PHMSA Gas Transmission (GT) Integrity Management
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Frequently-Asked Question FAQ #16

FAQ-16: Determining if a Pipeline is in an HCA

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Question: How will an operator determine if a pipeline is in an HCA?

Answer: The potential impact radius must be calculated along the pipeline using the following formula:

PIR = 0.69 * (p*d2)0.5


PIR = Potential Impact Radius (in feet)
p = maximum allowable operating pressure (in pounds per square inch)
d = nominal pipeline diameter (in inches), and

0.69 is a constant applicable to natural gas (constants for other gases must be determined in accordance with Section 3.2 of ASME B31.8S-2001)

Pipeline segments for which the circle defined by the potential impact radius includes 20 or more buildings intended for human occupancy or an identified site are considered high consequence areas.

Alternatively, Operators may treat all class 3 and 4 locations on their pipelines as high consequence areas. If they elect to use this option, the use of potential impact circles is limited to looking for identified sites in any areas of their pipeline which are not class 3 or class 4 or to considering housing density and identified sites in areas where the potential impact circle radius would exceed 660 feet (i.e., for large-diameter, high-pressure pipelines).

Operators can select either method for use on their entire pipeline system, or may use each method only on selected portions of their pipeline.

These Frequently Asked Questions (FAQs) are intended to clarify, explain, and promote better understanding of the pipeline integrity management rules. These FAQs are not substantive rules and do not create rights, assign duties, or impose new obligations not outlined in the existing integrity management regulations and standards. Requests for informal interpretations regarding the applicability of one or more of the pipeline integrity management rules to a specific situation may be submitted to PHMSA in accordance with 49 C.F.R. 190.11.
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