Impervious Chemical protective clothing is impervious to a chemical substance if the substance causes no chemical or mechanical degradation, permeation, or penetration of the chemical protective clothing under the conditions of, and the duration of, exposure.
40 CFR § 721.3
The definitions in section 3 of the Act, 15 U.S.C. 2602, and 720.3 of this chapter apply to this part. In addition, the following definitions apply to this part: