04-08-2009, 03:15 PM
Yes I agree this can be complex (though not as complex as me trying to post a reply to this question on thsi website.....). You clearly have the official definiton of risk but its not helping conceptually. I am only interested here in "safety risk" (which in its broadest sense is jsut another business risk but not what the IRSE exam is all about i think). I find it simplest to think of risk as being the opposite of safety - a measure of the absence of safety if you like. Nothing in life is risk free (i.e. totally safe) so we need to manage risk to achive an affordable balance between enterprise and harm.
So what are the biggest risks means what are the biggest safety issues. When you start taling about hazards it all gets more comlicated because hazards (or hazardous events) are not absolute. What is my hazard is not yours and vice versa. A hazard is only meaningful if it is defined with respect to a certain system or subsystem or product. Hazards exist at boundaries (this is a key YB theme) - causes - things that can lead to thema re within the system and therefore under your control to a greater or lesser extent. Events that arise from them are by defintion outside the direct control of your system and you lay yourslef at the feet of other mitigating measures that may get you off the hook (phew that was close) or limit the safety harm that you cause (good emergency response will reduce severity of casualties) i.e. the consequences, some, but not all, of which may be accidents. Once established it is then possible to construct credible accident sequences (little stories) that describe something happening and these can then be managed away to the extent necessary and reasoanbly practicable. In doing so youa re developign an approximate (remember that) model of how the world works under certain circumstances. This enables you to reason about risk and see waht happens if....
We need to do all this beacuse we are dealing with rare events and a system that ahs years of expericene built into it. Yet we have to change and modify that system all the tiem so we need a way fo makign sure that we arent affecting the risks unknowingly.
Going back to the defintion all it is tryign to do is allow us to balnce high frequency, low consequence events in a common currency with low frequency, high consequnce events (and all those less obviosu ones in between). So serious train crashes are rare but slips trips and falls on escalators are frequent. The first is low frequecy but high consequence the second is low consequence (usually) and high frequency. How do we know how mcuh effort we need to put in to protect agaisnt these - by using the concepts of risk to measure them agaisnt each other. BEWARE however that we are not makign an acceptabiltiy judgement - "risk tolerabiltiy" as it is called is something else all together - this is a givernment decision (hopefully made through some sort of consultation with the public) about how mcuh certain risks matter - so a serious train crash may not in fact have a higher risk as such but it may be less tollerable and therefore things have to be done to prevent or reduce that risk. In the UK we have seen this through the introducton of TPWS, elimitaion of mark1 rolling stock etc. They weren't the top risks in frequencyxseverity tersm but they were judged as being unacceptable to society and money was spent to elimiante or reduce them when actually the same amunt of money coudl have saved more lives spent elsewhere (on the railway or more controversially in the health service).
Oh, but dont be suprised if the examiners use risk in a more colleqial way in the exam - like the weahter forecasters with their risk of showers - you jsut have to work out when they mean real risk and when they jsut mean likelihood. Sorry!
So what are the biggest risks means what are the biggest safety issues. When you start taling about hazards it all gets more comlicated because hazards (or hazardous events) are not absolute. What is my hazard is not yours and vice versa. A hazard is only meaningful if it is defined with respect to a certain system or subsystem or product. Hazards exist at boundaries (this is a key YB theme) - causes - things that can lead to thema re within the system and therefore under your control to a greater or lesser extent. Events that arise from them are by defintion outside the direct control of your system and you lay yourslef at the feet of other mitigating measures that may get you off the hook (phew that was close) or limit the safety harm that you cause (good emergency response will reduce severity of casualties) i.e. the consequences, some, but not all, of which may be accidents. Once established it is then possible to construct credible accident sequences (little stories) that describe something happening and these can then be managed away to the extent necessary and reasoanbly practicable. In doing so youa re developign an approximate (remember that) model of how the world works under certain circumstances. This enables you to reason about risk and see waht happens if....
We need to do all this beacuse we are dealing with rare events and a system that ahs years of expericene built into it. Yet we have to change and modify that system all the tiem so we need a way fo makign sure that we arent affecting the risks unknowingly.
Going back to the defintion all it is tryign to do is allow us to balnce high frequency, low consequence events in a common currency with low frequency, high consequnce events (and all those less obviosu ones in between). So serious train crashes are rare but slips trips and falls on escalators are frequent. The first is low frequecy but high consequence the second is low consequence (usually) and high frequency. How do we know how mcuh effort we need to put in to protect agaisnt these - by using the concepts of risk to measure them agaisnt each other. BEWARE however that we are not makign an acceptabiltiy judgement - "risk tolerabiltiy" as it is called is something else all together - this is a givernment decision (hopefully made through some sort of consultation with the public) about how mcuh certain risks matter - so a serious train crash may not in fact have a higher risk as such but it may be less tollerable and therefore things have to be done to prevent or reduce that risk. In the UK we have seen this through the introducton of TPWS, elimitaion of mark1 rolling stock etc. They weren't the top risks in frequencyxseverity tersm but they were judged as being unacceptable to society and money was spent to elimiante or reduce them when actually the same amunt of money coudl have saved more lives spent elsewhere (on the railway or more controversially in the health service).
Oh, but dont be suprised if the examiners use risk in a more colleqial way in the exam - like the weahter forecasters with their risk of showers - you jsut have to work out when they mean real risk and when they jsut mean likelihood. Sorry!