From the International Electrotechnical Commission webstore:
“IEC 60243-1:2013 provides test methods for the determination of short-time electric strength of solid insulating materials at power frequencies between 48 Hz and 62 Hz. This standard does not cover the testing of liquids and gases, although these are specified and used as impregnates or surrounding media for the solid insulating materials being tested. Methods for the determination of breakdown voltages along the surfaces of solid insulating materials are included.”