KBR Inc. invoked federal laws shielding contractors during wartime in an effort to avoid a Texas trial over injuries claimed by troops who were exposed to toxic chemicals while guarding a work site in Iraq. KBR argued today before a U.S. Court of Appeals panel in El Paso, Texas, that contractor-on-the-battlefield statutes act as a firewall to litigation. Without that protection, KBR and other contractors might abandon military support work altogether, the company has said. “The judges were focused on how far can KBR stretch these government contracting defense doctrines to grab immunity for their conduct,” Mike Doyle, the soldiers’ lead attorney, said in an interview after the 75-minute hearing. The judges weren’t “overly receptive” to KBR’s claim of “blanket immunity,” Doyle said.