In unusual circumstances as specified in this section, the time limits prescribed in either Sec. 801.21 or Sec. 801.22, may be extended by written notice to the person making a request and setting forth the reasons for such extension and the date on which a determination is expected to be dispatched. Such notice will not specify a date that would result in an extension for more than 10 working days. As used in this paragraph, ``unusual circumstances,'' as they relate to any delay that is reasonably necessary to the proper processing of the particular request, means--
(a) The need to search for and collect the requested records from field facilities or other establishments;
(b) The need to search for, collect, and appropriately examine and process a voluminous amount of records which are the subject of a single request; or
(c) The need to consult with another agency that has a substantial interest in the disposition of the request or with two or more components of the agency having substantial subject-matter interest therein.