[SystemSafety] Who applies risk acceptance principles - Part 2

[nfr]

I am sure that most on this list will recognise that the criteria defined in the "design targets" below do not meet the UK's legal requirement. Reducing risks "so far as is reasonably practicable" does not allow for ceasing the reduction because some arbitrary numeric value (of accident probability or frequency) is deemed to have been achieved.

The UK Regulator's guidance (ALARP - as low as reasonably practicable) puts forward thresholds as guidance on when the approach to assessing the risk in hand might reasonably be adjusted, but the thresholds are not determinants of when risk reduction should cease.

Felix.



On 4 Jun 2013, at 12:08, ECHARTE MELLADO JAVIER wrote:

Myriam,
There is a new ERA Report about Risk Acceptance,  involving a “validation process”.
http://www.era.europa.eu/Document-Register/Pages/RAC-note-1-2013.aspx
Basically, this is the proposal:
The following design targets shall apply to failures of functions of technical systems:
(a) For a failure that has a typical credible potential to lead directly to an accident affecting a
group of people and resulting in fatalities and/or severe injuries and/or major damages to
the environment, the frequency of the failure of the function does not have to be reduced
further if it is demonstrated to be less than or equal to 10-9 failures per operating hour.
(b) For a failure that has a typical credible potential to lead directly to an accident affecting an
individual person and resulting in fatality and/or severe injury, the frequency of the failure of
the function does not have to be reduced further if it is demonstrated to be less than or
equal to 10-7 failures per operating hour.
(c) For a failure that has a typical credible potential to lead directly to an accident resulting in
one or more light injuries, the frequency of the failure of the function does not have to be
reduced further if it is demonstrated to be less than 10-5 failures per operating hour

The document includes some clarification and doubts, please read it before discussing it.
I think that it is better to define a proper risk matrix (adjusting the CENELEC 50126 one, for example). But in any case, the “old paradigm of 10e-9” do not make sense, in my opinion…
Javier Echarte
Altran Spain.

De: systemsafety-bounces at techfak.uni-bielefeld.de<mailto:systemsafety-bounces at techfak.uni-bielefeld.de> [mailto:systemsafety-bounces at techfak.uni-bielefeld.de] En nombre de M Mencke
Enviado el: jueves, 20 de septiembre de 2012 10:53
Para: systemsafety at techfak.uni-bielefeld.de<mailto:systemsafety at techfak.uni-bielefeld.de>
Asunto: [SystemSafety] Who applies risk acceptance principles - Part 2

Hello everybody,

A couple of months ago I started a thread under the subject "Who applies risk acceptance principles?", particularly in the railway field. With "who" I was referring to whether the client or the supplier should define what is a reasonable Tolerable Hazard Rate for a hazard associated and the risk associated with that hazard. Some people interpreted the question as "who" (in general) applies Probabilistic Risk Assessment.

Recently I have found some further answers to that question, particularly since a report regarding the revision of EC 352/2009 has been published. It is named "ERA_REC_02-2012_SAF - Accompanying Report on revision of CSM on risk assessment.doc".

The report confirms what I already suspected - there aren't any harmonised Risk Acceptance Criteria for Technical Systems for Railway, except for failures of functions with potential for catastrophic failure (4.3.1). They are only applied in aviation, nuclear and maritime sectors (Section 3.4.3).

I would recommend this report to anyone working in railway RAMS. Its title is "Agency report on the experience with the existing regulation (EC) No352/2009 on a common safety method on risk evaluation and assessment and on the revision of that regulation".

Kind Regards,

Myriam
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