An asset can sometimes fail in more than one way. Multiple failure modes or scenarios are used to capture the full range of possible effects. For example, one failure mode may be minor and easily repairable, while another could be catastrophic leading to full replacement.

Each failure scenario is given a relative probability. This represents the chance that, if there is a failure, that scenario will be the one to occur. Generally the sum of the scenarios is 100 percent, however it is more important that the failure scenarios be coordinated with the probability of failure curve. Whatever you meant by “failure” when you defined the curve, you should quantify failure scenarios accordingly.

The expected consequence of failure is the weighted sum of the consequence of each mode, as seen in the figure below.

Some scenarios may occur more than once before the asset is replaced. One approach to addressing this is to use an occurrence factor when calculating the expected consequence of failure.

Continue to occurrence factor.