1.1 This test method is to determine the air permeance of building materials at various pressure differentials with the intent of determining an assigned air permeance rate of the material at the reference pressure difference ( ?P ) of 75 Pa. 1.2 The method is intended to assess flexible sheet or rigid panel-type materials using a 1 m x 1 m specimen size. 1.3 The values stated in SI units are to be regarded as standard. No other units of measurements are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.