SIL
Contents
Introduction
Safety Integrity Level (SIL) is defined as a relative level of risk-reduction provided by a safety function, or to specify a target level of risk reduction. In simple terms, SIL is a measurement of performance required for a Safety Instrumented Function (SIF).
| SIL | PFD | RRF |
|---|---|---|
| 1 | 0.1-0.01 | 10-100 |
| 2 | 0.01-0.001 | 100-1000 |
| 3 | 0.001-0.0001 | 1000-10,000 |
| 4 | 0.0001-0.00001 | 10,000-100,000 |
Selection of SIL
There are many methods to select the safety Integrity Level, these include, Risk Matrix, Risk Graph, Layers of Protection Analysis (LOPA). With regards to LOC NASA has considerably lower levels of safety then in comparison to industry because, the crew are not considered civilians, and the gains of space exploration to be with the risk at least in terms of LOC.
Bellow is what is a graph of what is considered acceptable and intolerable in terms of fatalities by (HSE Books 2001)[1]. Of course these graphs would very depending on the size of the population and the significance of the endeavor.
Sill Selection Matrices
LOPA (Layers of Protection Analysis
Risk Graphs
Refferences
[1] - http://4-sightconsulting.co.uk/Current_Papers/Determining_SILs/Methods_of_Determining_Safety_Integrity_Level.pdf - Methods of Determining Safety Integrity Level (SIL) Requirements - Pros and Cons by W G Gulland (4-sight Consulting)
[2] http://www.iceweb.com.au/sis/target_sis.htm - Techniques for Assigning A Target Safety Integrity Level Angela E. Summers, Ph.D. This paper was published in ISA Transactions 37 (1998) 95-104.
