Chasing a Wild Goose Egg: Understanding Computer Plume Modeling for Carbon Dioxide Pipeline Ruptures

Chasing a Wild Goose Egg: Understanding Computer Plume Modeling for Carbon Dioxide Pipeline Ruptures (Part 1 of 4)
Author: Paul Blackburn, Bold Alliance
Sept. 23, 2024

Introduction

This is the first of a four-part blog series about carbon dioxide (CO2) pipeline ruptures and the computer models that can help determine the size of the danger zone following a rupture.  Here’s how the series breaks out:

• 1: Chasing a Wild Goose Egg: Understanding Computer Plume Modeling for Carbon Dioxide Pipeline Ruptures (The basics of CO2 pipeline ruptures and the need to know the danger zone following a rupture – Sept. 23, 2024)
• 2: Is Your Goose Cooked? The Potential Health Impacts of CO2 Pipeline Ruptures (Sept. 25, 2024)
• 3: A Tale of Perfect Goose Eggs: CO2 Plume Computer Modeling Options (The computer models available to predict the size of danger zones for CO2 pipeline ruptures – Sept. 30, 2024)
• 4: Good for the Goose, Good for the Gander: Who Should Have Access to Plume Modeling for CO2 Pipeline Ruptures? (Public access to CO2 pipeline rupture computer modeling and industry and government efforts to keep it secret – Oct. 2, 2024) 

The goal of this series is to help current and potential future neighbors of CO2 pipelines access technology that can help them understand whether or not they are at risk.  

The Dangers of CO2 Pipelines

Throughout the Midwest and Gulf Coast, CO2 pipeline developers are pushing projects, driven by the federal 45Q tax credit program.  This program is intended to transfer tens if not hundreds of billions of dollars from taxpayers to industrial facilities, such as power plants, oil refineries, ethanol plants, and chemical plants, as payment for capturing very large amounts of CO2 and then shipping it through pipelines to enhanced oil recovery operations and underground storage sites.  Essentially, taxpayers are supposed to pay the cost of building a private nationwide sewer system for CO2.  For those with the money to invest in this scheme, the 45Q tax credit is truly the goose that lays golden eggs – but eggs aren’t the only thing that comes out of the backside of a goose.  The investors get the gold, while neighboring landowners and communities get . . . well you know.  

One of the things that comes out the backside of the 45Q tax credit is the risk that a publicly funded CO2 pipeline would rupture, blasting enormous amounts of CO2 into the air.  What happens next?  CO2 is both an asphyxiant and intoxicant.  The greater the distance one is from a rupture site, the more diluted the CO2 becomes and the less risk it creates.  But, what if you live or work close to a CO2 pipeline?  How close is too close?  At high enough concentrations CO2 can quickly render people unconscious, stall car motors, and kill.  Even at lower concentrations, it can cause disorientation, seizures, confusion, and hearing and vision loss, making self-rescue impossible and creating risks to drivers and those using potentially dangerous machinery.  At what distance are you safe?  At what distance would death within minutes be the most likely outcome?  

Answering these questions is complicated, sort of like predicting the weather is complicated.  But just as for weather forecasting, scientists have developed a bunch of different computer models that attempt to predict how CO2 would spread from a pipeline rupture.  Figuring out where a plume of CO2 would go is complicated, because its movement is impacted by many factors including wind speed and direction, the shape of the land, the physical nature of CO2, the amount and rate of CO2 release, the type of vegetation, and other factors.  Taking all relevant factors into account requires complicated mathematics, computer code, the input of data about the pipeline, the geographic location of a rupture, and the expected weather, as well as money.  The more expensive computer models are better at estimating danger zones.  Simple cheap computer modeling software tends to be inaccurate because it doesn’t take all of the relevant factors into account and instead makes predictions based on simplistic mathematics and assumptions. 

When people’s lives are on the line and there’s plenty of time to do modeling, it makes sense to use the best, most accurate computer modeling available, especially given that even expensive computer modeling costs a tiny fraction of the total cost of building and operating CO2 pipelines.  

This isn’t to say that quick and dirty modeling software is bad or that more accurate software is always the best option – it depends on the circumstances.  After an actual rupture, emergency responders may have only minutes to run a model that can give them at least a sense of the danger zone.   So as long as simplistic software is used conservatively, it may save lives.  As software is improved and computers become more powerful, what is now expensive and time-consuming will hopefully become affordable and fast.  For now, we need to use the right tool for different jobs.  Hopefully, this blog will help you understand the basics of CO2 plume modeling, so you can advocate for the appropriate type of plume modeling and avoid a wild goose chase.  

Characteristics of CO2 Pipeline Ruptures

One form of goose excrement foisted on a CO2 pipeline’s involuntary neighbors is the risk of a rupture.  Depending on pipeline type, diameter, and the length between emergency shutoff valves, a rupture could release potentially tens of thousands of barrels of supercritical, liquid, or gaseous CO2.  

With regard to CO2 pipeline diameter, the largest existing CO2 pipeline in the U.S. is the 502-mile-long 30-inch diameter Cortez pipeline that can transport up to 30 million tons of CO2 annually from southwestern Colorado to west Texas.  For a list of existing CO2 pipelines, see page 6 of the U.S. Department of Energy, National Technology Laboratory’s report entitled, A Review of the CO2 Pipeline Infrastructure in the U.S.   In contrast, the proposed Summit project would include over 2,000 miles of pipelines with diameters from 4 inches to as large as 24 inches.  However, if the nation-wide plans of the CO2 pipeline industry come to full fruition, it would build a nationwide CO2 pipeline system that includes even larger diameter pipelines, with some routes estimated to need approximately 490 million tons of capacity per year – 16 times more capacity than the Cortez pipeline.  See pages 239 to 244 of the Princeton University study, Net-Zero America: Potential Pathways, Infrastructure, and Impacts.

So, how much CO2 would be released in the event of a pipeline rupture?  That depends on a number of factors, including pipeline diameter, the length of pipeline vented, the pressure and temperature of the CO2 at the time of the rupture, and how quickly isolation valves are closed.  

Pipeline diameter is a critical factor, because the amount of CO2 inside a pipeline increases exponentially as pipeline diameter increases.  I expect many readers would prefer to simply be shown what this means by example, rather than understand the math (for those who don’t already know the answer, here’s a hint: A = π r²).  The following table is from an Excel spreadsheet that calculates the liquid volumes of CO2 that would be contained inside pipelines of different diameters given current minimum valve placement safety standards.  These numbers provide a ballpark estimate of the volume of CO2 that would be released from full-bore ruptures of different diameter pipelines for 15- and 20-mile-long segments.  Notice that the amount released from very large diameter pipelines is much greater than from small diameter pipelines.  A 48-inch pipeline is 12 times larger in diameter than a 4-inch pipeline, but would release approximately 245 times more CO2 for the same length.   

Pipeline Outer Diameter (inches)	CO2 in 15 Miles of Pipeline (barrels)	CO2 in 15 Miles of Pipeline (gallons)	CO2 in 20 Miles of Pipeline (barrels)	CO2 in 20 Miles of Pipeline (gallons)
4	692	29,082	923	38,776
6	1,923	80,784	2,565	107,712
8	3,770	158,336	5,027	211,115
10	6,232	261,740	8,309	348,986
12	9,309	390,994	12,412	521,325
16	17,311	727,054	23,081	969,406
20	27,774	1,166,518	37,032	1,555,358
24	40,700	1,709,385	54,266	2,279,181
30	64,704	2,717,567	86,272	3,623,423
36	94,248	3,958,407	125,664	5,277,876
42	129,331	5,431,903	172,441	7,242,538
48	169,954	7,138,058	226,605	9,517,410

Remember, however, that the numbers in this table are the volume of liquid/supercritical CO2 that would be released.  Upon release, the CO2 would immediately convert to gaseous CO2 and expand in volume by approximately 400 to 900 times, depending on the initial pressure and temperature of the CO2 inside the pipeline. 

The purpose of the above table is not to provide an exact estimate of the CO2 that would be released from a specific pipeline rupture.  Instead, it is intended to provide a sense of the proportional risk of different diameter pipelines.  Larger diameter pipelines contain proportionally much more CO2 than smaller diameter pipelines of the same length.  Therefore, while all CO2 pipelines create risks, larger pipelines may be much more dangerous.

The length of a pipeline that vents upon rupture is also a critical factor.  The length vented depends on the distance between emergency valves used to isolate a damaged section of pipeline and prevent all of the CO2 in an entire pipeline system from pouring out.  Federal regulations applicable to new pipelines require isolation valves a minimum of every 15 miles when the pipeline is near populated areas, and every 20 miles near less populated areas.  However, these minimum valve distances were adopted only a couple of years ago and do not apply retroactively to previously constructed pipelines.  This being said, the regulations also require valves at pump stations, tanks, junctions between trunk lines and lateral lines, larger water crossings, and reservoirs, so a pipeline segment may be much shorter than 15 or 20 miles.  Also, while some pipelines span multiple states, others may be only a few miles long.  The 15 and 20-mile limits are an improvement, but they are one-size-fits-all solution and do not change based on pipeline diameter.  This is a problem because, as discussed above, the amount of CO2 released increases exponentially as pipeline diameter increases.  The 15/20-mile limit may reduce the harm caused by ruptures of smaller diameter pipelines to acceptable levels, but this valve spacing may be entirely inadequate for very large diameter pipelines. 

The pressure and temperature of the CO2 in a pipeline at the time of a rupture are also important factors in determining how much CO2 is released during a rupture, because the density of CO2 varies significantly depending on tis pressure and temperature.  At greater densities, the pipeline will contain more molecules of CO2.  The more molecules of CO2 in a pipeline, the bigger a plume would be.  While the exact pressure and temperature at the time of a rupture cannot be known beforehand, a range of operating pressures and temperatures or average operating pressures and temperatures may be disclosed during pipeline permitting.  Even if pipeline-specific pressure and temperature information is not known, generally speaking most supercritical/liquid CO2 pipelines will likely operate in similar pressure and temperature ranges.  In either case, it is possible to predict a range of CO2 that could be released from any pipeline, including the worst-case maximum amount.   

A further factor that may impact the amount of CO2 released is the timing of isolation valve closure.  In the event of a rupture, if control systems and valves work properly, a pipeline operator would close the nearest upstream and downstream valves within minutes to isolate the ruptured pipeline segment so that tens, hundreds, or even thousands of miles of pipeline do not vent.  The entire volume of CO2 in the pipeline between the emergency valves would vent uncontrollably to the atmosphere, except for a relatively small amount of gaseous CO2 that would remain inside the pipeline once the pressure in the pipeline dropped to atmospheric pressure.  But, a failure by a pipeline operator to close isolation valves quickly, due either to mechanical malfunction or operator error, would allow more CO2 to be released.  

While it is not possible to predict how much CO2 would flow out of any particular pipeline rupture, for emergency planning purposes it is reasonable and possible to estimate the worst-case discharge.  What is harder to predict is what happens next. 

When a supercritical or liquid CO2 pipeline ruptures the CO2 explosively decompresses into a gas and smoothers areas around the rupture site with a plume of gaseous CO2 that can asphyxiate and/or intoxicate nearby people and animals.  The best known example of a major CO2 pipeline rupture was The Gassing of Satartia, Mississippi.  There, a 24-inch diameter CO2 pipeline owned by Denbury Gulf Coast Pipelines, LLC, ruptured at 7:06 PM on Saturday, February 22, 2020.  Since 9.55 miles of pipeline vented, the rupture should have released about 26,000 barrels.  However, two hours after the rupture, at 9:06 PM, Denbury reported to the federal government that its pipeline had released just 222 barrels of CO2.  Then, on February 25th, two days after the rupture, Denbury increased its estimate to 21,873 barrels.  Nine months later on November 25, 2020, Denbury increased its estimate to 31,405 barrels (1.3 million gallons) of CO2, which exceeded the theoretical volume of 26,000 barrels, likely because Denbury failed to close one of its isolation valves until 10:25 PM, which allowed additional CO2 to escape.  According to the federal Pipeline and Hazardous Materials Safety Administration’s (PHMSA) Failure Investigation Report, PHMSA believed that even this last estimate was too low.  

Subsequent investigation of the Satartia rupture showed that the rupture was caused by shifting ground that tore the pipe open.  When the pipe broke, it explosively decompressed and blasted a crater 40 feet deep, throwing rocks and dirt over nearby Highway 433 as it snaked along a ridgeline through the surrounding forest.  The CO2 jetted into the sky for over four hours, instantly converting into supercooled gas mixed with dry ice “snow.”  Because gaseous CO2 is 53% heavier than air and dry ice is even heavier, much of the CO2 settled back to earth in the form of a cold CO2 cloud under the forest canopy, reportedly freezing vegetation within 1,000 feet of the rupture site.  February 22, 2020 was a nearly windless day, particularly under the forest canopy, so the CO2 was not dissipated by wind.  Instead, it flowed downhill under the influence of gravity, much of it toward the Town of Satartia the center of which was a mile away. 

I encourage you to check out the exact location of the Satartia rupture and a map of the surrounding area.  Just copy and paste these latitude and longitude numbers ( 32.65785, -90.53695 ), which are from the PHMSA Failure Investigation Report, into either the google maps or google earth search box.  Applying the “terrain” layer provides a topographical map showing that the rupture was just to the east of Highway 433 and just below a ridgeline, with Satartia to the north.  Since the rupture was near a ridgeline, some of the CO2 settled to the east and some to the west of the ridge and flowed downhill on both sides of the ridge.  

The first three victims of the Satartia rupture were in a car on Perry Creek Road about a half-mile north of the rupture site.  When the CO2 plume reached the car, its motor stalled because there was too much CO2 and too little oxygen to run the motor.  The three persons in the car passed out within a couple of minutes.  When the plume reached Satartia a few minutes later, it caused some people in the town to pass out, and people as far away as the banks of the Yazoo River (approximately one and a quarter mile from the rupture site) also passed out.  Many more townspeople became intoxicated and disoriented by the CO2.  A first responder described some of them as “zombies” walking in circles.  At least 49 residents were taken to local hospitals.  

What would have happened if a rupture of this magnitude occurred in the middle of a neighborhood?  

This map shows that existing CO2 pipelines run through Mississippi, Louisiana, and Texas.  If one changes to satellite view and zooms into the pipelines that, for example, enter north and south suburban Houston, such as those in Splendora and Webster, Texas, it is easy to find areas where relatively large CO2 pipelines pass through neighborhoods, across the street from hospitals and clinics, and through densely populated commercial centers.  Other pipelines pass through other densely populated areas elsewhere in Texas, Louisiana, and Mississippi.  

We should anticipate that many more CO2 pipelines may be built through neighborhoods throughout the U.S., because the Department of Energy has predicted that current CO2 pipeline mileage could increase from about 5,300 miles currently to as much as 96,000 miles, thereby putting many more people at risk.  

If you want to find out what types of existing pipelines are near you, check out PHMSA’s public map viewer.  Enter your state and county and then zoom in to your neighborhood.  Warning: if you zoom in too close, the website hides the pipelines and you will need to re-enter the state and county and start again.  PHMSA causes this to happen, because it doesn’t want terrorists to zoom in and see precisely where the pipelines are.  This precaution is kind of silly because pipeline rights of way by law are marked by signs and are generally visible on satellite maps.   Apparently, terrorists are silly geese that can’t read signs or use google maps.  Once you zoom as close as possible to your house or workplace, click on each nearby pipeline and then click “identify,” and the website will provide basic information including the pipeline’s name and owner.  CO2 pipelines are considered “hazardous liquid” pipelines, but this category also includes all types of petroleum and oil pipelines.   PHMSA does not have a separate category for CO2 pipelines.  Despite its limitations, the PHMSA map will give you a sense of what pipelines are near your home or business.  

Is My Family or Business at Risk?

If you live near an existing or proposed CO2 pipeline, would you survive a rupture?  This question should give you goosebumps.  Even though ruptures are rare, the potential for CO2 pipeline ruptures to smooth large areas in a suffocating blanket of CO2 and cause mass fatalities means that individuals, families, and communities should take reasonable efforts to prepare for them, just as we prepare for other rare but dangerous events, such as airliner and motor vehicle accidents, tornados, refinery and chemical plant explosions, etc.  

A CO2 pipeline rupture will cause three types of danger zones:

• a blast zone where a person could be harmed by flying debris; 
• a fatality zone where CO2 plume concentrations would likely be so high that exposed persons and animals would have a better than 50/50 chance of dying from asphyxiation; and 
• an intoxication zone where CO2 concentrations would probably not kill directly, but would put persons at risk due to passing out, intoxication, and disorientation.  

It is probably not necessary to define the blast zone, because anyone close enough to a CO2 pipeline rupture to be hurt by flying debris would likely die from asphyxiation.  But, it makes sense to delineate separate fatality and intoxication zones, because of the irreversible nature of death and the likelihood that the intoxication zone would extend much farther than the fatality zone and make emergency response risky.  These zones would need to be defined in terms of (a) the concentration of CO2 in a plume and (b) the possible duration of exposure.  

If you found this post helpful, consider reading the next blog in this series, which is a joint effort between myself and Dr. Kathleen Campbell.  It describes the potential health impacts of CO2 pipeline ruptures and the government exposure limits. 

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