Seismic risk assessment for oil and gas pipelines - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 680

provides an optional method that relies upon risk assessment to demon-
strate suggested reliability targets have been met. More explicit reliance on
risk assessments as a tool for gauging regulatory compliance are largely
confi ned to government agencies, most prominently those agencies respon-
sible for deciding the feasibility of recalls in the automotive and aviation
sectors to correct potential safety issues. Outside the regulatory environ-
ment, the relevance of risk assessments for oil and gas pipelines is largely
delegated to academic studies focused on regional or national economic
and societal impacts of extreme events (e.g., O'Rourke et al. , 1992) and
targeted studies performed for the insurance industry.
Information from the risk assessment can be used to gauge regulatory
compliance, when regulations dictate specifi c reliability targets, but are most
often used to support cost versus benefi t decisions on the part of regulatory
agencies or the pipeline owner. It is more common for oil and gas pipeline
owners to rely upon vulnerability assessment in which some quantitative
measure of the likelihood for pipeline damage is established. The informa-
tion on vulnerability is primarily used to guide decisions on capital improve-
ment projects related to increasing resiliency through pipeline replacement
or redundant transmission paths. In this approach, utility personnel are
responsible for relating the vulnerability to consequences, often based upon
qualitative or ranking measures, to determine whether identifi ed risks are
unacceptable.
25.3 Key steps in performing risk assessments for oil
and gas pipelines
Risk assessment of oil and gas pipelines involves many uncertainties.
Understanding these uncertainties and their causes is required to interpret
the results of the risk analysis. The analysis of uncertainties associated with
data, methods, and models used to estimate the risks involved should play
an important part in the overall risk analysis process.
The fi rst step is to defi ne the scope of the risk analysis. This involves
defi ning the objective of the risk analysis and includes consideration of the
confi guration of the system being assessed, the physical and functional
boundaries of the system, the environment in which the system operates,
operating conditions for the system, and the technical, environmental, orga-
nizational, and human circumstances relevant to the system. It is also neces-
sary to determine whether a qualitative or quantitative method of risk
assessment is appropriate for the scope and goals of the risk analysis.
It is important to clearly defi ne what constitutes a tolerable level of risk
at the outset of the process. Defi ning tolerable exposure criteria early on
in a site-specifi c risk analysis can greatly simplify the effort involved in the
risk analysis as some events may be able to be quickly identifi ed as having