Comparing Control Ratings

Alex Apostolou

Have you wondered how all the control ratings compare and how reliable a control is in the real-world? If so, this table might help.

It makes you realise that Soft Controls, those controls which are performed by people, need to have a lot of planning, infrastructure, training, oversight, etc. surrounding them to warrant anything by the lower-end of the ratings.

Standard Qualitative Values Quantitative Control Effectiveness Values Downtime per year
Effectiveness RRF PFD SIL Integrity minutes hours days
Assessed 1 1.0000 0.0 0.00000 525960 8766 365.25
Requires Improvement 3 0.3333 0.5 0.66667 175320 2922 121.75
Adequate 10 0.1000 1.0 0.90000 52596 877 36.53
Strong 30 0.0333 1.5 0.96667 17532 292 12.18
Excellent 100 0.0100 2.0 0.99000 5260 88 3.65
300 0.0033 2.5 0.99667 1753 29 1.22
1000 0.0010 3.0 0.99900 526 9 0.37
3000 0.0003 3.5 0.99967 175 3 0.12
10000 0.0001 4.0 0.99990 53 1 0.04

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