40 CFR § 59.625 - How do I select emission families?
(b) Group containers in the same emission family if they are the same in all the following aspects:
(1) Type of material (including pigments, plasticizers, UV inhibitors, or other additives that may affect control of emissions).
(2) Production method.
(3) Spout and cap design.
(4) Gasket material and design.
(5) Emission control strategy.
(6) Strategy for venting pressure.
(d) You may group containers that are not identical with respect to the things listed in paragraph (b) of this section in the same emission family if you show that their emission characteristics will be similar throughout their useful life.