This test method covers the evaluation of asbestos textiles with regard to (1) quality and ( 2) elevated temperature serviceability characteristics. Since asbestos textiles are usually composed of blends of asbestos with cotton or other organic carrier fibers, the latter being present in amounts up to 25 %, temperatures above 150°C (300°F) will promote the degradation of the cotton content and will reduce the structural reinforcement derived therefrom. In the higher grade asbestos textiles, wherein little or no carrier fibers are used and in which the longer asbestos fibers are necessary if a satisfactory yarn is to be produced, the degradation in strength resulting from heat-aging up to 540°C (1000°F) is low. In the case of the lower grade asbestos textiles, however, wherein amounts from 15 to 25 % carrier fibers are incorporated, asbestos fibers having shorter lengths may be utilized. Under the relatively low service temperatures to which such materials may be subjected, neither the cotton nor the cloth properties are greatly affected. However, the strength-imparting influence of the carrier fibers is reduced at elevated temperatures and the entwining properties of the shorter asbestos fibers primarily serve to establish the resultant tensile strength and other physical properties of the textile. In view of this, elevated temperature tests may serve to indicate the asbestos fiber grade or quality that may be used in a textile construction.

Another use and perhaps more practical application for the information to be derived from elevated temperature studies is the revelation of the ability of a subject textile to withstand known elevated temperature service conditions. It will be appreciated that temperature alone may not be the only degratory influence in the destruction of such materials; however, under normal operating conditions, high temperatures are usually the dominating factors in such degradation. The results obtained through such investigations therefore may be interpreted in terms of elevated temperature serviceability.