In any proceeding in which a Commission adjudication is made after hearing, or in any proceeding arising from an investigation under part 1b of this chapter beginning from the time the Commission initiates a proceeding governed by part 385 of this chapter, no officer, employee, or agent assigned to work upon the proceeding or to assist in the trial thereof, in that or any factually related proceeding, shall participate or advise as to the findings, conclusion or decision, except as a witness or counsel in public proceedings.