SUPERIOR, Wis. (AP) — A lawsuit alleges that negligence by the owners of Wisconsin's only oil refinery caused an explosion and fire that injured 36 people and caused a mandatory evacuation in the city of Superior.

The class action lawsuit against Husky Energy says the evacuation after the April 26 refinery explosion forced the three plaintiffs to spend extra money on food, supplies, transportation and childcare. The Star Tribune says one woman's mother, who was in home hospice, was so stressed by the evacuation that she died soon after.

The explosion sprayed shrapnel and pierced a tank of asphalt which ignited a massive fire . Federal investigators suspect a worn valve allowed air to mix with hydrocarbons, triggering the blast.

Husky Energy said Wednesday that the Canadian-based company has successfully closed about 98 percent of claims since the explosion and is cooperating fully with investigating agencies, but declined further comment on the ongoing litigation.