SUPERIOR, Wis. - A class action lawsuit has been filed against the owners of a Superior, Wisconsin refinery after an April explosion led to a forced evacuation.

The suit was filed on behalf of three Superior residents who were forced to evacuate their homes after the April 26 explosion. But the class action suit could still extend to the thousands of other Superior residents who had to leave. The evacuation covered more than 70 square miles.

Zimmerman Reed law firm in Minneapolis filed the suit, naming Husky Energy Inc. and Superior Refining Company LLC as defendants.

Attorney Gordon Rudd says the evacuation was significant to those residents.

"We've talked to fathers who had to evacuate with their children, seeing police officers going door to door with gas masks, not really knowing what was occurring," he said.

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The lawsuit claims that the defendants failed to exercise due care in operating the refinery, leading to the explosion and the evacuation. The complaint cites a U.S. Chemical Safety Board (CSB) report on the incident that states the suspected cause was a valve with internal wear that "failed to separate oxygen and hydrocarbons, allowing a flammable mixture to form."

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The suit is demanding damages for economic loss from the evacuation-related expenses, lost wages, disruption and inconvenience. It also states that the explosion caused "lingering malicious odor, noise, soot, ash and dust in the air" on the plaintiffs' properties.

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The CSB's report states that 36 people sought medical attention as a result of the explosion, including 11 workers.

A separate lawsuit filed last month by contractors inside the refinery at the time of the explosion makes personal injury claims.

Husky Energy provided a statement to KARE 11, saying:

"Since the April 26 fire, we have been working to resolve any related claims, including those for accommodation, food and lost wages. To date, about 98 percent of the claims presented to us have been successfully closed and we continue to address the others. 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."