[SystemSafety] SILs and Security Levels

[Maier, Thomas]

The standard uses "required safety integrity level", and also "required safety integrity" in its text throughout. However it is not a formally defined term.
There is no "achieved SIL", but the standard speaks about achieving the safety integrity level in its system realisation requirements.
The concept of SIL capability is not covered by a definition either. IEC 61508 does however use the concept of "compliant item", where the item is either a subsystem or element (both terms are formally defined concepts), and contains precise requirements on the information to be provided for a compliant item. The part of that information pertaining to safety integrity (in terms of fault tolerance, diagnostic coverage, failure behavior, failure rates, systematic capability) could be referred to as "SIL Capability".

Derived standards have defined terms to express the concept of SIL capability for a subsystem, as opposed to a plain SIL for a system-level safety function. IEC 62061  for example uses "SIL Claim Limit". IEC 61800-5-2 uses "SIL Capability" directly.

I would agree that most users of IEC 61508 are able to distinguish between these different SIL types or views and apply them correctly. Nevertheless it would be good if the standard introduced formal definitions. It will IMO not be difficult at all to do that, at least from a purely technical perspective.

Med venlig hilsen / Best regards / Mit freundlichen Grüssen

Thomas Maier
T: +45 42 13 74 52
E: Thomas.Maier at ul.com

-----Original Message-----
From: systemsafety [mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of Coq, Thierry
Sent: Tuesday, April 26, 2016 9:59 AM
To: systemsafety at lists.techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] SILs and Security Levels

Oh my, us poor sods using 61508, we have never seen the difference between a required SIL and an achieved SIL....
Please.

Best regards,
Thierry Coq
Mobile +33 06 80 44 57 92
www.dnvgl.com
The opinion expressed here is entirely my own!


-----Original Message-----
From: systemsafety [mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of Martyn Thomas
Sent: mardi 26 avril 2016 16:53
To: systemsafety at lists.techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] SILs and Security Levels

That seems an excellent starting position for work improving 61508.
There will be many details to be agreed, so when do we start?

Martyn



 On 26/04/2016 08:40, Peter Bernard Ladkin wrote:
> Ingo Rolle is a member of this list and the Secretary of the German
> National Committee responsible for matters concerning IEC 61508 as well as Secretary of the GNC responsible for IEC 62443 matters.
> The abnormaldistribuation blog has just published an essay from him on
> a suggestion for a refined allocation of SIL.
>
> http://www.abnormaldistribution.org/2016/04/26/sils-the-safety-related
> -system-lifecycle-and-security-level-ingo-rolle/
>
>



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