“As an interested but unschooled outsider, I confess to finding the topic of SIL, or Safety Integrity Level(s), to use the proper name, rather complex and hard to grasp.”
Well, that opened the proverbial floodgates and quite a number of readers kindly wrote in with advice and guidelines.
Now, without wanting to ignore anyone, I would like to make special mention of the e-mail I received from Mr Michael Mitchell at Cameron Flow Control.
In turns out that Mike actually presented a paper on this very subject during the Valve World 2010 Conference last December called, would you believe it, “SIL Made Simple”!
During his presentation he explained, in plain language, what SIL means, how it is determined, the relationship between SIL and failure rates and how SIL applies to particular products.
Sadly I missed that particular lecture, but fortunately Mr Mitchell still had a copy of his notes which he sent on.
So I have just spent a very instructive thirty minutes reading (and re-reading!) his text, which is well-written and very clear.
I now know, for example, why it is wrong to say “this is a SIL 4 actuator”.