Archives For fail safe

Toyota ECM (Image source: Barr testimony presentation)

Economy of mechanism and fail safe defaults

I’ve just finished reading the testimony of Phil Koopman and Michael Barr given for the Toyota un-commanded acceleration lawsuit. Toyota settled after they were found guilty of acting with reckless disregard, but before the jury came back with their decision on punitive damages, and I’m not surprised.

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Buncefield Tank on Fire (Image Source: Royal Chiltern Air Support Unit)

Why sometimes simpler is better in safety engineering.

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In June of 2011 the Australian Safety Critical Systems Association (ASCSA) published a short discussion paper on what they believed to be the philosophical principles necessary to successfully guide the development of a safety critical system. The paper identified eight management and eight technical principles, but do these principles do justice to the purported purpose of the paper?

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One of the canonical design principles of the nuclear weapons safety community is to base the behaviour of safety devices upon fundamental physical principles. For example a nuclear weapon firing circuit might include capacitors in the firing circuit that, in the event of a fire, will always fail to open circuit thereby safing the weapon. The safety of the weapon in this instance is assured by devices whose performance is based on well understood and predictable material properties.
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I’ve recently been reading John Downer on what he terms the Myth of Mechanical Objectivity. To summarise John’s argument he points out that once the risk of an extreme event has been ‘formally’ assessed as being so low as to be acceptable it becomes very hard for society and it’s institutions to justify preparing for it (Downer 2011).

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It appears that the underlying certification basis for aircraft safety in the event of a intermediate power turbine rotor bursts is not supported by the rotor failure seen on QF 32.

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Tweedle Dum and Dee (Image source: Wikipedia Commons)
How do ya do and shake hands, shake hands, shake hands. How do ya do and shake hands and state your name and business…

Lewis Carrol, Through the Looking Glass

You would have thought after the Leveson and Knight experiments that the  theory that independently written software would only contain independent faults was dead and buried, another beautiful theory shot down by hard cold fact.  But unfortunately like many great errors the theory of n-versioning keeps on keeping on (1).
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