Re: [SystemSafety] SIL ratings to be scrapped?

From: Inge, James Mr < >
Date: Fri, 23 Aug 2013 11:22:05 +0100


I believe that the aim of making these UK Defence Standards goal based was to allow flexibility, so that the MOD could specify the requirements it needs to meet its duty of care, but still gain the benefit of using the most appropriate modern industry standards. As John points out, specifying a particular system in the Def Stans caused confusion as they were different to the various different systems specified in other standards. Making Def Stan 00-56 goal based means that suppliers could propose to use standards like IEC61508, DO178C, ISO26262, or whatever is most appropriate for the project. If there was a need to use a particular standard for some reason, this could still be specified as a project-specific requirement.  

From: systemsafety-bounces_at_xxxxxx Sent: 23 August 2013 11:00
To: 'Bielefield SafetyList'
Subject: Re: [SystemSafety] SIL ratings to be scrapped?  

It is interesting to see this evolution in UK while at the same time the major defense operators (DCNS, Nexter, EADS, ...) in France are adopting IEC61508 straightforward and including it in their requirements, included for retrofits ...  

Bertrand RICQUE

Program Manager, Optronics and Defense Division  

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From: systemsafety-bounces_at_xxxxxx Sent: Friday, August 23, 2013 11:56 AM
To: 'Inge, James Mr'; 'Bielefield SafetyList' Subject: Re: [SystemSafety] SIL ratings to be scrapped?  

The SILs of the Defence Standard were different from those of IEC61508, which fact I have seen cause problems on more than one project...

I would not be at all surprised if the chattering classes take a DEF.STAN. change made almost a decade ago as an indicator of an imminent change in 61508.

From: systemsafety-bounces_at_xxxxxx Sent: 23 August 2013 10:41
To: Bielefield SafetyList
Subject: Re: [SystemSafety] SIL ratings to be scrapped?  

It is possible that this rumour might relate to the current work underway to revise Def Stan 00-55, Requirements for Safety Related Software in Defence Systems.  

A system of SILs was defined Def Stan 00-56 Issue 2, Safety Management Requirements for Defence Systems (1996), which was also used in Def Stan 00-55. However, SILs were removed from the mandatory part of 00-56 in Issue 3 (2004) as part of the move to a goal-based approach to requirements setting. Instead, the guidance in 00-56 Part 2 discussed setting integrity requirements in generic terms, rather than using a specific SIL scheme. However, the guidance made it clear (in Annex C, section C.2) that SIL schemes could still be used where they were suitable.  

Def Stan 00-55 was made obsolescent by the release of 00-56 Issue 3, and has not been re-issued. However, new work is currently underway to revise both standards. I have not seen recent drafts, but it is likely that neither standard will define a system of SILs, or require use of a specific SIL scheme. That said, it is also likely that use of suitable standard that incorporates SILs or a similar concept could still be part of the argument to demonstrate compliance with either 00-55 or 00-56.  

Regards,  

          James Inge    


Sent: 21 August 2013 16:59
To: safetyyork_at_xxxxxx Subject: Re: [SystemSafety] SIL ratings to be scrapped?  

I think there may have been a misunderstanding somewhere along the way here.  

UK MoD implemented the use of SILs into many of their projects a few years ago and these are now being replaced by

SIRs - Safety Integrity Requirements ( High / Medium / Low) . . . Don't know if this is a pointer in any direction . . .  

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Sent: 21 August 2013 15:26
To: 'Bielefield Safety List'
Subject: [SystemSafety] SIL ratings to be scrapped?  

Hi all,  

I have just been taking to one of my customers who do control systems for industrial systems. They have been told by someone they are doing a system for that SIL ratings will "soon be scrapped". Apparently "It will be replaced by ALARP". This seems like a completely misunderstood half a message. Though usually on this sort of thing there is a grain of reality (if miss reported or miss represented) in there somewhere.  

I know I have not been paying attention over the summer but I haven't seen anything. Is there a move on any standard to change from SIL ratings for projects?    

Regards

     Chris     

Eur Ing Chris Hills BSc CEng MIET MBCS FRGS FRSA Technical Specialist Phaedrus Systems Ltd Tel: FREEphone 0808 1800 358 Vat GB860621831 Co Reg #04120771
Http://www.phaedsys.com <http://www.phaedsys.com/> chills_at_xxxxxx    


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systemsafety_at_xxxxxx Received on Fri Aug 23 2013 - 12:22:28 CEST

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