In unusual circumstances as specified in this section, the time limits prescribed with respect to initial determinations or determinations on appeal may be extended by written notice from the officer handling the request (either initial or on appeal) to the person making such request setting forth the reasons for such extension and the date on which a determination is expected to be dispatched. No such notice shall specify a date that would result in a total extension of more than ten (10) working days. As used in this section, “unusual circumstances” means, but only to the extent reasonably necessary to the proper processing of the particular request:

(a) The need to search for and collect the requested records from field facilities or other establishments that are separate from the office processing the request;

(b) The need to search for, collect and appropriately examine a voluminous amount of separate and distinct records which are demanded in a single request; or

(c) The need for consultation, which shall be conducted with all practicable speed, with another agency having a substantial interest in the determination of the request or among two or more components of the agency having substantial subject matter interest therein.