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An explosion in Texas shows the hidden dangers of tanks holding heavy fuels

(Pictured above:  A tank used to emulsify asphalt caught fire and exploded early Tuesday, June 30, 2020 in a Camden County, New Jersey neighborhood, officials said. Credit: Pennsauken Fire Department)

This story appeared in Inside Climate News on June 6, 2021. It is the second in a series of articles.

By Sabrina Shankman (’09) and Julia Kane (’21)

Justin Chambers arrived at the U.S. Polyco plant in Ennis, Texas, on the morning of April 23, 2018, with a job to do. One of the asphalt tanks at the plant had been damaged and needed to be demolished, and the 32-year-old foreman was part of a five-man crew of contractors charged with getting it done.

Chambers and his team went over the plan and reviewed the permits, including one that cleared the crew to use a cutting torch to detach a catwalk that connected Tank #18, the damaged tank, to Tank #17, an asphalt tank six feet away, according to court documents.

Chambers climbed to the catwalk and got ready to separate it from the tops of the tanks. At 12:12 p.m., as he stood with one foot on the catwalk and the other on the lid of the Tank #17, Chambers lit his cutting torch, sending sparks flying.

Almost instantly, the tank he was standing on exploded.

Chambers was thrown across the catwalk and about 30 feet down into Tank #18, which held a few feet of cold, hardened asphalt, topped by about eight inches of stagnant water.

Chaos broke out, as flames erupted from one tank and Chambers’ co-workers were unsure if  he was alive inside the other one.

Over the last decade, at least 17 heated storage tanks containing asphalt or No. 6 fuel oil, another heavy oil, have exploded at asphalt plants or terminals around the United States, according to news reports and filings from the Occupational Safety and Health Administration. In some cases workers were injured or killed, and some explosions ignited fires in other, nearby tanks, causing whole neighborhoods to be evacuated.

More such explosions have probably gone unreported, said Kirsten Rosselot, a chemical engineer and the owner of Process Profiles, an environmental consulting firm, who has studied this type of tank.

Neither OSHA nor the U.S. Chemical Safety and Hazard Investigation Board, an independent federal agency charged with looking into industrial chemical accidents, has conducted a systematic investigation of these explosions. Yet there is reason to believe that changes in the way asphalt and No. 6 fuel oil are processed and stored may be contributing to them, and that workers—and residents who live near the tanks—may be at risk.

For decades, companies and regulators assumed that emissions from asphalt and No. 6 fuel oil were negligible because of the heavy nature of the products. But over the last 30 years, companies have increasingly used additives to enhance the products, changing their makeup. Those additives have increased the vapor pressure inside the tanks making them more vulnerable to explosion, Rosselot and others said.

As a recent investigation by Inside Climate News showed, those increased emissions are going largely unreported by companies. In some states, regulators do not require reporting, based on an incorrect assumption that there are no emissions to report. In states that do require that emissions be reported, companies estimate them, typically using a formula developed by the petroleum industry that is often wrong and leads to underestimates of vapor pressure and the levels of air pollution the tanks are emitting.

The EPA has been aware of problems with the formula since at least 2007, but has not called for its field offices to investigate the emissions or required that companies directly measure and report emissions.

Most of the explosions of heated storage tanks have taken place at asphalt plants, but in cities and towns across the country the tanks are often knit into neighborhoods, near schools, daycares and retirement homes.

Some industry experts believe that the changes in the volatility of the heavy fuel oils from additives may be behind many explosions in tanks containing asphalt and No. 6 fuel oil. Even in amounts far less than companies routinely use, the additives can have a dramatic effect on how explosive a product is, research shows.

Tank explosions occur in two main ways: Vapors ignite after hot torches or other ignition sources are lit nearby, or no ignition source is identifiable and the explosion seems to have occurred spontaneously. An unexpectedly high concentration of vapors emitted by the heavy oils is likely to play a role in both types of explosions, these experts say.

“The presence of these higher volatility molecules means that the concentrations of vapors in the tanks are higher than they used to be,” said Rosselot.

Gasoline is well known to be a volatile liquid and consequently, gasoline vapors are controlled using an internal floating roof to keep oxygen out and the vapors in, averting potential explosions. But storage tanks for asphalt and No. 6 fuel, because their emissions were thought to be negligible, are vented, allowing oxygen in and vapors out. When vapors above a certain concentration come into contact with an ignition source, Rosselot said, that’s when explosions can happen.

Rosselot added, “The potential for higher vapor concentrations needs to be recognized, so that care is taken to prevent the vapors in these tanks and the vapors being emitted from these tanks from coming into contact with a source of ignition.”

Explosions With No Obvious Cause

Deep inside the asphalt tank, Chambers lay, suffering from third degree burns to his face, back and abdomen and a shattered right leg. In court records, he is quoted saying that only skin was keeping his foot attached to his leg.

Chambers and his wife are suing U.S. Polyco and the plant safety manager for negligence that resulted in his injuries. U.S. Polyco has countered that R-Tex Services, Chambers’ employer, was at fault.

Two months before Tank #17 exploded, on Feb. 2, 2018, there had been an explosion in the other tank, Tank #18. The blast was so powerful that it sent the 12-foot diameter lid of the tank flying, before it landed on an employee’s car. One Twitter user recorded feeling the concussion from the explosion 25 miles away.

Flames shot out of the top of the damaged tank, and firefighters let the blaze burn out. Though there were workers at the plant at the time, no one was injured.

The February explosion had no obvious cause—no nearby sparks or fires. As is often the case in explosions without injuries or fatalities, there was no official investigation into the cause by the fire department or any state or federal regulatory agencies. U.S. Polyco later determined it to be “operator error,” according to court documents, but did not give any details about the incident. The company declined to respond to detailed questions sent by Inside Climate News, citing its ongoing lawsuit with Chambers, said Alisa Rhyno, a spokeswoman for the company.

Inside Climate News made repeated attempts to speak with Chambers, but messages left on his phone and email and with his family and his attorney were not returned.

Engineering experts say that such seemingly spontaneous explosions can be caused by the formation of what’s known as “pyrophoric material.” The word pyrophoric comes from the Greek “fire-bearing” and means capable of igniting spontaneously upon exposure to oxygen. These kinds of explosions in asphalt tanks have been documented at least since the 1980s.

recent publication by the Asphalt Institute, the main trade group for the industry, warned tank owners and operators about the dangers of pyrophoric material formation in asphalt tanks and advised them to evaluate whether their tanks could be affected. It included a section on the role that additives can play in contributing to these kinds of explosions.

“Asphalt additives affect the rate and type of chemical reactions during asphalt processing and storage,” the article said. “Thus, the potential of asphalt additives to influence the formation of pyrophoric materials in an asphalt storage tank cannot be ruled out.”

While the information contained in these trade publications rarely makes its way to the general public, the threat to homeowners and others in residential neighborhoods is real, given the dispersed location of such tanks throughout the country.

As refineries have gotten more efficient at squeezing every valuable drop of more profitable petroleum products, like gasoline or jet fuel, from crude oil, the products at the bottom of the vacuum stack, like asphalt or No. 6 fuel oil, have become more depleted than in the past, making them hard to work with. That’s where additives come in.

These additives are often proprietary chemicals or lighter hydrocarbons that would normally be further refined into diesel. Instead, they are mixed with heavy fuels like asphalt or No. 6, resulting in changes to the way the products perform—and what they emit.

The Asphalt Institute did not respond to questions submitted to them by Inside Climate News. However, the institute’s publication acknowledges that the additives can include lighter hydrocarbons. These materials are more volatile, can cause greater emissions and become explosive at lower temperatures than asphalt without the additives.

Paul Bommer, a petroleum engineer and senior lecturer at the University of Texas at Austin, said he once was called as an expert witness in a case in which a tank containing carbon black—a substance similar to asphalt and No. 6 fuel oil—exploded when a worker opened a hatch, allowing oxygen to enter the tank. In that case, it turned out the refinery had previously stored other, more volatile materials in the tank, and small amounts had remained and mixed in with the carbon black, leading to a build up of vapors inside the tank.

“If you add something that has a different explosive limit, you’re going to change the properties of the mixture,” he said.

But additives are not necessary for a pyrophoric explosion to occur. Asphalt naturally contains both sulfur and hydrogen, which, when they react, form hydrogen sulfide. The more asphalt is heated, the more hydrogen sulfide is created, and over time, high concentrations can build up. When hydrogen sulfide interacts with oxidized iron inside a tank (in the form of rust, for example), it can form a new compound called iron sulfide—a pyrophoric substance that, when exposed to air, can ignite.

On June 30, 2020, a tank holding asphalt mix at the Blueknight Energy Partners terminal in Gloucester City, New Jersey exploded. One man who lived near the terminal told a local news crew that he heard a loud boom at about 12:49 a.m. and saw that the top of the tank was engulfed by flames. People in the surrounding neighborhood were forced to evacuate and seek shelter in a nearby community center until fire crews extinguished the flames four hours later. Nearly a year later, Gloucester City Fire Marshal Patrick Hagan said the explosion is still under investigation, but that pyrophoric material buildup in the tank is one of the hypotheses about what caused it.

“The explosion of the asphalt tank is a terrifying example of what can happen to dangerous and polluting facilities in our communities,” Jeff Tittel, the director of the New Jersey Sierra Club, told a reporter at the time. “Even after it exploded, the asphalt tank was on fire for at least 3 hours, putting out thick, dark, toxic smoke into the community.”

Another explosion took place on March 23 in Suffolk County on Long Island. An asphalt tank at a plant owned by Rason Asphalt exploded in the early afternoon, causing a loud blast that rattled nearby homes. Though the incident is still under investigation, Melville Fire Chief David Kaplan said they haven’t ruled out a pyrophoric explosion.

Tanks Ready to Explode

After the explosion in Ennis, Tank #17 was left damaged beyond repair and in need of removal. And that’s what brought Chambers to the site that Spring morning.

Harvey Patel was eating lunch inside the Budget Inn Ennis on April 23, 2018 when he felt a shockwave rattle the building. The windows on both sides of the building shook, and Patel, the general manager of the motel, said he could feel the blast inside his body.

He ran out of the building to see what had happened. Across the street, at the U.S. Polyco plant, Patel saw smoke. It wasn’t long before sirens began wailing and fire engines arrived on scene.

Captain Josh Slovak, a 15-year veteran of the Ennis Fire Department at the time, was on the second engine to arrive at the plant. As black smoke wafted from the nearby tank, two men ran over and let Slovak know that someone was missing. One witness said he believed the missing man had fallen inside the tank that was to be demolished.

“We had two tanks right next to each other that we were dealing with: one with fire, one with rescue,” Slovak said. “We were able to look in a small cut that was in the side of the tank and actually see that he was there,” Slovak said. What’s more: Chambers was still alive.

They cut a hole through the tank wall to extract him. A helicopter ambulance was waiting to take him to a hospital in Dallas, but with his clothes covered in asphalt, they decided against it out of fear that the fumes from Chambers’ clothes and body would “overtake the pilot,” Slovak said.

A fire analyst named Ricky Jones, who reviewed the incident, wrote that Chambers’ description of what happened—that he had lit his torch, seen a small flame and then the top of Tank #17 blew off—was “consistent with the ignition of fugitive vapors from the product within Tank #17.”

“When fugitive vapors are ignited the flame will follow the vapors back to their origination. In this case it is inside Tank #17,” Jones wrote, according to court documents.

The explosion that injured Chambers was unexpected, but similar accidents had occurred in other places.

On Nov. 19, 2014, in La Crosse, Wisconsin, an employee used a torch to heat a clogged valve, igniting flammable vapors in a mostly empty asphalt tank and causing it to explode. The employee suffered minor burns, and the tank lid was blown into the air and landed 150 yard away. The asphalt in this case was a combination of asphalt and diesel fuel.

Six days earlier, a similar incident in Stafford, Texas left one man injured and another dead.

Unlike pyrophoric explosions, these explosions were characterized by the use of an ignition source, like a torch, that then lit nearby vapors on fire, triggering an explosion in the tank.

Hot work—the use of tools for cutting, grinding and welding that can create sparks—is common at industrial plants, and asphalt plants are no exception. OSHA, the American Petroleum Institute and other organizations have standard protocols to ensure the work is done in as safe a manner as possible.

But central to making determinations about safe protocol is knowing the dangers posed by the specific product you’re working with. In these cases, it is unclear whether the workers did.

In 2010, the U.S. Chemical Safety and Hazard Investigation Board issued a safety bulletin on preventing worker deaths during hot work in and around tanks. The bulletin was released in the wake of several incidents in which workers were killed or injured and includes summaries of 11 incidents, none of which involve residual fuels. Though each accident had different particulars, “all resulted from a flammable vapor coming in contact with an ignition source created by welding or cutting that was performed in, on, or near tanks that contained flammables.”

The bulletin included several key lessons from those accidents, including avoiding the work if possible, monitoring the atmosphere for gas and identifying any potential hazards prior to starting work.

A key indicator of how safe a product might be is its flash point—the temperature at which it becomes flammable.

“Asphalt tanks don’t really worry us very much,” said Mike Hildebrand, an expert in safety management and hazardous materials who wrote a handbook on emergency response for bulk storage tanks, because compared with other petroleum products, asphalt has a high flash point. Whereas some highly volatile materials can have low flashpoints, like gasoline at -40°F or ethyl alcohol at 55°F, asphalt’s can be listed as high as 450° or 500°F.

Inside a tank, asphalt is often heated to about 300°F, meaning that technically, it should be well below the point at which it could light on fire. No. 6 fuel oil has a lower flash point—companies list it between 140°F and 200°F—and is stored around 130°F. Though that is closer to the flash point, it still allows for a buffer.

But a 1997 study found that in several cases, fires and explosions had happened in materials like asphalt and No. 6 fuel oil despite temperatures never reaching the flash point. “In many cases, there was hot work or torch heating on or near the tanks,” wrote the author, Robert Zalosh. “However, in many other cases, the causes were either not identified or not publicly released because of the restrictions imposed during litigation.”

Zalosh’s study concluded that “flammable vapor concentrations measured in storage tanks of residual fuel oil and of asphalt have shown the presence of flammable concentrations even when the liquid is well below the flash point.”

What’s more, even a small amount of a lower flash point additive could affect the point of ignition of the substance it’s added to. “Laboratory tests have shown that addition of only three volume percent of heptane to Number 6 fuel oil, transformer oil, and asphalt, causes flash point reductions of between 60°C and 137°C,” he wrote in the 1997 study. Heptane, one of the main components of gasoline, is a lighter-end chemical that is sometimes included in the additives used in heavy fuels.

In the years since, companies increasingly have mixed additives into residual products. It is now common for additives to comprise up to 20 percent of stored asphalt or No. 6 fuel oil.

“If you have the contamination of higher flash point liquids with lower flash point liquids or the deliberate use of additives and you’re not aware of what it’s doing to the tank vapor space, that could potentially be a hazardous situation,” Zalosh said.

With more than 2 billion gallons of asphalt or residual fuel, much of it No. 6 oil, in bulk storage tanks across the United States, there’s the potential for more explosions like the one that injured Chambers or the ones that kill and injure other workers each year.

“There is no tolerance level for explosive concentrations of vapors in tanks that are vented to the atmosphere—it is unacceptable for these vapors to be near their explosive limit,” said Rosselot. “Who knows how many tanks around the country are an explosion hazard but have yet to get a spark?”

Production Staff & Crew

Julia Kane

Julia Kane ( 2021 )


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Sabrina Shankman ( 2009 )