This is one of a set of three questions undertaken in mock exam conditions.
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An interesting approach to answering a brief but broad question.
Within the first "definitions" section, I think that "Standards" should have been interpreted more widely; probably too much emphasis on "Railway Group Standards" which are only applicable to specifying the interface between Network Rail as the Infrastructure Manager and the various Train Operating Companies as the Railway Undertakings- they have no relevance (other than of course potentially being a "reference design" or incorporating "good practice") to any other railway. London Underground has its own suite of standards which are very different in content and character, the various minor railways in the UK have no requirement to conform, railways elsewhere all have their own standards. There is a wide range of non industry specific standards which a railway should follow (e.g. BS7671); typically being able to demonstrate compliance to a suitable set of standards is a good means by which one can stay legal (and can form a reasonable defence if in the end something nasty happens and one is then accused of not complying with the law!).
I felt that the answer spent too much time explaining the distinctions rather than truly focusing on how the sum total contribute to safety. I don't however think this is easy and this wouldn't have been a question I'd have attempted. However I certainly would have explained the significance of the Common Safety Method and the circumstances in which rigidly following tried and tested standards is appropriate and those circumstances where this not sensible or practical.
I think that I might have tackled by looking at what threats to safety exist.
1. It goes without saying that everyone wants a safe railway.
However there is a balance of other worthy considerations, many of which do tend to erode that safety intention:
a) limited finance available- if each project costs more, fewer can be achieved,
b) efficient , cost-effective railway; limited experienced staff to deliver the works,
c) minimum disruption to the public leading to limited possession times / site access,
d) desire for faster more frequent trains,
2. Mis-communication in it's widest sense, including:
a) Misunderstandings,
b) unchecked assumptions,
c) lack of clear split of responsibility,
d) hidden dependencies and interactions,
3. Unforeseen consequences
An intended change having undesirable effects that were just not anticipated.
Just reeling from an example of this myself; by pure good fortune rather than anything else stumbled upon something which could well have ended with the commissioning of an interlocking in a highly unsatisfactory state. At first sight the alteration was broadly the conversion of a shunt to a main running signal and in particular the change to it being first wheel replaced rather than last wheel replaced; a disastrous consequence of the actual design was that points in line of route from a signal on a parallel line were no longer held locked after the clearance of that signal and neither the affected signal route nor point had been identified as needing testing since there was no obvious change to either. Indeed if it hadn't been that a second example of an equivalent change had been implemented elsewhere on the same layout and the unintended consequence having revealed itself via an indication anomaly I think it highly probable that the fault would not have become apparent until re-commissioned into operational use and possibly only after being the cause of an accident.
Considering this "near miss" within the scope of the question and considering the contribution to safety that might have been provided to have prevented:
a) legislation- no possible contribution.
b) standards- hard to assess.
No clear contravention of any particular standard that was obviously applicable, except perhaps with the benefit of 100% hindsight. Clear mismatch between the vintage of the installation being modified and the contractually quoted standards of the project- hence dubiety of what standards should have been followed. In fact no actual standard really defined either the design or the testing- some certainly do exist that are partially relevant but there are several- none of which actually cover precisely and which themselves do not form a complete and coherent set. For example testing standards have only ever really been specified for testing "as new" a complete installation; nothing really defined for testing alterations
c) good practice- so much has evolved over the years that the "custom and practice" that existed at the time consistent with such installations has been swept away and wouldn't be regarded as acceptable in the current day environment even if it were possible to assemble a team of the competence and experience to work in the old manner. Much wasn't documented in detail anyway.
Typical circuits for the alterations were followed; it was just that there was "a trap for the unwary" hidden elsewhere in the circuitry and no-one had tumbled to the potential implication of a seemingly innocuous change. We are all much older and wiser now!
With this in mind I think it well worth including in the IRSE question answer discussion reference to the fact that
all the legislation, standards and good practice in the world does not guarantee a safe railway!
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Back to your answer.
I thought comment re NR specifying life-cycle, CEM/CRE Responsibilities etc. particularly valuable.
Less convinced that the discussion re obtaining deviation for using a different form of route indicator for a signal was as usefully presented; I think what you were trying to say was that sometimes need to adopt a solution that is actually contrary to the laid down standards to get the safest possible railway in a particular scenario and that if this is justified and peer reviewed then this is a legitimate thing to do- somehow your wording didn't drive that point home.
You did rather better when discussing the advantages and disadvantages o "typical circuits".
Similarly including the system approach and inter-disciplinary considerations added to your answer.
Overall I found the answer quite impressive. Perhaps a bit too much of an essay and it might have benefitted from a bit more of an obvious structure so that the examiners would be more likely to get an overview of its scope; I had to read it through several times to assimilate all that was in it. I think it ended very well with the bullet list in the last paragraph and more of that might have made it easier on the examiner (and I think more likely that as a candidate you'd get all credit due).
I think that the content might have warranted a Distinction; not sure if it would actually have been judged quite as highly, depending on how diligent the examiners would be at assimilating all that content when viewed as one more attempt at this particular question.
Note though that this question is one of those that features in the IRSE's commentary on sample answers.
http://www.irseexam.co.uk/forum-145.html
