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.
Karl Stephan writes an engineering ethics blog and teaches electrical engineering at Texas State University, San Marcos, Texas. He has a Ph. D. from the University of Texas at Austin, an M. Eng. from Cornell, and a B. S. in engineering from the California Institute of Technology. He has also taught at the University of Massachusetts Amherst and has worked in industry.