Deadly Hydrogen Sulfide Accident Puts Deer Park in Headlines Again

 

A friend once summarized much of engineering ethics to me in two words:  "No headlines."  If that's a good guideline for engineering ethics, the city of Deer Park has seen two major violations of it in less than a month. 

 

Following a giant pipeline fire that burned for four days in September, on last Thursday, Oct. 10, some contract employees at the PEMEX refinery in Deer Park were working on a pipe flange, and something went wrong, releasing the pipe's contents into the air.  They may or may not have known that the pipe was carrying hydrogen sulfide (H₂S), which is a byproduct of oil refining.  It is probably familiar to most readers as the "rotten egg" odor that comes from aged chicken products and sewer gas.  The human nose can detect it at concentrations as low as one part per billion.  Unfortunately, one of its toxic effects is to deaden the olfactory nerves, causing the perceived smell to go away and leading to a false sense of security as concentrations increase.  It is highly toxic, and concentrations as low as 100 parts per million are classified as "immediately dangerous to life and health."

 

Two contract workers died in the accident, which occurred around 4:40 in the afternoon, and 35 others were exposed to the gas to the extent of needing treatment.  The bodies were not recovered until 3:30 AM the next day after the area had been cleared of toxic gas.

 

The city of Deer Park sent out shelter-in-place orders to its residents around 6:30 PM, but due to technical difficulties with the alert system, some people were not alerted until they read about the incident on social media.  A supplemental siren system in the city is due for an upgrade soon.

 

The accident is under investigation by both local authorities and the U. S. Chemical Safety and Hazard Investigation Board, but no cause has yet been determined. 

 

As we noted two weeks ago when writing about the pipeline fire, residents of Deer Park and surrounding communities in Houston are no strangers to refinery-related emergencies.  Release of toxic chemicals in oil refineries has been happening ever since there were refineries, and the industry has adapted to steadily increasing standards for air and water pollution control and safety measures over the decades.  The PEMEX refinery where this accident occurred dates back to 1929, when it was built by Shell Oil.  In 1993, Shell sold half the facility to the Mexican national petroleum company PEMEX and operated it as a joint venture until 2022, at which point Shell sold its share and PEMEX became the sole owner and operator.  This change of ownership may or may not have anything to do with the accident, but management cultures can change with ownership changes, and the upcoming investigation may answer that question as well as many others.

 

Considering the extremes of temperature and pressure under which highly flammable and toxic chemicals are processed in refineries, it's a wonder that we don't have a refinery explosion every day.  But it's the job of engineers to make sure that every possible thing that can go wrong in a refinery is anticipated and forestalled, and far more than 99.9% of the time, this foresight prevents mishaps. 

 

As with airline accidents, by far the most frequent cause of chemical-plant accidents is human error rather than a simple failure of machinery, although the two can be mixed.  The accident in question could have happened because the workers involved misidentified a flange to be worked on.  An oil refinery is one of the most complicated pieces of plumbing on earth, with thousands of valves, flanges, pipes, processing units, and interconnections.  Refinery workers have to know exactly what they are dealing with before taking any action that could conceivably release a product, and it might have been a case of simply opening the wrong flange.  Or an operator may have believed that the pipe in question had been purged of H₂S when in fact it hadn't been.  You can't tell the contents of a steel pipe just by looking, so there must be elaborate protocols in place to verify what is where, especially when maintenance operations are in progress. 

 

It is incidents like this one which make refineries and petrochemical plants high on the NIMBY list—"not in my back yard."  Given that a country wants to have fossil-fuel products, and given that it has considerable expertise and resources to make them, we in the U. S. must have refineries somewhere.  According to a list of new refineries compiled by the U. S. Energy Information Agency, the U. S. refining industry has managed to add considerable refining capacity since 2014 by building new refineries, but they tend to be in or near existing ones—Houston, Corpus Christi, or various locations in Alaska.  It's a lot easier to upgrade an existing refinery or build a new one next to an existing one, than it is to install the infrastructure of pipelines and shipping facilities in a place without refineries at all.

 

For the foreseeable future, the global economy will rely on fossil fuels, and so we will have to put up with refineries and everything that goes with them.  But people who live near them and work in them have a right to expect that they will be operated as safely as human ingenuity can manage. 

 

That was obviously not the case at the PEMEX plant last week.  We will follow this accident in the future, and when the investigation concludes, perhaps we will learn what chain of events led to an accident that killed two people and endangered an entire community.  But until then, we can take some comfort in the fact that refineries rarely show up in headlines, despite all the dangerous stuff going on in them.

 

Sources:  I referred to articles on the H₂S accident by ABC News 13 in Houston at https://abc13.com/post/pemex-chemical-leak-crews-waiting-lower-levels-before-entering-unit-center-deadly-hydrogen-sulfide-deer-park/15416337/, an article in the Saturday Oct. 12 edition of the Austin American-Statesman, "2 dead, dozens of others injured in hydrogen sulfide leak near Houston," and the Wikipedia article on PEMEX Deer Park.  The Energy Information Agency data is from https://www.eia.gov/tools/faqs/faq.php.

The Pemex Vinyl Chloride Plant Explosion

Unless you work in the petrochemical industry, you have probably never been near the substance called vinyl chloride.  It is a chlorinated hydrocarbon that is made when one of the four hydrogen atoms in the compound called ethylene is replaced by a chlorine atom.  On the other hand, unless you live in a house whose plumbing is all more than forty or so years old, you probably use products made with vinyl chloride every day.  Polyvinylchloride (PVC) pipes are used in the plumbing of nearly all new residential and business construction, and about 40 million metric tons (units of 1,000 kg) of PVC plastic were made in 2013.  But all PVC pipes were once the toxic, flammable liquid called vinyl chloride, and that is what may have got loose at the Pemex chlorinate 3 plant in the Gulf Coast city of Coatzacoalcos, Mexico last Wednesday, Apr. 20.  The resulting explosion and fire killed at least 28 people and injured over a hundred, with more still missing as of today.

Besides the immediate human tragedy, this accident raises important questions about the safety record of the state-owned petroleum company Pemex.

At this writing, little is known about the cause of the blast.  Coatzacoalcos is a town at the very southernmost tip of the Gulf of Mexico, in the Mexican state of Veracruz between central Mexico and the Yucatan Peninsula.  It is one of the main export terminals for Mexican oil and is a logical location for a vinyl-chloride plant, since its manufacture requires large quantities of the petrochemical ethylene.  The chlorinate 3 plant is a joint venture between Pemex and a PVC-pipe manufacturer called Mexichem. 

As with many petrochemicals, vinyl chloride is hazardous in several ways.  If released into the air, it evaporates into a dense vapor and can catch fire if a source of ignition such as an automobile engine is nearby.  Worse yet, the products of combustion are themselves hazardous:  hydrogen chloride (which when dissolved in water makes hydrochloric acid), and phosgene, which was used as a poison gas in World War I.  Besides the danger of explosion and fire, vinyl chloride is extremely toxic, and causes liver damage in animals at concentrations in air as low as 500 parts per million.  Higher concentrations cause acute illness and even death.  Because of these hazards, vinyl chloride is usually stored in double-walled containers under pressure, with leak monitors that detect low levels of leakage from the inner container before the outer wall is breached. 

It may take months before we can learn exactly what happened at Coatzacoalcos, but it is obvious that a large amount of something flammable got loose.  Some reports mention a strong odor of ammonia, which could be from refrigeration machinery used in process cooling operations in the plant.  Whether or not vinyl chloride itself was released, the high death toll says several things about this accident.

First, one can ask why there were so many people in a hazardous area.  The trend in modern petrochemical operations is to reduce staffing to the point that in emergencies or during strikes, an entire plant can be operated safely from one central control room.  Although this is speculation, it is possible that Pemex, being owned by the Mexican government, has adopted a different policy and relies more on hands-on operators in its plants as a way of increasing government-paid employment.  Whatever the reason, Pemex's safety record is not good.  News reports of this accident relate that in 2012, 26 people were killed in a natural-gas facility owned by Pemex and in 2013, an explosion in Pemex's Mexico City facilities killed 37 people. 

Next, what kind of safety culture does Pemex have?  To run a complex petrochemical plant without accidents is a monumental task, and many safety priorities are expensive, in the sense that they take resources which otherwise could be used to enlarge the firm's bottom line.  With the recent crash in oil prices, there are reports that Pemex is cutting expenses, and this latest accident raises the question of whether safety has been sacrificed to budget considerations.

Finally, there is Pemex's status as a state-owned enterprise.  I am not familiar with Mexican law, but it is quite possible that it is either statutorily or practically difficult to sue Pemex.  Also, Pemex may be self-insured rather than purchasing hazard insurance on the open market.  Both of these factors, if true, remove two of the greatest incentives private firms have to run their operations safely:  fear of lawsuits from injured parties and financial pressure from private insurers to run a safe and low-claims operation.  Without such incentives, Pemex management has only its own integrity to rely on for worker safety, and the demands for sustaining profits in the face of falling oil prices may have overwhelmed safety concerns. 

I hope that the investigative bodies in Mexico have all the competence and authority they need, not only to get to the bottom of this tragedy, but to publicize its causes and assign responsibility wherever it needs to be assigned.  Again, the status of Pemex as a state-owned firm may lead to conflicts of interest between state officials who want to make workplaces safer, and other officials who do not want to see a state-owned enterprise called to account.  The loser in such a conflict will be the workers who have the choice of being paid to put their lives on the line in a hazardous workplace, or to go somewhere else and earn even less than the $12,000 US annual salary that was the average in 2005 for Mexican chemical engineers. 

If reports surface in English as to the cause of this accident, it will be interesting to learn whether poor safety practices contributed to it.  In the meantime, my sympathy goes to all of those who lost loved ones or were injured.  And I hope this latest incident leads to a re-evaluation of the entire safety culture of Pemex, which looks like it could use a lot of work.

Sources:  I referred to a Reuters report on the accident at http://www.reuters.com/article/us-mexico-pemex-idUSKCN0XH2N2, an ABC News report at http://abcnews.go.com/International/wireStory/death-toll-28-mexico-petrochemical-plant-explosion-38614458, a Fox News item at http://www.foxnews.com/world/2016/04/21/blast-at-mexico-petrochemical-plant-kills-3-injures-more-than-100.html, and a CNN report at http://www.cnn.com/2016/04/23/americas/mexico-pemex-petrochemical-blast/.  I also referred to statistics on PVC production at http://www.plasticstoday.com/study-global-pvc-demand-grow-32-annually-through-2021/196257501821043, a salary survey for Mexico at http://www.worldsalaries.org/mexico.shtml, and the Wikipedia articles on vinyl chloride and ethylene.