40 CFR §65.118

1. (a)Use of closed vent system and control device. Process units that are enclosed in such a manner that all emissions from equipment leaks are routed to a process or fuel gas system or collected and vented through a closed vent system to a control device meeting the requirements of § 65.115 are exempt from the requirements of §§ 65.106 through 65.114 and § 65.116. The enclosure shall be maintained under a negative pressure at all times while the process unit is in operation to ensure that all emissions are routed to a control device.
2. (b)Recordkeeping. Owners and operators choosing to comply with the requirements of this section shall maintain the following records:
   1. (1)Identification of the process unit(s) and the regulated materials they handle.
   2. (2)A schematic of the process unit, enclosure, and closed vent system.
   3. (3)A description of the system used to create a negative pressure in the enclosure to ensure that all emissions are routed to the control device.