All hearings shall be attended by the parties or their representatives and such other persons as the administrative law judge deems necessary and proper. The administrative law judge shall inquire fully into the matters at issue and shall receive in evidence the testimony of witnesses and any documents which are relevant and material to such matters. If the administrative law judge believes that there is relevant and material evidence available which has not been presented at the hearing, he may adjourn the hearing or, at any time, prior to the filing of the compensation order, reopen the hearing for the receipt of such evidence. The order in which evidence and allegations shall be presented and the procedures at the hearings generally, except as these regulations otherwise expressly provide, shall be in the discretion of the administrative law judge and of such nature as to afford the parties a reasonable opportunity for a fair hearing.