A picture of where the 2018 fire started from an investigation by the contractor EDT. (Screenshot from report)

The 2018 fire at the Clairton Coke Works is one of the most detailed and consequential examples of maintenance problems — that a new lawsuit says are endemic at the plant — to ever be made public.

This story is based on two reports produced by EDT Forensic Engineering and Consulting that identified the cause of the fire and concluded that only U.S. Steel could be held liable for the cause of the fire. EDT was hired by U.S. Steel’s insurance company, and a spokesperson for U.S. Steel declined to comment or identify additional court documents with an alternative explanation of the fire.

In response to questions about the fire, a U.S. steel spokesperson noted that the company has made a number of improvements at the facility since the fire that court documents state add up to at least $17.5 million. 

Ironically, the 2018 Christmas Eve fire at Clairton Coke Works started because of a problem with the system that was supposed to help extinguish fires: a sprinkler system.

To understand exactly what went wrong and how preventable the fire was, you have to dive into the bowels of how the Clairton Coke Works operates. 

A slide from a report by the consultant McKinsey and Company shows Clairton’s plant was only slightly above “reactive” in an assessment of its performance. (Screenshot of a slide in a report by Ranajit Sahu, an expert witness)

It’s helpful to think of the coke works as two separate facilities: one that makes coke for steel production directly and another that produces a kind of natural gas — a byproduct of the coke process — for all kinds of basic energy use at its three Mon Valley facilities. 

In the first part of the facility, the company heats up coal to high temperatures to burn off impurities. The process results in coke, a pure carbon, used in steelmaking because it can be heated to high temperatures without creating smoke that could damage the steel. 

Some pollution rises out of the top of these stacked coke ovens, where the coal is baked, and additional pollution escapes when workers pull out the finished coke or add in new coal to start the process again. Pollution also escapes through leaks and cracks in the old ovens. Ordinarily, these ovens are the main source of pollution that comes from the coke works. But it wasn’t the main source of pollution after the fire.

The second part of the coke works operates more like a gas or oil refinery you might find on the Gulf Coast. When the coal is heated, it releases a gas similar to the natural gas you might burn in your home, but with additional chemicals, including coal tar, ammonia, light oil, sulfur and compounds like benzene. The company has to separate these chemicals from the gas before it can be burned as fuel. This gas byproduct from the coking ovens is valuable: The company spent around $20 million to buy natural gas over the 100 days its pollution controls were out in place of the coke oven gas typically used.

A slide from a report by the consultant McKinsey and Company shows staff had serious concerns about the Clairton Coke Works maintenance program. (Screenshot of a slide in a report by Ranajit Sahu, an expert witness)

It was in this part of the plant that problems arose during the fire, as the gas was being cleaned in Control Room 2.

The process U.S. Steel uses in Control Room 2 is unique. It uses small cryogenic rocks supercooled to less than negative 258 degrees to remove impurities from the gas. When the temperature rises above negative 80 degrees, some nitric oxide residue becomes explosive. They use industrial vacuums to clean the rocks of these explosive impurities. 

The problem started on the rubber roof of Control Room 2. The roof had not been inspected in years, according to records produced in the lawsuit, and was leaking water below, causing metal to corrode. One of those pieces of metal joined together two emergency water pipes. If there was a fire, water from these pipes could douse the fire quickly. 

The company inspected the piping — from 45 feet below. After the fire, investigators found a number of other pipes that were only loosely held in place and others with significant corrosion. 

By the day of the fire, the metal that was supposed to secure a piece of piping was “paper thin” from corrosion and snapped off, allowing a piece of the pipe to fall. The falling pipe severed a piece of tubing on a vacuum machine that cleaned the supercooled rocks. The tubing was supposed to circulate lubricant oil. 

A piece of metal connecting two pipes had become "paper thin" after years of an undetected roof lead. This was the original cause of the 2018 fire at the Clairton Coke Works. (Screenshot from RDT investigation.)
A piece of metal connecting two pipes had become “paper thin” after years of an undetected roof lead. This was the original cause of the 2018 fire at the Clairton Coke Works. (Screenshot from RDT investigation)

The fire likely wouldn’t have lasted very long if a sensor in the lube oil system had been working to detect the loss in pressure. But the sensor malfunctioned and, as a result, lube oil continued to pour out. The oil was ignited by a nearby hot steam pipe.

It still could’ve been a small fire and a small problem.

But the lack of lubrication caused other problems. The motors in the vacuum rotate a long metal shaft thousands of times per second to give the vacuum the energy it needs to create intense pressure changes. But the metal shaft needs bearings to provide a buffer and prevent it from overheating. And those bearings need oil to stay cool. When the oil line was severed, however, the bearings overheated and the metal shaft dislodged.

This might not have been a problem except that one half of the metal shaft had a crack in it that went 80% of the way through. The shaft had been taken out and inspected only a couple months before, according to U.S. Steel records. Instead of bending under the pressure, the metal shaft snapped off entirely.

A picture of where the falling pipe severed the lub oil line that started the 2018 fires. (Screenshot from the Plunkett Report)
A picture of where the falling sprinkler “deluge” pipe severed the lube oil line that started the 2018 fires. (Screenshot from the Plunkett Report)

So the vacuum machine was rotating thousands of times per second but wasn’t well grounded on one side. It sent massive vibrations throughout the vacuum, loosening and breaking the bolts that were holding the machine down. Eventually the seals and bolts to the gas line itself broke. And suddenly, what could’ve been a small fire had an explosive fuel source.

Even this fire could’ve been contained because the gas line had a safety mechanism, which was supposed to prevent the gas from back flowing. But a “flapper” that was supposed to prevent the backflow had corroded and malfunctioned.

These failures led to thousands of tons of additional pollution in 2019 and an ongoing lawsuit to require the company to change its maintenance program to prevent a similar fire again.

Oliver Morrison is a PublicSource reporter. He can be reached at oliver@publicsource.org or on Twitter @ORMorrison.

This story was fact-checked by Matt Maielli.

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Oliver Morrison is a general assignment reporter at WESA. He previously covered education, environment and health for PublicSource in Pittsburgh and, before that, breaking news and weekend features for...