There are probably lots more things to add to that list. What could we do to prevent them? Not too much for some… a little more for others. But would those mitigations be practical? What tolerable risk can we accept for these fears and still enjoy life? If I never again swam in the ocean to avoid a shark attack, my life would still be pretty good. But if I had to curtail my traveling to avoid a plane crash, I don’t think I’d be as happy. Life is decided by choices we make… to travel, to live where we want, to swim or surf.
What about this fear: Do you worry if your SIF design is good enough for your safety application? Do you worry if the sensor or valve you selected is good enough? Will it provide a safe state when needed?
That can be a tall order, but manufacturers and certification agencies (like exida) go to great lengths to meet all the necessary requirements of a particular SIL for both hardware and software. It is not easy, but when the parties involved believe in the value and worth of the effort then it is just part of doing a good job. If my keyboard fails while I type this sentence, no harm will befall you or me. I can simply go type my thoughts at another computer. But if a level transmitter gets stuck at a valid in-range value, we may have a serious problem: an overfill, a spill, or possible explosion. We need that transmitter to give us a correct value, or tell us that it is not up to the task via its diagnostics. And we only know how much diagnostic coverage is needed through an analysis of fault modes and effects done against the proper SIL criteria. When safety really matters, I think this is what helps us sleep at night: that we’ve taken a practical and systematic approach to protect against hazards. It’s not too much work if we can mitigate a big risk.
We make a lot of choices for ourselves, and then we have to live with them. But sometimes decisions we make have an influence on other people. When we certify products for functional safety, we have influence on the SIS and SIF designers, and that can have far-reaching effects. We want to keep ourselves safe, but we should also help keep others safe, too.