PHMSA Gas Integrity Management
Time: 11/23/2009 08:35 PM

Frequently-Asked Question FAQ #144

FAQ-144: Calculating Potential Impact Radius of a Leak of Non-Flammable Gas

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Question: What is the preferred method for calculating the Potential Impact Radius (PIR) of a leak of a non-flammable gas within the context of Pipeline Integrity Management?

The regulation refers to ASME B31.8S-2001 Section 3.2 for calculation of PIR for gases other than natural gas. However, this document only deals with flammable gases. ASME B31.8S-2001 allows alternate models to be used for calculating impact radius, but provides no guidance as to preferred methods of modeling non-flammable or corrosive gases.

Answer: The potential impact circle concept is only applicable for flammable gases. Operators of pipelines carrying non-flammable gases must consider their entire pipelines as if they were in high consequence areas, or they may apply for a waiver to use another method that they may propose for defining HCAs.

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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