(1) No member of the board shall participate in the review proceeding of any appeal in which he has an interest nor shall any such member appeal in which he has an interest nor shall any such member represent any interested party or witness at any board proceeding. Any interested party may challenge any member of the board in writing, served upon the chairman of the board, five days in advance of any scheduled board proceeding stating the reasons therefore, and if the board shall find merit in the challenge, it shall disqualify the challenged member and appoint the substitute member to hear the appeal if it deems such appointment advisable.