[SystemSafety] A question about ISO26262

DREW Rae d.rae at griffith.edu.au
Thu Feb 16 12:05:38 CET 2017


Dave,
The whole idea of failures as "inability to perform a function" sounds like
a carry-over from 61508's focus on safety systems rather than system
safety.
Your problem goes away if failure is interpreted as "unable to meet
requirements, including safety requirements".

As with most safety standards, if it is applied and regulated with good
will and the intent to produce a safe system, you can fit the definitions
to the situation.

If someone wants to insist that a component which is spamming another
component whilst still doing its own job hasn't technically "failed" so
doesn't need to be fixed, you've got bigger problems than the precise
wording of the standard.

Drew

My safety podcast: disastercast.co.uk
My mobile: 0450 161 361

On 16 February 2017 at 20:37, David Haworth <david.haworth at elektrobit.com>
wrote:

> Hi everyone,
>
> I've just been reading in detail the definition of freedom
> from interference given in ISO26262, and it occurred to me
> that the definition might not be exactly what was intended.
>
> The following definitions are taken from ISO 26262-1:2011
> but the 2016 edition is not significantly different.
>
> "Freedon from interference" means:
>   absence of cascading failures between two or more elements that
>   could lead to the violation of a safety requirement
>
> where a "cascading failure" is:
>   failure of an element of an item causing another element or
>   elements of the same item to fail
>
> and "failure" means:
>   termination of the ability of an element to perform a function
>   as required
>
> However, it is possible to imagine scenarios where, in the absence
> of a protection mechanism, an element causes another element to fail
> while still continuing to perform its own function flawlessly.
>
> Any thoughts on the matter?
>
> All the best,
> Dave
>
> --
> David Haworth   OS Kernel Developer
> david.haworth at elektrobit.com
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