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We just read the Appendix F From 2018 Independent Forensic Team Report Oroville Dam Spillway Analysis. So, we decided to discuss a few points from our risk perspective.
It was a joy to read the statements the Independent Forensic Team made on “normalization of deviance” and the disproportionate influence some experts may exert on group deliberations. Indeed a Potential Failure Modes Analysis (PFMA) team generally includes various members bringing diverse perspectives into the process. Oftentimes one or two strongly opinionated persons, are capable of influencing the team.
We also welcomed the statements related to the need to prepare ahead of time group meetings and the requirement to develop clear definitions before starting any analysis or discussion.
Appendix F discusses the classic Failure modes and effects analysis (FMEA) approach.
Starting in the ’80s Failure modes and effects analysis (FMEA) was tweaked and simplified into dams’ Potential Failure Modes Analysis (PFMA). That was an informal identification and examination of “potential” failure modes for an existing dam. The aim was to identify areas of potentially serious and more-likely dam safety deficiencies. The ultimate goal is to use limited financial resources in ensuring dam and public safety.
The focus was and is to investigate those potential failure modes engineers judged to be most likely detrimental to public safety, and categorizing or ruling out others.
Reportedly, during the 2014 Oroville Dam Potential Failure Modes Analysis (PFMA), the team arbitrarily eliminated several potential failure modes related to the spillways from further consideration and ignored various scenarios. In our courses we state that scenarios should fall off the study “by themselves”. Not because someone arbitrarily censors the assessment.
The Independent Forensic Team reportedly formed the impression that most DWR staff and those involved in the Potential Failure Modes Analysis (PFMA) studies considered the use of the emergency spillway in terms of only an “extreme” flood event. The Independent Forensic Team notes that a “1 in 100” year storm might be considered an “extreme” event in an operational sense. However, from a dam safety viewpoint an “extreme” dam safety would be a much larger storm. For example a storm with a return period of several thousand years or even approaching the probable maximum flood (PMF). The above highlights the different viewpoints concerning extreme events. These may have affected the group evaluations of the likelihood of emergency spillway activation. Again an example of unclear glossary and definitions which lead to misleading evaluations of risks. (link)
As the report states, failure modes can be excluded from detailed consideration simply due the definition of “failure” which is used. This is again a point we adamantly discuss in all our courses and we always start our risk assessments by defining success and failure criteria and multidimensional consequence metrics.
From this first installment of the Independent Forensic Team Report Oroville Dam Spillway Analysis we can summarize the following:
We will later come back to this discussion. We will explore other aspects of the Independent Forensic Team report and how they relate to risk assessment approaches.