"Congressional committee hearings may be broadly classified into four types: 'legislative, oversight, investigative, and confirmation'. Hearings may be held on Capitol Hill or elsewhere (e.g., a committee member's district or state, or a site related to the subject of the hearing). These latter hearings are often referred to as 'field hearings'. See [http://www.crs.gov/products/guides/guidehome.shtml] for more information on legislative process. […] A single set of rules in each chamber governs the different kinds of hearings (Senate Rule XXVI and House Rule X, particularly clauses 2 and 3, and Rule XI, particularly clauses 2, 4, and 5). For example, House and Senate rules set conditions and procedures for closing any hearing to the public and press, all of which must otherwise remain open. Some other chamber rules, however, are more pertinent to certain kinds of hearings than to others. Within these rules, a chair has broad latitude in the organization and conduct of hearings."
CRS Report for Congress, 98-317