1.1 This method uses the change of electrical and/or chemical characteristics of transformer askarel to eliminate those materials which are not suitable due to their contaminating effect on the askarel. Delayed or long time contamination effects may not be detected. 1.2 This method also utilizes various physical tests on the electrical insulation and construction materials after controlled exposure to the askarel to eliminate those materials which are not suitable for further consideration. 1.3 This method is not suitable for the complete evaluation of the compatibility of insulating and structural materials with the askarels for any given application.