40 CFR § 211.212-3 - Test hearing protector preparation.
The manufacturer must select the test hearing protector according to § 211.212–2 before the official test, and must comply with the test protector preparation requirements described in this subpart:
(a) A test hearing protector selected according to § 211.212–2 must not be tested, modified, or adjusted in any manner before the official test unless the adjustments, modifications and/or tests are part of the manufacturer's prescribed manufacturing and inspection procedures.
(b) Quality controls, testing, assembly or selection procedures must not be, used on the completed protector or any portion of the protector, including parts, that will not normally be used during the production and assembly of all other protectors of that category to be distributed in commerce.