No examiner shall conduct or participate in any open record hearing, decision or recommendation in which the examiner has a direct or indirect substantial financial or family interest or concern, in which the examiner has had substantial prehearing contacts with proponents or opponents wherein the issues were discussed. This is not intended to prohibit necessary or proper inquiries on matters such as scheduling, but any such contacts are to be entered into the official record of the hearing. Whenever possible, such inquiries and the responses to such inquiries shall be in writing. [Code 1970 § 2.19.060.]