1. Between each intake and return air course, except that temporary controls may be used in any room that is located 600 feet or less from the centerline of the entry from which the room was developed. Unless otherwise approved by the Chief, such stoppings shall be maintained to and inclusive of the third connecting crosscut outby the working face.
2. To separate each belt conveyor haulage entry from any return air course, except where a belt entry is used as a return air course.
3. To separate the primary escapeway from any belt or trolley haulage entry, unless otherwise approved by the Chief.
4. In each return air course to direct air into adjacent worked-out areas.
B. Permanent stoppings shall be built of substantial, incombustible material such as concrete, concrete block, brick, tile, or other approved material; however, where physical conditions prohibit the use of such materials, timbers laid longitudinally “skin to skin” may be used.
C. The use of an air lock in the permanent intake stopping line near the section loading point is permitted to access the belt and transport supplies.
D. Stoppings shall be maintained to serve the purpose for which they were built and shall be reasonably airtight.