(1) Commissioners acting under this Act have the powers of the High Court to summon witnesses, and to call for the production of books, plans, and documents, and to examine witnesses and parties concerned on oath; and a commissioner is not liable to any action for any matter or thing done by him or her as commissioner. All summonses for the attendance of witnesses, or other persons, or the production of documents, may be in the form given in the Schedule, and shall be signed by one of the commissioners, and oaths may be administered by one of the commissioners, or by their secretary.