Section 4. The chairman shall have and exercise supervision and control over all the affairs of the commission. He shall preside at all hearings at which he is present, and shall designate a commissioner to act as chairman in his absence. He shall not, except as is otherwise provided herein, be charged with any administrative functions. In order to promote efficiency in administration he shall from time to time make such division or redivision of the work of the department among the commissioners as he deems expedient and may refer matters related to the need for, construction of, or siting of facilities, as defined in section sixty-nine G of chapter one hundred and sixty-four, as he deems appropriate to the energy facilities siting board in accordance with section sixty-nine H of chapter one hundred and sixty-four. All of the commissioners shall, if so directed by the chairman, participate in the hearing and decision of any matter coming before the commission. In the hearing of all matters other than those of formal or administrative character coming before the commission, at least 2 commissioners shall participate and in the decision of all such matters at least 2 commissioners shall participate; provided, that any such matter may be heard, examined and investigated by an employee of the department designated and assigned thereto by the chairman with the concurrence of one other commissioner. Such employee shall make a report in writing relative to every such matter to the commission for its decision thereon. For the purposes of hearing, examining and investigating any such matter such employee shall have all of the powers conferred upon a commissioner by section five A, and all pertinent provisions of said section shall apply to such proceedings. In every such case the concurrence of a majority of the commissioners participating in the decision shall be necessary therefor.