The Administrator is authorized to provide for such public hearings as he deems necessary to discharge the responsibility for action under section 22 vested in him by §§ 6.2 and 6.4(a). In view of the need, however, for prompt action on requests for action under section 22, public hearings shall be held in connection with investigations conducted under § 6.4(a) only when the Administrator determines that a public hearing is necessary to obtain supplementary information not otherwise available. Any public hearing which is held shall be conducted by representatives designated for the purpose by the Administrator; shall be preceded by such public notice as, in the opinion of the Administrator, will afford interested persons reasonable opportunity to attend and present information; and minutes of the proceedings at such hearing shall be obtained. Hearings shall be informal and technical rules of evidence shall not apply. Such hearings are for the purpose of obtaining information for the assistance of the Secretary. However, in discharging his responsibilities under section 22, the Secretary is not restricted to the information adduced at the hearings.