(a) Under section 18(c)(2) of the Act, a State plan must not include standards for products which are distributed or used in interstate commerce which are different from Federal standards for such products unless such standards are required by compelling local conditions and do not unduly burden interstate commerce. In Sec. 1902.3(c)(2) of this chapter this is interpreted as not being applicable to customized products, or parts not normally available on the open market, or to the optional parts, or additions to products which are ordinarily available with such optional parts, or additions.
(b) In situations where section 18(c)(2) is considered applicable, and provision is made for the adoption of product standards, the requirements of section 18(c)(2), as they relate to undue burden on interstate commerce, shall be treated as a condition subsequent in light of the facts and circumstances which may be involved.