46 CFR § 108.170 - Definitions.
(a) Classified locations are those in which flammable hydrocarbon gas or vapors, resulting from the drilling operations, may be present in quantities sufficient to produce an explosive or ignitable mixture. Location of these areas affect the design of the units' machinery, electrical, and ventilation systems. (See Notes 1 and 2).
(b) For the purpose of this subpart “semi-enclosed location” means a location where natural conditions of ventilation are notably different from those on open decks due to the presence of structures such as roofs, windbreaks, or bulkheads.
1. Further requirements with respect to hazardous locations are contained in part 111, subpart 111.105, of this chapter.
2. For specific requirements for machinery and electrical installations on mobile offshore drilling units see Subchapters “F” and “J” of this chapter.