One of the most impactful and chilling calculations in pipeline safety is a simple radius: the Potential Impact Radius (PIR). This invisible circle is used by pipeline operators to estimate the area where a gas pipeline failure could have a significant impact on people or property, and to determine the level of safety measures required for a pipeline.
The PIR formula, commissioned by the pipeline industry, has a history of underestimating the impact of pipeline failures. These miscalculations have claimed lives. In 2000, a family of 12 camping along the Pecos River in New Mexico was killed when a nearby gas transmission pipeline ruptured 675 feet away. Today’s PIR formula would have considered the family safe from potential fatality at a distance of 598 feet. Nearly two decades later, a gas transmission pipeline explosion in Danville, Kentucky, killed a woman in her mobile home. The home was located outside the PIR. These examples highlight a broader pattern of PIR calculations underestimating the real impact of a pipeline failure.
In 2019, in its investigation report on the Danville pipeline failure, the National Transportation Safety Board (NTSB ) warned that PHMSA’s Potential Impact Radius formula relies on assumptions that don’t align with real-world data. The report stated, “the Pipeline and Hazardous Materials Safety Administration’s equation for determining the potential impact radius of a pipeline rupture is based on assumptions that are inconsistent with findings from recent natural gas ruptures and human response data; thus, high consequence areas determined using the equation do not include the full area at risk.”
Five years later, in 2024, the Government Accountability Office (GAO) echoed that warning, finding that PHMSA still does not collect data comparing actual pipeline-rupture impacts with the PIR estimates used by operators, stating in its report that “when a pipeline incident occurs, PHMSA does not collect detailed data comparing the actual impact of the incident with the potential impact radius that the operator had calculated for the pipeline.”
When the PIR underestimates the true area of danger, lives are put at risk, exposing a troubling gap between regulatory definitions and the danger faced by those who reside near pipelines. As a cornerstone of pipeline safety planning, the PIR guides how operators design, test, inspect, and prepare for emergencies. When its calculations fall short, the result is a systemic error that leaves miles of pipeline built and operated under standards that may be insufficient to protect the people and places most at risk.
The Pipeline and Hazardous Materials Safety Administration (PHMSA) pledged to revisit how it calculates the Potential Impact Radius (PIR) and collects incident data. To truly protect people and places near gas pipelines, the PIR must be updated to reflect real-world data and realistic human reactions in the event of a rupture.
Nora Harren,
Thank you for your article, The Potential Impact Radius and What We Don’t Know. The application of “Potential Impact Radius” should be extended to pipelines transporting gasoline motor fuel (motor spirit) as was the case in the 1999 Bellingham disaster.
In Tulsa the Explorer Pipeline doubles down on the Bellingham disaster risk. In addition to transporting gasoline Explorer transports diluent headed to the Canadian tar sands after injecting butane to “improve” the solvent properties of the diluent, increasing the vapor pressure from 400 to 760 mm Hg.
While there were three innocents in Whatcom Falls Park on June 10, 1999, for 20 miles the right-of-way of the Explorer Pipeline (30” built in 1972) has become completely compromised by urbanization.
Please send me an email address where I can send more information.
Correction: The Explorer Pipeline is 24″.
Hi Nora
I agree with you completely. I have been critiquing the PIR model for years. I have just produced a paper for publication. The Model is indeed flawed…..and I know why. You can reach out to me if you want to learn more.
Marcello
It is important that the PIR take into account other factors.
1. if a crude oil pipeline and a natural gas pipeline are in the same 50′ easement how does this affect PIR?
In addition, operators should make PIR more widely known to cities and residents. I doubt many city planning departments or city councils consider PIR when making zoning decisions. Residents who live near pipelines or have easements should know before adding accessory buildings or ADUs.
Nora,
I have some of the same concerns. I have reviewed the PIR model in areas that affect people safety.
Steve
Please remember this simple 2003 approach was built to insure higher population densities termed High Consequence Areas (HCAs contain 22 or more structures for human occupation) receive the highest priority integrity assessments. Recently PHMSA has added Moderate Consequence Areas (MCAs contain 5 or more structures). Soon PHMSA plans to require assessment of 100% of all pipelines. Since tools were limited when this was adopted 25 years ago and there are over 300,000 miles of pipe to assess, this ensured that the higher population densities next to the pipelines were done first.
Thus the PIR is a SCREENING tool, an improvement over class location. It is intended to be used to insure the higher concentrations of people had their pipeline safety addressed first. It was never intended to replace a thermal consequence model appropriate to assess damage to people, property, and environment.
There are many reasons why there has been a few incidents of injuries and property damage beyond the PIR perimeter. Remember, the PIR was not built to assess damage only to help prioritize the periodic use of integrity assessment where the higher population lives.
Just to be clear, the prescriptive PIR approach does not set safety perimeters, and unless area meets the definition of “identified sites” lower population densities do not get addressed first.
There are commercial methods to determine the damage to people and property as a function of distance and kind of thermal energy released. EPA provides a selection that your taxes have paid for. Please refer to these to address the concerns expressed above.
I live within the PIR of an H2S line. Do you know if you could be impacted by a nearby pipeline leak, and do you have, and share your plan with family?
The technical basis of the PIR model (2000 report), I believe, has a technical error – the combustion efficiency factor. A follow report (2005 report) appears to have reverse engineered a justification for the initial error. Please read both reports carefully to understand what I’m talking about.
As a screening tool it fails to predict what happened at Carlsbad, NM. The model predicts zero fatalities, and thermal radiation levels low enough to enable people to escape to under the nearby bridge. 12 out 12 died!