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.
No comments:
Post a Comment