71:
target. The difference between the unmitigated risk and the tolerable risk, if the unmitigated risk is higher than tolerable, must be addressed through risk reduction of provided by the SIF. This amount of required risk reduction is correlated with the SIL target. In essence, each order of magnitude of risk reduction that is required correlates with an increase in SIL, up to a maximum of SIL4. Should the risk assessment establish that the required SIL cannot be achieved by a SIL4 SIF, then alternative arrangements must be designed, such as non-instrumented safeguards (e.g, a
366:
functional safety capability (FSC) of the organization, usually by assessment of its functional safety management (FSM) program, and the assessment of the design and life-cycle activities of the product to be certified, which is conducted based on specifications, design documents, test specifications and results,
70:
Assignment, or allocation of SIL is an exercise in risk analysis where the risk associated with a specific hazard, which is intended to be protected against by a SIF, is calculated without the beneficial risk reduction effect of the SIF. That unmitigated risk is then compared against a tolerable risk
365:
among others. Self-certification is also possible. The requirements of these schemes can be met either by establishing a rigorous development process, or by establishing that the device has sufficient operating history to argue that it has been proven in use. Certification is achieved by proving the
147:
is SIL 2". According to IEC 61508, the SIL concept must be related to the dangerous failure rate of a system, not just its failure rate or the failure rate of a component part, such as the software. Definition of the dangerous failure modes by safety analysis is intrinsic to the proper determination
179:
The SIL requirements for hardware safety integrity are based on a probabilistic analysis of the device. In order to achieve a given SIL, the device must meet targets for the maximum probability of dangerous failure and a minimum safe failure fraction. The concept of 'dangerous failure' must be
180:
rigorously defined for the system in question, normally in the form of requirement constraints whose integrity is verified throughout system development. The actual targets required vary depending on the likelihood of a demand, the complexity of the device(s), and types of redundancy used.
348:
Hazards of a control system must be identified then analysed through risk analysis. Mitigation of these risks continues until their overall contribution to the hazard are considered acceptable. The tolerable level of these risks is specified as a safety requirement in the form of a target
536:
139:"This system is a SIL N system because the process adopted during its development was the standard process for the development of a SIL N system", or use of the SIL concept out of context such as "This is a SIL 3
53:
standard, four SILs are defined, with SIL4 being the most dependable and SIL1 the least. The applicable SIL is determined based on a number of quantitative factors in combination with qualitative factors, such as
377:
Electric and electronic devices can be certified for use in functional safety applications according to IEC 61508. There are a number of application-specific standards based on or adapted from IEC 61508, such as
352:
Certification schemes, such as the CASS Scheme (Conformity
Assessment of Safety-related Systems) are used to establish whether a device meets a particular SIL. Third parties that can provide certification are
560:
A Methodology for the
Assignment of Safety Integrity Levels (SILs) to Safety-related Control Functions Implemented by Safety-related Electrical, Electronic and Programmable Electronic Control Systems of
740:
448:
394:
102:
The assignment may be tested using both pragmatic and controllability approaches, applying industry guidance such as the one published by the
467:
157:
106:. SIL assignment processes that use the HSE guidance to ratify assignments developed from Risk Matrices have been certified to meet
362:
707:
693:
669:
642:
382:
for the process industry sector. This standard is used in the petrochemical and hazardous chemical industries, among others.
95:
Of the methods presented above, LOPA is by far the most commonly used in large industrial facilities, such as for example
736:
508:
679:
610:
576:
516:
371:
358:
118:
There are several problems inherent in the use of safety integrity levels. These can be summarized as follows:
88:
602:
568:
103:
78:
There are several methods used to assign a SIL. These are normally used in combination, and may include:
59:
43:
131:
System complexity, particularly in software systems, making SIL estimation difficult to impossible.
595:
Methods for
Assessing the Safety Integrity of Safety-related Software of Uncertain Pedigree (SOUP)
760:
473:
725:
634:
593:
403:(functional safety of electrical/electronic/programmable electronic safety related systems)
505:
Safety
Integrity Level Selection: Systematic Methods Including Layer of Protection Analysis
17:
349:'probability of a dangerous failure' in a given period of time, stated as a discrete SIL.
8:
478:
122:
Poor harmonization of definition across the different standards bodies which utilize SIL.
191:) of low demand operation for different SILs as defined in IEC EN 61508 are as follows:
451:(guidelines for safety analysis, modelling, and programming in automotive applications)
703:
689:
665:
638:
606:
572:
512:
136:
31:
390:
The following standards use SIL as a measure of reliability and/or risk reduction.
662:
Practical SIL Target
Selection – Risk Analysis per the IEC 61511 Safety Lifecycle.
558:
429:
EN 50129 (railway applications – safety related electronic systems for signalling)
397:(functional safety of safety instrumented systems for the process industry sector)
765:
55:
744:
140:
96:
754:
426:
EN 50128 (railway applications – software for railway control and protection)
436:
367:
72:
62:. Other standards, however, may have different SIL number definitions.
268:
For continuous operation, these change to the following, where PFH is
730:
537:"Understanding the Use, Misuse, and Abuse of Safety Integrity Levels"
442:
418:
412:
406:
400:
379:
354:
161:
107:
50:
686:
Functional Safety – An IEC 61508 SIL 3 Compliant
Development Process
432:
EN 50657 (railway applications – software on board of rolling stock)
46:(SIF), i.e. the measurement of the performance required of the SIF.
144:
42:) is defined as the relative level of risk-reduction provided by a
592:
Jones, C.; Bloomfield, R.E.; Froome, P.K.D.; Bishop, P.G. (2001).
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defines SIL using requirements grouped into two broad categories:
700:
Functional Safety for the Mining and
Machinery-based Industries
461:
530:
528:
591:
509:
421:(implementing IEC 61508 in the domain of machinery safety)
525:
557:
Charlwood, Mark; Turner, Shane; Worsell, Nicola (2004).
719:
409:(implementing IEC 61508 in the process industry sector)
556:
172:. A device or system must meet the requirements for
633:(4th ed.). Kidlington and Cambridge, Mass.:
128:Estimation of SIL based on reliability estimates.
752:
415:(implementing IEC 61508 in the nuclear industry)
49:In the functional safety standards based on the
629:Smith, David J.; Simpson, Kenneth G.L. (2016).
135:These lead to such erroneous statements as the
125:Process-oriented metrics for derivation of SIL.
660:Hartmann, H.; Thomas, H.; Scharpf, E. (2022).
502:
151:
503:Marszal, Edward M.; Scharpf, Eric W. (2002).
628:
702:(2nd ed.). Tenambit, N.S.W.: Marcus Punch.
270:probability of dangerous failure per hour.
185:probability of dangerous failure on demand
468:High-integrity pressure protection system
158:International Electrotechnical Commission
676:SIL and Functional Safety in a Nutshell
534:
14:
753:
601:. Research Report 337/2001. Sudbury:
631:The Safety Critical Systems Handbook
624:
622:
498:
496:
494:
176:categories to achieve a given SIL.
24:
654:
25:
777:
713:
619:
491:
65:
733:- The IEC functional safety site
731:IEC Safety and functional safety
726:Functional Safety, A Basic Guide
567:. Research Report 216. Sudbury:
507:. Research Triangle Park, N.C.:
462:As low as reasonably practicable
684:Medoff, M.; Faller, R. (2014).
678:(2nd ed.). Prime Intelligence.
585:
550:
13:
1:
737:Safety Integrity Level Manual
485:
385:
357:(previously known as SIRA),
89:Layer of protection analysis
44:safety instrumented function
7:
674:Houtermans, M.J.M. (2014).
455:
170:systematic safety integrity
152:SIL types and certification
113:
10:
782:
342:100,000,000–1,000,000,000
166:hardware safety integrity
27:Measure in risk analysis
722:- The 61508 Association
535:Redmill, Felix (2000).
474:Reliability engineering
336:0.00000001-0.000000001
328:10,000,000–100,000,000
97:chemical process plants
698:Punch, Marcus (2013).
36:safety integrity level
635:Butterworth-Heinemann
445:(automotive industry)
322:0.0000001-0.00000001
314:1,000,000–10,000,000
189:risk reduction factor
148:of the failure rate.
73:pressure relief valve
60:lifecycle management
479:Spurious trip level
308:0.000001-0.0000001
688:(3rd ed.). Exida.
300:100,000–1,000,000
160:'s (IEC) standard
708:978-0-9807660-0-4
694:978-1-934977-08-8
670:978-1-934977-20-0
644:978-0-12-805121-4
355:CSA Group Testing
346:
345:
294:0.00001-0.000001
266:
265:
32:functional safety
16:(Redirected from
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56:risk assessments
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680:ASIN B00MTWSBG2
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262:10,000–100,000
256:0.0001–0.00001
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116:
68:
28:
23:
22:
15:
12:
11:
5:
779:
769:
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761:Process safety
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66:SIL allocation
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26:
9:
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4:
3:
2:
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745:Pepperl+Fuchs
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612:0-7176-2011-5
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605:. p. 6.
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437:gas detection
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540:. Retrieved
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395:ANSI/ISA S84
389:
376:
368:failure rate
351:
347:
283:PFH (power)
269:
267:
248:1000–10,000
203:PFD (power)
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39:
35:
29:
228:0.01–0.001
187:) and RRF (
143:" or "This
85:Risk graphs
58:and safety
755:Categories
747:SIL Manual
486:References
720:61508.org
603:HSE Books
569:HSE Books
443:ISO 26262
419:IEC 62061
413:IEC 61513
407:IEC 61511
401:IEC 61508
386:Standards
380:IEC 61511
234:100–1000
214:0.1–0.01
162:IEC 61508
137:tautology
108:IEC 61508
51:IEC 61508
741:Archived
561:Machines
456:See also
439:systems)
339:10 – 10
325:10 – 10
311:10 – 10
297:10 – 10
259:10 – 10
245:10 – 10
231:10 – 10
217:10 – 10
145:software
114:Problems
664:Exida.
470:(HIPPS)
464:(ALARP)
374:, etc.
220:10–100
766:Safety
706:
692:
668:
641:
609:
575:
542:7 July
515:
361:, and
104:UK HSE
91:(LOPA)
599:(PDF)
565:(PDF)
481:(STL)
449:MISRA
372:FMEAs
363:Exida
183:PFD (
743:) -
704:ISBN
690:ISBN
666:ISBN
639:ISBN
607:ISBN
573:ISBN
544:2023
513:ISBN
286:RRF
280:PFH
277:SIL
206:RRF
200:PFD
197:SIL
174:both
168:and
156:The
18:SIL4
359:TüV
75:).
40:SIL
30:In
757::
637:.
621:^
571:.
527:^
511:.
493:^
333:4
319:3
305:2
291:1
253:4
239:3
225:2
211:1
110:.
99:.
34:,
739:(
647:.
615:.
581:.
546:.
521:.
38:(
20:)
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