BLACK BETSY, W.Va. -- Investigators are still looking into what caused an explosion that injured two men at the Airgas plant in Putnam County on Monday.Doug Sherman, vice president of communications for Airgas Mid America, said Tuesday the plant on W.Va. 62 in Black Betsy likely would remain closed until Thursday.Sherman said he didn't have an update on the injured men's conditions. He would not release their names.The blast occurred at about 3:30 p.m. Monday in a concrete-enclosed cylinder-storage area outside the main plant. One man received burns to his face, the other to his arms. Fifty cylinders of acetylene were believed to be the source of the explosion, emergency officials said. Acetylene is a gas commonly used for welding and torch-cutting metal.Sherman said the plant would reopen once equipment destroyed in the blast is replaced.The U.S. Occupational Safety and Health Administration and the West Virginia Fire Marshal's Office are investigating the incident.