What is a RISK?

[PJW]

We are often asked to define a risk, to which the simple answer is:

risk = likelihood * severity

what is a safety risk; are we supposed to define the accidents which are the consequence, the hazard that led to the accident or the cause/precursor?

In the end I concluded that I've never read anywhere what a risk is, other than the definition provided above (and variations thereof). So how should we answer part B of 2005 Q6?

I summarised that we should talk about the chain as the risk: cause-hazard-accident; but can't find documentation anywhere that confirms this as either right or wrong . . .

??? Your thoughts ???

Interesting the coincidence and similarity between this and yesterday's question

Doug, if you don't know what is wanted re a hazard / pivotal event / risk, then I don't know who does.......

However for my twopennth, I think what I'd do for the IRSE Exam is to concentrate on the "potential accident".
However I do think that it is very sensible to include "the potential secondary accident".
A classic case is Clapham 1988. Rear end collision not even a particularly high speed even for conventional line- generally considered reasonably low risk; we don't provide TPWS protection even for New Works in 2009. However death toll high because another train ploughed into wreckage; thinking about the risks, the likelihood of the 2nd event on a Southern Region commuter line in rush hour following rapidly after a first accident is pretty high.

You can often present mitigations as a means of reducing the likelihood of a more major accident (i.e. one having higher consequence), rather than a means of reducing the consequences of the first event. OK it is "playing with words" but perhaps that is what you need to do in the exam so you show examiner that you do really know the meaning of "risk".

Hence perhaps we need to answer:

1. Collision between mainline train and tourist train (I don't see any significant difference between rear endd and head-on in these circumstances)
2. Derailment of tourist train
3. Secondary accident- train on top line runs into previous accident
4. Tourist train catches fire
5. Tourist who has left the train hit by mainline train

I do share your discomfort and actually wonder whether the examiners really meant risks. I think that instead I might go for hazardous events such as:
1. Tourist train set alight by sparks from loco exhaust
2. Tourist train fails in tunnel, passengers decide to escape from smokey environment by disembarking
3. Tourist train derails in tunnel due to gauge spread
4. Main line signal clears invalidly due to tourist train becoming lost to train detection when in tunnel
5. Main line train unable to brake effectively due to rail surface contamination left by tourist train.

Item 3 looks a bit too much like the accident but to me it is what happens next that would be significant- falling between the rails at slow speed would really be the equivalent of item 2, but could topple and fall foul of the other running line or crush people in flimsey carriages against the tunnel wall, result in item 4 etc.

In the exam it is more important to be able to show a diversity of different scenario (because it gives you plenty to talk about to display the width and breadth of knowledge) than necessarily actually get the "correct" top 5 risks. Hence item 5 could result in a mainline accident some distance beyond the tunnel not involving the tourist train at all- except for what it had left behind during its last passage.

In the discussion justifying why consider a high risk, your answer can work in all the other factors that add to the risk (e.g. all the foreign tourists on board who don't understand French, lack of visibility in the tunnel exacerbated by smoke, low crash resistance of rollingstock etc etc) so if those were the things the examiners were looking for you have worked them into your answer.

If I did decide to go for the "hazardous events" approach though, I'd caveat this to inform the examiners that this was my interpretation of the question- I'd certainly start off by briefly stating the actual risks (just as I have here) but then go on to describe the event sequence- indeed I suspect that this was somewhat similar to what Doug was describing.

No idea if I am right of course, but that is the way I'd have tackled.