As burning asphalt poured a plume of black smoke over Douglas County on April 26, a 15,000-pound chemical bomb was ticking. If everything had gone wrong that tense day, a vapor cloud of toxic hydrogen fluoride could have spread from the Husky oil refinery across the Twin Ports, injuring thousands.
Firefighters averted that worst-case scenario and extinguished the fire late that night. But the risk remains, and it probably will for years to come.
The technology exists to reduce or eliminate the hydrogen fluoride risk, and the mayors of Superior and Duluth have called on Husky Energy to make that investment. But if Husky Energy stops using the potentially deadly chemical and switches to a relatively safer alternative like sulfuric acid, it would be the first refinery to make the costly conversion.
"There has never been a facility switch from using hydrofluoric acid to sulfuric acid," the American Fuel and Petrochemical Manufacturers told the News Tribune.
Husky is making no promises about being the first.
"We are committed to looking at alternatives to hydrogen fluoride as part of our overall plans to rebuild the refinery," said Mel Duvall, spokesman for the Calgary-based refiner. "We are currently speaking with a variety of experts to fully understand the options. ... Until we have assembled all the facts, we will not be in a place to discuss this with the community. "
Hydrogen fluoride is an additive used by about 50 refineries nationwide to help produce gasoline suitable for vehicles. It would take a series of catastrophic failures to unleash the substance, and for decades the Superior refinery has successfully managed the risk without any chemical release.
In light of the fire and a growing community awareness of the risk, city leaders say it's time to add one more failsafe.
"I think there are five layers of protection - the sixth would be replacing it with something safer," Superior Mayor Jim Paine said.
Yet even if Husky decided to stop using hydrogen fluoride tomorrow - perhaps moving to a new technology a Salt Lake City refinery is now pursuing - it would take years to get a new system in place.
Of all the chemicals used at the refinery, hydrogen fluoride presents the greatest risk to the public. The caustic gas is deadly in high concentrations and burns the skin and lungs.
In a stack of papers in the basement of the Douglas County courthouse lives the refinery's potential hydrogen fluoride nightmare: "A worst-case scenario release from this facility would cover a radius that would encompass the entire populated area of the city of Superior and much of Duluth," the hazardous materials response plan reads. "The number of people affected would vary by season and current weather conditions but would range in the thousands any time of year."
This assumes a highly unlikely, though technically possible, event: A full tank of nearly 78,000 pounds of hydrofluoric acid emptying in 10 minutes. A vapor cloud could travel up to 25 miles, and depending on the speed and direction of the wind it could sicken thousands of people.
The chemical hazard plan kept and studied by Douglas County Emergency Management acknowledges the probability of such a release is "extremely remote."
"It would require a metallurgical failure or an extreme force from an outside source," says the plan, last updated in 2017. "The most probable worst-case scenario would be a failure of an unloading hose from a hydrofluoric acid tank truck or the failure of a flange. If either of these events were to happen it is unlikely that the contents of the entire tank would be released."
Even small releases at refineries around the country have been rare, and since 1987 none have been deadly. Still, in 2013 United Steelworkers issued a report that called hydrogen fluoride "a risk too great."
"We've pushed for the ones currently using hydrogen fluoride to switch to a modified form, which in theory lessons the ability for it to vaporize," Kim Nibarger, USW national oil bargaining chair, told the News Tribune. "Most companies are pretty cognizant this is a real risk."
Two other chemicals that Husky handles in Superior present airborne risks to about 7,000 nearby residents, according to the refinery's response plan. (As with hydrogen fluoride, the danger depends on the speed and volume of the release along with wind speed and direction.) Up to 1,650 pounds of chlorine are stored at the facility, and the potentially fatal gas could travel two miles if suddenly released. Up to 8,500 pounds of ammonia threaten a 1.8-mile radius.
For a major fire at the refinery, a vapor cloud explosion of mixed flammables would reach less than half a mile, according to Environmental Protection Agency records.
All those scenarios pale to the 25-mile reach of a worst-case hydrogen fluoride release, which is the very basis of emergency planning for accidents at the refinery.
"No industrial process risks more lives from a single accident than does (hydrogen fluoride)," the USW report said. "Fortunately, HF alkylation can be entirely eliminated. The industry has the technology and expertise. It certainly has the money. It lacks only the will."
Refineries need a special sauce to raise the octane of their gasoline, and for a long time only hydrogen fluoride and sulfuric acid would suffice.
While sulfuric acid presents its own risks, it does not turn into a vapor cloud and threaten the larger public by air when released. The Superior refinery currently stores up to 10,700 pounds of sulfuric acid, which would threaten those on site with severe burns and possibly death in a worst-case release scenario.
Should sulfuric acid become the new catalyst of choice for the Husky refinery, however, far more of it would be needed on site - and on the rails.
"A small refinery requiring perhaps one shipment of (hydrogen fluoride) per month might require substantially more shipments of sulfuric acid per month," Husky spokesman Mel Duvall said.
The company and other observers wouldn't speculate on precisely what it would cost to make the sulfuric acid switch in Superior, though an analysis Norton Engineering performed for Southern California refineries estimated the upfront cost at more than $100 million.
The American Fuel and Petrochemical Manufacturers was quick to count additional hurdles.
"Although the costs would vary per facility, and in many cases wouldn't be an option due to a number of technical and physical space factors, we know that the cost would be significant," the group said in an email. "A conversion would essentially involve construction of a brand-new process unit."
While a switch would be disruptive to operations over several years, it wouldn't be entirely cost-prohibitive. Across the company last year, Husky Energy spent $1.7 billion on capital projects and posted a profit of $605 million.
Then there is another hydrogen fluoride alternative that is just hitting the market: ionic liquids. Marketed by Honeywell - which invented the hydrogen fluoride and sulfuric acid processes for refineries more than 75 years ago - the technology could be a game-changer.
"Its handling requirements are much simpler," said Honeywell spokesman John Simley. "If it is exposed to the air, it remains a liquid. If it were to leak it would just pool on the ground, and you could contain it easily."
Chevron in Salt Lake City will be the first U.S. refinery to use ionic liquids and completely phase out hydrogen fluoride in 2020. If the switch is successful, more refiners could follow suit.
"Refineries are approaching us, and they're in wait-and-see mode," said Simley, who wouldn't speculate what implementing ionic liquids could cost in Superior. "They want to see the first unit up and running before they make the investment in this technology."
Nibarger with USW said that's a promising sign.
"Honeywell is the (major) hydrogen fluoride supplier for the U.S.," he said. "That tells me Honeywell thinks it's a viable option, or they wouldn't be interested in competing with themselves."
Barring any drastic and unexpected moves from Husky, hydrogen fluoride is here to stay for the time being. Yet even with a fire raging within sight of the storage tank in April, the chemical has yet to prove problematic for the community.
Since 1982, the Superior refinery has not reported an accidental hydrogen fluoride/hydrofluoric acid release of any volume, according to the U.S. Coast Guard's National Response Center database. Between 2012 and 2016, about 14 accident reports involving the chemical were made around the country each year.
EPA data shows the refinery releases or transfers less than 250 pounds of waste hydrogen fluoride per year.
The Occupational Safety and Health Administration faulted the refinery only once in the past 20 years, hitting former owner Calumet with a $21,000 fine over emergency response and flammable-liquids violations in 2015. The violations, which did not flag any issues with hydrogen fluoride, were marked as settled and the problems solved by the end of that year.
An OSHA investigation is ongoing in the wake of the April 26 fire, the cause of which remains unknown.
The fire did not damage the hydrogen fluoride tank at the refinery, which is protected by reinforced steel, an emergency water curtain and well-defined industry standards.
"With 80 years of developing best practices in handling it, there is a well-developed operating system," Simley said. "But it is costly to handle. It's not a simple thing."
Nibarger said refinery operators risk their ability to operate if there aren't sufficient safeguards that kick in when accidents do occur.
"Mitigation is not failsafe by any means, but there are a lot of things in the process to stop something if it does get released," he said.
That gives Superior Mayor Jim Paine some peace of mind, even as he calls on Husky to do away with hydrogen fluoride altogether.
"My concern is the tank's there right now, and it will be for the foreseeable future," Paine told the News Tribune last month. "We need to make sure it's protected right now."
- SEE ALSO: Twin Ports faces numerous chemical risks
Also called hydrofluoric acid, hydrogen fluoride is a highly toxic chemical used to produce gasoline suitable for vehicles. The Husky refinery in Superior can store nearly 78,000 pounds of the chemical, according to EPA records. At the time of the April fire, the refinery said there were 15,000 pounds on site. If exposed to the atmosphere, hydrogen fluoride travels quickly in a cloud and can cause burning and respiratory problems. The chemical can be fatal in high concentrations.
Refinery fire investigation continues
The cause of the explosion that punctured an asphalt tank, injured 21 people and led to a daylong fire at the Superior oil refinery April 26 remains under investigation. A community update will be held from 4:30 to 8 p.m. Tuesday at Superior Middle School, 3625 Hammond Ave. Representatives from the refinery and county, state and federal agencies will be on hand to answer questions.