Crews at Marathon Petroleum Co. in Texas City, Tex., worked to transfer hydrofluoric acid from a leaky refinery tank to railroad cars as about 3,000 people who fled fumes from the toxic acid waited to return home. The cloud of gas, which earlier sickened about 450 people, had dispersed and authorities said the air was clear. Some residents had already returned, Police Chief Jerry Purdon said. The leak started Friday when pipes leading to a tank of the acid were accidentally damaged, oil company officials said. They said the cleanup should be done by tonight.