Any party may request that the arbitrator exclude witnesses from the hearing except when they are testifying. If such a request is made, the arbitrator shall instruct the witnesses not to discuss the case outside the official hearing other than with the designated representatives or attorneys in the case. However, an individual who is a party or any other single party representative shall not be excluded under this rule. A witness or other person violating these instructions may be punished by the exclusion of evidence as the arbitrator deems appropriate.