CEI EN 60216-8

This part of IEC 60216 specifies the general ageing conditions
and simplified procedures to be used for deriving thermal endurance
characteristics, which are shown by temperature index (TI) and/or
relative temperature index (RTI) and the halving interval
(HIC).

The procedures specify the principles for evaluating the thermal
endurance properties of materials exposed to elevated temperature
for long periods.

In the application of this standard, it is assumed that a
practically linear relationship exists between the logarithm of the
time required to cause the predetermined property change and the
reciprocal of the corresponding absolute temperature (Arrhenius
relationship).

For the valid application of the standard, no transition, in
particular no first-order transition should occur in the
temperature range under study.

Throughout the rest of this standard the designation "insulating
materials" is always taken to mean "insulating materials and simple
combinations of such materials".