New Century and Integrity Plus Blog

Not Every HCA Analysis is Created Equal: Part III

Posted by Nicole Tebow & Ryan Huntley on Mar 20, 2017 10:30:00 AM

In the third and final portion of the series, Not Every HCA Analysis is Created Equal, we’ll explore the effect of the type of product being transported, and how to incorporate pipeline facilities into the analysis process. If you didn’t catch the first and second segments of the series be sure to check back before continuing on here to learn about ever changing HCA boundaries and realistic model inputs.

Common Concern: “Use of subjective, invalid, or non-conservative assumptions as a basis for the justification of exclusion of segment intersecting a HCA.”

FAQ 3.26 What HVLs should be assumed to affect drinking water?

The effect of HVLs on potential could affect an HCA segment can be found in Report TTO1, "Consequences of HVL Releases," dated December 31, 2002. The report is on the PHMSA public website at

Protocol Question: A valid analysis to justify the conclusion that a pipeline segment located within an HCA could not affect the HCA.  The operator’s analysis should consider the following factors: HVL properties, Topographical considerations, HCA properties.

Another consideration when modelling direct and indirect impacts, is what type of product is transported and the product’s characteristics. For example, if the pipeline transports highly volatile liquids (HVLs), the product will typically behave as a gas when released; however, depending on the product properties, there could be a liquid phase in a release scenario as well. A prudent operator and/or vendor would carefully consider the chemistry of products, and determine vapor and liquid phases. The air dispersion is also separated into flammability and overpressure components.  In addition, if there are hazardous/toxic components, such as hydrogen sulfide, the dispersion distance to an endpoint concentration of concern should be modelled.  The modelled results should include a buffer for the air dispersion potential impacts, as well as liquid overland flow results (Figure 3, Direct and Indirect HVL Impacts), which are modified based on the actual percentage of liquid to ground.  The ability to accurately separate the components of a potential spill based on pressure, temperature, and environmental conditions provides a much higher quality end product and a more realistic dataset to help make decisions within the IMP and for emergency response considerations.


Common Concern: “Nearby tank volumes not considered in spill volume calculations where appropriate.”

FAQ 3.17 Must non-pipe elements of a pipeline system that can affect HCAs (e.g., stations and facilities) have been identified?

Yes. While the assessment requirements of 49 CFR 195.452 are applicable to line pipe, all other requirements, including segment identification, are applicable to the entire pipeline system as defined in 49 CFR 195.2. PHMSA Pipeline Safety expects operators to understand which pump stations, terminals, and other facilities might also affect HCAs in the event of a failure.

Protocol Question: The operator’s approach for analyzing the potential effects of pipeline failures that could affect HCAs must define potential locations on the pipeline where releases could occur. An effective operator program would be expected to consider spills involving pipeline facilities (e.g., breakout tanks).

Lastly, another commonly overlooked area is pipeline facilities. Hazardous liquids facilities include asset types such as pump stations, manifolds, breakout tanks, and station piping, and PHMSA guidance is clear that facilities are subject to could-affect determination requirements. A common assumption is that these facilities are equipped with adequate secondary containment that will keep any released materials within the facility. However, there have been numerous documented instances in which facility releases have migrated off operator property. Furthermore, operators should also apply air dispersion modeling for facilities that handle HVL products. Figure 4, Facility Spill – Spill Plume and Elevation Base Map, illustrates a potential liquid release at a facility modelled over a digital elevation model (DEM).


Not all modelling products are created equal.  It is important for the operator to have an understanding of not only the procedures that are used to calculate potential could affect impacts, but also the quality of the modelled products.  Were the tools used to analyze the HCA impacts able to perform the analysis with the level of detail required to accurately draw conclusions regarding impacts? Were the spill plumes modelled with enough detail to account for the total volume (including drain down), the terrain, and the timing of product release?  Does the tool provide enough detail regarding indirect impacts from air dispersion, overland flow plumes, and stream impacts, with conservative results?  Those are important questions that the operator must answer when choosing the tools or services to run their HCA analysis, while considering the key components and challenges involved.

Key Components:

  • Meeting all regulatory requirements conservatively
  • Performing HCA analyses to accomplish goals within IMP
  • Obtaining realistic results that provide value
  • Reducing potential impacts and costs


  • Incorporating a variety of formats of data to prepare for analyses
  • Providing accurate, realistic response times
  • Obtaining accurate and updated HCA data
  • Performing adequate QC/verification of results

Unfortunately, many operators have been lulled into a false sense of security with respect to their could-affect determinations. As the first step in integrity management, HCA analyses are critical to the implementation of a successful program, and operators should be vigilant in doing these studies. Just because a vendor or your GIS department performed your analysis, don’t assume it is right. Take the time to understand all the inputs and model settings, and ensure your written programs sufficiently detail your process and technical approach. 

contact us; we're here to help answer any questions, and to discuss our HCA services.  To view this series in full, visit our publications page

Topics: HCA, High Consequence Area, Pipeline Facilities, Spill Modeling

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