Many (perhaps even most) EPCs and Owner companies do not really understand best practices related to risk analysis and independent protection layers (IPLs). This is unfortunate. This lack leads to a lot of wasted resources. Also, many owner companies do not implement the management systems and discipline needed to maintain IPLs once identify. It is Far more important to properly maintain and test the IPLs you have (including human IPLs) than to add more IPLs. We have still not found a major accident that was safeguarded by two, properly sized/designed and properlu maintained IPLs. The major accidents occur when IPLs are NOT truly independent, or not size/design right, or not Maintained/Tested (including human IPLs). So, a shortcut to LOPA (and all risk assessments) is:
- Do we have 2 true IPLs against this scenario? (including are the IPLs truly Independent?)
- Are the IPLs designed and implemented Properly?
- Are the IPLs validated in the field often enough?
- Do we retain the validation data?
If so, the major accident will not happen in the life of the facilty. But, since all of the questions above are really part of making sure the IPLs are each valid, an even shorter risk assessment would be:
- Do we have 2 true IPLs against this scenario?
- Are both truly needed for this scenario?
Using these questions you will also never see the scenario occur. But with the Two question approach, you will also end up with only one IPL in many cases, which for pressure vessels protected by a PSV, may be enough safeguarding, in many cases.
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