Paul Blackburn: Rotten Eggs: SOLVED! The Case of the Missing Hydrogen Sulfide in Satartia, Mississippi

Rotten Eggs: SOLVED! The Case of the Missing Hydrogen Sulfide in Satartia, Mississippi
by Paul Blackburn, Bold Alliance
June 25, 2026

Two years ago, I wrote a blog post about ethanol industry claims that ruptures of pipelines filled with carbon dioxide (CO2) captured from ethanol plants would not have the health impacts seen following the rupture of a Denbury/Exxon CO2 pipeline near the town of Satartia, Mississippi, on February 22, 2020.  The industry claimed that the injuries to Satartia residents were caused by the presence of H2S in the CO2, and not the CO2 itself.  The ethanol industry argued that since CO2 from ethanol plants contains no H2S, it is as safe as the fizz in your soda.

My blog investigated whether the available data supported or refuted the ethanol industry’s claims.  While the circumstantial data indicated that H2S concentrations in the Satartia plume were low, I could not conclude this definitively, because hard data was not available: 

“After a preliminary investigation, I have not found evidence of the actual concentration of H2S at the time of the Satartia rupture, nor have I found evidence directly proving or disproving that Denbury removes H2S from its CO2 before transporting it by pipeline.  Due to its corrosion and commercial impacts, Denbury almost certainly tracks H2S concentrations in its CO2, but this doesn’t mean that it publishes this data.  We can assume that Denbury has direct evidence of the concentration of H2S released by the Satartia rupture, but it appears that this data has not been released to the public.”

I admitted to not having enough evidence to solve the case of the missing H2S, but thought it possible that Denbury provided H2S concentration data to PHMSA.  So, I submitted a Freedom of Information Act request to PHMSA seeking, among other things, H2S concentration data. 

It turns out, I was correct.  

The very last of 776 pages provided by PHMSA contains a chart of Denbury “Weekly Analyzer Data” showing CO2, methane, nitrogen, and H2S concentrations inside Denbury’s pipeline at the Tinsley Pump Station immediately upstream from the rupture site for the week of and the year proceeding the rupture.  For the week ending February 22, 2020 (the date of the rupture), Denbury recorded an H2S concentration of 35.01 parts per million (ppm).  Over the prior year, H2S concentrations averaged 36.70 ppm.  The maximum recorded H2S concentration was 45.83 ppm during the week ending December 28, 2019.  

The data also shows that the concentration of CO2 inside the pipeline was 99.01 percent (not ppm), and concentrations of methane and nitrogen were 0.49 percent and 0.50 percent, respectively.  Denbury was transporting nearly pure CO2.  

What can we conclude from this data?  First, here are the symptoms of H2S exposure and H2S exposure limits established by the federal government (more fully explained in my prior blog):

H2S Concentration (ppm)	Symptoms/Effects
0.00011-0.00033	Typical background concentrations
0.01-1.5	Odor threshold range. Odor becomes more offensive at 3-5 ppm. Above 30 ppm, odor described as sweet or sickeningly sweet.  An Iowa State study found that the average “recognition threshold” for smelling H2S is 0.047 ppm.
2-5	Prolonged exposure may cause nausea, tearing of the eyes, headaches or loss of sleep. Airway problems (bronchial constriction) in some asthma patients.
20	Prolonged exposure may cause possible fatigue, loss of appetite, headache, irritability, poor memory, dizziness.
50-100	Slight conjunctivitis (pink eye) and respiratory tract irritation after 1 hour. May cause digestive upset and loss of appetite.
100	Coughing, eye irritation, loss of smell after 2-15 minutes (olfactory fatigue). Altered breathing, drowsiness after 15-30 minutes. Throat irritation after 1 hour. Gradual increase in severity of symptoms over several hours. Death may occur after 48 hours.
100-150	Loss of smell (olfactory fatigue or paralysis).
200-300	Marked conjunctivitis (pink eye) and respiratory tract irritation after 1 hour. Pulmonary edema (fluid in the lungs) may occur from prolonged exposure.
500-700	Staggering, collapse in 5 minutes. Serious damage to the eyes in 30 minutes. Death after 30-60 minutes.
700-1,000	Rapid unconsciousness, “knockdown” or immediate collapse within 1 to 2 breaths, breathing stops, death within minutes.
1,000-2,000	Nearly instant death

 

Exposure Limit	Type of Limit
10 ppm	Recommended Exposure Limit: a non-binding limit for maximum H2S exposure concentration over 10 minutes
20 ppm	Average Exposure Limit a legally enforceable limit providing the average level of H2S to which an employee may be exposed during an 8-hour shift
50 ppm	Short-Term Exposure Limit a legally enforceable limit establishing the maximum concentration to which a worker may be exposed for up to 10-minutes over an 8-hour shift
100 ppm	Immediately Dangerous to Life or Health (IDLH) a limit established to (1) ensure that workers can escape from a contaminated environment in the event of failure of respiratory protection equipment; and (2) indicate the concentration above which an employer is legally required to provide a highly reliable breathing apparatus providing maximum worker protection.

Thus, prolonged exposure to H2S concentrations as low as 2 to 5 ppm may cause nausea, tearing of the eyes, headaches or loss of sleep, and airway problems (bronchial constriction) in some asthma patients, but federal workplace standards allow exposures as high as 20 ppm on average over an 8-hour shift.  Short-term exposure impacts don’t start until concentrations reach the 50 to 100 ppm range.  

In contrast, H2S concentrations inside Denbury’s pipe were recorded at 35.01 ppm.  If a person stuck their head into the pipe at the rupture site, the H2S concentration still would have been below the federal short-term H2S exposure limit of 50 ppm, but the person would have been instantly suffocated and flash frozen by the gushing CO2.  

After the Denbury pipeline ruptured, the H2S and CO2 dispersed in a plume that flowed downhill to Satartia.  While it was flowing, the H2S and CO2 mixed with air, meaning that the concentration of CO2 and H2S both decreased the further the plume moved away from the rupture site.  

What was the concentration of H2S at Satartia?  We don’t know exactly, but it couldn’t have been more than 30 ppm.  Assuming the H2S and CO2 were diluted approximately proportionally, and given that on the following day CO2 concentrations inside houses were as high as 28,000 ppm or 2.8 percent, this concentration of CO2 is approximately 35 times lower than the concentration in the pipeline (99 percent).  If H2S concentrations dropped proportionally, then H2S concentrations on the following day might have been approximately 1 ppm.  However, air quality monitoring after the rupture detected no H2S, probably because H2S is lighter than CO2 and may have dissipated into the atmosphere more quickly.  Shortly after the rupture, CO2 concentrations at peak in Satartia may have been in the 10 percent range or about 10 times less than at the rupture site.  Assuming a similar dilution, H2S concentrations in Satartia could have been as high as about 3 ppm – still well below federal workplace safety standards.  Since people can smell H2S at concentrations from 0.01 to 1.5 ppm, this would explain why residents reported a “rotten egg” smell that indicates the presence of H2S.  But, while smelling the H2S from a rotting egg is unpleasant, it isn’t dangerous.

In any case, based on Denbury’s data, the H2S concentrations in Satartia following the rupture were almost certainly well below all federal worker safety standards, such that the harm caused by that rupture were not due to H2X and instead were caused by high CO2 concentrations. 

What lessons can we learn?  First, don’t believe what the ethanol industry says about its CO2 being pure and therefore not dangerous.  The Satartia rupture proves otherwise.  Large releases of supercritical or liquid CO2 can suffocate or harm you, your family, pets, and livestock – if you are unlucky enough to be close to a rupture.  Second, during the entire time that the ethanol industry was running around blaming H2S for the Satartia health impacts, both Denbury and PHMSA knew full well that H2S concentrations in the pipeline at the time of the rupture were too low to cause the injuries reported at Satartia, yet they said nothing.  Therefore, we should expect neither PHMSA nor the CO2 industry to come clean about potential CO2 pipeline risks.  

While the smell of rotten eggs disappeared from Satartia long ago, the smell of rotten industry claims and government collusion still lingers.

Denbury hydrogen sulfide (H2S) reported data:

2026-06-08 PHMSA FOIA Response Chemical Comp Data h2S 02-2019 to 02-22-2020