A fire at an oil refinery in Whiting, Ind., caused a tank as big as a house to explode, killing two workers and critically injuring two others when liquid asphalt burned through their clothing, authorities said. It was not immediately clear what caused the fire and explosion at the Amoco Oil Co. refinery’s No. 3 oxidizer unit, which makes industrial asphalt, said Elise Sims, an Amoco spokeswoman. The refinery’s firefighting crew controlled the fire within half an hour, she said. A doctor at an East Chicago hospital said that two of the workers were in critical condition, with severe burns. A third worker, he said, was in serious condition.