An ad hoc consensus study committee will review the relevance, accuracy, and technical soundness of the potential impact radius (PIR) formula that can be used by natural gas pipeline operators to calculate the area around a pipe segment where a failure could have a significant impact on people or property if present. The committee will report on the findings from this review and, if warranted from these findings, examine possible alternatives to the formula and/or its underlying assumptions. The committee will also identify any additional data that are needed to better understand the actual impact of pipeline incidents.
Specifically, the study will address the following four tasks:
Task 1: Review the Demonstrated Accuracy of the PIR Formula
To the extent possible from available incident records, the committee will assess whether the impact circles calculated by the formula have aligned with the size of areas that have experienced “significant impact on people or property” from a natural gas transmission pipeline failure.
Task 2: Review the Relevance and Technical Soundness of the PIR Formula
The committee will review the origins of the PIR formula and its relationship to the regulatory interest of calculating the size of potential impact circles for the purpose of identifying areas where “the potential failure of a pipeline could have significant impact on people or property” (i.e., HCAs). The committee will consider whether the formula’s focus on fires and thermal radiation from ignited ruptures is sufficient and appropriate for HCA hazard characterization and whether the assumptions that underlie the formula are technically sound and sufficiently representative of real-world circumstances. The committee will review the rationale for these assumptions; previous technical critiques of the formula; and the basis for concerns raised by the National Transportation Safety Board and others that the PIR formula is based on assumptions that are not sufficiently conservative and can underestimate potential impact areas.
Task 3: Consider Alternatives to the PIR Formula as Appropriate
If the committee finds fault with the relevance of the formula for sizing potential impact areas or with the assumptions that underlie the formula, the committee will identify possible alternatives to the formula and/or its underlying assumptions. In identifying alternatives, the committee will describe their advantages and disadvantages, including potential effects on the complexity of sizing potential impact areas and in establishing HCAs. The committee will review pipeline incident records to compare the accuracy of the alternatives with the accuracy of the current formula in estimating impact areas.
Task 4: Identify Data Needs
Based on its review of incident reporting data, the PIR formula, and alternatives, the committee will advise PHMSA on any additional data that are needed to better understand the actual impact of pipeline failures and to assess, validate, and/or improve the methods used for calculating potential impact areas, including incident reporting data.
Informed by the findings from these tasks, the committee will make recommendations to the Pipeline and Hazardous Materials Administration, as appropriate, for improving the methods and data that are available for calculating potential impact areas for compliance with pipeline safety regulations.