The Office shall have the authority at all times of day or night in the performance of the duties imposed by the provisions of this Act, to enter upon and examine any building or premises where any fire has occurred and other buildings and premises adjoining or near the same. All investigations held by or under the direction of the Office may, in its discretion, be private, and persons other than those required to be present by the provisions of this Act, may be excluded from the place where such investigation is held, and witnesses may be kept separate and apart from each other and not allowed to communicate with each other until they have been examined.
425 ILCS 25/8a