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Guidance on safe design of non-safety critical systems

Andy Millar

Here's a very good question I've just been asked. For those of us who work in safety critical electronic / programmable designs we have nice clear guidance / standards in the form of IEC 61508 and its derived standards on managing the safe design. But what guidance is there for designers of electronic / programmable systems whose core function is NOT safety related, so it would be over the top to apply 61508 etc, but they could still create some sort of hazard if they were not properly designed? So they should probably be applying a safety V lifecycle at least as a thought process, to make sure that they've thought about the standards that should be applied and any additional safety requirements that should be put in for any residual risks. But how do they know that?

So taking e.g. computer monitor design (just because that's what I'm looking at right now!), if you're designing a new type of monitor, is there a guidance document that takes you through the process of thinking "what hazards might there be? Electric shock, EMC, glare" (I'm making this up by the way so don't shoot me if the example's slightly wrong!) "Ok, we've got standards for the first two, but not for the third, what requirements should we set for that?" "Ok, the designs done, have we met those safety requirements?"

Does anyone know of any good guidance documents etc? Particularly for systems involving software.

    tagging you as I thought you might have some good ideas.

I can appreciate that point of view of the person who originally asked this question (they asked a friend who asked me), I spent the first 10 years of my career designing non-safety critical systems, and the next 30 working on safety critical systems, and there's lots of things I could now tell my 25 year old self!

Thanks,

Andy

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  • 0

    I'm most familiar with RTCA DO-178C, the safety standard or software in aircraft.  That defines a number of safety levels from A (if it goes wrong, people will probably die) down to level D (it will inconvenience the flight crew, increasing the probability of a mistake).  Level E is not safety critical at all.  The amount of "ceremony" increases as you go up the levels.

    Level D should be meetable by good quality software that's been formally tested against a set of requirements.  Level A requires extensive testing and many reviews of requirements, designs, code and all the other work products.

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  • 0

    I'm most familiar with RTCA DO-178C, the safety standard or software in aircraft.  That defines a number of safety levels from A (if it goes wrong, people will probably die) down to level D (it will inconvenience the flight crew, increasing the probability of a mistake).  Level E is not safety critical at all.  The amount of "ceremony" increases as you go up the levels.

    Level D should be meetable by good quality software that's been formally tested against a set of requirements.  Level A requires extensive testing and many reviews of requirements, designs, code and all the other work products.

Children
  • 0 in reply to Simon Barker

    Hi Simon, and similarly in the rail sector we have EN50126/8/9 which do the same. However what we regularly find (although this wasn't the example that started the question, which I believe came from another industry *) is that there are ancillary systems where these don't - or may not need - to be applied, even at the lowest level (Basic Integrity in the case of those standards). A borderline one is ventilation systems, if they are purely to maintain a comfortable temperature the supplier may not (rightly or wrongly) be asked to develop them to standards, if they are for smoke removal to allow safe evacuation during a fire (e.g. on the Elizabeth Line), and therefore have a clear "safety" function, they should be. 

    But probably a better example is the type of equipment which we come across in our daily life and in our homes, where we'd like to feel the developers knew how to think about hazards in the same way that those who do have to work to aerospace, rail, etc standards do.

    * My friend wouldn't tell me what the actual application was that prompted the question, it may be an "if I told you I'd have to shoot you" situation Slight smile

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