Every so often, I read an article that really grabs me. I read one the other day in “The Chemical Engineer” magazine (March 2009). The author (Clive de Salis) opens with the sentence …
“To have a SIL- (safety integrity level) rated safety loop is not a success, it’s a failure….”
How could one not read an article with that opening salvo?
It did get me thinking. I visited the IEC (International Electrotechnical Commission) website and found that this international organisation has 375 publications on safety, including IEC61511 (on Safety Instrumented Systems) and IEC61882 (HAZOP Application Guide).
As a process engineer, what does this mean? Is this an “invasion into our expertise”? I have observed many owner / operators are starting to think in line with safety being a subset of instrumentation. Owners are very interested in completing SIL assesments (which I think is good). But … what is in place to ensure the BEST safety system is achieved? Consider a very simple example … high pressure protection of a pipe. Using instrumentation, we will:
measure the pressure with a transmitter (or multiple transmitters with a voting system, if high pressure is critical)
transmit and analyse the pressure reading
implement automated actions based on the pressure reading
maintain the integrity of our 4-20 mA signals, response times, etc
provide the basis for ongoing assessments (for example, a Layer of Protection Analysis – LOPA)
A process engineer will ask … “why did this pipe require instrumented protection? Why not just increase the wall thickness?” There are several possible valid reasons (retrofit, size of pipe and assoicated pipe supports, pipe already in place and new scenario discovered, etc), but was extra wall thickness considered? Was it considered by the people evaluating the safety instrumented system? And this begs the question … if pipe wall thickness is a valid alternative to a safety instrumented system, then should wall thickness (and the associated corrosion monitoring program) be managed with the same level of periodic assessments as safety instrumented systems? And should it be managed by the same department?
Ultimately we have safeguards that are not being designed, installed, and maintained in a uniform manner, but are being used in a unifrom manner for ongoing risk assessment. A LOPA appears to treat all layers equally. I am quite happy if instrumentation engineers become the new safety departement, but I am not clear on what needs to be put into place to ensure the instrumentation engineers (and their associated standards) are multi-discipline and holistic in nature.
What is your view in this matter? Please contact us and let us know. I will share interesting opinions in future newsletters.