1. Oral evidence shall be taken only on oath or affirmation.

  2. Each party shall have these rights:

    1. To call and examine witnesses;
    2. To introduce exhibits;
    3. To cross-examine opposing witnesses on any matter relevant to the issues, even though that matter was not covered in the direct examination;
    4. To impeach any witness regardless of which party first called him to testify;
    5. To rebut the evidence against him.

  3. If respondent does not testify in his own behalf, he may be called and examined as if under cross-examination.

  4. The hearing need not be conducted according to technical rules relating to evidence and witnesses. Any relevant evidence shall be admitted if it is the sort of evidence on which responsible xersons are accustomed to rely in the conduct of serious affairs, regardless of the existence of any common law or statutory rule which might make improper the admission of such evidence over objection in civil actions. Hearsay evidence may be used for the purpose of supplementing or explaining any direct evidence but shall not be sufficient in itself to support a finding unless it would be admissible over objection in civil actions. The rules of privilege shall be effective to the same that they are now or hereafter may be recognized in civil actions, and irrelevant and unduly repetitious evidence shall be excluded.

  5. All evidence, oral or written, and all exhibits, shall be recorded at the time of the hearing and all records shall be maintained for a period of time as specified by law or as determine by the Air Pollution Control Board.