Cause-consequence analysis (CCA) is a method for analyzing consequence chains and can be used individually or as a supportive method for other analysis methods. The objective of the analysis is to recognize consequence chains developing from failures or other unwanted events, and to estimate these consequences with their probabilities. The cause-consequence structure of the analysis is formed by combining two different types of tree structures together. To the consequence tree, built from left to right, includes the examined primary event and its follow-up events leading eventually to a failure or some other unwanted event like for example a serious injury of a person.
The causes and the probabilities for the realization of the primary event and the follow-up events are defined to cause trees built from top to down. Often cause trees describe failures and are therefore called fault trees. The top level of the cause tree is at the same time a node in the consequence tree describing an event realizing or not. Cause and consequence tree together create a visual consequence chain to help illustrate the relations between causes and consequences that lead into different damages. Consequence tree shows the possible consequence chains and damages of a single event, whereas cause trees (fault trees) describe the causes and probabilities of each consequence.
Cause-consequence analysis includes the following phases:
- Recognizing damage chains
- Recognizing the primary event (failure or some unwanted event that triggers the damage chain)
- Recognizing the follow-up events (events between primary event and final damages)
- Final consequence damages (damages coming from different levels of follow-up events)
- Defining causes of primary and follow-up events to cause/fault trees
- Inputting realization probabilities (failure data) for the causes of primary and follow-up events
Cause-consequence analysis is an effective tool when confirming that the operational safety features have been taken into account already on the design phase. The method can be applied especially when examining complex event chains where there are many possible consequence damages for a single primary event.
The results of cause-consequence analysis include among other things:
- Visual and logical description of the consequence chain evolving from the examined primary event
- Probabilities for the final consequence damages based on the cause-consequence structure
- Cause-consequence relations (causalities) between events
- Requirements for the safety features