Monday, May 18, 2020

Questions Remain About Visakhapatnam Gas Leak

Here's what we know so far.  In the early morning hours of Thursday, May 7, workers at a petrochemical plant in the southeastern India coastal city of Visakhapatnam were trying to restart the plant, which had been shut down earlier due to lockdown restrictions imposed in connection with the COVID-19 pandemic.  Around 3:30 AM, a gas leak occurred and spread rapidly throughout the densely-populated area surrounding the plant.  At least 200 people wound up hospitalized, and as of May 8, 13 had died from the effects of the leak. 

The plant is presently owned by the South Korean firm LG Chem, but was founded in 1961 and has passed through several changes of ownership since then.  Its main output is polystyrene plastic, and to make polystyrene requires styrene, a benzene-like molecule that is liquid at room temperature.  About 2,000 metric tons of the monomer were stored onsite in tanks.

A Chevron safety sheet on the styrene "monomer" (what the molecule is called before it is polymerized into a chain) emphasizes the main danger from storing it:  runaway polymerization.  Most polymers have to be forced into polymerizing, but evidently styrene is an exception:  it will polymerize if given half a chance, and especially at temperatures above about 68 F (20 C).  When it polymerizes, it gives off heat, which makes it polymerize faster, and the resultant heat and pressure buildup can cause an explosion.

This is why storage tanks of styrene are normally refrigerated to keep them cooler than 20 C, so that spontaneous polymerization doesn't happen.  While the exact sequence of events is not yet clear, it appears that a computer glitch or other problem interfered with the refrigeration of the styrene tanks.  Once the temperature rose much above 20 C, polymerization in the tanks would have raised the temperature and pressure, and eventually a safety valve somewhere must have opened, or else a rupture in the tank or piping occurred.

At any rate, a large amount of styrene monomer escaped the limits of the plant and must have traveled hundreds of meters, affecting several villages that have sprung up around the plant in the sixty or so years since its founding.  Styrene, being heavier than air, sticks to the ground, and in sufficient density it will suffocate you.  But lower concentrations than that will still cause intense respiratory problems and death, as it did for 13 people that night.  Eventually, authorities evacuated a 3-km-radius area around the plant, but by that time most of the damage had been done.

While this accident pales in comparison to the well-known Bhopal tragedy of 1984 in which about half a million people were exposed to a toxic chemical and thousands died, even one death of a resident near a chemical plant is unnecessary.  What lessons can be learned so far from the LG Chem plant accident?

A common thread that shows up in many chemical-plant accidents is that they tend to occur when a plant is being started up after a shutdown.  There are several reasons why starting up is a dangerous time.  Conditions in the system have to be brought from a low-pressure, low-temperature state to operating pressures and temperatures without straying into combinations that can be dangerous to equipment or personnel.  This requires more than typical vigilance from operating personnel, who may not have experienced that many shutdowns and restarts in their careers.  The procedures for starting up a plant can be much more complex than those required to keep it running, and more mistakes can be made in a complicated, time-sensitive process than simply one in which your job is to make sure everything stays the way it is and runs smoothly.  Last but not necessarily least, it seems that a favorite time for doing a startup is after the beginning of the midnight shift.  Whether the implied secrecy of early morning is appealing in case anything goes wrong, or whether it is simply a more convenient time with regard to plant schedules, I don't know.  But from the viewpoint of sounding an alarm to the general public if anything goes wrong, the period from late evening to early morning is the worst possible time to do something that might cause problems to people outside the plant, who will all be asleep and hard to evacuate in an emergency.

Another factor in this accident is the presence of densely-populated villages just outside the plant boundaries.  According to one news report, in 1961 the region where the plant was erected was rural, but with the subsequent population growth of cities such as Visakhapatnam, that changed.  The permit status of the plant is reportedly in a legal gray area, which might result from the fact that if the plant were to be built from scratch today in the same location, it might not be allowed at all, or at a minimum a large buffer zone would be required between the active plant and the surrounding populated areas.  As is true in most parts of the world, the land surrounding chemical plants is where you find some of the lowest-priced housing, and the kind of people who live in low-priced housing are generally poor people.  While they are not happy to be taking an unknown risk of sudden death or long-term illness by living within the sights, sounds, and smells of a chemical plant, they may not have much of a choice.

At last report, an investigative team from LG Chem's South Korean headquarters was onsite trying to determine the accident's cause.  But that is little comfort for those who lost loved ones or the hundreds who were injured in this accident. 

Absolute safety in industrial processes is virtually impossible without exiling plants to an uninhabited island operated entirely by robots.  And in any case, such an operation would be undercut in cost by operations such as LG Chem that runs with human beings and in proximity to people who may not know they are taking a chance every day of their lives just by living close by.  In a sovereign nation, the only force that can generally make sure powerful manufacturing interests don't hurt or kill too many people is the various branches of government, with perhaps private insurance companies coming in a distant second.  I hope that this accident teaches all concerned—corporations operating in India, the government officials responsible for regulation, and the Indian people—how to do things better next time, and to make it a long time before the next such accident occurs.

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