The industrial commission shall conduct investigations of all matters directly or indirectly connected with, or bearing upon the success of, any of the utilities, industries, enterprises, and business projects under its management, and of all matters which directly or indirectly may affect the methods, operations, processes, products, or results thereof. In aid of any such investigation the commission may summon and compel the attendance of witnesses and examine them under oath. Any member of the commission may administer such oath. It shall have access to, and may order the production of, all books, accounts, papers, and property material to such investigation. Witnesses other than those in the employ of the state are entitled to the same fees as witnesses in civil cases in the district court.