Negative air pressure shall be provided continuously while a smoking room is in use and until it has been cleared as specified in section 3 of this subchapter, to assure that the flow of air is from smoke-free spaces into the smoking room. The more that normal leakage occurs, such as through cracks and under doors, the greater will be the direct exhaust required to provide adequate negative air pressure to meet the conditions in OAC 310:355-13-1.
Okla. Admin. Code § 310:355-11-1