40 CFR 65.118: Alternative means of emission limitation: Enclosed-vented process units.

(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.

(b) Recordkeeping. Owners and operators choosing to comply with the requirements of this section shall maintain the following records:

(1) Identification of the process unit(s) and the regulated materials they handle.

(2) A schematic of the process unit, enclosure, and closed vent system.

(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.