According to Muhlbauer (1999), because the risk of pipeline failure is sensitive to unmeasurable or unknowable initial conditions, risk efforts are often not attempts to predict how many failures will occur or where the next failure will occur. Instead, efforts are designed to systematically and objectively capture everything that is known and use the information to make better decisions.
Risk assessments can guide pipeline operators to make decisions and take precautions that allow the risks to be minimized or avoided entirely. Risk management is a systematic focusing of limited resources on those activities and conditions with the greatest potential for reducing risk.
In risk management, decision makers take the results from risk assessments and use them to prioritize risk reduction actions. Risk controls can involve measures both to prevent adverse events and to mitigate their magnitude. One reduces the likelihood; the other reduces the severity of impact. Another step in risk management is the monitoring of performance to determine whether risk control measures are effective. The process can be repeated to further address and reduce overall risk.
The first step in defining risk is to identify a potential hazard or dangerous situation and describe the mechanisms by which the hazard can cause harm to people, property, and the environment. Risk is then analyzed for each hazard or hazard scenario. In terms that can be analyzed, risk is defined as the product of (a) severity of impact and (b) the likelihood of impact from an adverse event. The severity of impact, often called consequences, can be expressed in human terms such as fatalities or injuries or some other metric such as dollars lost.
The likelihood of occurrence of an adverse event can be estimated with a variety of methods, ranging from prior experience with the frequency of occurrence, perhaps using statistical data of similar events, to computations based on mathematical models. Likelihood can also be determined by examining the probability of the adverse event occurring in a Bayesian sense, a prior perception of probability.
The example of automobile travel can clarify the concepts. The consequences of an automobile crash can be damage to the car and injury or death to the driver or passengers. More than 40,000 Americans are killed in automobile crashes each year, and several hundred thousand more are injured. Fender benders and other minor crashes are even more frequent. From these data, the risk for large automobiles or small, local streets or Interstate highways, fender bender or serious crashes can be quantified.
If a person never rides in an automobile, the risk of death, injury, or damage to one’s personal property is zero, except as a nonmotorist (e.g., pedestrian, bicyclist). By similar reasoning, a person who makes a living traveling in automobiles is more likely to experience harm than a person who rides occasionally, even given the differences in driving skill. The difference in the likelihood of experiencing harm is a concept known as exposure. The greater the exposure, the higher the risk.
Data on pipeline incidents are collected and analyzed by OPS for each reportable safety incident. These data provide the number of incidents that result in death, injury, or significant property damage. They also provide the general causes of these incidents, including damage by outside force, corrosion, construction defects, operator error, natural forces such as ground movement, and many other categories. At some level of aggregation, the data can be used to determine, or quantify, the risk from various types and sizes of pipelines.
On the basis of this experience, one can begin to identify factors that determine risk.
The principle of exposure can be applied to pipelines as well. For an individual who seldom crosses or comes near a pipeline right-of-way—a person who has little exposure—the risk is minimal, while people who live, work, or congregate near pipelines have greater exposure. Exposure is a function of time near a pipeline and effective distance. Exposure to the potential dangers of a pipeline leak or rupture is the result of proximity to the pipeline, natural or man-made barriers, and the mobility of people near the pipeline. People pursuing activities on or near the pipeline that can cause damage to the pipeline have the greatest exposure.