FTA-Top/Down approach to Risk Analysis

alimary15

Involved In Discussions
Good afternoon,

Just a general question regarding risk analysis and FTA:

In establishing a top-down approach to perform risk analysis, at what level of details do you decide to stop with your anaylsis?

In my case the top event for our FTA would be an hazardous situation (E.g. Patient is treated with innacurate instrument) and we would use this hazardous situation together with FTA to identify the sequence of events that could lead to the situation occurring. We would then decide to apply measures to the basic events in the FTA, changing so the probability of occurence of that hazardous situation.

We might end up with very complex trees, and with risk control measures that might be on different levels of such FTA trees. How would you handle this and is there a best practice for documentation?

Any suggestion and help is much appreciated!

Thanks
 

Peter Selvey

Leader
Super Moderator
In reality it will depend on the structure of your risk controls.

If an issue is serious enough (high severity) usually there will be some form of relatively independent protection or action that limits the risk from a wide range of sources. I call this gate theory: the image of someone standing at a gate and double checking everything is OK before letting it through. The risk control in this case is usually robustly designed so that the specific cause is irrelevant.

It could be protection in the equipment, or a production test or a redundant system.

In such as case FTA (or FMEA) can be simplified, there is no need to list thousands of causes. Grouping can be used (e.g. control system fault; production error etc).

If an issue is not serious (low severity) then usually only relatively small number of events have high enough frequency to warrant attention. There is little point listing thousands of rare events since it is obvious the risk will be acceptable. For these lower severity cases, risk controls tend to tailored react to the specific cause, so it is important to be more specific about the cause.
 
Top Bottom