(a) Official notice may be taken of such matters as might be judicially noticed by the courts, or of technical or scientific facts within the general knowledge of the Commission as an expert body, provided, that where a decision or part thereof rests on the official notice of a material fact not appearing in the evidence in the record, the fact of official notice shall be so stated in the decision, and any party, upon timely request, shall be afforded an opportunity to show the contrary.

(b) Whenever there is offered in evidence (in whole or in part) a public document, such as an official report, decision, opinion, or published scientific or economic statistical data issued by any of the executive departments (or their subdivisions), legislative agencies or committees, or administrative agencies of the Federal Government (including Government-owned corporations), or a similar document issued by a state or its agencies, and such document (or part thereof) has been shown by the offeror to be reasonably available to the public, such document need not be produced or marked for identification, but may be offered in evidence as a public document by specifying the document or relevant part thereof. [Rule 226.]