesWell that snookers all my experiences in the Chemical Industry ! ........
Completely fail safe - I don’t believe it .
If I were involved in SIL rated designs using Durag (have used other flame detectors) I would ignore it’s certification and query why it could not fail to danger.
Having done SIL rated designs with fail to danger information (many manufacturers decline to supply), it makes the accuracy of calculation very much easier; and a little kudos to the manufacturers who supply it.
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