The ratio ranged from 2X to 4X based on product type. The differences seem to be related to site training, site procedures and other variables that some have called “Safety Culture.”
| Level | Description |
|---|---|
| SSI 4 | Perfect - Repairs are always correctly performed. Testing is always done correctly and on schedule, equipment is always replaced before end of useful life, equipment is always selected according to the specified environmental limits and process compatible materials, electrical power supplies are clean of transients and isolated, pneumatic supplies and hydraulic fluids are always kept clean, etc. This level is generally considered to be extremely hard to achieve, but possible in some organizations. |
| SSI 3 | Almost Perfect - Repairs are correctly performed. Testing is done correctly and on schedule, equipment is normally selected based on the specified environmental limits and a good analysis of the process chemistry and compatible materials. Electrical power supplies are normally clean of transients and isolated, pneumatic supplies and hydraulic fluids are mostly kept clean, etc. Equipment is replaced before end of useful life, etc. |
| SSI 2 | Good - repairs are usually correctly performed. Testing is done correctly and mostly on schedule, most equipment is replaced before end of useful life, etc. |
| SSI 1 | Medium - Many repairs are correctly performed. Testing is done and mostly on schedule, some equipment is replaced before end of useful life, etc. |
| SSI 0 | None - Repairs are not always done. Testing is not done, equipment is not replaced until failure, etc. |
SSI is a quantitative model that allows the impact from what many people call “systematic failures” to be realistically included in SIL verification. SSI can provide a way to show the cost impact of alternative operational and maintenance processes.
SSI can be comprehensively evaluated with an on-site third party audit. Those interested in this service, please contact exida.