Intervention under these rules shall not be allowed, except that, in the discretion of the Judicial Officer, or the Judge, any person showing a substantial interest in the outcome of the proceeding shall be permitted to participate in oral or written argument pursuant to Sec. Sec. 1.169 and 1.170. [45 FR 6587, Jan. 29, 1980, as amended at 60 FR 8458, Feb. 14, 1995]