Re: [SystemSafety] WG: words you cannot use at GM

From: Nancy Leveson < >
Date: Thu, 22 May 2014 11:18:25 -0400

There is nothing wrong with saying "acceptably safe" (of course you need to
define what you mean by "acceptable" or the statement is useless). The
problem is in *defining* "safe" as "acceptably safe" and then simply
declaring that the system is "safe." Safe is not the same as "acceptably
safe with a probability of 10^-9 (or whatever).

Nancy

On Thu, May 22, 2014 at 9:25 AM, <peter.sheppard_at_xxxxxx
> wrote:

>
> I don't see what is wrong with "acceptably safe". No system is ever 100%
> safe, thus an expert, professional judgement on what is acceptably safe has
> to be made.
>
> In the UK railways it was agreed that "acceptably safe" for rail workers
> was different to what "acceptably safe" was for passengers (still can't
> call them customers!)
>
> Regards
>
> Peter
>
> Peter Sheppard
> Senior Safety Engineer and Validator
>
> Mobile: +44 7920 247931
>
>
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> drucken
>
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>
>
> *Peter Bernard Ladkin <ladkin_at_xxxxxx > <ladkin_at_xxxxxx > Sent by: systemsafety-bounces_at_xxxxxx > 22/05/2014 13:46
> To
> systemsafety_at_xxxxxx > cc
> Subject
> Re: [SystemSafety] WG: words you cannot use at GM
>
>
>
>
>
>
> On 2014-05-22 14:31 , Nancy Leveson wrote:
> > I think saying that "acceptably safe" is safe is a ridiculous
> definition.
>
> Nevertheless, it is de rigeur in Europe. The UK Health and Safety
> Executive says that is how it
> judges, with "acceptably safe" usually meaning a one in a million elevated
> chance of dying:
> http://www.hse.gov.uk/risk/theory/r2p2.htm
>
> PBL
>
> Prof. Peter Bernard Ladkin, Faculty of Technology, University of
> Bielefeld, 33594 Bielefeld, Germany
> Tel+msg +49 (0)521 880 7319 www.rvs.uni-bielefeld.de
>
>
>
>
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-- 
Prof. Nancy Leveson
Aeronautics and Astronautics and Engineering Systems
MIT, Room 33-334
77 Massachusetts Ave.
Cambridge, MA 02142

Telephone: 617-258-0505
Email: leveson_at_xxxxxx
URL: http://sunnyday.mit.edu



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Received on Thu May 22 2014 - 17:18:37 CEST

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