30 CFR § 77.308
Structures housing other facilities; use of partitions.
Thermal dryer systems installed after June 30, 1971 in any structure which
also houses a tipple, cleaning plant, or other operating facility shall be
separated from all other working areas of such structure by a substantial
partition capable of providing greater resistance to explosion pressures than
the exterior wall or walls of the structure. The partition shall also include
substantial, self-closing fire doors at all entrances to the areas adjoining
the dryer system.