40 CFR 63.1424 - Emission standards.
(1) Sections 63.1425 through 63.1430 for process vents;
(5) Section 63.1435 for heat exchangers;
(b) When emissions of different kinds (i.e., emissions from process vents subject to §§ 63.1425 through 63.1430, storage vessels subject to § 63.1432, process wastewater, and/or in-process equipment subject to § 63.149) are combined, and at least one of the emission streams would require control according to the applicable provision in the absence of combination with other emission streams, the owner or operator shall comply with the requirements of either paragraph (b)(1) or (2) of this section.
(1) Comply with the applicable requirements of this subpart for each kind of emission in the stream as specified in paragraphs (a)(1) through (5) of this section; or
(2) Comply with the most stringent set of requirements that applies to any individual emission stream that is included in the combined stream, where either that emission stream would be classified as requiring control in the absence of combination with other emission streams, or the owner chooses to consider that emission stream to require control for the purposes of this paragraph.