1.1 This practice is intended to define the exposure conditions of plastics at various temperatures when exposed solely to hot air for extended periods of time. Only the procedures for heat exposure are specified, not the test method or specimen. The effect of heat on any particular property may be determined by selection of the appropriate test method and specimen; however, it is recommended that Practice D 3826 be used to determine the embrittlement endpoint, which is defined as that point in the history of a material when 75 % of the specimens tested have a tensile elongation at break of 5 % or less at an initial strain rate of 0.1 mm/mm min. 1.2 This practice should be used as a guide for comparing the thermal-aging characteristics of materials as measured by the change in some property of interest (that is, embrittlement by means of loss of elongation). It is very similar to Practice D3045 but is intended for use in evaluating plastics designed to be oxidized easily after use. The exposure times used for this practice will be significantly shorter than those used for Practice D3045. 1.3 The type of oven used can affect the results obtained from this practice. The user can use one of two methods for oven exposure. The results based on one method should not be mixed with those based on the other. 1.3.1 Procedure A: Gravity-Convection Oven-Recommended for film specimens having a nominal thickness not greater than 0.25 mm (0.010 in.). 1.3.2 Procedure B: Forced-Ventilation Oven-Recommended for specimens having a nominal thickness greater than 0.25 mm (0.010 in.). 1.4 This practice recommends procedures for comparing the thermal aging characteristics of materials at a single temperature. Recommended procedures for determining the thermal aging characteristics of a material at a series of temperatures for the purpose of estimating time to a defined property change at some lower temperature are also described. This practice does not predict thermal aging characteristics where interactions between stress, environment, temperature, and time control failure. 1.5 The values stated in SI units are to be regarded as the standard. 1.6 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. Note 1-There is no ISO standard that is equivalent to this standard.