SIL Rated Equipment

https://www.crossco.com/resources/articles/determining-safety-integrity-levels-for-your-process-application/

Some and all of those plus of course the almighty insurance company.

Regulations (by national or supra-national authorities) are often vague in their wording that things have to be "adequately" protected.

LoPA / SIL / SIS has been a way of putting numbers and structure to the analysis of risk, severity and frequency.

I think (and I may be way off here) that there is no requirement to use the LoPA analysis and purchase SIL equipment. However if it all went to shit the refinery exploded killed a few caused billions of damage, at the inquiry if you just said. Well we kicked it around over a few beers in the bar and decided we didn't need all that safety equipment then you would probably be in trouble and on the hook personally.

HAZOP / LoPA etc are very good tools that provide a rigorous structure to safety analysis. They have their flaws - HAZOPs can be interminably tedious and repetitive. They are also widely respected and understood and taken as industry standard. I know if I were an insurance assessor and a refinery wanted a quote and they had not carried out either analysis but had done their own company standard methodology I would be very skeptical and would uprate the premiums.

As an engineer with a large number of companies on my CV I like that we all us the same methodology so that I dont need to relearn stuff from company to company.

Similarly we all use API 520 / 521 in sizing and specifying relief valves. There is no reason why one of the super majors would not have done all the research themselves and have their own version but they do not. BP / Shell do have their own standards but they are a growth from API not a reinvention of the wheel.

That said it must be remembered that Industry standards are not always safe. I am old enough to recall when blowdown / depressurization studies started being done. Younger engineers today can not believe that this hadn't always been done but the first equipment I specified only had a relief valve.

It feels a little that I am saying we use SIL because everyone does. Its much better than that its a well researched tool that has proven its worth in use. But its not the only way to do the safety / risk analysis. I don't know what another way would be because I am not clever enough; I dont have the time or money to research another system and so we all use SIL

Thanks for your help!