A lawsuit filed against the owners of the Husky Energy oil refinery in Superior, Wis., alleges that the company’s negligence caused the spring explosion and fire that injured 36 people and forced thousands to flee the city in a mandatory evacuation.

The three plaintiffs allege the evacuation forced them to spend money on things like food, supplies, transportation and child care. One woman said her mother, who was in home hospice, was stressed by the evacuation to a hospital and died shortly afterward. A man said the fire left his house covered in ash.

The federal class-action lawsuit filed by the Minneapolis law firm of Zimmerman Reed could potentially represent thousands of people whose lives were upended that day, according to the plaintiffs.

A Husky spokeswoman said the company has already addressed about 98 percent of the claims presented to the company, and that they’re working on the others.

“Since the April 26 fire, we have been working to resolve any related claims, including those for accommodation, food and lost wages,” Husky spokeswoman Kim Guttormson said in an e-mail Wednesday. “We are cooperating fully with those agencies investigating the incident. As this matter is before the courts, it would not be appropriate to comment further.”

The blast sent shrapnel flying at the Husky plant, Wisconsin’s only oil refinery, piercing a tank of asphalt which then ignited in a massive fire. City officials ordered the evacuation amid fears that a nearby tank of highly toxic hydrogen fluoride might also leak.

A federal report released Aug. 2 said investigators suspect that a worn valve allowed air to mix with flammable hydrocarbons, causing the blast.

Hope Koplin, one of the suit’s plaintiffs, said she was at home with her mother when the blast occurred. Her mother had been in home hospice care, but up until that day was eating and visiting with family members. After she was evacuated to a hospital, Koplin’s mother mistakenly believed she was being taken to a hospital or nursing home, against her wishes. She died May 3.

Superior homeowner Neil Miller said his house was covered with ash when he returned after the evacuation, and that Husky told him the company would help clean up the mess. Nothing’s been done so far, he said.

The lawsuit alleged that the refinery’s former owner, Murphy Oil, paid a $179,100 fine in 2008 to settle more than 30 federal safety violations. The Occupational Safety and Health Administration also cited the refinery in 2015 for violations involving flammable and combustible liquids, hazardous waste operations, and emergency response, the suit said.

The four-count suit not only says that Husky Energy was negligent on April 26 of this year, causing a nuisance and the trespass on private land of soot, ash and toxic substances, but that the plant’s use of hydrogen fluoride poses grave risks regardless of how safely the owners handle the toxic substance.

An Environmental Protection Agency worst-case scenario for the plant says a massive leak of the hydrogen fluoride tank would put 180,000 people at risk, or most of the Twin Ports population.

The lawsuit was filed Aug. 20, a few days after seven refinery workers filed a lawsuit in state court for injuries they suffered in the blast.

The men said they had to “run for their lives to escape the inferno,” after they were thrown to the ground and showered with debris and shrapnel. They were burned and injured by shrapnel, and continue to suffer mental pain and anguish, the suit says.

The men, all of whom reside in Texas or Louisiana, work for Evergreen North America and Jamar Contractors, Inc., two companies hired by Husky Energy to do refinery maintenance.

The workers said in their suit that they ran from their work area when they heard a strange knocking noise coming from the refinery. Husky employees told them to go back to work, however, and about 30 to 45 minutes later the refinery blew up.