(1) Unless otherwise limited by order of the impartial hearing officer, the scope of discovery is as follows:

(a) in general, parties may obtain discovery regarding any matter not privileged, which is relevant to the subject matter involved in the pending action, whether it relates to the claim or defense of the party, including the existence, description, nature, custody, condition and location of any books, documents or other tangible items, and the identity and location of persons having knowledge of any discoverable material;

(b) a party may discover facts known or opinions held by an expert who has been retained or especially employed by another party in anticipation of litigation or preparation for hearing.