5.1 These measurements give semiquantitative estimates for the gas transmission of single pure gases through film and sheeting. Correlation of measured values with any given use, such as packaged contents protection, must be determined by experience. The gas transmission rate is affected by conditions not specifically provided for in these tests, such as moisture content (Note 2), plasticizer content, and nonhomogeneities. These tests do not include any provision for testing seals that may be involved in packaging applications.

Note 2: The tests are run using gas with 0?% moisture changes.

5.2 The historic Interlaboratory testing has revealed that permeances measured by these procedures exhibit a strong dependence on the procedure being used, as well as on the laboratory performing the testing. The historic method relied upon manual calibrations of Hg capillary columns and manual data readings of pressure. The references and use of Hg and capillary columns have been removed from this standard as current D1434 instruments rely upon readily calibrated vacuum gauges and automated recording of data. It is planned that the next revision of this standard includes an updated ILS with modern instrumentation. Additionally, it has been noted that an agreement with other gas transmission rate methods is sometimes poor and may be material-dependent. The materials being tested often affect the between-laboratory precision. The causes of these variations are not precisely known at this time, but is likely due to the fact that this method analyzes ALL gasses from the sample and not just the Test gas. This includes pre-absorbed water vapor within the sample and any free solvents remaining within the specimen. The 48?hr desiccator drying period outlined within the method may not be long enough for all materials. Additionally, other gas transmission rate methods (as those used for oxygen transmission rate, water vapor transmission rate and carbon dioxide transmission rate) often incorporate test gas specific sensors and therefore would minimize influence from other gasses. It is suggested that this method not be used for referee purposes unless purchaser and seller can both establish that they are measuring the same quantity to a mutually agreed upon level of precision.

5.3 Use of the permeability coefficient (involving conversion of the gas transmission rate to a unit thickness basis) is not recommended unless the thickness-to-transmission rate relationship is known from previous studies. Even in essentially homogeneous structures, variations in morphology (as indicated, for example, by density) and thermal history may influence permeability.