A legal motion that would trigger the first class-action lawsuit filed by the victims of the runaway train that killed 50 in a small Quebec town claims faulty tanker-car designs and three railway workers’ negligent handling of the train caused the disaster.

“If I had to summarize the entire event in one word, it would be this: Tragedy,” attorney Jeff Orenstein of Consumer Law Group Inc. of Montreal said Thursday. “It was really the coming together of many events that led to the tragedy being as great as it is.”

A team of Canadian lawyers, including Orenstein, filed an amended motion Wednesday for authorization to proceed with the lawsuit. If a Quebec Superior Court judge approves the motion, the lawsuit could be among the largest in Canadian history, but Orenstein said that no dollar amount on the damages sought will be available for some time.

“It will require interviews with the people of the city and expert evaluators as well,” Orenstein said. “There is no number I can pin down without much further research and expertise.”

The proposed lawsuit names as defendants train owner Montreal, Maine and Atlantic Railway, parent company Rail World Inc. of Chicago, Rail World President Edward Burkhardt and engineer Thomas Harding, among others.

The runaway Montreal, Maine and Atlantic train derailed in Lac-Megantic on July 6, igniting several of its 72 tanker cars carrying crude oil from the Bakken oil fields in North Dakota to the Irving Oil refinery in Saint John, New Brunswick. Thirty-seven bodies have been recovered from the explosion site in the center of the town. Thirteen more people are missing and likely dead, Canadian officials said.

The tragedy has forced Montreal, Maine and Atlantic Railway to lay off 79 of its 179 workers, closed a major track into Quebec and spurred rail safety reviews on both sides of the border.

The plaintiffs in the legal motion are Lac-Megantic residents Yannick Gagne and Guy Ouellet. The motion also names Irving Oil Operations Ltd., World Fuel Services Inc. and Dakota Plains Holdings Inc. as defendants.

The motion claims that the DOT-111 tanker cars used to carry oil were not built to handle Bakken light crude, which is extremely flammable.

The plaintiffs said the oil companies own the tankers and were negligent in using such unsafe tanker cars.

Burkhardt and officials from World Fuel did not return telephone calls seeking comment. An official at Dakota Plains referred comment to another company official who did not immediately return a telephone message seeking comment.

Irving Oil spokeswoman Carolyn Van der Veen said the company extends its deepest sympathies to the victims and residents of Lac-Megantic, but suggested that the plaintiffs erred in naming Irving as a defendant in the amended complaint.

“The crude oil was destined for our Saint John, New Brunswick refinery. However, we did not own or control the crude oil or its transportation at any time,” Van der Veen said in a statement. “Within hours of the tragedy, we sent personnel to the site and provided firefighting foam.”

“We will continue to offer our support to all governmental authorities as this tragedy is investigated,” she added.

The Transportation Safety Board of Canada and the U.S. National Transportation Safety Board have noted that the DOT-111 model tank cars have multiple design flaws, including a lack of double hulls, “which result in a high incidence of tank failures during collisions, and render them less suitable for the transport of dangerous products,” the complaint states.

“Many of the tanks involved in the train derailment were older model DOT-111 tanks that were not reinforced, thus remaining highly prone to rupture in the event of a collision,” the lawsuit states. “These tanks are multi-purpose, non-pressure tank cars that are widely known to all the Respondents and to regulators to be vulnerable to leaks, ruptures and explosions.”

The Canadian safety board noted at least five train collisions or derailments since 1994 in which tanker design flaws contributed to the release of several hundred thousand gallons or liters of methanol, sulfuric acid and denatured alcohol.

A timeline of the Lac-Megantic disaster within the lawsuit culled largely from news accounts states that Harding parked the train in Nantes, Quebec, for the night at about 11:25 p.m. July 5 and left it to stay in a local hotel. Several minutes later Nantes residents noticed a train fire.

Nantes firefighters doused a small fire in the locomotive believed to have been caused by a ruptured oil or fuel line in the engine. By 12:15 a.m. July 6, they left the train with two unnamed Montreal, Maine and Atlantic Railway workers, who certified the train was safe. About 45 minutes later, the train began its descent on the 1.2 percent grade toward Lac-Megantic, where it derailed and exploded in the town center.

“We know that not all the handbrakes were applied,” Orenstein said. “You are talking about many factors coming together to produce this tragedy.”

Under Canadian law, Orenstein and his partners in the lawsuit, which include an attorney whose office was destroyed by the train explosion, will not be able to depose the defendants, victims and witnesses to the incident unless a judge approves the lawsuit.

He expects to begin collecting statements from victims and witnesses in September, but said that might be pushed back if the defendants are slow in answering to the motion for authorization.

According to its website, Montreal, Maine and Atlantic owns 510 route miles of track in Maine, Vermont and Quebec and employs 100 people since its layoffs this week. MMA operates about 15 trains daily with a fleet of 26 locomotives. Main-line operations are conducted regularly between Millinocket and Searsport, Maine, and from Brownville Junction, Maine, to Montreal, Quebec.

Service also is provided between Farnham, Quebec, and Newport, Vt., the website states.