An Introduction to SIL3
“What is SIL3” is an increasingly common question in automation, but what does it mean?
A common misconception is that SIL3 is a single feature that can be added to a piece of equipment to make it extra safe. SIL3 isn’t a ‘thing’ as such. Rather it is a way of calculating the chances that something will fail in an unpredictable and potentially hazardous way. The higher the SIL number the less likely it is to fail. Levels go from SIL1 to SIL4 with SIL1 being the most basic and SIL4 being your average plane, train or nuclear power station.
If you have ever toyed with buying a new car you will know that they come with numerous options that you can add to the basic model. Manufacturers might even package a number of them together and sell that as the luxury model. Let’s say that you can only upgrade the engine, seats, stereo and paint. But when the manufacturer sells you the luxury version of the car how many of these upgrades have they included? You might assume all of them but is that really the case?
So let’s translate this back to SIL3 and the safety of your equipment. How many parts of that equipment meet this enhanced level of safety known as SIL3? Is the emergency stop SIL3? When the brakes are applied is this done to a SIL3 level? Is the positioning function, the bit that determines where the hoist is moving to, performed to a SIL3 level. There are more but I think you can see my point.
I’ve probably created more questions for you than answers but that is a good thing. Whether your luxury car package actually includes the stereo upgrade is not the difference between someone having an accident or not, how you choose your SIL3 package might be. So if you have questions then be certain to ask your automation supplier those questions and see what they say. But remember not every situation requires every possible safety function to operate at this high level, SIL2 or even 1 might be perfectly acceptable. So if they don’t offer every possible option or you don’t think you need every possible option then that might be just fine. But if you don’t ask then you don’t know and if they can’t tell you, then why don’t they
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